Help designing analog filter designs for an audio activated 8x8x8 LED cube

[mp4nerd]

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.

 

[AlephZero]

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

Change that to

MP3 Player Audio signal --> Filter --> Amplify --> Bias --> uP

You should be able to combine the Amplify and Bias steps into one op-amp stage. Look up "level shifting op amp circuits" if you are still stuck.

 

[NascentOxygen]

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:

Hi mp4nerd, http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif

It seems that you are provisioned with only single ended power supplies. Rather than modify circuits to power op-amps off a single ended supply, it may be more expedient for you to employ a switching regulator module to produce a negative supply rail for the op-amps in your filter, amplifier, etc. There exist active filter designs that can provide all of LP, BP, and HP outputs from the one circuit, e.g., http://mysite.du.edu/~etuttle/electron/elect65.htm

Follow this active filter stage with a separate buffer stage incorporating the required gain and adding some DC bias there.

Good luck with your colourful project! http://img571.imageshack.us/img571/7470/rainbowf.gif