A 400-BPS Vocoder using Line Spectral Frequencies and Frame Repeat Coding

A 400-bps vocoder utilizing frame repeat vector quantization is described that is designed to be used with fixed data rate systems. It combines several improvements over existing 400-bps systems. Line spectrum frequency parameters are vector quantized using a perceptually meaningful distortion metric. Frames to be repeated are determined from a buffer's length of data, which determines the coding delay. Excitation parameters are trellis coded using a variable lookahead approach to minimize throughput delay.