Martin Schied found a interesting distortion. Nothing new I guess but worth some analysation.
haut-parleur-doppler.pd is the original file from Martin, the other one my variation to get a better glimpse at it. If you like sunn o))) or similar you might like it. But I suggest you first look at how it behaves without feedback.
Sounds really cool with a guitar and with high gain (around 50). What's nice is the change in the spectrum depending on the volume of the input.
But all waveshapers also do change the spectrum according to the volume (except those that are linear, which basically means those waveshapers that are configured to do nothing.)
This is wrong for this distortion. And that again is what is interesting about it. The distortion depends only on the travel speed of the vd~. But if you multiply the signal with a gain you also change the velocity by that amount. A negative velocity (down to a delay of 0) means a pitchshift upwards. While a positive velocity means a downshift. At a velocity of 1ms/ms is the turning point, for faster modulation the signal is played in reverse. A reflection at 0Hz, which is basically the same as a Nyquist reflection. The parallel up/downshifting leads to a chaotic spectrum change. With a speed of .7 ms/ms we have at the same time the signal with 30% and 170% playback speed. Which clearly has no relation to the original pitch and no harmonic relation left. This is only intensified through the reversed playback and the constant velocity change. While typical (soft-)clipping only generates harmonics related to the fundamental. The more I think about it the more fascinated I am that this results in something interesting to the ear.
So what we have here is some kind of natural asymmetrical distortion. As the velocity is the important factor it has the interesting property of being frequency (and amplitude) dependant! A modulation frequency (amplitude) of *2 results in a velocity of *2. This means: the higher the input frequency (or amplitude) the harsher the distortion. If wanted this can be compensated for with a simple lop~, who has a rolloff of -6 Db/dec or in rms: a frequency increase of *2 means a amplitude reduction to 0.5. So every frequency above the cut-off-frequency has now (almost) the same impact on the distortion.
Please correct me if I'm wrong somewhere. And have fun.