Method for speech coding, method for speech decoding and their apparatuses
View Patent ↗A high quality speech is reproduced with a small data amount in speech coding and decoding for performing compression coding and decoding of a speech signal to a digital signal. In speech coding method according to a code-excited linear prediction (CELP) speech coding, a noise level of a speech in a concerning coding period is evaluated by using a code or coding result of at least one of spectrum information, power information, and pitch information, and various excitation codebooks are used based on an evaluation result.
1. A speech decoding method according to code-excited linear prediction (CELP), the method comprising:
receiving a coded speech signal including a linear prediction parameter code, a gain code, and an adaptive code;
obtaining an adaptive code vector from an adaptive codebook based on the received adaptive code;
decoding a set of gains from the received gain code in a decoding period corresponding to the coded speech signal;
obtaining a time series vector with a number of samples with zero amplitude-value from an excitation codebook;
selectively modifying the time series vector based on at least one gain from the set of decoded gains such that the number of samples with zero amplitude-value is changed;
weighting the adaptive code vector and the selectively modified time series vector using the set of decoded gains;
adding together the weighted adaptive code vector and the weighted time series vector;
decoding a linear prediction parameter from the received linear prediction parameter code; and
synthesizing a speech signal using the linear prediction parameter and the added weighted adaptive code vector and weighted time series vector.
2. The method of claim 1 , wherein the adaptive codebook is based on a past excitation.
3. The method of claim 1 , where in the speech is synthesized using a synthesis filter.
4. The method of claim 3 , wherein the decoded linear prediction parameter corresponds to coefficients of the synthesis filter.
5. The method of claim 1 , wherein the time series vector is selectively modified based on a noise level.
6. The method of claim 5 , wherein the noise level is evaluated using a code.
7. The method of claim 1 , wherein selectively modifying the time series vector includes not modifying the times series vector based on the at least one gain from the set of decoded gains.
8. A speech decoding apparatus that operates according to code-excited linear prediction (CELP), the speech decoding apparatus being configured to:
receive a coded speech signal including a linear prediction parameter code, a gain code, and an adaptive code;
obtain an adaptive code vector from an adaptive codebook based on the received adaptive code;
decode a set of gains from the received gain code in a decoding period corresponding to the coded speech signal;
obtain a time series vector with a number of samples with zero amplitude-value from an excitation codebook;
selectively modify the time series vector based on at least one gain from the set of decoded gains such that the number of samples with zero amplitude-value is changed;
weight the adaptive code vector and the selectively modified time series vector using the set of decoded gains;
add together the weighted adaptive code vector and the weighted time series vector;
decode a linear prediction parameter from the received linear prediction parameter code; and
synthesize a speech signal using the linear prediction parameter and the added weighted adaptive code vector and weighted time series vector.
9. The apparatus of claim 8 , wherein the adaptive codebook is based on a past excitation.
10. The apparatus of claim 8 , where in the speech is synthesized using a synthesis filter.
11. The apparatus of claim 9 , wherein the decoded linear prediction parameter corresponds to coefficients of the synthesis filter.
12. The apparatus of claim 8 , wherein the time series vector is selectively modified based on a noise level.
13. The apparatus of claim 12 , wherein the noise level is evaluated using a code.
14. The method of claim 8 , wherein selectively modifying the time series vector includes not modifying the times series vector based on the at least one gain from the set of decoded gains.
15. A speech decoding method according to code-excited linear prediction (CELP), the method comprising:
receiving a coded speech signal including a linear prediction parameter code, a gain code, and an adaptive code;
obtaining an adaptive code vector from an adaptive codebook based on the received adaptive code;
decoding a gain of the adaptive code vector and a gain of a time series vector from the gain code in a decoding period corresponding to the coded speech signal;
obtaining the time series vector with a number of samples with zero amplitude-value from an excitation codebook;
selectively modifying the time series vector based on the gain of the adaptive code vector such that the number of samples with zero amplitude-value is changed;
weighting the adaptive code vector using the decoded gain of the adaptive code vector;
weighting the selectively modified time series vector using the decoded gain of the time series vector;
adding together the weighted adaptive code vector and the weighted time series vector;
decoding a linear prediction parameter from the received linear prediction parameter code; and
synthesizing a speech signal using the linear prediction parameter and the added weighted adaptive code vector and weighted time series vector.
16. The method of claim 15 , wherein the adaptive codebook is based on a past excitation.
17. The method of claim 15 , where in the speech is synthesized using a synthesis filter.
18. The method of claim 17 , wherein the decoded linear prediction parameter corresponds to coefficients of the synthesis filter.
19. The method of claim 15 , wherein the time series vector is selectively modified based on a noise level.
20. The method of claim 19 , wherein the noise level is evaluated using a code.
21. The method of claim 15 , wherein selectively modifying the time series vector includes not modifying the times series vector based on the gain of the adaptive code vector.
22. A speech decoding apparatus that operates according to code-excited linear prediction (CELP), the speech decoding apparatus being configured to:
receive a coded speech signal including a linear prediction parameter code, a gain code, and an adaptive code;
obtain an adaptive code vector from an adaptive codebook based on the received adaptive code;
decode a gain of the adaptive code vector and a gain of a time series vector from the gain code in a decoding period corresponding to the coded speech signal;
obtain the time series vector with a number of samples with zero amplitude-value from an excitation codebook;
selectively modify the time series vector based on the gain of the adaptive code vector such that the number of samples with zero amplitude-value is changed;
weight the adaptive code vector using the decoded gain of the adaptive code vector;
weight the selectively modified time series vector using the decoded gain of the time series vector;
add together the weighted adaptive code vector and the weighted time series vector;
decode a linear prediction parameter from the received linear prediction parameter code; and
synthesize a speech signal using the linear prediction parameter and the added weighted adaptive code vector and weighted time series vector.
23. The apparatus of claim 22 , wherein the adaptive codebook is based on a past excitation.
24. The apparatus of claim 22 , where in the speech is synthesized using a synthesis filter.
25. The apparatus of claim 24 , wherein the decoded linear prediction parameter corresponds to coefficients of the synthesis filter.
26. The apparatus of claim 22 , wherein the time series vector is selectively modified based on a noise level.
27. The apparatus of claim 26 , wherein the noise level is evaluated using a code.
28. The apparatus of claim 22 , wherein selectively modifying the time series vector includes not modifying the times series vector based on the gain of the adaptive code vector.