See posts 39, 40 at:
http://amfone.net/Amforum/index.php?topic=33505.msg259485#msg259485There are two options given..one PC based, and the other done with building a circuit.
For the PC based one, use one for THD tone tests, or two for 2-tone IMD testing...Also has a white noise function.
Jim
WD5JKO