most elegant ways to make diode clipping frequency dependent?

[MrStab]

i have two experiences with this, which aren't exactly groundbreaking, on overdrives i've made.

First up, in the OP's diagram, imagine a pot instead of R4. This allows the LPF corner frequency to be changed - it's a bit like one of those "cap blend" pots people like to stick on the front of fuzz pedals. It doesn't do much for the highs, but it is quite an effective mod for just a few extra parts.

Naturally, that parallel resistance would change the op-amp's gain as it turns, but this can mostly be eliminated by placing a fixed resistor to limit the minimum gain (then calculating your overall gain off of that minimum parallel resistance) and by using a reverse-log pot (which also gives you a smooth frequency sweep). The high-resistance side of a 100k-or-so pot doesn't make much difference to the total paralleled resistance, and rev-log taper limits the problematic effects of lower resistance.

Another thing i've tried is leaving the clipping stage's bandwidth fixed (or wider than usual) and slamming a semi-parametric EQ into that. That approach takes a lot of fine-tuning to get the thresholds right, but it allows for quite intuitive control of frequency-dependent clipping.

just my 2 pence! (i THINK that was rev-log btw, might've just been log...)