Tonight I solved a hardware problem with the Pokey module that had been a mystery for quite some time. In celebration, it only makes sense to post about an unrelated change from last weekend.

When the Pokey adjusts pitch on a noise waveform, it can often change timbre completely or even go silent. With analog tuning control, an incoming voltage can end up teetering on the brink of stability between two different sounds. For very slow pitch changes, it can end up sounding like a bad connection.

Click here to hear some “before” pitch changes

A common solution would be to add hysteresis. That is, keep a record of *how* the signal is changing. If it has been increasing and keeps increasing, let it pass as-is. If it has been increasing and tries to decrease, ignore the change unless it is more than some set amount.

That sure is a lot of logic to add, though. It requires looking at the last direction moved, the current direction, and how far it is trying to move. Instead, I went with a simpler approach. I’ll spare the math, but the resulting process looks like the following graph. Red is the noisy input signal and blue is the smoothed output.

The red represents the eternal struggle between order and chaos... or something

Red represents the eternal struggle between order and chaos... or something

It looks just like it’s been low pass filtered, but the overall frequency response has actually changed very little.

Click here for some “after” pitch changes

Listen to how sudden the transitions are now. There is no more loitering between timbres.

I’m currently doing an updated circuit board layout with all the minor changes I made to the prototype. Hopefully in a matter of weeks I will have the first few completed modules to use for demos and beta testing.

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