Tree coding combined with harmonic scaling of speech at 6.4 kbps

Tree coding is combined with time-domain harmonic scaling (TDHS) for speech coding at 6.4 kbit/s. A 2-to-1 TDHS compression is used and the coder is fully backward adaptive. Experiments on selecting window type, pitch extractor, code tree, and gain adaptation rule are reported. A novel backward adaptive pitch predictor greatly enhances performance. Paired comparison listening tests show quality equivalent to 6-bit log-pulse code modulation (PCM) at a sampling rate of 6400 samples/s.<>