Abstract
Code-excited, linear prediction (CELP) has become an accepted method for low bit rate, high quality coding of digital speech. The success of fixed rate CELP schemes has led to increased interest in variable rate techniques to provide lower average bit rates for a given quality level. This work develops new techniques, referred to as widely variable CELP parameter updates, which dynamically adapt the transmit frequency of the CELP spectral parameters to the characteristics of the input speech for variable rate CELP speech coding. After a presentation of speech coding basics, general CELP coding concepts and several specific fixed and variable rate CELP coders are described. The widely variable CELP parameter update techniques are then developed in detail. Various experiments are run to determine the performance of the developed techniques in terms of coding rate and speech quality. Three key contributions are provided by this research. The evaluation CELP coder developed in this work is the first known CELP configuration to utilize a variable frame rate. Formant and pitch parameter distortion measures were developed to vary the parameter transmit frequency through the use of thresholds. New CELP parameter interpolation techniques were developed which facilitated widely variable parameter updates and provided a means for controlling maximum coding delay.
Moodie, Myron L. (1995). Variable rate CELP speech coding using widely variable parameter updates. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1995 -THESIS -M665.