David. let me pose a question: if you converted the digitized voice signal to mp3 or ogg format, is this similar to (or the same as) a freq domain data stream? The data compression from CD wav file to mp3 is around 10 to 1; you are certainly not storing a digital copy of the sound wave. Voice compression may not be so good but still should result in the need to transfer considerably less data in order to assure a useful voice recovery on the receiving end.
Mike W5FTD > Stuart Rohre wrote: >> In the basics of digitizing the signal you have to clock the conversion at >> least twice the highest frequency you want to reproduce in the voice (or >> audio) signal. > That's only at the input to the encoding chain (and technically it is > twice the bandwidth, not twice the highest frequency). > However, I would imagine all digital modes that would be used for > communications, rather than broadcasting (and for that matter, also > those used in modern broadcasting systems) don't send time domain data. > One way or another they send frequency domain data, often in the form > of just the formant frequencies used in a model of vocal tract resonances. > The critical rate for these systems is the syllable rate, not the > frequency of the highest component. I seem to remember that the > military were using 2400 bits per second codecs maybe a couple of > decades ago. I suspect that was partly do do with how fast they could > encrypt. > Mobile phone codecs tend to be vocal tract model based, although they > use more than 2400 bps so that the voice sounds reasonably natural (but > try them on modem tones or even music!). > To get much better than 2400 bps, I think you would probably have to > recognize phonemes, which is basically the continuous speech voice > recognition problem. I think that might get you down to about 300 > bits per second. _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
