Multiple-stage vector excitation coding of speech waveforms

An approach to vector-excitation-coding (VXC) speech compression utilizing multiple-stage vector quantization (VQ) is considered. Called multiple-stage VXC (MSVXC), this technique facilitates the use of high-dimensional excitation vectors at medium-band rates without substantially increasing computation. The basic approach consists of successively approximating the input speech vector in several cascaded VQ stages, where the input vector for each stage is the quantization error vector from the preceding stage. It is shown that if a number of VQ stages is increased sufficiently, MSVXC can be expressed as a form of transform coding, in which the computationally intensive excitation codebook search is completely eliminated