I understand that, I was just wondering where the 35kbit/sec number comes from. It sounds like a rule of thumb and not a theoretical limit. If it were a theoretical limit, it should apply in a lab-type setting, too, and yet it would be fairly easy to inject a signal into a telephone codec which got any arbitrary sequence of codes out of the ADC, which could then deliver a data rate of 64 kbits/sec. Even with a kilometer of wire in front of the codec, it could be done in the lab by doing system identification on the wire to determine the transfer function and then pre-distorting the signal to compensate. In fact, this must actually be possible (not quite 64kbps) in a real-world situation on a high-quality phone line since 56 kbps modems do work on at least one analog end. Sean On Tue, Nov 16, 2010 at 5:47 PM, Olin Lathrop w= rote: > Sean Breheny wrote: >> If it were a purely analog line >> then the throughput would be governed by the bandwidth (fixed at about >> 8kHz) and the signal to noise ratio (which could always be improved >> and so does not impose a theoretical limit). > > But it's not a purely analog line and it does have inherent signal to noi= se > limits. =A0The ends may be analog, but everything in between is digital. = =A0Even > if the analog ends are perfect, the digitization sets a upper limit on th= e > signal to noise ratio. > > > ******************************************************************** > Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products > (978) 742-9014. =A0Gold level PIC consultants since 2000. > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .