I upgraded the synth to use 2x oversampling on the state-variable filter this evening. This means that before the filter runs, the incoming samples from the oscillator are upsampled(for every 1 incoming sample, two are generated). We generate the new samples by convolving the Blackman-Harris window over the old ones. The SVF is run over this double-rate buffer, and the output is subsequently decimated back down to the original rate. The resulting filter is more accurate and smoother-sounding.

The patch I made after doing this modulates cutoff, resonance, and amplitude over a sawtooth - it's perhaps not the most challenging example, but the timbre is very reliant on filter quality, and it hits my soft spot for long, evolving pad sounds.