What kind of distortion effect is this?

Question

Here is the image of a plugin distortion I have applied to a sine wave. The sound characteristic is heavily distorted and digital but still good sounding bass wave.

Any ideas what kind of distortion this is and where to look for implementation? I currently implemented a wave shape distortion it squares the wave and doesn't sound nearly as good.

Thanks

Answer 1

If a sine wave was going in, because of the asymmetric waveshape coming out, it can't be a straight memoryless waveshaper. The half wave coming out looks the impulse response of an overdamped or critically damped 2nd-order all-pole IIR filter.

So I think the sinewave is going in and

1. first getting clipped symmetrically, same for positive and negative (so polarity is not important). This will generate only odd-numbered harmonics. So it can be a soft clipper as described here but has to be reasonably high order and have a lotta input gain to make it look like hard clipping.
2. Then that clipped signal is getting a differentiator to turn the up and down edge into up and down impulses.
3. Then the up and down impulses are going into some second-order all-pole filter that is either overdamped or critically damped.

overdamped: $$ h(t) = \big(e^{-\alpha_1 t} - e^{-\alpha_2 t}\big) \, u(t) $$

where $0 < \alpha_1 < \alpha_2$ or

critically damped: $$ h(t) = t \, e^{-\alpha t} \, u(t) $$