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 for decoding a speech code including a linear prediction parameter code, an adaptive code, and a gain code according to code-excited linear prediction (CELP), the speech decoding method comprising:
decoding a linear prediction parameter from the linear prediction parameter code;
obtaining an adaptive code vector corresponding to the adaptive code concerning a decoding period from an adaptive codebook;
decoding a gain of the adaptive code vector and a gain of an excitation code vector from the gain code;
evaluating a noise level related to the speech code based on the adaptive code concerning the decoding period;
obtaining a weight based on the evaluated noise level;
obtaining an excitation code vector based on the weight and an excitation codebook;
weighting the adaptive code vector and the excitation code vector by using the decoded gains;
obtaining an excitation signal by adding the weighted adaptive code vector and the weighted excitation code vector; and
synthesizing a speech by using the excitation signal and the linear prediction parameter.
2. A speech decoding apparatus for decoding a speech code including a linear prediction parameter code, an adaptive code, and a gain code according to code-excited linear prediction (CELP), the speech decoding apparatus comprising:
a linear prediction parameter decoding unit for decoding a linear prediction parameter from the linear prediction parameter code;
an adaptive code vector obtaining unit for obtaining an adaptive code vector corresponding to the adaptive code concerning a decoding period from an adaptive codebook;
a gain decoding unit for decoding a gain of the adaptive code vector and a gain of an excitation code vector from the gain code;
an evaluating unit for evaluating a noise level related to the speech code based on the adaptive code concerning the decoding period;
a weight obtaining unit for obtaining a weight based on the evaluated noise level;
an excitation code vector obtaining unit for obtaining an excitation code vector based on the weight and an excitation codebook;
a weighting unit for weighting the adaptive code vector and the excitation code vector by using the decoded gains;
an excitation signal obtaining unit for obtaining an excitation signal by adding the weighted adaptive code vector and the weighted excitation code vector; and
a speech synthesizing unit for synthesizing a speech by using the excitation signal and the linear prediction parameter.