What are the different kinds of FFT Processing Possible?

Feb 8, 2011 at 6:19pm

What are the different kinds of FFT Processing Possible?

I’ve read and seen stuff on a bunch of different topics so just to get an idea of the how broad a field it is, I thought I’d put the question out there..

From what I’ve seen so far, there’s:

- Phase Vocoders
- Spectral Morphing / Cross Synthesis
- Spectral Delay

I’m sure there are alot more out there though…

Feb 8, 2011 at 8:04pm

Some things I have tried except a few ones:

- keep only magnitudes higher than a threshold (spectral gating), lower than a threshold (only noise remains in sounds with acoustic origin), or between two thresholds.
- split with threshold(s) and send to differents destinations (to different loudspeakers = spatialization). You can also send to different circuits of transformation ;
- keep only a given number of the highest magnitudes.
- reduce/increase contrast of magnitudes.
- reverse spectrum (a bit deceiving as FFT works in a linear scale).
- increase or reduce the magnitudes variations between consecutive frames.
- remove magnitudes below/over a specific band number (high-slope highpass/lowpass filtering) or between/outside two band numbers (notch/bandpass).
- remove/keep one in two/three/four/n bands (kind of comb filtering).
- multiply each magnitude by a value stored in a buffer~ (graphic filter)
- split according to band number (crossover filter, spatialization)
- apply an offset on bands (frequency shift)
- keep only n bands and copy them as many times as needed to fill the whole spectrum between O Hz and Nyquist
- switch bands (kind of spectral blurring), for instance odd and even or randomly
- spectral interlacing (take m bands from one sounds, n next bands from another…)
- freeze
- substract one sound’s magnitudes from those of another (kind of inverted convolution…)
- shift phases (to increase spatial width for instance).
- detect transients
- detect pitch

Feb 8, 2011 at 8:32pm

hmm… i am not an expertt on this field but you can think that all the ideas you have in your mind when you deal with a bank of bandpass filters of fixed frequency and resonanse can be done..

so there is very big number of apps for spectral manipulation and repair like spectral compresor( like multiband compressor), spectral gate,spectral denoiser,spectral panning or a spectral waveshaping…

also you have the possibility to extract results for your spectrum and you can use these results for other purposes- for a example a beat detector ( the bitter trouth is that i never find a trustable beat detector in max world)

the more interesting thing in fft is that you have a very big number of “filters” that it is impossible to have it in digital world because of the high cpu..

Feb 11, 2011 at 2:14pm

great – thanks for you replies. sounds like there’s alot of interesting stuff to explore doing more manual operations on the bins directly



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