METHOD FOR PITCH-ALIGNED HIGH-FREQUENCY REGENERATION IN RELP VOCODERS

A method for pitch-aligned high frequency regeneration of a speech signal which has been sampled at a known sampling frequency f.sub.S and decimated at a known integer decimation ratio N practiced in the receiver portion of a RELP vocoder includes the steps of: providing at least one local carrier signal(s), (each) at a frequency which is an exact integer multiple of a baseband pitch estimate frequency recovered from received data; amplitude modulating each of the local carrier signals with baseband residual data recovered in the receiver portion to provide partial spectrum data; removing, only if the decimation ratio is even, the lower sideband data from the lowest frequency local carrier signal to obtain partial spectrum data; and adding the residual baseband data to the partial spectrum data to obtain PA-HFRed output data from which to reconstruct the speech signal. The method results in a more natural sounding regenerated spectrum than ordinary spectral folding and doesn't require modification of the existing REPL transmitter section. An even decimation ratio is preferred because an improvement in the quality of the reconstituted speech is realized and considerably less processor time and memory are required. Because even decimation ratios result in spectral inversion of the baseband signals, high-pass filtering is used is remove the lower sideband associated with a first local carrier from the rengenerated signal.