pretty much OT: acoustic coupling

On 24/03/07, Randy Dawson <rdawson16 at hotmail.com> wrote: Sorry, but no. As a previos poster has pointed out, you'll hit the codec (not G.711, but likely AMR for GSM phones, SMV for CDMA, or some older codecs on TDMA systems), which tends to be speech specific, and thus be really bad for any type of modulation coding. All POTS modems assume a more-or-less linear channel. You'll also hit against a few of Shannons' laws... in any case, you can't get data through a channel at any rate higher than the lowest in the chain - and the aforementioned codecs will give you decent speech quality even down below 10 kbps. Furthermore, the CDMA codecs are variable rate, since you're sharing badwidth with everyone else. It comes down to that you really can't do better than using the data mode of your handset. It's just that the codecs are so good the you have the impression you're on a good line most of the time (and when they fail, they degrade _really_ bad). I've worked on the AMR-WB, VMR-WB and AMR-WB+ codecs (hello to anyone yet. The technology to have cell phones sound better than landlines (even at 14kbps and below) has been around for years now. Joe. PS. There is also a reason modems will never ever go above 56k. 56k can only happen in the ideal case where you are really close to your local office. At that point, the analog signal is digitized (u or a-law) and sent over a 64kbps digital circuit - a slice of a T1 or T3 or OCwhatever. One of the bits is stolen for signaling - so your bitrate is 7/8th of 64kbps: 56kbps. That is the slowest link in the system to your "analog modem" ISP. And this will only work if the ISP gets your circuit on a digital line (so the "analog modem" of the ISP is actually fully digital) - the 56kbps modulation scheme does not withstand a second D/A-A/D conversion. Hooray for ADSL...