A high-efficiency speech coding algorithm based on ADPCM with multi-quantizer

Adaptive differential PCM (ADPCM) is an effective coding scheme to simplify the hardware and shorten the processing delay to realize a high-efficiency speech codec. The ADPCM with Multi-Quantizer (ADPCM-MQ) coding has been proposed as one of the highly efficient coding methods. In the ADPCM-MQ codec several ADPCM coding blocks with different quantization step-size update rates are operated in parallel, and the quantizer that gives the best characteristics is found and selected dynamically for each frame. This paper describes a new 8 to 9.6 kbps ADPCM-MQ coding algorithm that includes tree coding to improve the per-sample quantizing characteristic, and sub-band coding with high frequency band reconstruction to realize a lower bit rate coding. Computer simulation indicates good quality for speech reproduced by this algorithm with a segmental signal-to-noise ratio of 14 to 15 dB. Adaptive postfiltering can be added to enhance the subjective characteristics of the reproduced speech.