This is the code to accompany two blog-posts I wrote about transfering
data between computers using a jury rigged sound-card modem.

Note that these programs are mainly educational, and if you want to do this
in a critical situation, you'll at the very least want to add Hamming-code or
some other error correction scheme.

The source code consists of a multitude of programs.

* playback and record plays and record a data stream using OSS. If you don't have OSS support, ALSA can emulate it with the 'aoss' wrapper.
* generate turns a binary file into raw wave data.
* generate_psk does the same, except encoding it with phase shift keying.
* analyze turns a recording into data again
* analyze_psk does it for PSK-encoded data.

The articles can be found here:
http://awesomegeekblog.blogspot.com/2009/04/file-transfer-over-sound-card.html
http://awesomegeekblog.blogspot.com/2009/04/file-transfer-over-sound-card-ii-phase.html

The code is public domain.