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On Tue, May 31, 2005 at 09:13:20AM +1000, Angus Lees wrote:
> At Fri, 27 May 2005 13:04:21 +1000, Jeff Waugh wrote:
> > What's the most sensible and reliable way to record a phone conversation,
> > assuming a standard phone, using Free Software (and probably a bit of
> > hardware)?
>
> You can get phone audio into a computer by using one of those old
> voice-modems with the right AT commands (often not full-duplex, but
> that isn't a problem here), or a telephony card with an FXO port.
> Whether something like asterisk will make the software side easier or
> not, I'll leave as an exercise for the reader -- but even using
> asterisk for this step wouldn't require anyone to use VoIP, assuming
> you had a PSTN double-adaptor thingy at your end.
I have tested this with the Netcomm "Webmaster" CD1800 56k V90 and
yes it works and the AT commands are moderately well documented
(not by Netcomm, you need to search around). Roughly it is something
like:
AT+FCLASS=8
AT+VCID=1
AT+VSM=128,8000
AT+VLS=1
AT+VRX
Then modem sends "CONNECT" followed by a stream of 8 bit unsigned
samples. There are some other bits of stuff encoded in the samples
as a DLE (0x10) followed by a single byte so you should strip those
out afterwards.
To hang up, you send:
AT
ATH
The exact numbers after the "=" depends on the modem and what sort
of codecs it supports. The CD1800 is about $70 retail and supports
only one codec which is 8 bit unsigned linear PCM at 8kHz.
Voice quality is reasonable, not fantastic but better than most
mobile phones. You need to split your phone line and feed it parallel
into the modem and the handset which seems to make the handset a
little bit quieter (but maybe I'm going deaf).
This is about the easiest way I can think of for recording a phone
conversation to computer and sox will convert the resulting file
into something more presentable:
/usr/bin/sox -v2.0 -r8000 -db -fu $infile $outfile lowp 2000
or something similar...
- Tel ( http://bespoke.homelinux.net/ )
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