sorry to bump an old thread...Jinsai wrote:Hard sync makes one wave (the slave) reset its waveform when the other wave (the master) restarts.
The "resetting within a cycle" effect of hard sync effectively changes the shape of the wave, which changes the harmonic structure and thus the timbre or sound of the oscillator.
Pulse waves are unique in that they are just on/off - there's no ramp or slope to them. That means when you reset them, you're effectively changing the duty cycle (the length of the on/off parts of the wave).
What else could do that? Well, once you think about it, you realize that changing the pitch of a pulse wave would have the same effect. A higher pitch produces shorter duty cycles clumped together frequently, lower pitch slightly longer duty cycles less frequently. Of course, because you're changing the duty cycle AND the frequency/periodicity, the pitch varies, too.
Pulse Width Modulation literally modulates the width of the pulses while keeping the actual pitch - the periodicity of the wave - the same. But because of the shifting width, there is some illusion of pitch variation (and thus, "fatness").
Since these things are close together, it's totally possible to fake PWM using hard sync:
Set both oscillators to the same pitch
Set your "slave" oscillator to a square wave
Set your "master" oscillator to a square wave
If you turn "Sync" on now, you probably won't hear any difference. Turn it back off.
Set up an LFO with a triangle or sine wave. Assign it to control the pitch of your slave oscillator, and give it a frequency and depth that is sort of like a reasonably fast police siren. Wee-ooo-wee-ooo, not weeeeeeeeeeooooooo.
Now turn Sync on.
You've got your fake PWM...except it's not really fake. You're effectively modulating the pulse width of oscillator 1, but in a sneaky way.
Slave oscillator has fixed duty cycle (timbre) and periodicity (pitch) on its own. But the LFO you set to it makes the periodicity vary up and down, so you hear the pitch variation.
But when you slave it to oscillator 2, oscillator 2 forces the wave to re-start its duty cycle at a fixed periodicity.
The net effect is the duty cycle changes at the rate your LFO is modulating the slave oscillator, but the pitch is determined by your master oscillator due to the hard sync. It's pretty clever.
This trick only works with pulse waves, because of their on/off nature. With any other sloped or non/on-off waveshape, you end up with timbral changes instead of PWM-ish sounds. (There's a different way to fake that kind of stuff for other waves using square LFOs, but I won't go into that now).
I'm interested in all the possible ways to "fake" PWM! some synths lack it, some others implement it very badly...
can you explain further?