Talk:Fast Fourier transform: Difference between revisions
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::This is the closest thing I have found so far to an easy-to-read code block, and I am very grateful to have found it here (I'm looking mostly at the C++ one, but having all the different languages here make it much easier to see the common elements of the code) but it isn't quite complete. A few more examples of input/output data would be a huge help to anybody reading this (any language)
::Thanks again for writing-
::Sam
::: So, ok, let's say that you have 22khz mono 100ms of samples. As I understand it, 22khz means you are taking 22050 samples per second, or 2205 samples in 100 ms. This will not work for FFT since 2205 is not a power of 2. The nearest power of 2 is 2048 (92.87 ms). You can do a fourier transform with 2205 samples, but it will be a general fourier transform and not the fast one documented here. So let's say you've got 2048 samples and they are 16 bit samples. And, let's further say that you are using the J implementation (since that is the one I am most familiar with). In the J implementation, the first number is the amplitude of the dc component of
::: (Note also that the J implementation needs to be scaled by the number of samples when you convert back. So, in this case, you would need to divide fft(fft(samples)) by 2048 - or you could modify fft so that it divides by the square root of the number of samples...). Presumably other implementations will have similar issues, but it's easy enough to plug in some values and see. (make an array of 2048 instances of the value 1, run fft on it, run fft on it again - if the result is 2048 instances of the value 2048 that means you need to divide by 2048 to get the right volume.)
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