Speech coder including an excitation quantizer for retrieving positions of amplitude pulses using spectral parameters and different gains for groups of the pulses

• US 5,963,896 A
• Filed: 08/26/1997
• Issued: 10/05/1999
• Est. Priority Date: 08/26/1996
• Status: Expired due to Term

• Current Assignee: Rakuten, Inc. (Rakuten Group, Inc.)
• Original Assignee: NEC Corporation
• Inventors: Ozawa, Kazunori
• Primary Examiner(s): Hudspeth, David R.
• Assistant Examiner(s): Chawan, Vijay B.
• Application Number:
  US08/917,713
• Time in Patent Office: 770 Days
• Field of Search: 704/219, 704/222, 704/223, 704/216, 704/207, 704/240, 704/230, 704/208, 704/225, 704/262, 704/214
• US Class Current: 704/219
• CPC Class Codes: G10L 19/10 the excitation function being a multipulse excitation
• CPC Class Codes: G10L 2019/0005 Multi-stage vector quantisation
• CPC Class Codes: G10L 25/06 the extracted parameters being correlation coefficients

Abstract

In a speech coder, an excitation quantizer 360 retrieves the positions of M non-zero amplitude pulses, which together constitute an excitation, by using spectral parameters and with a different gain for each group of the pulses less in number than M.

Claims

1. A speech coder comprising a spectral parameter computer for obtaining a plurality of spectral parameters from an input speech signal, and quantizing the spectral parameters thus obtained, and an excitation quantizer for retrieving positions of M non-zero amplitude pulses which constitutes an excitation signal of the input speech signal with a different gain for each set of the pulses for each group of pulses less in number than M.

2. A speech coder according to claim 1, wherein the excitation quantizer includes a codebook for jointly quantizing the amplitudes or polarities of a plurality of pulses.

3. A speech coder comprising a spectral parameter computer for obtaining a plurality of spectral parameters from an input speech signal, and quantizing the spectral parameters thus obtained, an excitation quantizer for retrieving positions of M non-zero amplitude pulses which constitutes an excitation signal of the input speech signal with a different gain for each group of the pulses less in number than M, and a second excitation quantizer for retrieving the positions of a predetermined number of pulses by using the spectral parameters, the outputs of the first and second excitation quantizers being used to compute distortions of the speech so as to select the less distortion one of the first and second excitation quantizers.

4. A speech coder according to claim 3, wherein the excitation quantizer includes a codebook for jointly quantizing the amplitudes or polarities of a plurality of pulses.

5. The speech coder according to claim 3, which further comprises a mode judging circuit for obtaining a feature quantity from the input speech signal, judging one of a plurality of different modes from the obtained feature quantity and outputting mode data, the first and second excitation quantizers being used switchedly according to the mode data.

6. The speech coder according to claim 4, which further comprises a mode judging circuit for obtaining a feature quantity from the input speech signal, judging one of a plurality of different modes from the obtained feature quantity and outputting mode data, the first and second excitation quantizers being used switchedly according to the mode data.

7. A speech coder comprising a spectral parameter computer for obtaining spectral parameters from an input speech signal and quantizing the spectral parameters thus obtained, an impulse response computer for computing impulse responses corresponding to the spectral parameters, a first correlation computer for computing correlations of the input signal and the impulse response, a second correlation computer for computing correlations among the impulse responses, a first pulse data computer for computing positions of first pulses from the outputs of the first and second correlation computers, a third correlation computer for correcting the output of the first correlation computer by using the output of the first pulse data computer, and a second pulse data computer for computing positions of second pulses from the outputs of the third and second correlation computers, the pulse data computation being made by executing the correlation correction and the pulse data computation iteratedly a predetermined number of times.

8. A speech coder comprising a spectral parameter computer for obtaining a plurality of spectral parameters from an input speech signal and quantizing the obtained spectral parameters, an adaptive codebook means for obtaining a delay corresponding to a pitch period from the input speech signal, computing a pitch prediction signal, and executing pitch prediction, and an excitation quantizer for forming an excitation signal of the input speech signal with M non-zero amplitude pulses, obtaining a sample position corresponding to a pulse position meeting a predetermined condition with respect to the computed pitch prediction signal, setting a pulse position retrieval range on the basis of a position obtained by shifting the obtained sample position by a predetermined number of samples, retrieving a best position in the pulse position retrieval range thus set, and outputting data of the retrieved best position.

12. The speech coder according to claim 8, wherein the excitation quantizer includes a codebook for jointly quantizing the amplitudes or polarities of a plurality of pulses.

9. A speech coder comprising a spectral parameter computer for obtaining a plurality of spectral parameters from an input speech signal and quantizing the obtained spectral parameters, an adaptive codebook means for obtaining a delay corresponding to a pitch period from the input speech signal, computing a pitch prediction signal, and executing pitch prediction, and an excitation quantizer for forming an excitation signal of the input speech signal with M non-zero amplitude pulses, obtaining a sample position meeting a predetermined condition with respect to the pitch prediction signal in a time interval equal to the pitch period from the forefront of a frame, setting a pulse position retrieval range for retrieving a pulse position on the basis of a position obtained by shifting the obtained sample position by a predetermined number of samples, retrieving a best position in the pulse position retrieval range thus set, and outputting data of the retrieved best position.

10. The speech coder according to claim 9, wherein the excitation quantizer includes a codebook for jointly quantizing the amplitudes or polarities of a plurality of pulses.

11. A speech coder comprising a spectral parameter computer for obtaining a plurality of spectral parameters from an input speech signal and quantizing the obtained spectral parameters, an adaptive codebook means for obtaining a delay corresponding to a pitch period from the input speech signal, computing a pitch prediction signal, and executing pitch prediction, and an excitation quantizer for forming an excitation signal of the input speech signal with M non-amplitude pulses, obtaining a sample position corresponding to a pulse position meeting a predetermined condition with respect to the computed pitch prediction signal in a time interval equal to the pitch period from the forefront of a frame, setting pulse position candidates through shifting the obtained sample position by the pitch period on the basis of the position shifted by predetermined numbers of samples from the sample position, retrieving the position candidates for a best position, and outputting data of the retrieved best position.

13. The speech coder according to claim 11, wherein the excitation quantizer includes a codebook for jointly quantizing the amplitudes or polarities of a plurality of pulses.

14. A speech coder comprising a spectral parameter computer for obtaining a plurality of spectral parameters from an input speech signal and quantizing the obtained spectral parameters, an adaptive codebook means for obtaining a delay corresponding to a pitch period from the input speech signal, computing a pitch prediction signal, and executing pitch prediction, and an excitation quantizer for forming an excitation signal of the input speech signal with M non-zero amplitude pulses, obtaining a sample position meeting a predetermined condition with respect to the computed pitch prediction signal, setting a plurality of pulse position retrieval ranges on the basis of positions obtained by shifting the obtained sample position by corresponding shift extents, making retrieval of the pulse position retrieval ranges to select a best combination of a shift extent and a pulse position, and outputting data of the selected best combination.

18. The speech coder according to claim 14, wherein the excitation quantizer includes a codebook for jointly quantizing the amplitudes or polarities of a plurality of pulses.

15. A speech coder comprising a spectral parameter computer for obtaining a plurality of spectral parameters from an input speech signal and quantizing the obtained spectral parameters, an adaptive codebook means for obtaining a delay corresponding to a pitch period from the input speech signal, computing a pitch prediction signal, and executing pitch prediction, and an excitation quantizer for forming an excitation signal of the input speech signal with M non-zero amplitude pulses, obtaining a sample pulse position meeting a predetermined condition with respect to the computed pitch prediction signal in a time interval equal to the pitch period from the forefront of a frame, setting a plurality of pulse position retrieval ranges on the basis of positions obtained by shifting the obtained sample position by corresponding shift extents, making retrieval of the pulse position retrieval ranges to select a best combination of a shift extent and a pulse position, and outputting data of the selected best combination.

16. The speech coder according to claim 15, wherein the excitation quantizer includes a codebook for jointly quantizing the amplitudes or polarities of a plurality of pulses.

17. A speech coder comprising a spectral parameter computer for obtaining a plurality of spectral parameters from an input speech signal and quantizing the obtained spectral parameters, an adaptive codebook means for obtaining a delay corresponding to a pitch period from the input speech signal, computing a pitch prediction signal, and executing pitch prediction, and an excitation quantizer for forming an excitation signal of the input speech signal with M non-zero amplitude pulses, obtaining a sample pulse position meeting a predetermined condition with respect to the computed pitch prediction signal in a time interval equal to the pitch period from the forefront of a frame, setting pulse position candidates through shifting the obtained sample position by the pitch period on the basis of the position shifted by predetermined numbers of samples from the sample position, retrieving the position candidates for a best position, and outputting data of the retrieved best position.

19. The speech coder according to claim 17, wherein the excitation quantizer includes a codebook for jointly quantizing the amplitudes or polarities of a plurality of pulses.

20. A speech coder comprising a spectral parameter computer for obtaining a plurality of spectral parameters from an input speech signal and quantizing the obtained spectral parameters, a mode judging means for extracting a characteristic amount from the input speech signal, judging a plurality of modes from the extracted feature quantity, and outputting mode data, an adaptive codebook means for obtaining a delay corresponding to a pitch period from the input speech signal, computing a pitch prediction signal, and making pitch prediction, and an excitation quantizer for forming an excitation signal of the input speech signal with M non-zero amplitude signals, obtaining a sample position meeting a predetermined condition with respect to the pitch prediction signal when the mode data represents a predetermined mode, setting a pulse position retrieval range on the basis of the obtained sample position, retrieving a best position in the pulse position retrieval range, and outputting data of the retrieved best position.

21. The speech coder according to claim 20, wherein the feature quantity is an average pitch prediction gain.

22. The speech coder according to claim 20, wherein the mode judging means judges the modes on the basis of comparison of the average pitch prediction gain with a plurality of threshold values.

23. A speech coder comprising a spectral parameter computer for obtaining a plurality of spectral parameters from an input speech signal and quantizing the obtained spectral parameters, an adaptive codebook means for obtaining a delay corresponding to a pitch period from the input speech signal, computing a pitch prediction signal, and executing pitch prediction, and an excitation quantizer for obtaining a position meeting a predetermined condition with respect to the pitch prediction signal computed in the adaptive codebook means, setting a plurality of pulse position retrieval ranges for respective pulses constituting an excitation signal, and retrieving the best positions of the pulses in the pulse position retrieval ranges.