DVDdoug:
First off, you need the "right" connection or the "right" microphone/circuit, etc.Typically, you'll use a line-level headphone-level) audio signal and bias the input so you can read the negative-half of the audio signal. My post for [u]The Worlds Simplest Lighting Effect[/u] has an attached schematic for a bias circuit.
SO I tried this, but it's quite inaccurate and provides a ton of false positives even with a 1.5k Hz low pass filter, it works better with a 795 Hz low pass filter, but it's still not what I'm looking for, there are times for which the the LED is solid, probably due to your average adjusting way too slow