I’ve been comparing the output of the VVVV FFT node with my C audio processing programme which uses the FFTW library.
The VVVV documentation doesn’t really spell out precisely what the FFT calculates. Here is what I think it does based on observations. Would one of the VVVV source crew like to confirm:
- As you would expect the output is a function of the log of the power density. * EDIT: As clarified below this isn’t right. It is just the power density, not the log *
- There is an (adaptive?) noise filter that rescales the output to cut off a large amount of low-power noise that would otherwise appear.
- The most odd feature is that there appears to be an EQ filter applied which increases the response with higher frequency. If you feed the FFT with white noise you get a slopeing output.