CODER

摘要

A coder comprising a differential pulse code modulation loop (1) including a quantizer (4), followed by a variable length coder VLC (5) and a buffer (8). The VLC (5) assigns words from a codebook to the different output levels from the quantizer (4), and the buffer (8) smooths the bit rate of the signals received from the VLC prior to transmission over a fixed rate channel (9). When the buffer approaches the overflow condition it signals the quantizer (4) to cause a reduction in the number of quantization thresholds. This causes only a subset of the codebook words to be assigned, and a reduction in the bit rate if a codebook is used which is sub-optimized in normal operation but gives a better overflow performance.