[sdiy] Multiple oscillator detuning

Tom Wiltshire tom at electricdruid.net
Mon Dec 10 18:41:34 CET 2012

Hi Richie,

Thanks for your thoughts. Many good points as usual.

> Notice in that paper how the detune control law is not linear.  You get lots of fine control over the slight detunings which are more muscially useful, and then it kicks in with more severe detuning in the last part of the potentiometer's range for your hoover leads ;-))  (Why the author tried to fit a 10th order polynomial to data that's clearly piecewise linear is beyond me though!)

It struck me that this was probably the most important thing in the paper. That control response gives a great deal of control over very fine detuning, and access to some more severe detuning if required. That's a good lesson to learn whatever style of detuning I go with eventually.

As you say..I've no idea what he thought he was on with with the polynomial fitting. The raw data looks like piecewise linear, with three slopes. And even if you decided to fit a curve to it (not unreasonable in principle) I'd have made sure that the curve was of low enough order to be nice and smooth for the region of interest. His 10th or 11th order curve is so detailed that it captures a little wiggle in the raw data and reproduces it! Ugh! Finally, there's no way on earth the Roland synths evaluate such a monstrosity every time anyone tweaks the knob - it's a lookup table, and the equation is only any use once to generate the values to put in the table.


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