Does anyone know about a good ALSA compatible tone generator which I could use to find the peaks? My sound card (well, a 24/96 one, ummm ...) and my Sennheiser 580 phones should be able to provide a near-flat frequency response up to about 20 kHz...
You could use XMMS and add a url tone://12000 to the playlist (you need the tone generator plugin, of course). Or try Audacity, even though that's kind of oversized ;)
Robert