I am working on designing a music visualization system using LEDs. I would like to create an analog design that uses op amps to filter, amplify, and add DC bias to an audio signal so it can be read into the A/D of a 5V microprocessor. The input signal is a +/- 1.5V volt audio signal coming from an MP3 player. From this signal I need to produce three output signals. This means that I need to design three filters (a lowpass, a bandpass, and a highpass). These filters also need to amplify and bias the input signal so it will be a 0 to 5V signal that can be read by the processor's A/D at the maximum resolution. So basically what I have pictured is to first bias the signal, then amplify it, then filter it: MP3 Player Audio signal --> Bias --> Amplify --> Filter --> uP I am familiar with building filters with amplification, but I am not sure about the correct way to go about adding a DC bias to the filters with amplification. Lowpass (bass range): cutoff f @ ~500 Hz Bandpass (mid range): center f @ ~2250 Hz Highpass (high range): cutoff f @ ~4kHz The parts I have available for use are: LT1632 dual op-amps, resistors, 100nF capacitors Measuring the output signal from the iPhone: V(peak-to-peak): ~2.85V centered around 0V Required Gain: ~1.75 Available Power supply units: +5V and +12V DC I've tried designing these filters by hand, and using TI's FilterPro software, however I have not been able to achieve the DC bias affect. I have been simulating the filters using LTSpice. I have the design files for the three filters though if it would help in describing my current problem. Any help in this area would be greatly appreciated.