Hi Patrick, > At each 1/T it was necessary to send NxL elements of >information, which gives the final rate.
Im not shure i understand your method 100%. My own tests found that you can transfer comprehensible, but unvoiced speech with 10 carriers. But i did not restrict number of levels. For voiced (natural sounding) speech the addition of a pitch-carrier is necessary. I did those tests with ideas and help from G3PLX. But this might not be the easiest way. The EZ way would be to use an existing 1400bps codec, and squeeze the 1400bps into a 500hz wide multi- carrier qam-16 or psk-16 (4 bits per symbol) modulation. The codec produces 54 bits per 40ms. 54 / 4 = 14 carriers. 40ms = 25 baud, proposed carrier spacing 37.5 hz, BW = 37.5 * 14 = 525 hz. 500hz BW should be possible with a little tweaking. >With 23 carriers, 8 levels and T=40 ms (which can >be send through a 500 Hz channel), it is very difficult >to understand a (French) speech. 23 * 8 bit = 69 bit per 40ms. 69*25=1725 bps. More than enough for the 1400bps codec. I can help you with this codec if needed. 73, Cesco
