Sound encoding method and sound decoding method, and sound encoding device and sound decoding device
AssigneeMitsubishi Denki Kabushiki Kaisha
InventorTadashi Yamaura
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Abstract
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.
Claims2
A speech decoding method according to code-excited linear prediction (CELP) wherein the speech decoding method receives a coded speech including a linear prediction parameter code and an adaptive code, and a gain code, and synthesizes a speech using at least an excitation codebook, the speech decoding method comprising:
- obtaining an adaptive code vector from an adaptive codebook based on the received adaptive code;
- obtaining a time series vector with a noise level from the excitation codebook based on the excitation code;
- decoding a gain of the adaptive code vector and a gain of the time series vector from the gain code;
- determining whether modification of the time series vector is necessary;
- if modification of the time series vector is determined to be necessary, modifying the time series vector such that the density of zero-amplitude samples is changed as a function of whether the coded speech is voiced or unvoiced;
- weighting the adaptive codebook vector and the time series vector using the decoded gains as weights;
- adding together the weighted adaptive codebook vector and the weighted time series vector;
- decoding a linear prediction parameter from the received linear prediction parameter code;
- and
- synthesizing a speech using the linear prediction parameter and the addition result.
A speech decoding apparatus according to code-excited linear prediction (CELP) wherein the speech decoding apparatus receives a coded speech including a linear prediction parameter code, an excitation code, an adaptive code, and a gain code, and synthesizes a speech using at least an excitation codebook, the speech decoding apparatus comprising:
- a time series vector modulator for:
- obtaining an adaptive code vector from an adaptive codebook based on the received adaptive code,
- obtaining a time series vector with a noise level from the excitation codebook based on the excitation code,
- decoding a gain of the adaptive code vector and a gain of the time series vector from the gain code, and
- determining whether modification of the time series vector is necessary and for modifying the time series vector such that the density of zero-amplitude samples is changed as a function of whether the coded speech is voiced or unvoiced if modification of the time series vector is determined to be necessary;
- and
- a speech synthesizer for:
- weighting the adaptive codebook vector and the time series vector using the decoded gains as weights,
- adding together the weighted adaptive codebook vector and the weighted time series vector,
- decoding a linear prediction parameter from the received linear prediction parameter code, and
- synthesizing a speech using the addition result.
Dependencies are inferred from the claim text.