Combined time-domain harmonic compression and CVSD for 7.2 kbit/s transmission of speech signals

In this presentation we report on preliminary results obtained with a speech encoding scheme which combines time-domain harmonic compression (TDHC) and CVSD for digital transmission of speech signals at 7.2 kbit/s. The harmonic compression at the transmitter and the harmonic expansion at the receiver are performed with the recently developed time-domain harmonic scaling (TDHS) algorithms. By using a frequency-scaling factor of 2 and the encoding of the frequency-divided signal with a 7.2 kbit/s CVSD coder, the reconstructed speech has a quality close to that achieved by a 14.4 kbit/s plain CVSD. The complexity of the proposed system is significantly lower than more elaborate waveform coders or vocoders which can operate at 7.2 kbit/s. Issues involved in the proposed combination are discussed and computer simulation results are presented.