voice modem variations

Adam Megacz (megacz@usa.net)
Wed, 8 Oct 1997 06:41:36 +0200



For your needs, you might consider a cheap Rockwell modem (you can find
them for $40 these days). It won't do fax (Class 1 only, which is a no-no
under UNIX), but the voice goes up to 8bit 11.025khz (read: roughly half
the quality of an 8bit sound card; for voice recordings the quality is
excellent; just don't go listening to CDs over your voicemodem). To my
ear, the quality of the recording exceeds the quality of most phone lines;
hence, it is at "optimal quality".

As far as cheap modem feature loss, among other things you lose:
 1) fancy compression codecs to save disk space (I just encode stuff
  as mp3, though; much better than any modem's compression algorithm)
 2) Class 2 Fax (read: you lose all UNIX-based faxing ability)
 3) A few arcane features like Fax Polling (I've never found a use for
  this)
 4) Caller ID.

>  - do modems handle silence detection (so they hang up properly) all by
> 	themselves? does mgetty have to monitor that and hang up after
> 	some amount of silence?

Actually, I think that there is an actual voltage signal sent on the phone
line when you hang up. Hangup has nothing to do with the sound that is
passing over the line. However, silence detection is supported for
compression purposes (i.e., if volume falls below x, pause the recording.)

I have a Rockwell (paid $40). It works fine except the hangup detection is
poor, but that's because I'm running a really old version of vgetty. I
will upgrade soon, and if you like, let you know how it works.

 - AJ

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