[sdiy] Sine width modulation?

[harrybissell]

screw it if it HAS been covered, it sounds interesting...

You could do this with a cirucit that can morph from
sawtooth, to triangle to reverse sawtooth... feeding a sine-wave
shaper. That should be a lot easier to keep in tune than
the FM approach (if slightly more distorted)

iirc. Ian Fritz has a circuit for the triangle / saw on his site...
and I think Don Tillman has one as well.

I've done the triangle / saw morph and was not overly impressed...
kind of like a gentle PWM.  With a sine converter it could only
get less exciting.  But who can say, it might be worth the effort
for some folks

H^) harry

Amos wrote:
> 
> Apologies if this has been covered before, but I am curious...
> 
> Is it practical or musically useful to investigate per-cycle sinewave
> FM, a la pulse-width modulation?
> I envisioned an FM process such that for example, the rising/positive
> portion of each sinewave cycle is at a higher frequency while the
> falling/negative portion is at a lower frequency.  (or vice-versa I
> suppose, for >50% duty cycle)
> Would this still be considered sinusoidal?  Does it sound like
> anything other than a pulse waveform with very-low-cutoff lowpass
> filter applied?
> 
> I feel like this is perhaps an ignorant question, but I would be
> grateful for any replies on the topic.
> 
> Thanks!
> 
> [for implementation, I was thinking that a Pulse wave at the same
> fundamental frequency as the sine to be modulated could be used, with
> the pulse duration corresponding to the amount of frequency offset for
> the positive portion of the sinewave.  The means by which the one
> should influence the other (specifically how to create positive and
> negative half-waves of differing frequency without artifacts) is still
> unclear to me...]