Short-time synthesis procedures in vector adaptive transform coding of speech

The authors discuss various possible synthesis procedures for frequency-domain vector-excited coding (VXC). The algorithm, called vector adaptive transform coding (VATC), is a two-stage vector quantizer for the short-time Fourier transform (STFT) of speech. One stage represented by an adaptive codebook based on long-term prediction and the other based by a random codebook. The authors focus on the differences between time and frequency VXC, stressing the importance of the long-term prediction. A fast algorithm for long-term prediction is introduced, and different strategies for noise reduction are proposed. VATC is presented as a particular case of a general vector linear prediction (VLP) scheme. Following this approach, a coder based on a self-spectral shaping procedure is proposed. This coder has the potential of producing telephonic-quality speech at rates lower than 4.8 kb/s