[AdamM]

Here's a handy little online frequency test tone generator gizmo:

http://www.rhintek.com/tutorial/Frequency/index.php

It can do 20Hz<->20KHz sweeps, and pure sine waves at a bunch of increments in between.

There's a bit of noise in with the tones, but it's not too bad.  A quick test to see if you can hear 15Khz!

Cheers,
/A