Method of converting codes between speech coding and decoding systems, and device and program therefor

• US 20030033142A1
• Filed: 06/11/2002
• Published: 02/13/2003
• Est. Priority Date: 06/15/2001
• Status: Active Grant

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Murashima, Atsushi
• Granted Patent: US 7,318,024 B2
• Time in Patent Office: Days
• US Class Current: 704/219
• CPC Class Codes: G10L 19/06 Determination or coding of the spectral characteristics, e.g. of the short-term prediction coefficients
• CPC Class Codes: G10L 19/173 Transcoding, i.e. converting between two coded representations avoiding cascaded coding-decoding

Abstract

A second evaluation value calculation circuit calculates an evaluation value from a first linear prediction coefficient, a second linear prediction coefficient stored and held, a third linear prediction coefficient read from a table in which a plurality of linear prediction coefficients are stored in advance, and a fourth linear prediction coefficient selected, stored and held among the third linear prediction coefficients read from the table in the past, while a second evaluation value minimizing circuit selects the third linear prediction coefficient with which the evaluation value is the minimum and outputs a code corresponding to the selected third linear prediction coefficient as a code decodable by a second coding and decoding system.

Claims

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

a first step of obtaining a first linear prediction coefficient from a code corresponding to a linear prediction coefficient out of said first code string,

a second step of storing and holding said first linear prediction coefficient as a second linear prediction coefficient,

a third step of calculating, from said first linear prediction coefficient, said second linear prediction coefficient and a third linear prediction coefficient sequentially read from a table in which a plurality of linear prediction coefficients are stored in advance, an evaluation value for each said third linear prediction coefficient, and

a fourth step of selecting said third linear prediction coefficient with which said evaluation value is the minimum from said table to output a code corresponding to selected said third linear prediction coefficient as a code corresponding to a linear prediction coefficient in the second code string.

2. The code conversion method as set forth in claim 1, wherein

at said third step,

from said first linear prediction coefficient, said second linear prediction coefficient, said third linear prediction coefficient sequentially read from said table, and a fourth linear prediction coefficient selected, and stored and held among the third linear prediction coefficients read in the past from said table, an evaluation value for each said third linear prediction coefficient is calculated, and

at said fourth step,

said third linear prediction coefficient with which said evaluation value is the minimum is selected from said table to output a code corresponding to selected said third linear prediction coefficient as a code which is corresponding to the linear prediction coefficient in the second code string and is decodable by a linear prediction coefficient decoding method in a second coding and decoding system, and which further comprises:

a fifth step of storing and holding selected said third linear prediction coefficient as the fourth linear prediction coefficient.

3. The code conversion method as set forth in claim 1, wherein

at said third step,

a first square error is calculated from said first linear prediction coefficient and said third linear prediction coefficient and a second square error is calculated from said second linear prediction coefficient and said third linear prediction coefficient to calculate an evaluation value from said second square error and said first square error.

4. The code conversion method as set forth in claim 2, wherein

at said third step,

a first square error is calculated from said first linear prediction coefficient and said third * linear prediction coefficient, a first amount of change in time is calculated from said first linear prediction coefficient and said second linear prediction coefficient, a second amount of change in time is calculated from said third linear prediction coefficient and said fourth linear prediction coefficient, and a second square error is calculated from said first amount of change in time and said second amount of change in time to calculate an evaluation value from said second square error and said first square error.

5. The code conversion method as set forth in claim 3, wherein

said second square error is multiplied by a control coefficient and the multiplication result is added to said first square error to calculate an evaluation value.

6. The code conversion method as set forth in claim 3, wherein

a value obtained by internally dividing said first square error and said second square error by a ratio determined by said control coefficient is taken as an evaluation value.

7. The code conversion method as set forth in claim 4, wherein

said first amount of change in time is calculated from a difference between said first linear prediction coefficient and said second linear prediction coefficient and said second amount of change in time is calculated from a difference between said third linear prediction coefficient and said fourth linear prediction coefficient.

8. The code conversion method as set forth in claim 5, wherein

a third amount of change in time is calculated from said first linear prediction coefficient and said second linear prediction coefficient and-said control-coefficient is calculated from said third amount of change in time.

9. The code conversion method as set forth in claim 8, wherein

said third amount of change in time is calculated from a difference between said first linear prediction coefficient and said second linear prediction coefficient.

10. The code conversion method as set forth in claim 8, wherein

when said third amount of change in time is less than a first threshold value, said control coefficient is expressed by a first constant, when said amount of change in time is not less than said first threshold value and less than a second threshold value, said control coefficient is expressed by a function of said third amount of change in time and in the remaining cases, said control coefficient is expressed by a second constant.

11. A code conversion device for converting a first code string into a second code string, comprising:

a linear prediction coefficient decoding circuit for obtaining a first linear prediction coefficient from a code corresponding to a linear prediction coefficient out of said first code string,

a storage circuit for storing and holding said first linear prediction coefficient as a second linear prediction coefficient,

an evaluation value calculation circuit for calculating, from said first linear prediction coefficient, said second linear prediction coefficient and a third linear prediction coefficient sequentially read from a table in which a plurality of linear prediction coefficients are stored in advance, an evaluation value for each said third linear prediction coefficient, and

an evaluation value minimizing circuit for selecting said third linear prediction coefficient with which said evaluation value is the minimum from said table to output a code corresponding to selected said third linear prediction coefficient as a code corresponding to a linear prediction coefficient in the second code string.

12. The code conversion device as set forth in claim 11, wherein

said evaluation value calculation circuit

calculates an evaluation value for each said third linear prediction coefficient from said first linear prediction coefficient, said second linear prediction coefficient, said third linear prediction coefficient sequentially read from said table, and a fourth linear prediction coefficient stored and held, and

said evaluation value minimizing circuit

selects said third linear prediction coefficient with which said evaluation value is the minimum from said table to output a code corresponding to selected said third linear prediction coefficient as a code corresponding to the linear prediction coefficient in the second code string, and which further comprises:

a second storage circuit for storing and holding selected said third linear prediction coefficient as the fourth linear prediction coefficient.

13. The code conversion device as set forth in claim 11, wherein

said evaluation value calculation circuit

calculates a first square error from said first linear prediction coefficient and said third linear prediction coefficient and calculates a second square error from said second linear prediction coefficient and said third linear prediction coefficient to calculate an evaluation value from said second square error and said first square error.

14. The code conversion device as set forth in claim 12, wherein

said evaluation value calculation circuit

calculates a first square error from said first linear prediction coefficient and said third linear prediction coefficient, calculates a first amount of change in time from said first linear prediction coefficient and said second linear prediction coefficient, calculates a second amount of change in time from said third linear prediction coefficient and said fourth linear prediction coefficient, and calculates a second square error from said first amount of change in time and said second amount of change in time to calculate an evaluation value from said second square error and said first square error.

15. The code conversion device as set forth in claim 13, wherein

said evaluation value calculation circuit multiplies said second square error by a control coefficient and adds the multiplication result to said first square error to calculate an evaluation value.

16. The code conversion device as set forth in claim 13, wherein

said evaluation value calculation circuit takes a value obtained by internally dividing said first square error and said second square error by a ratio determined by said control coefficient as an evaluation value.

17. The code conversion device as set forth in claim 14, wherein

said evaluation value calculation circuit calculates said first amount of change in time from a difference between said first linear prediction coefficient and said second linear prediction coefficient and calculates said second amount of change in time from a difference between said third linear prediction coefficient and said fourth linear prediction coefficient.

18. The code conversion device as set forth in claim 15, wherein

said evaluation value calculation circuit calculates a third amount of change in time from said first linear prediction coefficient and said second linear prediction coefficient to calculate said control coefficient from said third amount of change in time.

19. The code conversion device as set forth in claim 18, wherein

said evaluation value calculation circuit calculates said third amount of change in time from a difference between said first linear prediction coefficient and said second linear prediction coefficient.

20. The code conversion device as set forth in claim 18, wherein

when said third amount of change in time is less than a first threshold value, said evaluation value calculation circuit expresses said control coefficient by a first constant, when said amount of change in time is not less than said first threshold value and less than a second threshold value, expresses said control coefficient by a function of said third amount of change in time and in the remaining cases, expresses said control coefficient by a second constant.

21. A code conversion program for conducting code conversion by controlling a computer which forms a code conversion device for converting a first code string into a second code string, comprising the functions of:

(a) of obtaining a first linear prediction coefficient from a code corresponding to a linear prediction coefficient out of said first code string,

(b) of storing and holding said first linear prediction coefficient as a second linear prediction coefficient,

(c) of calculating, from said first linear prediction coefficient, said second linear prediction coefficient and a third linear prediction coefficient sequentially read from a table in which a plurality of linear prediction coefficients are stored in advance, an evaluation value for each said third linear prediction coefficient, and

(d) of selecting said third linear prediction coefficient with which said evaluation value is the minimum from said table to output a code corresponding to selected said third linear prediction coefficient as a code corresponding to a linear prediction coefficient in the second code string.

22. The code conversion program as set forth in claim 21, wherein

said function (c)

causes the computer to execute a function of calculating an evaluation value for each said third linear prediction coefficient from said first linear prediction coefficient, said second linear prediction coefficient, said third linear prediction coefficient sequentially read from said table, and a fourth linear prediction coefficient stored and held, and

said function (d)

causes the computer to execute a function of selecting said third linear prediction coefficient with which said evaluation value is the minimum from said table to output a code corresponding to selected said third linear prediction coefficient as a code corresponding to the linear prediction coefficient in the second code string, and which further comprises:

a function (e) of storing and holding selected said third linear prediction coefficient as the fourth linear prediction coefficient.

23. The code conversion program as set forth in claim 21, wherein

said function (c)

causes the computer to execute a function of calculating a first square error from said first linear prediction coefficient and said third linear prediction coefficient and calculating a second square error from said second linear prediction coefficient and said third linear prediction coefficient to calculate an evaluation value from said second square error and said first square error.

24. The code conversion program as set forth in claim 22, wherein

said function (c)

causes the computer to execute a function of calculating a first square error from said first linear prediction coefficient and said third linear prediction coefficient, calculating a first amount of change in time from said first linear prediction coefficient and said second linear prediction coefficient, calculating a second amount of change in time from said third linear prediction coefficient and said fourth linear prediction coefficient, and calculating a second square error from said first amount of change in time and said second amount of change in time to calculate an evaluation value from said second square error and said first square error.

25. The code conversion program as set forth in claim 23, which

causes the computer to execute a function of multiplying said second square error by a control coefficient and adding the multiplication result to said first square error to calculate an evaluation value.

26. The code conversion program as set forth in claim 23, which

causes the computer to execute a function of taking a value obtained by internally dividing said first square error and said second square error by a ratio determined by said control coefficient as an evaluation value.

27. The code conversion program as set forth in claim 24, which

causes the computer to execute a function of calculating said first amount of change in time from a difference between said first linear prediction coefficient and said second linear prediction coefficient and calculating said second amount of change in time from a difference between said third linear prediction coefficient and said fourth linear prediction coefficient.

28. The code conversion program as set forth in claim 25, which

causes the computer to execute a function of calculating a third amount of change in time from said first linear prediction coefficient and said second linear prediction coefficient to calculate said control coefficient from said third amount of change in time.

29. The code conversion program as set forth in claim 28, which

causes the computer to execute a function of calculating said third amount of change in time from a difference between said first linear prediction coefficient and said second linear prediction coefficient.

30. The code conversion program as set forth in claim 28, which

causes the computer to execute a function of, when said third amount of change in time is less than a first threshold value, expressing said control coefficient by a first constant, when said amount of change in time is not less than said first threshold value and less than a second threshold value, expressing said control coefficient by a function of said third amount of change in time and in the remaining cases, expressing said control coefficient by a second constant.

31. A code conversion method of converting a first code string into a second code string, comprising the steps of:

a first step of obtaining a first gain from a code corresponding to a gain out of said first code string,

a second step of storing and holding said first gain as a second gain,

a third step of calculating, from said first gain, said second gain and a third gain sequentially read from a table in which a plurality of gains are stored in advance, an evaluation value for each said third gain, and

a fourth step of selecting said third gain with which said evaluation value is the minimum from said table to output a code corresponding to selected said third gain as a code corresponding to a gain in the second code string.

32. The code conversion method as set forth in claim 31, wherein

at said third step,

an evaluation value for each said third gain is calculated from said first gain, said second gain, said third gain sequentially read from said table, and a fourth gain selected, stored and held among third linear prediction coefficients read from said table in the past, and

at said fourth step,

said third gain with which said evaluation value is the minimum is selected from said table and a code corresponding to selected said third gain is output as a code which is corresponding to the gain in the second code string and is decodable by a linear prediction coefficient decoding method in a second coding and decoding system, and which further comprises:

a fifth step of storing and holding selected said third gain as the fourth gain.

33. The code conversion method as set forth in claim 31, wherein

at said third step,

a first square error is calculated from said first gain and said third gain and a second square error is calculated from said second gain and said third gain to calculate an evaluation value from said second square error and said first square error.

34. The code conversion method as set forth in claim 32, wherein

at said third step,

a first square error is calculated from said first gain and said third gain, a first amount of change in time is calculated from said first gain and said second gain, a second amount of change in time is calculated from said third gain and said fourth gain, and a second square error is calculated from said first amount of change in time and said second amount of change in time to calculate an evaluation value from said second square error and said first square error.

35. The code conversion method as set forth in claim 33, wherein

said second square error is multiplied by a control coefficient and the multiplication result is added to said first square error to calculate an evaluation value.

36. The code conversion method-as set forth in claim 33, wherein

a value obtained by internally dividing said first square error and said second square error by a ratio determined by said control coefficient is taken as an evaluation value.

37. The code conversion method as set forth in claim 34, wherein

said first amount of change in time is calculated from a difference between said first gain and said second gain and said second amount of change in time is calculated from a difference between said third gain and said fourth gain.

38. The code conversion method as set forth in claim 35, wherein

a third amount of change in time is calculated from said first gain and said second gain to calculate said control coefficient from said third amount of change in time.

39. The code conversion method as set forth in claim 38, wherein

said third amount of change in time is calculated from a difference between said first gain and said second gain.

40. The code conversion method as set forth in claim 38, wherein

when said third amount of change in time is less than a first threshold value, said control coefficient is expressed by a first constant, when said amount of change in time is not less than said first threshold value and less than a second threshold value, said control coefficient is expressed by a function of said third amount of change in time and in the remaining cases, said control coefficient is expressed by a second constant.

41. A code conversion device for converting a first code string into a second code string, comprising:

a gain decoding circuit for obtaining a first gain from a code corresponding to a gain out of said first code string,

a storage circuit for storing and holding said first gain as a second gain,

an evaluation value calculation circuit for calculating, from said first gain, said second gain and a third gain sequentially read from a table in which a plurality of gains are stored in advance, an evaluation value for each said third gain, and

an evaluation value minimizing circuit for selecting said third gain with which said evaluation value is the minimum from said table to output a code corresponding to selected said third gain as a code corresponding to a gain in the second code string.

42. The code conversion device as set forth in claim 41, wherein

said evaluation value calculation circuit

calculates an evaluation value for each said third gain from said first gain, said second gain, said third gain sequentially read from said table, and a fourth gain stored and held, and

said evaluation value minimizing circuit

selects said third gain with which said evaluation value is the minimum from said table to output a code corresponding to selected said third gain as a code corresponding to the gain in the second code string,

and which further comprises:

a second storage circuit for storing and holding selected said third gain as the fourth gain.

43. The code conversion device as set forth in claim 41, wherein

said evaluation value calculation circuit

calculates a first square error from said first gain and said third gain and a second square error from said second gain and said third gain to calculate an evaluation value from said second square error and said first square error.

44. The code conversion device as set forth in claim 42, wherein

said evaluation value calculation circuit

calculates a first square error from said first gain and said third gain, a first amount of change in time from said first gain and said second gain, a second amount of change in time from said third gain and said fourth gain, and a second square error from said first amount of change in time and said second amount of change in time to calculate an evaluation value from said second square error and said first square error.

45. The code conversion device as set forth in claim 43, wherein

said second square error is multiplied by a control coefficient and the multiplication result is added to said first square error to calculate an evaluation value.

46. The code conversion device as set forth in claim 43, wherein

a value obtained by internally dividing said first square error and said second square error by a ratio determined by said control coefficient is taken as an evaluation value.

47. The code conversion device as set forth in claim 44, wherein

said first amount of change in time is calculated from a difference between said first gain and said second gain and said second amount of change in time is calculated from a difference between said third gain and said fourth gain.

48. The code conversion device as set forth in claim 45, wherein

a third amount of change in time is calculated from said first gain and said second gain to calculate said control coefficient from said third amount of change in time.

49. The code conversion device as set forth in claim 48, wherein

said third amount of change in time is calculated from a difference between said first gain and said second gain.

50. The code conversion device as set forth in claim 48, wherein

when said third amount of change in time is less than a first threshold value, said control coefficient is expressed by a first constant, when said amount of change in time is not less than said first threshold value and less than a second threshold value, said control coefficient is expressed by a function of said third amount of change in time and in the remaining cases, said control coefficient is expressed by a second constant.

51. A code conversion program for conducting code conversion by controlling a computer which forms a code conversion device for converting a first code string into a second code string, comprising the functions of:

(a) of obtaining a first gain from a code corresponding to a gain out of said first code string,

(b) of storing and holding said first gain as a second gain,

(c) of calculating, from said first gain, said second gain and a third gain sequentially read from a table in which a plurality of gains are stored in advance, an evaluation value for each said third gain, and

(d) of selecting said third gain with which said evaluation value is the minimum from said table to output a code corresponding to selected said third gain as a code corresponding to a gain in the second code string.

52. The code conversion program as set forth in claim 51, wherein

said function (c)

causes the computer to execute a function of calculating an evaluation value for each said third gain from said first gain, said second gain, said third gain sequentially read from said table, and a fourth gain stored and held, and

said function (d)

causes the computer to execute a function of selecting said third gain with which said evaluation value is the minimum from said table and outputting a code corresponding to selected said third gain as a code corresponding to the gain in the second code string, and which further comprises:

a function (e) of storing and holding selected said third gain as the fourth gain.

53. The code conversion program as set forth in claim 51, wherein

said function (c)

causes the computer to execute a function of calculating a first square error from said first gain and said third gain and a second square error from said second gain and said third gain to calculate an evaluation value from said second square error and said first square error.

54. The code conversion program as set forth in claim 52, wherein

said function (c)

causes the computer to execute a function of calculating a first square error from said first gain and said third gain, a first amount of change in time from said first gain and said second gain, a second amount of change in time from said third gain and said fourth gain, and a second square error from said first amount of change in time and said second amount of change in time to calculate an evaluation value from said second square error and said first square error.

55. The code conversion program as set forth in claim 53, which

causes the computer to execute a function of multiplying said second square error by a control coefficient and adding the multiplication result to said first square error to calculate an evaluation value.

56. The code conversion program as set forth in claim 53, which

causes the computer to execute a function of taking a value obtained by internally dividing said first square error and said second square error by a ratio determined by said control coefficient as an evaluation value.

57. The code conversion program as set forth in claim 54, which

causes the computer to execute a function of calculating said first amount of change in time from a difference between said first gain and said second gain and said second amount of change in time from a difference between said third gain and said fourth gain.

58. The code conversion program as set forth in claim 55, which

causes the computer to execute a function of calculating a third amount of change in time from said first gain and said second gain to calculate said control coefficient from said third amount of change in time.

59. The code conversion program as set forth in claim 58, which

causes the computer to execute a function of calculating said third amount of change in time from a difference between said first gain and said second gain.

60. The code conversion program as set forth in claim 58, which

causes the computer to execute a function of, when said third amount of change in time is less than a first threshold value, expressing said control coefficient by a first constant, when said amount of change in time is not less than said first threshold value and less than a second threshold value, expressing said control coefficient by a function of said third amount of change in time and in the remaining cases, expressing said control coefficient by a second constant.