Patent ID: 7222069

Claim:
A voice code conversion apparatus, in which a fixed number of samples of a voice signal. is adopted as one frame, for obtaining a first LPC code obtained by quantizing linear prediction coefficients (LPC coefficients), which are obtained by frame-by-frame linear prediction analysis, or LSP parameters found from these LPC coefficients; a first pitch-lag code, which specifies an output signal of an adaptive codebook that is for outputting a periodic sound-source signal; a first noise code, which specifies an output signal of a noise codebook that is for outputting a noisy sound-source signal; and a first gain code obtained by quantizing adaptive codebook gain, which represents amplitude of the output signal of the adaptive codebook, and noise codebook gain, which represents amplitude of the output signal of the noise codebook; wherein a method for encoding the voice signal by these codes is assumed to be a first voice encoding method and a method for encoding the voice signal by a second LPC code, a second pitch-lag code, a second noise code and a second gain code, which are obtained by quantization in accordance with a quantization method different from that of the first voice encoding method, is assumed to be a second voice encoding method; and wherein voice code that has been encoded by the first voice encoding method is input to said apparatus for being converted to voice code of the second voice encoding method; said apparatus comprising: LPC code conversion means for dequantizing the first LPC code by an LPC dequantization method according to the first voice encoding method, and quantizing the dequantized values of LPC coefficients using an LPC quantization table according to the second voice encoding method to find the second LPC code; pitch-lag conversion means for converting the first pitch-lag code to the second pitch-lag code by conversion processing that takes into consideration a difference between the pitch-lag code according to the first voice encoding method and the pitch-lag code according to the second voice encoding method; noise code conversion means for converting the first noise code to the second noise code by conversion processing that takes into consideration a difference between the noise code according to the first voice encoding method and the noise code according to the second voice encoding method; gain dequantization means for dequantizing the first gain code by a gain dequantization method according to the first voice encoding method to thereby find a gain dequantized value; and gain code conversion means for quantizing the gain dequantized value using a gain quantization table according to the second voice encoding method to convert the gain dequantized value to the second gain code.