A new adaptive quantizer which uses a combination of instantaneous and syllabic adaptation is presented for use in speech codecs. It can be designed to adapt to changes in the mean, variance, and pdf shape of its input signal, and to quantize the signal using one or more bits/sample. It is therefore called the generalized hybrid adaptive quantizer (GHAQ). An efficient procedure for optimizing the GHAQ using a training sequence of signal samples is described, and the effects on the performance of the GHAQ of varying the memory length and the syllabic compandor time constant are investigated. It is found that an optimized version of the two-bit GHAQ offers improved signal-to-noise ratio over Jayant's adaptive quantizer with a one-word memory when it is used in a predictive speech codec with a zero-, first-, or second-order fixed predictor.>

We present two new forms of "hybrid companding" delta modulation for speech encoding. These algorithms differ from the earlier hybrid companding delta modulation (HCDM) scheme in that they employ Song voice adaptation as the basis of the instantaneous companding, rather than constant factor adaptation. We show that although the two new algorithms produce SQNR curves which are similar to that of HCDM, a subjective evaluation of the three systems significantly favors the new ones. In addition, the new algorithms offer simpler implementation in digital hardware.