Convolution has been around for a while, mostly relegated to reverbs and guitar cabinets. They use samples, called impulse responses, which are recordings of the sound a space makes after a noise burst or sine sweep has been played into it, and apply complex maths that I don’t fully understand to combine input audio and these IR’s to make all kinds of neat sounds. I may not be able to explain how it works as it is indeed digital black magic fuckery, but I can show some neat ways it can be used!

Delay

If your IR contains basically any delayed signal (some sound repeated rhythmically), you can then play any sound into the convolver and get a neat smearing delay sound which is more prominent with fast stabs than longer sounds. You can even use rhythmic patterns rather than straight delays to get unique swung delays. Faster clicky sounds will produce cleaner delays than more complex or longer delayed sounds.

Filters

This is a weird one, but if your IR is effectively a bubble pop sound (sine wave pitched up with an envelope to make a “oip” sound) that fades out very quickly, you can make lowpass filters (too long and you’ll get weird frequency shifter effects, which is also cool). The higher the base pitch (and shorter the tail), the higher the cutoff frequency. You can also make highpass filters if you use an IR that’s effectively a click starting at various frequencies and going up from there. Bandpass filters are formed by combining both the oips and the clicks, but for the clicks you want them to be bandpassed somewhat narrowly and have the oips go through the band’s range. You can also make formant filters using this method with multiple bands in the IR. You can even employ clicks as wide asymmetric bandpass filters to make EQs that emulate speakers or microphones.

Weird stuff

• You can employ digital noise with stepped amplitude modulation to get glitchy reverbs. You can fade in said noise cleanly to get reverse reverb sounds.

• You can implement pulsar synthesis to create a vocal sweep, then use that as an IR to get 2012 dubstep yoy sounds (the yo will happen as you hold a sound, the oy will happen after the sound stops).

• Similarly, if you make an oil like for a lowpass filter IR but then pulsar it, you can get FFT phaser sounds.

• If you generate a noise, such as that of cicadas, then pitch it up abruptly part way through, and use that as an IR, you’ll get a delayed step in the sound.

• A relatively short sine sweep down across the full spectrum will create Disperser-like sounds.

• the tiniest click but with some resonance (such to create a click with a very short sinusoidal tail) can be used to create a stereo inverter by simply flipping one of the clicks and using it on one side of a stereo pair. This does only work for stereo convolvers, but it’s a neat trick a la 2600 reverb.

• you can impose the harmonic structure of chords onto other sounds by running a short noise burst through a chord resonator and using that as an IR.

• Similarly, you can make laser noises and use that as an IR to make any sound have a laser noise imposed on it!

So yeah, convolution is neat. I highly suggest synthesizing your own IRs to make various sounds, from reverbs to filters to delays to everything in between. Enjoy!