This video example doesn't have to do anything with the VCO and its tracking. It is about how the distorting filter reacts on the VCO.

On 23.09.17 23:58 , a11@... 1 wrote:

Thank you for your reply, Florian.

The reason I ask this is, that sometimes when you VC tune/pitch-V/Oct a VCO, the sound changes, so you can not play a decent melody.

You can notice it here in this video - not so clearly - from 6.16 and at 7.06 minute.
If the signal was distorted more and more , the changes in sound would be also more and more.

It's a pity, because the OptoFet filter has some very nice [sweetspot] distorted sounds.

https://youtu.be/Hsf7nTXDhYw t=6m16s