My problem was that a short segment of random isn't spectrally
straigh-line flat.
If you feed this into a resonator (waveguide) you can hear a difference
between one random grain and another with another random sequence.
This is usally a desired effect that makes the sound alive,
but in my case I wanted to eliminate this for then moment.
And it doesnt help to synthesize a flat random sequence with FFT since it's
not flat after evenveolping/windowing.
I managed to get a flatter response the follwing way:
create a segment of exp decay padded with silence
repeat:
FFT (of double size) and set all magnitudes to 1
iFFT
set second half of time signal to zero
/repeat
it seems to converge to a flat aproximately exponentially decaing signal
(I have only done 20 or so iterations manually so I am not sure how it
behaves)
Dont ask me why, maybe its just a simple genetic algorithm thing
The result is a little bit strange however, slightly metallic
and when you convolve it with it self several times you get some kind of
multichirp soundwise
where sparse narrow dips and phase delay appears at random places across
the spectrum
Similar to a spring or allpass chain but with multiple random "resonances"
Am 28.07.2016 um 19:17 schrieb Tito Latini:
sorry, that's a decay, so out is "(1 - y) * rand()":
T = 1 / samplerate
p = exp(log(0.001) * T / t60)
y = 1 + p*(y1 - 1)
y1 = y
out = (1 - y) * rand(-1.0, 1.0) * gain
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