sketchbook: ghetto convolution reverb

Convolution reverb is a hell of a trick — it lets you record the reverb of a real-world environment (or a hardware reverb unit) and apply that reverb to a signal, with amazingly realistic results. Normally, those reverbs are recorded very carefully using high quality equipment, but I wanted to see what I could manage with something more modest: my phone.

Convolution is to reverb what sampling is to synthesis; like a sampler, a convolution reverb can sound uncannily real, but it can only reproduce the reverbs you have recorded, as opposed to an algorithmic reverb that can create all manner of different and musically-useful reverb sounds without ever quite being able to recreate a completely realistic sound. The recorded reverbs are called “impulse responses” — they’re literally recordings of how a physical space responds over time to an “impulse”: a very brief, loud signal that covers the frequency spectrum.

There’s a highly reverberant stairwell at work, and with no option to bring in specialised equipment to record it, I figured I’d take a stab at it with that I did have at hand. I took my Android phone to the stairs, set TapeMachine recording, and used a clap of my hands as my impulse. The result is surprising — it’s very “coloured”, due to limited frequency coverage of both my mic and my impulse sound, but it’s definitely a reverb, and it might even be one that comes in handy for certain applications. For my testing, I set it up on a bus in Ardour using the excellent Jconvolver and then piped in some drums, setting up sends as I thought appropriate.

The sketch below has three versions of the same drum sequence: the first is dry, the second uses the CALF Reverb plugin, and the third uses my convolution reverb. It’s not subtle (nor should it be, given how strongly reverberant the space I recorded the impulse in was), but I like the sound on the snare — with some work, I think that could sit nicely in the mix on the right track.

mp3 | vorbis | 0:51

Leave a Reply

Your email address will not be published. Required fields are marked *