CELP base-band coder for high quality speech coding at 9.6 to 2.4 kbps

A baseband coder is discussed and its subjective quality compared with code-excited linear prediction (CELP) and vector-quantized transform coding at various bit rates from 9.6 to 4.8 kb/s. It is also with that CELP-BB coding is capable of producing natural, intelligible and smooth speech at 2.4 kb/s. The code-book search in CELP-BB requires no convolution. The pitch filter memory is subtracted from the original baseband signal to form the reference signal, which is directly matched by the code-book sequences. Because most of the computation is performed on the baseband, which is decimated, and during code-book search only the pitch filter response is considered, the complexity of CELP-BB is very much less than that of CELP and its speech quality is not affected by LPC quantization error to such an extent as in CELP