Generation of impulse responses using chaotic oscillators
( use in convolution reverbs like Altiverb)
Principle
We'll start with a spectral representation of the logistic equation. Here it is - spectrum for R = 2.573 :
This spectrum corresponds to a near harmonic sound - near, because the fundamental is missing.
Now let's reverse this graph :
And let's consider it as an audio file (a time / amplitude representation instead of the frequency / amplitude representation) :
... this is an impulse response corresponding to a multi-tap delay !
So : if we take the spectrum of an oscillator, export it as an audio file, it makes an impulse response for a convolution reverb.
This is confirmed when comparing :
- the spectrum got from one of the behaviours of the Lorenz system, converted into an audio file :
Possible examples
OK, this is a multi-tap delay :
Another multi-tap delay, slightly more exotic.
Now, a mix of delay / reverb - in other words, first reflections / diffuse field :
A mix of two "taps" and bursts of diffuse field :
A first loud reflection, then plain diffuse field :
Pure diffuse field :
Mono / Stereo issues
The principle described above leads to mono -> mono impulse responses. This is possible if we change the initial conditions of the oscillator : generation of IRs with the same global aspect but different details. But, only the chaotic parts are subject to the "initial condition sensivity".
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