Have not messed with this yet but it looks interesting...
The aim of auch is to visualize harmonics in musical recordings and the effect of analog/digital filters on the spectrum. There are plenty of tools that visualize the spectrum. The difference here is that one or two octaves can be focused on, so that notes, chords, and harmonics become clear. Another feature is that this tool is aimed comparing audio out (eg. a .wav file) with audio in. This way, external filters added between the audio output and input of your sound card can be studied.
http://www.4cko.be/auch-www/index.html
