Abstract: In a speech encoder, a gain codebook switching circuit is supplied with short-term prediction gains from a short-term prediction gain calculator circuit and with mode information through an input terminal and compares the short-term prediction gains with a predetermined threshold value when the mode information indicates a predetermined mode. As a result of comparison, the gain codebook switching circuit produces gain codebook switching information which is delivered to a gain quantizer circuit. The gain codebook quantizer circuit is supplied with adaptive code vectors, excitation code vectors, impulse response information, and the gain codebook switching information, and gain code vectors from a particular gain codebook connected to one of a plurality of input terminals that is selected by the gain codebook switching information.

Abstract: In a speech signal encoder device comprising a frame divider (31) for producing original speech frames, a mode decision circuit (49) decides a predetermined number of modes by using feature quantities which are extracted from each current speech frame segmented from an input speech signal at a predetermined frame period of as short as 5 ms and from a previous speech frame segmented at least one frame period prior to the current speech frame. Preferably, a weighing circuit (47) provides the current speech frame by perceptually weighting the original speech frames into weighed speech frames. It is possible to provide the feature quantities by a primary quantity and as a secondary quantity by a rate of variation in the primary quantity. Each feature quantity is preferably adjusted into an adjusted quantity in response to each current mode decided by using the current speech frame and a previous mode decided at least one frame period prior to the current mode.

Abstract: An excitation codebook 351 includes a plurality of codevectors each generated with pulse positions and amplitudes obtained by training such as to reduce the distance between the codevector and training speech data. The excitation codebook 351 further includes a plurality of sparse codevectors each generated with the pulse number, pulse positions and amplitudes obtained by training such as to reduce the distance between the codevector and training speech data, the individual codevectors having different pulse numbers.