Triple-function voice coder (TRIVOC)
J. E. Roberts, Caldwell P. Smith, R. H. Wiggins · The Journal of the Acoustical Society of America · 1975
The first-formant region of the speech spectrum must be characterized with a high degree of accuracy in order to attain good speech quality and naturalness in a narrow-band speech processing system. This consideration led to the concept of using linear predictive coding for the first-formant region, vocoder channels for the upper spectrum, and detection and coding of the excitation function, to establish a narrow-band voice digitizer. This concept has advantages in the tradeoff of speech quality versus data rate, in comparison with the use of either channel vocoding or linear prediction alone. Such a triple-function voice coder (TRIVOC) has been implemented and investigated using a CSP-30 Digital Signal Processor. Processing algorithms have been established to permit comparison of various combinations of baseband and vocoder channels, LPC coefficients, and data rates ranging from 2400 to 4800 bits per second. Subjective results have confirmed the superior speech quality attainable by this method. Several versions of TRIVOC processing are presented, together with some results of subjective assessment of performance.