Richard D. James on tuning and drift in his interview with Tatsuya Takahashi:
RDJ: …I guess some people like their Osc’s drifty and others not so. It changes with the context I guess. Also, if you’re doing FM you might want to keep them dead on, and for analogue lead sounds, really drifty. Anyway I think I mentioned it before, but the drift on the monologue sounds REALLY nice. It seems to move, but then never go out… Sounds to me like it gets reset/synced at some point…
TT: That’s bang on! So same thing in the minilogue and the volcas too: the oscillators are re-tuned when they’re not being used.
Mark Boyd (biminiroad) has posted a few patches on the Audulus forum exploring different approaches to simulating oscillator drift and detuning. His Drifting Gateable Quantizer doesn’t drift so much as introduce small pitch deviations that can be dialed in post-quantizer to get a pseudo micro-detuning effect. Simple (and light on CPU) but effective.
His Drift VCO takes a more complex approach: When the oscillator frequency is below 1000Hz, an adjustable amount of FM feedback (also scaled by the pitch) is sent to the oscillator’s input, and since the lower frequencies have more feedback, they are also more out of tune. Above 1000Hz (roughly two octaves above middle C) a slow sine LFO modulates the pitch in order to avoid FM noise. I’ve been taking a look at the patch and wondering how best to introduce something similar – a reset when there’s a pause in activity.
It’s interesting that now that we have the possibility of perfectly tuned oscillators we yearn for the beauty of slight imperfections. Certain of Jerobeam Fenderson’s visualizations in his oscilloscope tutorial come to mind – the spinning (around 5 mins into the video) introduced by an overtone having a slightly imperfect ratio, for example.