On 2013-12-11 Adam Thompson wrote:
LOL. That *is* a modem, only slowed down by about 10x and somewhat mangled. It sounds like a fax machine, to me.
Ya, it does sound like a fax handshake but with about 5-8 dropouts every second, and yes, probably slowed down.
Are you sure your homebrew voicemail and .wav conversion is working proeprly? Are you receiving voicemails that are similarly mangled? If you answered the phone at whatever a.m. when this comes in, it probably sounds like a normal fax (we're guessing)?
Are you using mgetty+vgetty for this? Converting from the weird vgetty/modem format to WAV and resampling isn't trivial, and perhaps a setting is wonky in there. You could try sending yourself a fax from somewhere at a known time and seeing if you get the same results.
PS: setting up vgetty to allow incoming faxes may also shed some light: at least you'd see what the fax is about!