[sdiy] Sine width modulation?

[Sean Costello]

This is essentially the phase distortion algorithm used in the Casio CZ synths. I think that it used a sine wavetable indexed by a ramp oscillator, where a "kink" could be placed in the ramp, such that the first half of the sine wave was indexed at a different rate than the second half. Harry Bissell's saw/triangle morph through a sine waveshaper would work just as well. 

Sean Costello
  ----- Original Message ----- 
  From: Amos 
  To: Synth DIY 
  Sent: Wednesday, January 18, 2006 7:59 PM
  Subject: [sdiy] Sine width modulation?


  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...]
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