> Books that have been done in the past did not have narrow bandwidth > as their main objective.
Look at the LPC-10 codec. You could try it by downloading internet telephony software from speakfreely.org. The codec was developed with the low bandwidth in mind and its intelligibility is on the threshold what I would accept. If IVOX is able to squeeze LPC-10 to 1200bps with the same intelligibility, than it is great. The proposal that you gave will certainly not work. You describe a system, that computes spectrum and compares it to a library of spectra, one by one. It may work for some vowels, but it will certainly not work for the other phonemes. The task is much more difficult than you think. The fricatives - d, t, f, s etc are hard to detect. The sound is quite complex and spectrum of a single phoneme changes in time. The sound starts with quiet pause, then explosion, then some transient of the explosion. The hidden Markov classifier is a kind of probabilistic network, is often used on spectra and is a good system for detection of phonemes. As I already wrote, if you get the consonants wrong, your system will mumble. Even for vowels, you would have to keep more spectra for a single phoneme in the lookup table, sampled for different pitch. You don't want to learn to speak with a constant pitch. Phoneme detection is described in every voice recognition text book. Writing papers about phoneme detection for HAM radio is reinventing the wheel. 73, Vojtech OK1IAK
