Determination of gain for pitch period in coding of speech signal

• US 5,832,180 A
• Filed: 02/23/1996
• Issued: 11/03/1998
• Est. Priority Date: 02/23/1995
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Nomura, Toshiyuki
• Primary Examiner(s): Hafiz, Tariq R.
• Application Number:
  US08/604,743
• Time in Patent Office: 984 Days
• Field of Search: 395/2.1, 395/2.28-2.34
• US Class Current: 704/223
• CPC Class Codes: G10L 19/12 the excitation function being a code excitation, e.g. in code excited linear prediction [CELP] vocoders
• CPC Class Codes: G10L 2019/0003 Backward prediction of gain
• CPC Class Codes: G10L 2019/0011 Long term prediction filters, i.e. pitch estimation

Abstract

A speech signal coding apparatus includes a dividing section for dividing a speech signal in units of sub-frames. A spectrum parameter section calculates a spectrum parameter for each sub-frame. An error signal generating section generates a perceptual sensitivity weighted error signal from a reproduction signal and the speech signal for a sub-frame. An adaptive code book is referred to based on the perceptual sensitivity weighted error signal so that an adaptive code vector and a pitch period is selected. Also, an excitation code book is referred to based on the perceptual sensitivity weighted error signal so that an excitation code vector from the excitation code book is selected. In a gain code vector section having a gain code book which stores gain code vectors, a gain code book is referred to based on the perceptual sensitivity weighted error signal, so that a gain code vector is selected. Gains are determined from the selected gain code vector in units of time intervals shorter than the sub-frame, and the reproduction signal is generated by weighting the adaptive code vector and excitation code vector with the determined gains in units of time intervals.

Claims

1. A speech signal coding apparatus comprising:

dividing means for dividing a speech signal in units of first predetermined time intervals;

spectrum parameter means for calculating a spectrum parameter for each first predetermined time interval;

error signal generating means for generating a perceptual sensitivity weighted error signal from an inputted excitation signal and the spectrum parameter for said each first predetermined time interval of speech signal;

adaptive code vector means having an adaptive code book which stores adaptive code vectors, for referring to said adaptive code book to select an adaptive code vector and a pitch period based on the perceptual sensitivity weighted error signal;

excitation code vector means having an excitation code book which stores excitation code vectors, for referring to said excitation code book to select an excitation code vector from said excitation code book based on the perceptual sensitivity weighted error signal; and

gain code vector means having a gain code book which stores gain code vectors, for referring to said gain code book to select a gain code vector based on the perceptual sensitivity weighted error signal, and for determining gains from said selected gain code vector for every second predetermined time interval shorter than said first predetermined time interval, and for producing said excitation signal from said adaptive code vector, said excitation code vector and the determined gains.

2. A speech signal coding apparatus according to claim 1, wherein said gain code vector means includes:

said gain code book;

dividing means for dividing each of said adaptive code vector and said excitation code vector into a plurality of segments, each segment having the second predetermined time interval;

gain providing means for referring to said gain code book to read out the selected gain code vector based on said weighted error signal and for determining gains for said segments from said selected gain code vector; and

excitation signal generating means for generating said excitation signal from said segments of said adaptive code vector, said segments of said excitation code vector, and said determined gains for said segments.

3. A speech signal coding apparatus according to claim 1, wherein said gain code vector means includes:

said gain code book;

dividing means for dividing each of said adaptive code vector and said excitation code vector into a plurality of segments, each segment having the second predetermined time interval;

gain providing means for referring to said gain code book to read out the selected gain code vector based on said weighted error signal;

calculating means for interpolating and/or extrapolating, based on gains of said selected gain code vector for at least two segments of each of said adaptive code vector and said excitation code vector, gains for segments of each of said adaptive code vector and said excitation code vector other than said at least two segments; and

excitation signal generating means for generating said excitation signal from said segments of said adaptive code vector, said segments of said excitation code vector, and said gains for said segments.

4. A speech signal coding apparatus according to claim 1, wherein said gain code vector means includes:

said gain code book;

dividing means for dividing each of said adaptive code vector and said excitation code vector into a plurality of segments, each segment having the second predetermined time interval;

storing means for storing a gain of for a second predetermined time interval of each of said adaptive code vector and said excitation code vector in a previous first predetermined time interval;

gain providing means for referring to said gain code book to read out the selected gain code vector based on said weighted error signal;

calculating means for interpolating and/or extrapolating, based on gains of said selected gain code vector for at least one segment of each of said adaptive code vector and said excitation code vector and said gains stored in said storing means, gains for segments of each of said adaptive code vector and said excitation code vector other than said at least one segment; and

excitation signal generating means for generating said excitation signal from said segments of said adaptive code vector, said segments of said excitation code vector, and said calculated gains for said segments.

5. A speech signal coding apparatus according to claim 1, wherein said second predetermined time interval is shorter than said pitch period.

6. A speech signal coding apparatus according to claim 1, wherein said second predetermined time interval is equal to said pitch period.

7. A method of transmitting a speech signal, comprising the steps:

dividing a speech signal in units of first predetermined time intervals;

calculating a spectrum parameter for each first predetermined time interval to quantizing the spectrum parameter for outputting the quantized spectrum parameter;

generating a perceptual sensitivity weighted error signal from an excitation signal and the spectrum parameter for said each first predetermined time interval of speech signal;

referring to an adaptive code book to select an adaptive code vector and a pitch period based on the perceptual sensitivity weighted error signal, the pitch period being outputted;

referring to an excitation code book to select an excitation code vector from said excitation code book based on the perceptual sensitivity weighted error signal, an index of said selected excitation code vector being outputted;

referring to said gain code book to select a gain code vector based on the perceptual sensitivity weighted error signal, an index of said selected gain code vector being outputted; and

determining gains from said selected gain code vector for every second predetermined time interval shorter than said first predetermined time interval to produce said excitation signal from said adaptive code vector, said excitation code vector and the determined gains.

8. A method according to claim 7, wherein said determining step includes:

dividing each of said adaptive code vector and said excitation code vector into a plurality of segments, each segment having the second predetermined time interval;

referring to said gain code book to read out the selected gain code vector based on said weighted error signal and for determining gains for said segments from said selected gain code vector; and

generating said excitation signal from said segments of said adaptive code vector, said segments of said excitation code vector, and said determined gains for said segments.

9. A method according to claim 7, wherein said determining step includes:

dividing each of said adaptive code vector and said excitation code vector into a plurality of segments, each segment having the second predetermined time interval;

referring to said gain code to read out the selected gain code vector book based on said weighted error signal;

interpolating and/or extrapolating, based on gains of said selected gain code vector for at least two segments of each of said adaptive code vector and said excitation code vector, gains for segments of each of said adaptive code vector and said excitation code vector other than said at least two segments; and

generating said excitation signal from said segments of said adaptive code vector, said segments of said excitation code vector, and said gains for said segments.

10. A method according to claim 7, wherein said determining step includes:

dividing each of said adaptive code vector and said excitation code vector into a plurality of segments, each segment having the second predetermined time interval;

storing a gain for a second predetermined time interval of each of said adaptive code vector and said excitation code vector in a previous first predetermined time interval;

referring to said gain code book to read out the selected gain code vector based on said weighted error signal;

interpolating and/or extrapolating, based on gains of said selected gain code vector for at least one segment of each of said adaptive code vector and said excitation code vector and said stored gains, gains for segments of each of said adaptive code vector and said excitation code vector other than said at least one segment; and

generating said excitation signal from said segments of said adaptive code vector, said segments of said excitation code vector, and said calculated gains for said segments.

11. A method according to claim 7, wherein said second predetermined time interval is shorter than said pitch period.

12. A method according to claim 7, wherein said second predetermined time interval is equal to said pitch period.

13. A speech signal coding apparatus, comprising:

a dividing section for dividing a speech signal in units of first predetermined time intervals;

an error signal generating section for generating an error signal corresponding to a difference between the speech signal and a reproduction signal for said first predetermined time interval;

a vector generating section for generating an adaptive code vector associated with a pitch period in said first predetermined time interval of said speech signal and an excitation code vector associated with a predetermined excitation signal such that the power of the error signal has a minimum value;

a weighting section for determining gains for second predetermined time intervals of said first predetermined time interval and weighting said adaptive code vector and said excitation code vector with the determined gains for said second predetermined time intervals to produce said reproduction signal.

14. A speech signal coding apparatus according to claim 13, wherein said weighting section includes a section for calculating, based on gains for at least two second predetermined time intervals within the same first predetermined time interval, gains for other second predetermined time intervals within the same first predetermined time interval.

15. A speech signal coding apparatus according to claim 13, wherein said weighting section includes a section for calculating, based on gains for at least one second predetermined time interval within a current first predetermined time interval frame and gains for at least one second predetermined time interval within a previous first predetermined time interval, gains for other second predetermined time intervals within the current first predetermined time interval.