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It can certainly be done - I think it is more a question of sound quality (intelligibility / speaker recognition / artifacts). At 600bps I doubt you will achieve speaker recognition. There are a few papers floating around for waveform codecs around the 1200-600bps range, but the lowest rate standard codec I've heard of is half rate MELP, which comes in at 1200bps. I don't know of any full implementations which go lower. From what I've seen so far, waveform codecs seem to be on an approximate par with LPC based codecs. If its a commercial project, I would suggest you propose 1200bps or less - which it totally achievable. If you hit 600bps, all the better - but don't waste too much engineering time assuming 600bps until you actually hit the rate. Peter |