Some sound devices, have a mixer input on the record logic block,
which connects to the stereo output of the playback block. This
has been termed "what you hear" by one company, as their
terminology. On my current custom mixer control panel, in
the record section this is called "Stereo Mix".
(The control panel on my sound - Stereo Mix, is for recording what is playing)
http://img148.imageshack.us/img148/4818/untitledsy0.jpg
If you enable the Stereo Mix on the recording side, then you should
be able to record what is happening on the playback output.
In this example, I used the free program "Audacity" (not shown)
to generate some test tones (something to make my speakers beep).
Then, I used the Sound Recorder included in WinXP, plus the
Stereo Mixer setting in my SoundMax mixer control panel.
You can see in the picture, Sound Recorder is receiving
the same sounds as are going to the speakers.
http://img692.imageshack.us/img692/7236/stereomix.gif
By using Stereo Mix ("what you hear") mode, the recording software
is relatively unimportant. All you need, is a program that isn't
too clumsy (or stupid - like programs that override the buttons
in that control panel).
So I'd say, if you wanted a conventional solution, you'd check
for that first.
It may also be possible, to intercept the digital samples, before
they get to the sound card and are converted to analog. And then,
you're right, finding the right fancy program, might just do the
job. But if the Stereo Mix feature is working in hardware, you'll
have a bit less work to do to find a solution.
My $10 CMedia card, looking at the block diagram, it doesn't have
Stereo Mix. But many of my motherboard audio solutions (onboard
AC'97) have the Stereo Mix feature on the record mixer.
When that feature is missing, sometimes it's the OSes fault.
But as far as I know, WinXP is OK. The feature may have been
removed on later OSes. In which case, you'd need a pretty
fancy program.
If you were trying to do this in Windows 7, you'd take a Y cable
from Line Out, plug one output into Line In, and the other
path would go to your speakers. If the OS won't allow you
to record Stereo Mix, you can fake it with cabling instead.
Paul
