iOscilloscope (App Store link) is a new $.99 app that turns your iPhone into a virtual oscilloscope that can measure sound waves in real time.
iOscilloscope lets you do do several different things:

FFT allows you to view the sound waves in Fast Fourier transform mode.
Mute, mutes the sound so that there is no feedback.
Sonogram allows you [...]

This is sort of stupidtacular, but at least it can handle the Prodigy.
Here’s how it works:
A hard drive voice coil circuit is hacked to allow it to be directly connected to a stereo output. This allows audio to move the hard drive read write head. Mirrors are positioned on the center of the platter and [...]