I'm working on a project that involves taking the audio output from a consumer device like an iPod or whatever, filtering for low, mid, and high frequencies, and then converting the levels into a PWM to drive LEDs for each frequency range. Passive filters will separate the low (<500 Hz), mid (500>1000 Hz), and high (>1000 Hz) frequencies, at which point I will rectify the separate signals to get a DC voltage level, which will be used to derive pulse-width modulation to drive LEDs color coded to each range. If Wikipedia is to be trusted, typical peak voltage for the input signal from most consumer devices will be 0.45 volts or so. Should I be trying to amplify before my passive filters, or after? I noticed that radio shack carries the NTE890. I think it might serve to translate the DC voltage into the PWM I want to drive my LEDs. Does anyone have any experience with the NTE890 in regards to this application? Would I be better off just using 555 timer ICs to accomplish this?