ALL electronic music VCO’s have some distortion somewhere. To completely remove those distortions would raise the cost so much that people would not probably buy them. Also it is hard to remove some distortions over the total range of the VCO too. The most typical distortion is overshoot at sudden transitions of the waveform. There is also sagging on sawtooth waves, square waves that are not symmetrical or don’t have flat tops, things like that.
These distortions give the VCO it’s unique sound compared to other VCO’s. Otherwise a perfect saw would sound exactly the same as any other perfect saw. When people say a certain VCO is fatter sounding or smother sounding or any other descriptor that is used to differentiate one VCO from another, theses distortions are what they are truly talking about. ANY perfectly executed waveform will have the same harmonice, hence the same SOUND and any other perfectly executed waveform of the same shape.
-James
Thanks for the explanation.