The idea here is to modulate the clock rate and the bias of Marbles with a relatively slow LFO so the note sequence speeds up as it gets higher pitched, then it slows down again as the notes get lower.

The Bogaudio LFO has a built in sample and hold, which I found very useful. By changing the sample rate I could modify the “steppiness” of the changes and with the scale knob the total range (see scope). I added another LFO which modulates some characteristics of the timbre (brightness, damping etc.) to have some variety in the sound over time.