Tandem transcoding without distortion accumulation for memoryless and predictive vector quantizers

Two tandem transcoding algorithms based on waveform coding are described. The memoryless vector quantization can be realized via lookup tables, whereas the predictive vector quantization requires online calculations. Computer simulations have revealed a 6-dB improvement in the case of 16-kb/s predictive vector quantizers, with 48-kb/s PCM (pulse-code modulation) and four tandems. The proposed technique is also applicable to adaptive predictive vector quantization.