22. Appendix B: Analog Voice Infeasible Over Non-Voice Modem
Sometimes people look for software that will allow them to transmit ordinary analog voice over a modem that doesn't support voice. It doesn't exist since it's just not very feasible to do this. Of course, one can use VOIP to send digital voice over a modem. And when one makes a call and the other side picks up the line, one might be able to hear voice for a few seconds until negotiations for a connection begin.
But once a modem is connected, sending analog voice over it just isn't feasible. For phase-amplitude modulation, carrier frequencies of fixed values are used which doesn't allow the continuously variable frequencies required in analog voice. V.90 and V.92 might be feasible, but if line conditions deteriorate, they fall back to phase-amplitude modulation which won't work. Furthermore, V.90 uses phase-amplitude in one direction. Also, both V.90 and V.92 don't permit all amplitudes to be used, which limits the waveshapes which can be created.
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