note: this requires the aoss program, which is part of alsa's OSS compatibility package (alsa-oss is a likely package name)

How to capture streaming audio with linux

The ALSA file plugin can do this.

Try putting this in ~/.asoundrc:

pcm.fileout {
type file
slave.pcm "hw:0,0"
file alsaout.raw

...then aplay -D fileout foo.wav

will create a file called alsaout.raw

Of course, in that case it's easier to just cp foo.wav!

It's likely you'll want to record the output from realplayer or
something. If you have OSS emulation set in ALSA, try adding this to the
same .asoundrc:

pcm.dsp0 {
type plug
slave.pcm "fileout"

# aoss realplay

*should* record realplay output to the same fileout.raw

(Note: aoss uses LD_PRELOAD hackery)

Audacity had/has a raw importer which [shows] a small graph of the
waveform and you could try different combos.