[sdiy] square to sine
David G Dixon
dixon at mail.ubc.ca
Wed Oct 10 18:44:51 CEST 2012
> If you're going to use 2164 VCAs to get the expo conformity
> then I'd definitely go with a sinewave oscillator from the
> outset. It's crazy messing about with shaping squarewaves or
> tracking filters if you don't have to.
Yeah, I've abandoned the square-to-sine idea now. I'm going to shape a
> The quality of the sinewave output is going to be much better
> if you can start with a half-decent sinewave oscillator,
> instead of trying to strip away the harmonics from a
> squarewave. Those lightning fast edges of the squarewave
> will do their best to couple onto all signals on your PCB and
> find their way to polute the sinewave output with nasty
> high-order harmonics!
> If you design a state-variable filter such that it is just
> slightly unstable to start with, and then add some
> level-dependent damping (feedback from the BP output,) you
> should get a very pure sinewave output from the LP output.
> This is because any tiny amount of clipping that happens to
> control the amplitude is done at the front end, and this is
> double integrated before it arrives at the LP output. The
> two lots of integration do a good job of attenuating what
> little distortion is introduced during any soft clipping.
> That's the route I would take now, knowing a little more
> about your intentions.
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