[sdiy] Imperfect VCO

[Oakley Sound]

Theo > Don't know the ION but a real 0:100 digital saw wave has a lot of
aliasing going on.

Actually, I was just rounding up those values. The Ion doesn't actually
have a value specified for either rise or fall times. You just get a wee
picture on a display. I used the terms 0:100 very loosely, since the
display rise time does indeed go vertical on the display. I knew that
any system with a finite BW will not be able to produce instantaneous
rise times. I am not too sure why this should cause aliasing since the
effective BW should be limited to 20KHz (or whatever) directly in the
waveform generating software. Maybe its not though... do they really try
to produce instantaneous rise/fall times with these things?

MC > So it is hard for me to understand why a normal VCO core should
have such a bad ratio like 1% or so.

I don't think it does, but I need to do some maths before I can work out
what effect even a slight slewing on the flayback will have on the
harmonic structure of the sound. But it does seem likely that it should
not have a significant audible effect, and that there is indeed another
source for any sonic difference in VCOs.

MC > I mean this is basically the circuit for a tri core to saw
converter.

Yes, that's right. But I was quite suprised that I could hear the
difference before I could see the difference on the scope. Even on a
harmonically rich sawtooth.

Regards,

Tony Allgood                       Penrith, Cumbria, England

Oakley Sound Systems                   www.oakleysound.co.uk
Modular Synthesisers      www.oakleysound.co.uk/projects.htm