Hello,

I'm thinking of building my own audio FFT display and I'm looking into various methods of doing this. I know the simplest with low amount of components would be performing FFT with the use of a microcontroller but that method is out of the question for me. Another method would be to use bandpass filters but the amount of components and the bandwidth of each bandpass would likely be too high.

The method I'd like to use is the following. Your feedback on this method would be appreciated. I think the pro's of this circuit is I'd be increasing the bandwidth of the audio signal making the bandpass filtering more effective.

1. Perform a sweep multiplication of the input audio using the CD4046, Decade Counter & AND Gate.
2. Amplitude modulate the CD4046 output using the input audio with simple jfet/opamp circuit.
3. 200khz Bandpass filter output of jfet/opamp
4. Peak detection circuit
5. A2D and send to display

Kind regards,
Kevin

 

To make it clearer, say I was looking for 1kHz signal. With the CD4046 I would multiply the output times 200. I would then amplitude modulate so that I would not lose its power. I would then use a 200khz bandpass filter to remove all other frequencies. Then I would use a peak detector to then sample A2D. And then output to bar graph per say.