Pitch detection with computeSpectrum() return FFT values

Question

• I\'m developing using Actionscript 3.0 for Flash Player 10.3
• I\'m using computeSpectrum() on a loaded .mp3
• Running *Event.ENTER_FRAM

Answer 1

What are you trying to do?

I haven't used computeSpectrum() before, but the first half of my career as a DSP engineer.

If it does what the docs say, then you don't need to autocorrelate the results.

In your byte array, the index represents the frequency bin, and the index value represents the magnitude of that particular frequency.

If by pitch detection, you mean find the strongest frequency, then you need to loop through the byte array and calculate the sqrt(left*left+right*right) for each index. Find the max value of these. The index of the max value represents thr strongest frequency.

Assuming fs=44.1kHz, and i is your index, then the strongest frequency is

f = (i/255) * (44100 / 2);

Keep in mind that you are limited by the bin spacing for frequency resolution. If you need higher resolution, you need to interpolate the data.