how hard can step-sequencing a filter be?

Yesterday I had a suggestion to add a “woody” sound, like a bowed string instrument, to my “daybreak” track, and while I don’t think I’ll be editing that track now, it did inspire me to grab some instrument samples and see what I could do with them. One effect I wanted to try was running sound through a filter that has it’s cutoff frequency controlled by a step sequencer, which gives the sound a bit of a rhythmic, glitchy feel. Short of buying an Evolver, was there a way I could do this under Linux?

I tried a few approaches, and did actually get this working in a couple of ways, but none exactly to my liking yet:

  • JACK Rack can control plugin parameters using MIDI, so I set it up with a Calf Filter, configured the cutoff for MIDI control, and created a sequence of parameter changes in Qtractor. This was quick to set up, and it kinda worked, but the timing wasn’t stable — I’m not sure if JACK Rack’s MIDI support is meant to be used this way.
  • The next idea was to use a modular synth. I tried AlsaModularSynth, but I’m not sure that its step sequencer is generic enough to use for modulation, instead of playing notes — I had it all hooked up but just couldn’t get it working. Ingen looked a bit more promising, but it’s still very alpha, and crashed too often for me to be bothered dealing with.
  • Following that line of thought, I fired up Pure Data (“Pd” to its friends) and tried to get to grips with it. Pd is one of the many programmatic audio/music synthesis environments available for Linux, and I’ve been looking for an excuse to check one out; this seemed to fit the bill pretty well. Pd is a bit like a modular synth, but much lower-level — it doesn’t have a step-sequencer, but I was able to build one! I got a working setup, but the resonant bandpass filter I used didn’t sound ideal to me, and I had hassles trying to pull in a better one, either as a Pd add-on or through LADSPA. I could’ve actually built a better filter, but that wasn’t something I was interested in doing today.
  • Moving on from Pd, I had another crack with SuperCollider, another synthesis environment. Unlike Pd, which is graphical, SuperCollider is based around writing code, which should mean that it’s more to my liking. I can get sound out of it, and it has some good filters, but the sequencing stuff is gonna take a bit of work to get my brain around.

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