Exactly, that's why it's called PWM. You open or close it up and it changes shape and sounds from squarish to sawish and all sounds in between.

Lets here a sample

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I did this in a jiffy...I don't change the sound too much on this one. I'll try to find a better example.

OK, so sounds like your passing an LFO to the PWM or something?


How can you actually change the waveform from square to saw though. I thought pulsewidth was just the space in between the cycles in the waveform and didnt have anything to do with the waveform type itself?!

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I think what he's talking about is actually Pulse Modulation, which is often incorrectly labelled as PWM. Pulse modulation is sort of like using an LFO, except that the modulating oscillator is a square (pulse) and is at the same frequency as the synthesizing oscillator (not a "low frequency"). The resulting sound can be modulated by changing the pulse width of the square; it sounds like it would be called PWM, but the term PWM is already used in the engineering world for transmission of digital signals.

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quote:

Originally posted by DigiNut I think what he's talking about is actually Pulse Modulation, which is often incorrectly labelled as PWM. Pulse modulation is sort of like using an LFO, except that the modulating oscillator is a square (pulse) and is at the same frequency as the synthesizing oscillator (not a "low frequency"). The resulting sound can be modulated by changing the pulse width of the square; it sounds like it would be called PWM, but the term PWM is already used in the engineering world for transmission of digital signals.

which would make it Frequency Modulation right, since your using a carrier wave and a modulation wave (the square) to modulate the actual waveform as opposed the just modulating the PWM on a single waveform?

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quote:

Originally posted by Axolotyl which would make it Frequency Modulation right, since your using a carrier wave and a modulation wave (the square) to modulate the actual waveform as opposed the just modulating the PWM on a single waveform?

If anything, PWM is really a special case of AM.

I find there's a great deal of confusion out there about what FM really is. Frequency Modulation involves changing the frequency of a carrier signal based on the amplitude of the modulator.

It's actually rare (but not impossible) to see true FM in synthesis. Most of the time, synthesizers actually just modulate the phase, not the frequency, and knowledgeable synth designers will refer to this as PM instead (Phase Modulation). However, some synths refer to this as FM, and many synths will actually just modulate the amplitude of the carrier, but still call it FM for some reason - it's very confusing.

With PWM, we're just multiplying by a pulse, which is only modulating the amplitude of the carrier. It "zeroes out" part of the signal. The main difference between this and traditional AM is that the pulse width (the percentage of an oscillation period when the pulse's amplitude is at 100% as opposed to 0%) can be changed, so the "pulse" is no longer a real "square" wave, it's a special waveform. The frequency of the pulse, however, does not change during this process either. All of the frequencies of all of the signals remain the same.

Very often people use a constant pulse width, say 25% or 50% (which is a square wave). Technically the pulse width isn't really being "modulated" here, which is why I said earlier that a more apt name would be simply Pulse Modulation. However, some synths (z3ta+, for one), will actually let you use an LFO to modulate the pulse width, which is true PWM.

Hope that helps to clear things up...

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actually almost every synth allows you real PWM.. and fast PWM sounds near a saw just a bit thinner!

And the nut comes through with the goods once again Thanks, that makes a bit more sense now.

So PWM is basically just like a fast LFO on the amplitude, thus altering the waveform itself into something less harmonic?

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quote:

Originally posted by Axolotyl And the nut comes through with the goods once again Thanks, that makes a bit more sense now. So PWM is basically just like a fast LFO on the amplitude, thus altering the waveform itself into something less harmonic?

no, PWM is the modulation of a "square" and not the amplitude or the frequency..




you modulate the duty cycle of a pulse so that the waveform change..

Cool thanks for pics. Right.. its all there. It'll make sense soon, I'm sure of it Just need to get some sleep .. hehe..

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Good PM on 2 detuned pule waves (plus unison) can sound very powerful, and makes excellent leads. Add portamento and its a killer