600-Bit-Per-Second Voice Digitizer (Linear Predictive Formant Vocoder).
Kang,George S, David C. Coulter · Defense Technical Information Center (DTIC) · 1976
Past efforts to achieve practical formant vocoders have been plagued with problems of formant tracker instability, resulting in unnatural warbles in the synthesized speech. A new approach to formant frequency determination, combined with a digital implementation, promises to eliminate these effects and to yield a useful formant vocoder. Additional redundancy reduction of information is obtained by means of a pattern-matching technique, which encodes the three formant frequencies into seven bits per frame to provide speech synthesis at 600 bps. This is accomplished by using an existing 2400-bps linear-predictive-encoder (LPE) with some additional processing. A demonstration record of processed speech at 600 bps is included with the report. (Author)