LOW BIT RATE VOCODER MEANS AND METHOD

Efficient coding speech information for low rate (e.g., 600 bps) channels using a four frame superframe (SF) includes: (1) coding spectral information using alternative quantizers one of which is chosen for each superframe so that 3 bits/SF identify the optimal quantizer and 28-32 bits/SF contain the quantized spectral information; (2) coding pitch using 5 bits/SF if voiced and if unvoiced assigning the pitch bits to error correction; (3) coding energy using 9-12 bits/SF by a 4d vector quantizer (4dvQ); and (4) coding voicing using 3-4 bits/SF by a 4d VQ, for a total of 54 bits/SF including 1 sync bit and 0-1 error correction bits. When combined with a unique perceptual weighting scheme, output speech quality comparable to that of vocoders operating at almost four times the channel capacity is obtained.