40 lines
1.7 KiB
HTML
40 lines
1.7 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<TITLE> Modem-HOWTO: Appendix B: Analog Voice Infeasible Over Non-Voice Modem</TITLE>
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<H2><A NAME="s22">22.</A> <A HREF="Modem-HOWTO.html#toc22">Appendix B: Analog Voice Infeasible Over Non-Voice Modem</A></H2>
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<P>Sometimes people look for software that will allow them to transmit
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ordinary analog voice over a modem that doesn't support voice. It
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doesn't exist since it's just not very feasible to do this. Of
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course, one can use VOIP to send digital voice over a modem. And when
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one makes a call and the other side picks up the line, one might be
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able to hear voice for a few seconds until negotiations for a
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connection begin.</P>
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<P>But once a modem is connected, sending analog voice over it just isn't
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feasible. For phase-amplitude modulation, carrier frequencies of
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fixed values are used which doesn't allow the continuously variable
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frequencies required in analog voice. V.90 and V.92 might be feasible,
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but if line conditions deteriorate, they fall back to phase-amplitude
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modulation which won't work. Furthermore, V.90 uses phase-amplitude
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in one direction. Also, both V.90 and V.92 don't permit all
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amplitudes to be used, which limits the waveshapes which can be
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created.</P>
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