Recently, Modulo‐PCM (MPCM) was proposed as one of the waveform speech coding schemes. The MPCM is considered to be a possible alternative to the DPCM. This is because the MPCM has only granular noise without overload although it has the “anomaly errors” instead of the overload noise. The variable bit rate modulo‐PCM (VBR‐MPCM) has been proposed which applies the variable rate coding method to the Modulo‐PCM. This paper proposes the improved variable bit rate modulo‐PCM (improved VBR‐MPCM) whose performance is the same and whose complexity is about half compared with that of the conventional VBR‐MPCM. Moreover, the variable bit rate modulo‐PCM using adaptive predictor (VBR‐MPCM‐AP) also is proposed which uses second‐order pole and sixth‐order zero adaptive predictors instead of the fixed ones used in the improved VBR‐MPCM. From the computer simulation results, it is confirmed that the VBR‐MPCM‐AP is about 0 to 8 dB in segmental SQNR (SQNRseg), which is better than the conventional VBR‐MPCM, MPCM‐AQF and ADPCMs. From the listening test results, it is also confirmed that the proposed VBR‐MPCM‐AP is able to obtain good reconstructed speech.
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