This Audio Unit for Mac OS X combines computer vision head tracking with a low pass filter. For this simple example, the x-position of the head controls the cutoff frequency and the y-position controls filter resonance. I presented this work at HAID ’09 (Haptic and Audio Interaction Design) in Dresden, Germany.
If you’d like to try this for yourself, click on the link below to download an installer. It works only on Intel macs with a built-in iSight camera. You can activate the plug-in through AU Lab, GarageBand, or Logic: