[sdiy] VCO autotune for poly analog modular

[jays at aracnet.com]

I do a lot of calibration code for test and measurement instruments and yes this is do-able. Biggest problem is that calibration is probably going to take a fair amount of time. Mainly because at low frequencies it will take time to get your samples and do a loop for the calibration.

First off don't base your calibration on a single period measurement. Measure the period of N cycles multiple times. Doing N cycles will minimize the error for a single cycle. Getting the multiple times, throwing out the high and low measurements and doing an average helps stablize the data.

Calculate the correction factor and do it again until things get into tune. Maybe use some sort of binary search to zone in on the value needed.

You might be able just to tune at octives and then use linear interpolation to get all the notes in between. So experiment and see what works best for you in your system.

Jay S.