A study of time-encoded speech

The technique of Time-Encoded Speech (TES) has shown considerable promise in transmitting good quality speech at bit rates below 16 kb/s. The central concept of this approach depends upon the transmission of coded shape descriptors for successive extended segments of the speech waveform. For transmission over a constant rate data channel, buffer management via a first-in first-out store is required. A modified time encoding method for speech signals which is basically a kind of extremal coding is described. This technique enables the low frequencies of speech waveform to be reconstructed more faithfully, and this is desirable for human perception. With linear encoding and transmission rate at about 12¿16 kb/s, the TES output speech quality approaches that of public telephone quality, and little improvement can be gained by further increase in the data rate.