Code conversion method, apparatus, program, and storage medium

• US 20050010400A1
• Filed: 11/12/2002
• Published: 01/13/2005
• Est. Priority Date: 11/13/2001
• Status: Active Grant

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Murashima, Atsushi
• Granted Patent: US 7,630,884 B2
• Time in Patent Office: Days
• US Class Current: 704/219
• CPC Class Codes: G10L 19/08 Determination or coding of the excitation function; Determination or coding of the long-term prediction parameters
• CPC Class Codes: G10L 19/173 Transcoding, i.e. converting between two coded representations avoiding cascaded coding-decoding
• CPC Class Codes: G10L 2019/0001 Codebooks
• CPC Class Codes: G10L 2019/0011 Long term prediction filters, i.e. pitch estimation

Abstract

The object of this invention is converting a code that has been obtained by encoding speech by one particular system is converted to code that can be decoded by another system with high speech quality, and moreover, with a low computational load in transmitting speech signal between different systems. This invention comprising an adaptive codebook (ACB) delay search range control circuit (1250 in FIG. 7) for calculating a search range control value from first adaptive codebook delay that is stored and held and said second adaptive codebook delay that is stored and held, and an adaptive codebook encoding circuit (1220 in FIG. 7) for calculating autocorrelation using speech signal from ACB delay including excitation signal and delay that is within a range stipulated by said search range control value, and selects the maximum autocorrelation as second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.

Claims

1. A code conversion method for converting a first code string to a second code string, the method comprising steps of:

obtaining a first linear prediction coefficient and excitation signal information from said first code string and generating an excitation signal from said excitation signal information; and

using a first adaptive codebook delay that is contained in said excitation signal information and said excitation signal, or a speech signal that is generated from said excitation signal and said first linear prediction coefficient to select a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.

2. A code conversion method for converting a first code string to a second code string, the method comprising steps of:

obtaining a first linear prediction coefficient and excitation signal information from said first code string, and generating an excitation signal from said excitation signal information;

storing and holding a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string; and

using said second adaptive codebook delay that is stored and held and said excitation signal, or a speech signal that is generated from said first linear prediction coefficient and said excitation signal to select a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.

3. A code conversion method for converting a first code string to a second code string, the method comprising:

a first step of obtaining a first linear prediction coefficient from said first code string;

a second step of obtaining excitation signal information from said first code string;

a third step of obtaining an excitation signal from said excitation signal information;

a fourth step of driving a filter having said first linear prediction coefficient by means of said excitation signal to generate a speech signal; and

a fifth step of using said speech signal to select a second adaptive codebook delay from delay that is within a range stipulated by a search range control value and said first adaptive codebook delay that is contained in said excitation signal information, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.

8. A code conversion method according to any one of claims 3 to 7, wherein said search range control value is calculated from a constant or said first adaptive codebook delay and said second adaptive codebook delay.

9. A code conversion method according to any one of claims 3 to 8, wherein:

for delay that is within said range, an autocorrelation or a normalized autocorrelation is calculated from said speech signal or said excitation signal; and

delay for which said autocorrelation or normalized autocorrelation is a maximum is selected as second adaptive codebook delay.

4. A code conversion method for converting a first code string to a second code string, the method comprising:

a first step of obtaining a first linear prediction coefficient from said first code string;

a second step of obtaining excitation signal information from said first code string;

a third step of obtaining an excitation signal from said excitation signal information;

a fourth step of driving a filter having said first linear prediction coefficient by means of said excitation signal to generate a speech signal;

a fifth step of storing and holding a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string; and

a sixth step of using said speech signal to select a second adaptive codebook delay from delay that is within a range stipulated by a search range control value and said second adaptive codebook delay that has been stored and held, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.

5. A code conversion method for converting a first code string to a second code string, the method comprising:

a first step of obtaining a first linear prediction coefficient from said first code string;

a second step of obtaining excitation signal information from said first code string;

a third step of obtaining an excitation signal from said excitation signal information;

a fourth step of driving a filter having said first linear prediction coefficient by means of said excitation signal to generate a speech signal;

a fifth step of, in at least one of subframes, which are divisions of a frame that is a time unit of converting a code string, using said speech signal to select a second adaptive codebook delay from delay within a range stipulated by a search range control value and a first adaptive codebook delay that is contained in said excitation signal information, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string; and

a sixth step of, in at least one subframe in said frame, using the relation between said first adaptive codebook delay and a first delay code that corresponds to this first adaptive codebook delay and the relation between said second adaptive codebook delay and a second delay code that corresponds to this second adaptive codebook delay to place said first adaptive codebook delay in correspondence with said second adaptive codebook delay and thereby convert from said first delay code to said second delay code, and supplying said second delay code as code of an adaptive codebook delay in said second code string.

6. A code conversion method for converting a first code string to a second code string, the method comprising:

a first step of obtaining a first linear prediction coefficient from said first code string;

a second step of obtaining excitation signal information from said first code string;

a third step of obtaining an excitation signal from said excitation signal information;

a fourth step of driving a filter having said first linear prediction coefficient by means of said excitation signal to generate a speech signal;

a fifth step of, in each of subframes that are divisions of frames that are the time units of converting code strings, storing and holding a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string;

a sixth step of, in at least one subframe in said frames, using said speech signal to select a second adaptive codebook delay from delay within a range that is stipulated by a search range control value and said second adaptive codebook delay that has been previously found, stored and held, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string; and

a seventh step of, in at least one subframe in said frame, using the relation between said first adaptive codebook delay that is contained in said excitation signal information and a first delay code that corresponds to this first adaptive codebook delay and the relation between said second adaptive codebook delay and a second delay code that corresponds to this second adaptive codebook delay to place said first adaptive codebook delay in correspondence with said second adaptive codebook delay and thereby convert from said first delay code to said second delay code, and supplying said second delay code as code of an adaptive codebook delay in said second code string.

7. A code conversion method for converting a first code string to a second code string, the method comprising:

a first step of obtaining a first linear prediction coefficient from said first code string;

a second step of obtaining excitation signal information from said first code string;

a third step of obtaining an excitation signal from said excitation signal information;

a fourth step of driving a filter having said first linear prediction coefficient by means of said excitation signal to generate a speech signal;

a fifth step of, in each of subframes that are divisions of frames that are the time units of converting code strings, storing and holding a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string;

a sixth step of, in at least one subframe in said frames, using said speech signal to select a second adaptive codebook delay from delay that is within a range stipulated by a search range control value and a first adaptive codebook delay that is contained in said excitation signal information, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string; and

a seventh step of, in at least one subframe in said frame, using said speech signal to select a second adaptive codebook delay from delay that is within a range that is stipulated by said search range control value and said second adaptive codebook delay that has been previously found, stored, and held, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.

10. A code conversion method for converting a first code string to a second code string, the method comprising:

a first step of obtaining a first linear prediction coefficient and excitation signal information from said first code string;

a second step of obtaining a second linear prediction coefficient from said first linear prediction coefficient;

a third step of driving a filter having said first linear prediction coefficient or said second linear prediction coefficient by means of a first excitation signal that is obtained from said excitation signal information to generate a speech signal;

a fourth step of using a first adaptive codebook delay that is contained in said excitation signal information and a second excitation signal that has been previously calculated, stored, and held to successively generate an adaptive codebook signal, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string;

a fifth step of obtaining a second excitation signal from said selected adaptive codebook signal; and

a sixth step of storing and holding said second excitation signal.

11. A code conversion method for converting a first code string to a second code string, the method comprising:

a first step of obtaining a first linear prediction coefficient and excitation signal information from said first code string;

a second step of obtaining a second linear prediction coefficient from said first linear prediction coefficient;

a third step of driving a filter having said first linear prediction coefficient or said second linear prediction coefficient by means of a first excitation signal that is obtained from said excitation signal information to generate a speech signal;

a fourth step of storing and holding a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string;

a fifth step of using said second adaptive codebook delay that has been stored and held and a second excitation signal that has been previously calculated, stored and held to successively generate an adaptive codebook signal, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string;

a sixth step of obtaining a second excitation signal from said selected adaptive codebook signal; and

a seventh step of storing and holding said second excitation signal.

12. A code conversion method for converting a first code string to a second code string, the method comprising:

a first step of obtaining a first linear prediction coefficient from said first code string;

a second step of obtaining excitation signal information from said first code string;

a third step of obtaining a first excitation signal from said excitation signal information;

a fourth step of obtaining a second linear prediction coefficient from said first linear prediction coefficient;

a fifth step of driving a filter having said first linear prediction coefficient or said second linear prediction coefficient by means of

said first excitation signal to generate a speech signal;

a sixth step of successively generating an adaptive codebook signal from a second excitation signal that has been previously calculated, stored, and held for delay that is within a range that is stipulated by a search range control value and a first adaptive codebook delay that is contained in said excitation signal information, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string;

a seventh step of obtaining a second excitation signal from said selected adaptive codebook signal; and

an eighth step of storing and holding said second excitation signal.

17. A code conversion method according to any one of claims 12 to 16, wherein:

said search range control value is calculated from a constant or said first adaptive codebook delay and said second adaptive codebook delay.

18. A code conversion method according to any one of claims 12 to 17, wherein:

for delay that is within said range, an autocorrelation or a normalized autocorrelation is calculated from said speech signal or said excitation signal; and

delay for which said autocorrelation or normalized autocorrelation is a maximum is selected as second adaptive codebook delay.

13. A code conversion method for converting a first code string to a second code string, the method comprising:

a first step of obtaining a first linear prediction coefficient from said first code string;

a second step of obtaining excitation signal information from said first code string;

a third step of obtaining a first excitation signal from said excitation signal information;

a fourth step of obtaining a second linear prediction coefficient from said first linear prediction coefficient;

a fifth step of driving a filter having said first linear prediction coefficient or said second linear prediction coefficient by means of said first excitation signal to generate a speech signal;

a sixth step of storing and holding a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string;

a seventh step of successively generating an adaptive codebook signal from a second excitation signal that has been previously calculated, stored, and held for delay that is within a range that is stipulated by a search range control value and said second adaptive codebook delay that has been stored and held, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string;

an eighth step of obtaining a second excitation signal from said selected adaptive codebook signal; and

a ninth step of storing and holding said second excitation signal.

14. A code conversion method for converting a first code string to a second code string, the method comprising:

a first step of obtaining a first linear prediction coefficient from said first code string;

a second step of obtaining excitation signal information from said first code string;

a third step of obtaining a first excitation signal from said excitation signal information;

a fourth step of obtaining a second linear prediction coefficient from said first linear prediction coefficient;

a fifth step of driving a filter having said first linear prediction coefficient or said second linear prediction coefficient by means of said first excitation signal to generate a speech signal;

a sixth step of, in at least one subframe, which is a division of frames that are the time units for converting code strings, successively generating an adaptive codebook signal from a second excitation signal that has been previously calculated, stored, and held for delay that is within a range that is stipulated by a search range control value and a first adaptive codebook delay that is contained in said excitation signal information, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string;

a seventh step of, in at least one subframe in said frames, using the relation between said first adaptive codebook delay and a first delay code that corresponds to said first adaptive codebook delay and the relation between said second adaptive codebook delay and a second delay code that corresponds to said second adaptive codebook delay to place said first adaptive codebook delay in correspondence with said second adaptive codebook delay and thus convert from said first delay code to said second delay code, and supplying said second delay code as code of an adaptive codebook delay in said second code string;

an eighth step of obtaining a second excitation signal from said selected adaptive codebook signal; and

a ninth step of storing and holding said second excitation signal.

15. A code conversion method for converting a first code string to a second code string, the method comprising:

a first step of obtaining a first linear prediction coefficient from said first code string;

a second step of obtaining excitation signal information from said first code string;

a third step of obtaining a first excitation signal from said excitation signal information;

a fourth step of obtaining a second linear prediction coefficient from said first linear prediction coefficient;

a fifth step of driving a filter having said first linear prediction coefficient or said second linear prediction coefficient by means of said first excitation signal to generate a speech signal;

a sixth step of, in each of subframes, which are divisions of frames that are the time units of converting code strings, storing and holding a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string;

a seventh step of, in at least one subframe in said frames, successively generating an adaptive codebook signal from a second excitation signal that has been previously calculated, stored, and held for delay that is within a range that is stipulated by a search range control value and said second adaptive codebook delay that has been previously found, stored, and held, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string;

an eighth step of, in at least one subframe in said frames, using the relation between a first adaptive codebook delay that is contained in said excitation signal information and a first delay code that corresponds to this first adaptive codebook delay and the relation between said second adaptive codebook delay and a second delay code that corresponds to this second adaptive codebook delay to place said first adaptive codebook delay in correspondence with said second adaptive codebook delay and thus convert from said first delay code to said second delay code, and supplying said second delay code as code of an adaptive codebook delay in said second code string;

a ninth step of obtaining a second excitation signal from said selected adaptive codebook signal; and

a tenth step of storing and holding said second excitation signal.

16. A code conversion method for converting a first code string to a second code string, the method comprising:

a first step of obtaining a first linear prediction coefficient from said first code string;

a second step of obtaining excitation signal information from said first code string;

a third step of obtaining a first excitation signal from said excitation signal information;

a fourth step of obtaining a second linear prediction coefficient from said first linear prediction coefficient;

a fifth step of driving a filter having said first linear prediction coefficient or said second linear prediction coefficient by means of said first excitation signal to generate a speech signal;

a sixth step of, in each of subframes, which are divisions of frames that are the time units of converting a code string, storing and holding a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string;

a seventh step of, in at least one subframe in said frames, successively generating an adaptive codebook signal from a second excitation signal that has been previously calculated, stored, and held for delay that is within a range that is stipulated by a search range control value and a first adaptive codebook delay that is contained in said excitation signal information, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string;

an eighth step of, in at least one subframe in said frames, successively generating an adaptive codebook signal from a second excitation signal that has been previously calculated, stored, and held for delay that is within a range stipulated by a search range control value and said second adaptive codebook delay that has been previously found, stored and held, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string;

a ninth step of obtaining a second excitation signal from said selected adaptive codebook signal; and

a tenth step of storing and holding said second excitation signal.

19. A code conversion device for receiving a first code string as input, converting to a second code string, and supplying said second code string as output, the device comprising:

a speech decoding circuit for obtaining a first linear prediction coefficient and excitation signal information from said first code string and driving a filter having said first linear prediction coefficient by means of an excitation signal that is obtained from said excitation signal information to generate a speech signal; and

an adaptive codebook code generation circuit for using said speech signal and a first adaptive codebook delay that is contained in said excitation signal information to select a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.

20. A code conversion device for converting a first code string to a second code string, comprising:

a linear prediction coefficient decoding circuit for obtaining a first linear prediction coefficient from said first code string;

an excitation signal information decoding circuit for obtaining excitation signal information from said first code string;

an excitation signal calculation circuit for obtaining an excitation signal from said excitation signal information;

a compound filter for generating a speech signal by driving a filter having said first linear prediction coefficient by means of said excitation signal;

an adaptive codebook delay storage circuit for storing and holding a first adaptive codebook delay that is contained in said excitation signal information;

a second adaptive codebook delay storage circuit for storing and holding a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string;

an adaptive codebook delay search range control circuit for calculating a search range control value from said first adaptive codebook delay that is stored and held and said second adaptive codebook delay that is stored and held; and

an adaptive codebook encoding circuit for using said speech signal to select a second adaptive codebook delay from delay that is within a range stipulated by said search range control value and said first adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.

21. A code conversion device according to claim 20, wherein said adaptive codebook delay storage circuit is provided with:

means for, in each of subframes, which are divisions of frames that are the time unit of converting code strings, successively storing said first adaptive codebook delay, and holding said first adaptive codebook delay for a predetermined number of subframes;

said second adaptive codebook delay storage circuit is provided with;

means for, in each of said subframes, successively storing said second adaptive codebook delay and holding said second adaptive codebook delay for a predetermined number of subframes;

said adaptive codebook delay search range control circuit is provided with;

means for calculating the absolute value of the difference between said first adaptive codebook delay that has been stored and held and said second adaptive codebook delay that has been stored and held that correspond to the same subframe for all first adaptive codebook delays and second adaptive codebook delays that are held; and

means for taking, as said search range control value, a value that is obtained by adding, for said number of subframes, values obtained by multiplying said absolute values by a weighting coefficient.

25. A code conversion device according to any one of claims 20 to 24, wherein:

said adaptive codebook encoding circuit, for delay within said range, calculates an autocorrelation or a normalized autocorrelation from said speech signal, and selects delay for which said autocorrelation or normalized autocorrelation is a maximum as second adaptive codebook delay.

22. A code conversion device for converting a first code string to a second code string, comprising:

a linear prediction coefficient decoding circuit for obtaining a first linear prediction coefficient from said first code string;

an excitation signal information decoding circuit for obtaining excitation signal information from said first code string;

an excitation signal calculation circuit for obtaining an excitation signal from said excitation signal information;

a compound filter for generating a speech signal by driving a filter having said first linear prediction coefficient by means of said excitation signal;

an adaptive codebook delay storage circuit for, for each of subframes, which are divisions of frames that are the time units of converting code strings, successively storing a first adaptive codebook delay that is contained in said excitation signal information, and holding said first adaptive codebook delay for a predetermined number of subframes;

a second adaptive codebook delay storage circuit for, for each of said subframes, successively storing a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string, and holding said second adaptive codebook delay for a predetermined number of subframes;

an adaptive codebook delay search range control circuit for calculating the absolute value of the difference between said first adaptive codebook delay that has been stored and held and said second adaptive codebook delay that has been stored and held that correspond to the same subframe for all of said first adaptive codebook delays and said second adaptive codebook delays that are held, and taking as a search range control value a value that is obtained by adding, for said number of subframes, values obtained by multiplying said absolute values by a weighting coefficient;

an adaptive codebook encoding circuit for, in at least one subframe in said frame, using said speech signal to select a second adaptive codebook delay from delay that is within a range stipulated by said search range control value and said first adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string; and

an adaptive codebook code conversion circuit for, in at least one subframe in said frame, using the relation between said first adaptive codebook delay and a first delay code that corresponds to this first adaptive codebook delay and the relation between said second adaptive codebook delay and a second delay code that corresponds to this second adaptive codebook delay to place said first adaptive codebook delay in correspondence with said second adaptive codebook delay and thus convert from said first delay code to said second delay code, and supplying said second delay code as code of an adaptive codebook delay in said second code string.

33. A code conversion device according to any one of claims 22, 23, 29, and 30, further comprising a switching device for receiving the output of said adaptive codebook code conversion circuit and said adaptive codebook code generation circuit, and selecting and supplying one of these inputs as output.

53. A code conversion device according to any one of claim 22, claim 23, claim 29, and claim 30, said code conversion device being provided with a switching device for receiving the output of said adaptive codebook encoding circuit and said adaptive codebook code conversion circuit, and supplying one of these inputs as code of an adaptive codebook delay in said second code string.

23. A code conversion device for converting a first code string to a second code string, said code conversion device comprising:

a linear prediction coefficient decoding circuit for obtaining a first linear prediction coefficient from said first code string;

an excitation signal information decoding circuit for obtaining excitation signal information from said first code string;

an excitation signal calculation circuit for obtaining an excitation signal from said excitation signal information;

a compound filter for generating a speech signal by driving a filter having said first linear prediction coefficient by means of said excitation signal;

an adaptive codebook delay storage circuit for, for each of subframes, which are divisions of frames that are the time units of converting code strings, successively storing a first adaptive codebook delay that is contained in said excitation signal information, and holding said first adaptive codebook delay for a predetermined number of subframes;

a second adaptive codebook delay storage circuit for, for each of said subframes, successively storing a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string, and holding said second adaptive codebook delay for each of a predetermined number of subframes;

an adaptive codebook delay search range control circuit for calculating the difference between said first adaptive codebook delay of consecutive subframes for said first adaptive codebook delay that has been stored and held and said first adaptive codebook delay of the current subframe, calculating the absolute value of the difference, and taking as a search range control value a value that is obtained by adding, for said number of subframes, values obtained by multiplying said absolute values by a weighting coefficient;

an adaptive codebook encoding circuit for, in at least one subframe in said frame, using said speech signal to select a second adaptive codebook delay from delay that is within a range stipulated by said search range control value and said second adaptive codebook delay that has been previously found, stored, and held, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string; and

an adaptive codebook code conversion circuit for, in at least one subframe in said frame, using the relation between said first adaptive codebook delay and a first delay code that corresponds to this first adaptive codebook delay and the relation between said second adaptive codebook delay and a second delay code that corresponds to this second adaptive codebook delay to place said first adaptive codebook delay in correspondence with said second adaptive codebook delay and thus convert from said first delay code to said second delay code, and supplying said second delay code as code of an adaptive codebook delay in said second code string.

24. A code conversion device for converting a first code string to a second code string, said code conversion device comprising:

a linear prediction coefficient decoding circuit for obtaining a first linear prediction coefficient from said first code string;

an excitation signal information decoding circuit for obtaining excitation signal information from said first code string;

an excitation signal calculation circuit for obtaining an excitation signal from said excitation signal information;

a compound filter for generating a speech signal by driving a filter having said first linear prediction coefficient by means of said excitation signal;

an adaptive codebook delay storage circuit for, for each of subframes, which are divisions of frames that are the time units of converting code strings, successively storing a first adaptive codebook delay that is contained in said excitation signal information, and holding said first adaptive codebook delay for a predetermined number of subframes;

a second adaptive codebook delay storage circuit for, for each of said subframes, successively storing a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string, and holding said second adaptive codebook delay for each of a predetermined number of subframes;

an adaptive codebook delay search range control circuit for, in at least one subframe in said frame, calculating the absolute value of the difference between said first adaptive codebook delay that has been stored and held and said second adaptive codebook delay that has been stored and held that correspond to the same subframe for all of said first adaptive codebook delays and said second adaptive codebook delays that are held, and taking as a search range control value a value that is obtained by adding, for said number of subframes, values obtained by multiplying said absolute values by a weighting coefficient; and

in other subframes, calculating the difference between said first adaptive codebook delay of consecutive subframes for said first adaptive codebook delay that has been stored and held and said first adaptive codebook delay of the current subframe, calculating the absolute value of said difference, and taking as a search range control value a value that is obtained by adding, for said number of subframes, values obtained by multiplying said absolute values by a weighting coefficient; and

an adaptive codebook encoding circuit for, in at least one subframe in said frame, using said speech signal to select a second adaptive codebook delay from delay that is within a range stipulated by said search range control value and said first adaptive codebook delay, and taking code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string; and

in other subframes, using said speech signal to select a second adaptive codebook delay from delay that is within a range stipulated by said search range control value and said second adaptive codebook delay that has been previously found, stored, and held, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.

26. A code conversion device for converting a first code string to a second code string, said code conversion device comprising:

a speech decoding circuit for obtaining a first linear prediction coefficient and excitation signal information from said first code string, and driving a filter having said first linear prediction coefficient by means of a first excitation signal that is obtained from said excitation signal information to generate a speech signal;

a linear prediction coefficient code conversion circuit for obtaining a second linear prediction coefficient from said first linear prediction coefficient;

an adaptive codebook code generation circuit for using a first adaptive codebook delay that is contained in said excitation signal information and a second excitation signal that has been previously calculated, stored, and held to successively generate an adaptive codebook signal, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string;

a second excitation signal calculation circuit for obtaining a second excitation signal from said selected adaptive codebook signal; and

a second excitation signal storage circuit for storing and holding said second excitation signal.

27. A code conversion device for converting a first code string to a second code string, said code conversion device comprising:

a linear prediction coefficient decoding circuit for obtaining a first linear prediction coefficient from said first code string;

an excitation signal information decoding circuit for obtaining excitation signal information from said first code string;

an excitation signal calculation circuit for obtaining a first excitation signal from said excitation signal information;

a compound filter for generating a speech signal by driving a filter having said first linear prediction coefficient by means of said first excitation signal;

a linear prediction coefficient encoding circuit for obtaining a second linear prediction coefficient from said first linear prediction coefficient;

an adaptive codebook delay storage circuit for storing and holding a first adaptive codebook delay that is contained in said excitation signal information;

a second adaptive codebook delay storage circuit for storing and holding a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string;

an adaptive codebook delay search range control circuit for calculating a search range control value from said first adaptive codebook delay that has been stored and held and said second adaptive codebook delay that has been stored and held;

an adaptive codebook encoding circuit for, for delay that is within a range that is stipulated by said search range control value and said first adaptive codebook delay, successively generating an adaptive codebook signal from a second excitation signal that has been previously calculated, stored, and held, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string;

a second excitation signal calculation circuit for obtaining a second excitation signal from said selected adaptive codebook signal; and

a second excitation signal storage circuit for storing and holding said second excitation signal.

28. A code conversion device according to claim 27, wherein:

said adaptive codebook delay storage circuit is provided with means for, for each of subframes, which are divisions of frames that are the time units for converting code strings, successively storing said first adaptive codebook delay and holding said first adaptive codebook delay for a predetermined number of subframes;

said second adaptive codebook delay storage unit is provided with means for successively storing said second adaptive codebook delay for each of said subframes and holding said second adaptive codebook delay for a predetermined number of subframes; and

said adaptive codebook delay search range control circuit is provided with means for calculating the absolute value of the difference between said first adaptive codebook delay that has been stored and held and said second adaptive codebook delay that has been stored and held that correspond to the same subframe for all of said first adaptive codebook delays and said second adaptive codebook delays that are held, and taking as said search range control value a value that is obtained by adding, for said number of subframes, values that are obtained by multiplying said absolute values by a weighting coefficient.

32. A code conversion device according to any one of claims 27 to 31, wherein:

said adaptive codebook encoding circuit, for delay that is within said range, selects said adaptive codebook signals and delays such that the squared error between said first reconstructed speech signal and said speech signal is a minimum, and takes said selected delay as second adaptive codebook delay.

29. A code conversion device for converting a first code string to a second code string, said code conversion device comprising:

a linear prediction coefficient decoding circuit for obtaining a first linear prediction coefficient from said first code string;

an excitation signal information decoding circuit for obtaining excitation signal information from said first code string;

an excitation signal calculation circuit for obtaining a first excitation signal from said excitation signal information;

a compound filter for generating a speech signal by driving a filter having said first linear prediction coefficient by means of said first excitation signal;

a linear prediction coefficient encoding circuit for obtaining a second linear prediction coefficient from said first linear prediction coefficient;

an adaptive codebook delay storage circuit for, for each of subframes, which are divisions of frames that are the time units of converting code strings, successively storing a first adaptive codebook delay that is contained in said excitation signal information and holding said first adaptive codebook delay for a predetermined number of subframes;

a second adaptive codebook delay storage circuit for, for each of said subframes, successively storing a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string, and holding said second adaptive codebook delay for a predetermined number of subframes;

an adaptive codebook delay search range control circuit for calculating the absolute value of the difference between said first adaptive codebook delay that has been stored and held and said second adaptive codebook delay that has been stored and held that correspond to the same subframe for all of said first adaptive codebook delays and said second adaptive codebook delays that are held, and taking as said search range control value a value that is obtained by adding, for said number of subframes, values that are obtained by multiplying said absolute values by a weighting coefficient;

an adaptive codebook encoding circuit for, for at least one subframe in said frame, successively generating an adaptive codebook signal from a second excitation signal that has been previously calculated, stored, and held for delay that is within a range that is stipulated by said search range control value and said first adaptive codebook delay, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string;

an adaptive codebook code conversion circuit for, in at least one subframe in said frame, using the relation between said first adaptive codebook delay and a first delay code that corresponds to this first adaptive codebook delay and the relation between said second adaptive codebook delay and a second delay code that corresponds to this second adaptive codebook delay to place said first adaptive codebook delay in correspondence with said second adaptive codebook delay and thus convert from said first delay code to said second delay code, and supplying said second delay code as code of an adaptive codebook delay in said second code string;

a second excitation signal calculation circuit for obtaining a second excitation signal from said selected adaptive codebook signal; and

a second excitation signal storage circuit for storing and holding said second excitation signal.

30. A code conversion device for converting a first code string to a second code string, said code conversion device comprising:

a linear prediction coefficient decoding circuit for obtaining a first linear prediction coefficient from said first code string;

an excitation signal information decoding circuit for obtaining excitation signal information from said first code string;

an excitation signal calculation circuit for obtaining a first excitation signal from said excitation signal information;

a compound filter for generating a speech signal by driving a filter having said first linear prediction coefficient by means of said first excitation signal;

a linear prediction coefficient encoding circuit for obtaining a second linear prediction coefficient from said first linear prediction coefficient;

an adaptive codebook delay storage circuit for, for each of subframes, which are divisions of frames that are the time units of converting code strings, successively storing a first adaptive codebook delay that is contained in said excitation signal information, and holding said first adaptive codebook delay for a predetermined number of subframes;

a second adaptive codebook delay storage circuit for, for each of said subframes, successively storing a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string, and holding said second adaptive codebook delay for a predetermined number of subframes;

an adaptive codebook delay search range control circuit for calculating the difference between said first adaptive codebook delay of consecutive subframes for said first adaptive codebook delay that has been stored and held and said first adaptive codebook delay of the current subframe, calculating the absolute value of said difference, and taking as a search range control value a value that is obtained by adding, for said number of subframes, values that are obtained by multiplying said absolute values by a weighting coefficient;

an adaptive codebook encoding circuit for, in at least one subframe in said frame, successively generating an adaptive codebook signal from a second excitation signal that has been previously calculated, stored, and held for delay that is within a range that is stipulated by said search range control value and said second adaptive codebook delay that has been previously found, stored, and held, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string;

an adaptive codebook code conversion circuit for, in at least one subframe in said frame, using the relation between said first adaptive codebook delay and a first delay code that corresponds to this first adaptive codebook delay and the relation between said second adaptive codebook delay and a second delay code that corresponds to this second adaptive codebook delay to place said first adaptive codebook delay in correspondence with said second adaptive codebook delay and thus convert from said first delay code to said second delay code; and

supplying said second delay code as code of an adaptive codebook delay in said second code string;

a second excitation signal calculation circuit for obtaining a second excitation signal from said selected adaptive codebook signal; and

a second excitation signal storage circuit for storing and holding said second excitation signal.

31. A code conversion device for converting a first code string to a second code string, said code conversion device comprising:

a linear prediction coefficient decoding circuit for obtaining a first linear prediction coefficient from said first code string;

an excitation signal information decoding circuit for obtaining excitation signal information from said first code string;

an excitation signal calculation circuit for obtaining a first excitation signal from said excitation signal information;

a compound filter for generating a speech signal by driving a filter having said first linear prediction coefficient by means of said first excitation signal;

a linear prediction coefficient encoding circuit for obtaining a second linear prediction coefficient from said first linear prediction coefficient;

an adaptive codebook delay storage circuit for, for each of subframes, which are divisions of frames that are the time units of converting code strings, successively storing a first adaptive codebook delay that is contained in said excitation signal information, and holding said first adaptive codebook delay for a predetermined number of subframes;

a second adaptive codebook delay storage circuit for, for each of said subframes, successively storing a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string, and holding said second adaptive codebook delay for a predetermined number of subframes;

an adaptive codebook delay search range control circuit for, in at least one subframe in said frame, calculating the absolute value of the difference between said first adaptive codebook delay that has been stored and held and said second adaptive codebook delay that has been stored and held that correspond to the same subframe for all of said first adaptive codebook delays and said second adaptive codebook delays that are held, and taking as a search range control value a value that is obtained by adding, for said number of subframes, values obtained by multiplying said absolute values by a weighting coefficient; and

in other subframes, calculating the difference between said first adaptive codebook delay of consecutive subframes for said first adaptive codebook delay that has been stored and held and said first adaptive codebook delay of the current subframe, calculating the absolute value of said difference, and taking as a search range control value a value obtained by adding, for said number of subframes, values obtained by multiplying said absolute values by a weighting coefficient;

an adaptive codebook encoding circuit for, in at least one subframe in said frame, successively generating an adaptive codebook signal from a second excitation signal that has been previously calculated, stored, and held for delay that is within a range that is stipulated by said search range control value and said first adaptive codebook delay, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay of said second code string; and

in other subframes, successively generating an adaptive codebook signal from a second excitation signal that has been previously calculated, stored, and held for delay that is within a range that is stipulated by a search range control value and said second adaptive codebook delay that has been previously found, stored, and held, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string;

a second excitation signal calculation circuit for obtaining a second excitation signal from said selected adaptive codebook signal; and

a second excitation signal storage circuit for storing and holding said second excitation signal.

34. A program for causing a computer, which constitutes a code conversion device for converting a first code string to a second code string, to execute processes of:

obtaining a first linear prediction coefficient and excitation signal information from said first code string, and generating an excitation signal from said excitation signal information; and

using a first adaptive codebook delay that is contained in said excitation signal information and said excitation signal or a speech signal that is generated from said excitation signal and said first linear prediction coefficient to select a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.

52. A recording medium for recording said program according to any one of claims 34 to 51.

35. A program for causing a computer, which constitutes a code conversion device for converting a first code string to a second code string, to execute processes of:

obtaining a first linear prediction coefficient and excitation signal information from said first code string, and generating an excitation signal from said excitation signal information;

storing and holding a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string; and

using said second adaptive codebook delay that has been stored and held and said excitation signal or a speech signal that is generated from said excitation signal and said first linear prediction coefficient to select a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.

36. A program for causing a computer, which constitutes a code conversion device for converting a first code string to a second code string, to execute:

a first process of obtaining a first linear prediction coefficient from said first code string;

a second process of obtaining excitation signal information from said first code string;

a third process of obtaining an excitation signal from said excitation signal information;

a fourth process of driving a filter having said first linear prediction coefficient by means of said excitation signal to generate a speech signal; and

a fifth process of using said speech signal to select a second adaptive codebook delay from delay that is within a range stipulated by a search range control value and a first adaptive codebook delay that is contained in said excitation signal information, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in the second code string.

41. A program according to any one of claim 36 to claim 40, wherein said search range control value is calculated from a constant or said first adaptive codebook delay and said second adaptive codebook delay.

42. A program according to any one of claim 36 to claim 41, wherein:

an autocorrelation or a normalized autocorrelation is calculated from said speech signal or said excitation signal for delay that is within said range; and

delay for which said autocorrelation or normalized autocorrelation is a maximum is selected as second adaptive codebook delay.

37. A program for causing a computer, which constitutes a code conversion device for converting a first code string to a second code string, to execute:

a first process of obtaining a first linear prediction coefficient from said first code string;

a second process of obtaining excitation signal information from said first code string;

a third process of obtaining an excitation signal from said excitation signal information;

a fourth process of driving a filter having said first linear prediction coefficient by means of said excitation signal to generate a speech signal;

a fifth process of storing and holding a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string; and

a sixth process of using said speech signal to select a second adaptive codebook delay from delay that is within a range stipulated by a search range control value and said second adaptive codebook delay that has been stored and held, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.

38. A program for causing a computer, which constitutes a code conversion device for converting a first code string to a second code string, to execute:

a first process of obtaining a first linear prediction coefficient from said first code string;

a second process of obtaining excitation signal information from said first code string;

a third process of obtaining an excitation signal from said excitation signal information;

a fourth process of driving a filter having said first linear prediction coefficient by means of said excitation signal to generate a speech signal;

a fifth process of, in at least one of subframes, which are divisions of a frame that is a time unit of converting a code string, using said speech signal to select a second adaptive codebook delay from delay within a range stipulated by a search range control value and a first adaptive codebook delay that is contained in said excitation signal information, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string; and

a sixth process of, in at least one subframe in said frame, using the relation between said first adaptive codebook delay and a first delay code that corresponds to this first adaptive codebook delay and the relation between said second adaptive codebook delay and a second delay code that corresponds to this second adaptive codebook delay to place said first adaptive codebook delay in correspondence with said second adaptive codebook delay and thereby convert from said first delay code to said second delay code, and supplying said second delay code as code of an adaptive codebook delay in said second code string.

39. A program for causing a computer, which constitutes a code conversion device for converting a first code string to a second code string, to execute:

a first process of obtaining a first linear prediction coefficient from said first code string;

a second process of obtaining excitation signal information from said first code string;

a third process of obtaining an excitation signal from said excitation signal information;

a fourth process of driving a filter having said first linear prediction coefficient by means of said excitation signal to generate a speech signal;

a fifth process of, in each of subframes that are divisions of frames that are the time units of converting code strings, storing and holding a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string;

a sixth process of, in at least one subframe in said frames, using said speech signal to select a second adaptive codebook delay from delay within a range that is stipulated by a search range control value and said second adaptive codebook delay that has been previously found, stored and held, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string; and

a seventh process of, in at least one subframe in said frame, using the relation between said first adaptive codebook delay that is contained in said excitation signal information and a first delay code that corresponds to this first adaptive codebook delay and the relation between said second adaptive codebook delay and a second delay code that corresponds to this second adaptive codebook delay to place said first adaptive codebook delay in correspondence with said second adaptive codebook delay and thereby convert from said first delay code to said second delay code, and supplying said second delay code as code of an adaptive codebook delay in said second code string.

40. A program for causing a computer, which constitutes a code conversion device for converting a first code string to a second code string, to execute:

a first process of obtaining a first linear prediction coefficient from said first code string;

a second process of obtaining excitation signal information from said first code string;

a third process of obtaining an excitation signal from said excitation signal information;

a fourth process of driving a filter having said first linear prediction coefficient by means of said excitation signal to generate a speech signal;

a fifth process of, in each of subframes that are divisions of frames that are the time units of converting code strings, storing and holding a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string;

a sixth process of, in at least one subframe in said frames, using said speech signal to select a second adaptive codebook delay from delay that is within a range stipulated by a search range control value and a first adaptive codebook delay that is contained in said excitation signal information, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string; and

a seventh process of, in at least one subframe in said frames, using said speech signal to select a second adaptive codebook delay from delay that is within a range that is stipulated by said search range control value and said second adaptive codebook delay that has been previously found, stored, and held, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.

43. A program for causing a computer, which constitutes a code conversion device for converting a first code string to a second code string, to execute:

a first process of obtaining a first linear prediction coefficient and excitation signal information from said first code string;

a second process of obtaining a second linear prediction coefficient from said first linear prediction coefficient;

a third process of driving a filter having said first linear prediction coefficient or said second linear prediction coefficient by means of a first excitation signal that is obtained from said excitation signal information to generate a speech signal;

a fourth process of using a first adaptive codebook delay that is contained in said excitation signal information and a second excitation signal that has been previously calculated, stored, and held to successively generate an adaptive codebook signal, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string;

a fifth process of obtaining a second excitation signal from said selected adaptive codebook signal; and

a sixth process of storing and holding said second excitation signal.

44. A program for causing a computer, which constitutes a code conversion device for converting a first code string to a second code string, to execute:

a first process of obtaining a first linear prediction coefficient and excitation signal information from said first code string;

a second process of obtaining a second linear prediction coefficient from said first linear prediction coefficient;

a third process of driving a filter having said first linear prediction coefficient or said second linear prediction coefficient by means of a first excitation signal that is obtained from said excitation signal information to generate a speech signal;

a fourth process of storing and holding a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string;

a fifth process of using said second adaptive codebook delay that has been stored and held and a second excitation signal that has been previously calculated, stored and held to successively generate an adaptive codebook signal, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string;

a sixth process of obtaining a second excitation signal from said selected adaptive codebook signal; and

a seventh process of storing and holding said second excitation signal.

45. A program for causing a computer, which constitutes a code conversion device for converting a first code string to a second code string, to execute:

a first process of obtaining a first linear prediction coefficient from said first code string;

a second process of obtaining excitation signal information from said first code string;

a third process of obtaining a first excitation signal from said excitation signal information;

a fourth process of obtaining a second linear prediction coefficient from said first linear prediction coefficient;

a fifth process of driving a filter having said first linear prediction coefficient or said second linear prediction coefficient by means of said first excitation signal to generate a speech signal;

a sixth process of successively generating an adaptive codebook signal from a second excitation signal that has been previously calculated, stored, and held for delay that is within a range that is stipulated by a search range control value and a first adaptive codebook delay that is contained in said excitation signal information, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string;

a seventh process of obtaining a second excitation signal from said selected adaptive codebook signal; and

an eighth process of storing and holding said second excitation signal.

50. A program according to any one of claim 45 to claim 49, wherein:

said search range control value is calculated from a constant or said first adaptive codebook delay and said second adaptive codebook delay.

51. A program according to any one of claim 45 to claim 50, wherein:

for delay that is within said range, an autocorrelation or a normalized autocorrelation is calculated from said speech signal or said excitation signal; and

delay for which said autocorrelation or normalized autocorrelation is a maximum is selected as second adaptive codebook delay.

46. A program for causing a computer, which constitutes a code conversion device for converting a first code string to a second code string, to execute:

a first process of obtaining a first linear prediction coefficient from said first code string;

a second process of obtaining excitation signal information from said first code string;

a third process of obtaining a first excitation signal from said excitation signal information;

a fourth process of obtaining a second linear prediction coefficient from said first linear prediction coefficient;

a fifth process of driving a filter having said first linear prediction coefficient or said second linear prediction coefficient by means of said first excitation signal to generate a speech signal;

a sixth process of storing and holding a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string;

a seventh process of successively generating an adaptive codebook signal from a second excitation signal that has been previously calculated, stored, and held for delay that is within a range that is stipulated by a search range control value and said second adaptive codebook delay that has been stored and held, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string;

an eighth process of obtaining a second excitation signal from said selected adaptive codebook signal; and

a ninth process of storing and holding said second excitation signal.

47. A program for causing a computer, which constitutes a code conversion device for converting a first code string to a second code string, to execute:

a first process of obtaining a first linear prediction coefficient from said first code string;

a second process of obtaining excitation signal information from said first code string;

a third process of obtaining a first excitation signal from said excitation signal information;

a fourth process of obtaining a second linear prediction coefficient from said first linear prediction coefficient;

a fifth process of driving a filter having said first linear prediction coefficient or said second linear prediction coefficient by means of said first excitation signal to generate a speech signal;

a sixth process of, in at least one subframe, which is a division of frames that are the time units for converting code strings, successively generating an adaptive codebook signal from a second excitation signal that has been previously calculated, stored, and held for delay that is within a range that is stipulated by a search range control value and a first adaptive codebook delay that is contained in said excitation signal information, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string;

a seventh process of, in at least one subframe in said frames, using the relation between said first adaptive codebook delay and a first delay code that corresponds to this first adaptive codebook delay and the relation between said second adaptive codebook delay and a second delay code that corresponds to this second adaptive codebook delay to place said first adaptive codebook delay in correspondence with said second adaptive codebook delay and thus convert from said first delay code to said second delay code, and supplying said second delay code as code of an adaptive codebook delay in said second code string;

an eighth process of obtaining a second excitation signal from said selected adaptive codebook signal; and

a ninth process of storing and holding said second excitation signal.

48. A program for causing a computer, which constitutes a code conversion device for converting a first code string to a second code string, to execute:

a first process of obtaining a first linear prediction coefficient from said first code string;

a second process of obtaining excitation signal information from said first code string;

a third process of obtaining a first excitation signal from said excitation signal information;

a fourth process of obtaining a second linear prediction coefficient from said first linear prediction coefficient;

a fifth process of driving a filter having said first linear prediction coefficient or said second linear prediction coefficient by means of said first excitation signal to generate a speech signal;

a sixth process of, in each of subframes, which are divisions of frames that are the time units of converting code strings, storing and holding a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string;

a seventh process of, in at least one subframe in said frames, successively generating an adaptive codebook signal from a second excitation signal that has been previously calculated, stored, and held for delay that is within a range that is stipulated by a search range control value and said second adaptive codebook delay that has been previously found, stored, and held, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string;

an eighth process of, in at least one subframe in said frames, using the relation between a first adaptive codebook delay that is contained in said excitation signal information and a first delay code that corresponds to this first adaptive codebook delay and the relation between said second adaptive codebook delay and a second delay code that corresponds to this second adaptive codebook delay to place said first adaptive codebook delay in correspondence with said second adaptive codebook delay and thus convert from said first delay code to said second delay code, and supplying said second delay code as code of an adaptive codebook delay in said second code string;

a ninth process of obtaining a second excitation signal from said selected adaptive codebook signal; and

a tenth process of storing and holding said second excitation signal.

49. A program for causing a computer, which constitutes a code conversion device for converting a first code string to a second code string, to execute:

a first process of obtaining a first linear prediction coefficient from said first code string;

a second process of obtaining excitation signal information from said first code string;

a third process of obtaining a first excitation signal from said excitation signal information;

a fourth process of obtaining a second linear prediction coefficient from said first linear prediction coefficient;

a fifth process of driving a filter having said first linear prediction coefficient or said second linear prediction coefficient by means of said first excitation signal to generate a speech signal;

a sixth process of, in each of subframes, which are divisions of frames that are the time units of converting a code string, storing and holding a second adaptive codebook delay that corresponds to code of an adaptive codebook delay in said second code string;

a seventh process of, in at least one subframe in said frames, successively generating an adaptive codebook signal from a second excitation signal that has been previously calculated, stored, and held for delay that is within a range that is stipulated by a search range control value and a first adaptive codebook delay that is contained in said excitation signal information, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string;

an eighth process of, in at least one subframe in said frames, successively generating an adaptive codebook signal from a second excitation signal that has been previously calculated, stored, and held for delay that is within a range stipulated by a search range control value and said second adaptive codebook delay that has been previously found, stored and held, using said speech signal and a first reconstructed speech signal that is successively generated by driving a compound filter having said second linear prediction coefficient by means of said adaptive codebook signal to select an adaptive codebook signal and a second adaptive codebook delay, and supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string;

a ninth process of obtaining a second excitation signal from said selected adaptive codebook signal; and

a tenth process of storing and holding said second excitation signal.

54. A code conversion device, said code conversion device:

supplying a code separation circuit with code string data that are realized by multiplexing code in which a speech signal has been encoded by a first system that conforms with an encoding mode wherein;

a speech signal is subjected to spectral analysis and resolved into a spectral envelope component and a residual component, said spectral envelope component is represented as a spectral parameter, and code that corresponds to a signal component that is closest to residual waveform of that speech signal that is to be encoded is selected from a codebook having signal components that represent residual components;

based on code that has been separated by said code separation circuit, converting to code that conforms to a second system that is different from said first system

supplying this converted code to a code multiplexing circuit; and

supplying as output code string data that are realized by multiplexing said converted code from said code multiplexing circuit;

said code conversion device comprising;

a circuit for, based on linear prediction coefficient code that has been separated by said code separation circuit, generating a first linear prediction coefficient that is realized by decoding by said first system;

a speech decoding circuit for receiving as input excitation signal information that contains adaptive codebook code and gain code that have been separated by said code separation circuit, and for synthesizing and supplying a speech signal by driving a linear prediction compound filter having said first linear prediction coefficient by means of an excitation signal that is obtained from said excitation signal information; and

an adaptive codebook code generation circuit for selecting a second adaptive codebook delay based on a first adaptive codebook delay that has been decoded from said excitation signal information and said speech signal that has been synthesized by said speech decoding circuit; and

supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in code string data of said second system.

55. A code conversion device according to claim 54, wherein said adaptive codebook code generation circuit comprises:

an ACB delay search range control means for calculating a search range control value from a first adaptive codebook delay that is stored in a first storage means and a second adaptive codebook delay that is stored in a second storage means;

an ACB encoding means for;

calculating an autocorrelation from said speech signal and then selecting the delay for which said autocorrelation is a maximum from among a first adaptive codebook delay that is contained in said excitation signal information and delay that is within a range of values that is stipulated by said search range control value;

taking said selected delay as the second adaptive codebook delay; and

then both supplying code that corresponds to said second adaptive codebook delay as an adaptive codebook delay in code string data of said second system and storing said selected second adaptive codebook delay in said second storage means.

56. A code conversion device according to claim 55, wherein said ACB delay search range control means:

calculates the absolute value of the difference between said first adaptive codebook delay that is stored in said first storage means and said second adaptive codebook delay that is stored in said second storage means that correspond to the same subframe for all of said first adaptive codebook delays and all of said second adaptive codebook delays that are stored; and

takes as said search range control value a value that is obtained by adding, for the number of said subframes, values obtained by multiplying said absolute values by a weighting coefficient.

57. A code conversion device according to claim 54, comprising:

an adaptive codebook code conversion circuit for receiving an adaptive codebook delay code that has been separated and supplied as output by said code separation circuit, converting the adaptive codebook delay code to code that can be decoded by a first encoding system, and supplying the converted adaptive codebook delay code as second adaptive codebook delay code to a code multiplexing circuit; and

a switching device for receiving the output of said adaptive codebook code conversion circuit and the output of said adaptive codebook code generation circuit, selecting one of these outputs, and supplying the selected output to said code multiplexing circuit.

58. A code conversion device according to claim 57, wherein:

in a predetermined subframe, the output of said adaptive codebook code converting circuit is supplied by way of said switching device to said code multiplexing circuit; and

second adaptive codebook delay information that is supplied as output from said adaptive codebook code conversion circuit is supplied to said adaptive code generation circuit and stored in a storage means.

59. A code conversion device according to claim 57, wherein said adaptive codebook code generation circuit includes:

an ACB delay search range control means for;

calculating the difference between first adaptive codebook delay of consecutive subframes for a past first adaptive codebook delay that is stored in a first storage means and the first adaptive codebook delay of the current subframe;

calculating the absolute value of said difference; and

taking as said search range control value a value that is obtained by adding, for the number of said subframes, values that are obtained by multiplying said absolute values by a weighting coefficient; and

an ACB encoding means for, in at least one subframe in a frame, calculating an autocorrelation using said speech signal;

selecting the second adaptive codebook delay for which said autocorrelation is a maximum from delay that is within a range stipulated by said search range control value and a second adaptive codebook delay that has been previously found, stored, and held; and

supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.

60. A code conversion device according to claim 54, said adaptive codebook code conversion circuit is provided with:

an ACB delay search range control means for;

in at least one subframe in said frame, calculating the absolute value of the difference between said first adaptive codebook delay that is stored in a first storage means and said second adaptive codebook delay that is stored in a second storage means that correspond to the same subframe for all said first adaptive codebook delays and said second adaptive codebook delays that are stored and held, and taking as a search range control value a value that is obtained by adding, for said number of subframes, values that are obtained by multiplying said absolute values by a weighting coefficient; and

in other subframes, calculating the difference between said first adaptive codebook delay of consecutive subframes for said first adaptive codebook delay that has been stored and held and said first adaptive codebook delay of the current subframe;

calculating the absolute value of said difference; and

taking as a search range control value a value that is obtained by adding, for said number of subframes, values obtained by multiplying said absolute values by a weighting coefficient; and

an ACB encoding means for;

in at least one subframe in said frames, using said speech signal to select a second adaptive codebook delay from delay that is within a range that is stipulated by said search range control value and said first adaptive codebook delay; and

supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string; and

in other subframes, using said speech signal to select a second adaptive codebook delay from delay that is within a range that is stipulated by said search range control value and said second adaptive codebook delay that has been previously found, stored, and held; and

supplying code that corresponds to said second adaptive codebook delay as code of an adaptive codebook delay in said second code string.

61. A code conversion device according to claim 55, wherein said adaptive codebook code conversion circuit is provided with:

a weighting signal calculation means that uses said first linear prediction coefficient to constitute an auditory weighting filter, and that supplies, to said ACB encoding means, an auditory weighted speech signal that is obtained by driving said auditory weighting filter by means of said speech signal that is supplied as output from said speech decoding circuit.

62. A code conversion device according to any one of claim 54 to claim 61, comprising:

a fixed codebook code conversion circuit for;

acquiring second FCB code by using the correspondence between code in said first system and code in said second system to rewrite first fixed codebook code (referred to as “

FCB code”

) that is received from said code separation circuit; and

supplying said second FCB code to said code multiplexing circuit as code that can be decoded by an FCB decoding method in said second system; and

a gain code conversion circuit for;

decoding first gain code that has been received from said code separation circuit by means of a gain decoding method in said first system to acquire first gain;

quantizing and encoding said first gain by means of a gain quantization method and encoding method in said second system to acquire a second gain code; and

supplying said second gain code to said code multiplexing circuit as code that can be decoded by means of a gain decoding method in said second system.

63. A code conversion device, said code conversion device:

supplying a code separation circuit with code string data that are realized by multiplexing code in which a speech signal has been encoded by a first system that conforms with an encoding mode wherein;

a speech signal is subjected to spectral analysis and resolved into a spectral envelope component and a residual component, said spectral envelope component is represented as a spectral parameter, and code that corresponds to a signal component that is closest to residual waveform of that speech signal that is to be encoded is selected from a codebook having signal components that represent residual component;

based on code that has been separated by said code separation circuit, converting to code that conforms to a second system that is different from said first system

supplying this converted code to a code multiplexing circuit; and

supplying as output code string data that are realized by multiplexing said converted code from said code multiplexing circuit;

said code conversion device comprising;

a circuit for generating a first and second linear prediction coefficient that are realized by decoding by said first system and said second system based on a linear prediction coefficient code that has been separated by means of said code separation circuit;

a speech decoding circuit for receiving as input excitation signal information that contains adaptive codebook code that has been separated by said code separation circuit and decoding said excitation signal information, and

driving a compound filter having said first linear prediction coefficient by means of an excitation signal that is obtained from said excitation signal information to synthesize and supply a speech signal;

an adaptive codebook code generation circuit;

an impulse response calculation circuit;

a fixed codebook code generation circuit;

a gain code generation circuit;

a second excitation signal calculation circuit; and

a second excitation signal storage circuit;

wherein said adaptive codebook code generation circuit comprises;

means for calculating a first target signal from decoded speech from said speech decoding circuit and said first and second linear prediction coefficients;

means for finding a second adaptive codebook delay, a second adaptive codebook signal, and optimum adaptive codebook gain from a past second excitation signal that are stored and held in said second excitation signal storage circuit, an impulse response signal from said impulse response calculation circuit, and said first target signal; and

means for supplying said first target signal to said fixed codebook code generation circuit and said gain code generation circuit;

supplying said optimum adaptive codebook gain to said fixed codebook code generation circuit;

supplying said second adaptive codebook signal to said fixed codebook code generation circuit, said gain code generation circuit, and said second excitation signal calculation circuit; and

supplying code that can be decoded by said second system and that corresponds to the adaptive codebook delay to said code multiplexing circuit as the second adaptive codebook code;

said impulse response calculation circuit comprising;

means for using said first and second linear prediction coefficient to constitute an auditory weighting compound filter, and supplying the impulse response signal of said auditory weighting compound filter to said adaptive codebook code generation circuit, said fixed codebook code generation circuit, and said gain code generation circuit;

said fixed codebook code generation circuit comprising;

means for receiving said first target signal, said second adaptive codebook signal, and said optimum adaptive codebook gain that are supplied from said adaptive codebook code generation circuit;

receiving an impulse response signal that is supplied from said impulse response calculation circuit; and

calculating a second target signal from said first target signal, said second adaptive codebook signal, said optimum adaptive codebook gain, and said impulse response signal;

means for finding a fixed codebook signal for which the distance from said second target signal is a minimum from said second target signal, a fixed codebook signal that has been stored in a storage means, said impulse response signal; and

means for supplying code that can be decoded by said second system and that corresponds to said fixed codebook signal as the second fixed codebook code to said code multiplexing circuit, and further supplying said fixed codebook signal to said gain code generation circuit and said second excitation signal calculation circuit;

said gain code generation circuit comprising;

means for;

receiving as input said first target signal and second adaptive codebook signal (referred to as “

second ACB signal”

) that are supplied from said adaptive codebook code generation circuit, a second fixed codebook signal (referred to as “

second FCB signal”

) that is supplied from said fixed codebook code generation circuit, and an impulse response signal that is supplied from said impulse response calculation circuit;

finding ACB gain and FCB gain for which the weighting squared error between said first target signal and reconstructed speech is a minimum, this ACB gain and FCB gain being calculated from said first target signal, second ACB signal, second FCB signal, said impulse response signal, and ACB gain and FCB gain that are stored in a storage means;

supplying code that can be decoded by said second system and that corresponds to said ACB gain and FCB gain as second gain code to said code multiplexing circuit; and

supplying said ACB gain and FCB gain as second ACB gain and second FCB gain, respectively, to said second excitation signal calculation circuit;

said second excitation signal calculation circuit comprising;

means for;

receiving a second ACB signal that is supplied from said adaptive codebook code generation circuit, a second FCB signal that is supplied from said fixed codebook code generation circuit, and second ACB gain and second FCB gain that are supplied from said gain code generation circuit;

acquiring a second excitation signal by adding a signal obtained by multiplying said second ACB signal by second ACB gain with a signal obtained by multiplying said second FCB signal by said second FCB gain; and

storing and holding said second excitation signal in said second excitation signal storage circuit;

wherein said second excitation signal storage circuit supplies a second excitation signal that was previously received, stored, and held to said adaptive codebook code generation circuit.

64. A code conversion device according to claim 63, said code conversion device including:

an adaptive codebook code conversion circuit for;

receiving adaptive codebook delay code that has been separated by said code separation circuit;

converting adaptive codebook delay code to code that can be decoded by said second encoding system; and

supplying the converted adaptive codebook delay code as second adaptive codebook delay code to said code multiplexing circuit; and

a switching device for receiving output of said adaptive codebook code conversion circuit and output of said adaptive codebook code generation circuit, selecting one of these outputs, and supplying the selected output to said code multiplexing circuit.

65. A code conversion device, said code conversion device receiving code data that are realized by encoding a speech signal by a first system and that contain linear prediction coefficient code, codebook code, and gain code;

converting said received code data to code that conforms with a second system that differs from said first system, and supplying said converted code data as output;

said code conversion device being provided with;

means for finding an adaptive codebook delay based on decoded speech that is synthesized using a decoded linear prediction coefficient, codebook information, and gain information; and

supplying code that corresponds to said adaptive codebook delay as adaptive codebook code of said second system.