METHOD OF AND DEVICE FOR QUANTIZING SPECTRAL PARAMETERS IN DIGITAL SPEECH CODERS

A method of and a device for speech signal digital coding are described, where spectral parameters are quantized at each frame in order to exploit the actual correlation inside a frame or between contiguous frames. The quantization devices (DQ) recognize strongly correlated signal periods by using a first set of indexes (j.sub.1), representing the parameters and provided by the spectral analysis circuits (ABT, ALT), and in these periods they convert the same indexes into a second set of indexes (j4) which can be coded with a lower number of bits and which is inserted into the coded signal in place of the first set.