Microphone Pitch/Freq Detection (actionscript 3.0 in particular)

Question

So, I'm trying to detect the average frequency of a sound recorded from the microphone. It can be assumed that this sound will be in mp3 or wav form. My final goal is to do this live (or close enough), but for now simply finding the average frequency of an mp3 or wav is good enough to start with.

I'm having an unbelievably hard time finding any classes in actionscript 3.0 that can help me with this task. Can anyone help me out by possibly suggesting classes in AS3.0 or algorithms for me to look at for this particular task ?

Thanks to all in advance.

Answer 1

The best approach varies depending on the audio you're analyzing. For monophonic input, such as a singer, flute, or trumpet, an autocorrelation approach can work well. The idea here is that you're trying to find the period of the wave form by comparing it against itself at various intervals to find the best match. Imagine you have a sound wave with a period that starts over after every 400 samples. If you were to iterate over some number of samples, always comparing the sample at index i with the sample at index (i + 400), perhaps by subtracting one from another and adding this result to a running total, you'd find that your total would be 0 if the wave was a perfect match of itself at this interval of 400. Of course, you don't know that 400 is your magic number, and so you need to check a variety of intervals that fall within your possible range. You could exclude intervals that would result in a frequency that's impossibly low or high. You also would obviously not expect to find a perfect match, but generally speaking, the interval where the match is closest is your frequency for a monophonic pitch.

For polyphonic sources, or instruments with a timbre that's very rich in harmonics like violin or guitar, you may need to use a different approach. FFT based approaches are widely used for this in order to break down audio segments into their harmonic pitch content. It's then a matter of applying some rules that you come up with for deciding which frequencies coming out of the FFT are your best bet.