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A noise source useful in generating cymbal type of sounds.
(A rising edge on the boolean input changes the "seed" of the generator, it helps simulating hitting a cymbal on different places).
Generating cymbal like sounds is something quite challenging.
I fond a few papers in Sound on Sound about the topic:
I experimented quite a lot with these, but i was not convinced by the result i obtained.
Thus i listened to cymbal sounds and looked at sonograms to find what characteristics i wanted for a noise source.
- lots of spectrals peaks and notches
- beatings and pseudo random variations of the amplitude of the peaks
- slow evolving position of peaks
To obtain these characteristics with low memory (no samples) and low CPU (no "physical" modelling),
cymbal uses 4 congruential pseudo random generators.
- These pseudo random generators are used as complex waveform generators so, it is spectrally rich with lots of peaks and notches.
- each pseudo random generators is reset with a different period (that produces beatings).
- the reset value slowly changes with time, this makes the sound evolve with time
- the 4 pseudo random generators are doubled with twin generators offset by half a period, this trick enforces the spectral peaks and notches.
Note that it is a noise generator, it can be used with dynamic filters and other objects to synthesize convincing cymbal - or other - sounds.