This post discusses one of the most important relationships in all of sound design: filters and distortion!
I used to think that resonant low-pass filters were kinda doofy. They produce a lot of sounds like this:
I don’t have much use for synth ducks.
However, combine that filter with its good friend distortion, and you can create some amazing growl bass sounds:
(This might be a bit loud.)
The filter’s going to rampage through the frequency spectrum and smash any overtones it finds into the distortion to produce a complex, evolving sound, so we want to make sure there’s plenty of harmonic content for it to play with.
Your sound source will provide that harmonic content. It should be bright and buzzy – sawtooth waves are the most commonly used, but things like low-pulse-width square waves and horn samples can also work really well. In the example above, I combined a sawtooth with a 1/8th pulse-width square tuned down an octave.
Low-pass, high-pass, band-pass – they all work. For this particular sound, I’m using a 2-pole low-pass filter since I want to keep the low end intact. If I wanted something thin and biting, I’d use a band- or high-pass, something that gets rid of the lower frequencies.
We also need to control the filter’s frequency. I prefer to use a mod wheel, but if you find yourself without one, an envelope or an LFO can do in a pinch.
Distortion gives us two equally important things: besides the crazed frequency content, it also creates a constant volume level. Distortion is basically compression gone mad, and it can give a sound a lot of strength by flattening the dynamics.
Where you get your distortion is up to you. Most synths have some type of distortion module included. I’m using FXpansion’s Strobe, and I’m taking advantage of both its pre- and post-filter VCA saturation: pre-filter to generate more harmonic content for the filter to play with, and post-filter to mangle the resonant sound.
When I want to add effects like reverb or chorus, I always slot them in before the post-filter distortion. We’re turning our sound wave into a bit of a brick, and keeping post-brick effects below the digital clipping point would be a nightmare.
This is a specific example of the interplay between filters and distortion, but I actually rarely use one without the other. Whenever I’m creating a distorted sound, I reach for filters or EQ to shape it, and whenever I’m working with filters, I like to add at least a little distortion to provide some quick and dirty dynamics management. My sound design improved a whole lot when I started experimenting with this relationship, and I’m sure yours will too.