Abstract: A speech synthesis system in which coefficients of a speech synthesis filter are quantized. An LSP or other filter coefficient representation which evolves slowly with time is generated for each of a series of N input speech frames to produce p coefficients in respect of each frame. The coefficients related to the N frames define a p.times.N matrix, with each row of the matrix containing N coefficients and each coefficient of one row being related to a respective one of the N frames. The matrix is split into a series of submatrices each made up from one or more of the rows, and each submatrix is vector quantized independently of the other submatrices using a composite time/spectral weighting function which for example emphasises distortion associated with high energy regions of the spectrum of each of the N input speech frames and is also proportional to the energy and degree of voicing of each of the N input speech frames.

Abstract: Adaptive bit allocation to the channels of a sub/band coder (or to the coefficients of a transform coder) by using a fixed set of numbers of bits, only the selection of those channels to which the available bits are assigned being varied.

Abstract: Speech is coded such that it can be generated by a pulse excitation sequence filtered by an LPC (linear preductive coding) filter. The sequence contains, in each of successive frame periods, pulses whose positions and amplitudes may be varied. These variables are selected at the coding end to reduce the error between the input and regenerated speech signals. The selection process involves derivation of an initial estimate followed by an iterative adjustment process in which pulses having a low energy contribution are tested in alternative positions and transferred to them if a reduced error results.