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Author Topic: PWM, getting "pops" and "snaps"  (Read 385 times)

Sotsirc

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PWM, getting "pops" and "snaps"
« on: March 18, 2013, 09:41:13 am »
When I use PWM using a square wave as modulation, I get random pops and snaps.

beefinator

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Re: PWM, getting "pops" and "snaps"
« Reply #1 on: March 19, 2013, 06:33:38 pm »
Happens on mine, too.

But there's not really a way to avoid it, with analog VCOs.
The popping comes from when the PWM causes a jump in the waveform that isn't in sync with the jumps present in the square waveform itself.  For there to be no pops or snaps, the changes in duty cycle would have to occur exactly in sync with the frequency of the square wave, at exactly the right moment in the oscillator's waveform, which just isn't going to happen.
AFAIK, the pops aren't actually peaking above the square wave itself, so it won't mess up a mix or anything.  But we hear it as pops because it's jumps in the waveform that aren't harmonically related to the original square wave.

I'm just speculating, this could be wrong.

Sotsirc

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Re: PWM, getting "pops" and "snaps"
« Reply #2 on: March 19, 2013, 08:36:16 pm »
Strange though, some people (on another forum) claim not to get these pops.

tbn

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Re: PWM, getting "pops" and "snaps"
« Reply #3 on: March 26, 2013, 05:12:54 pm »
I think beefinator is right in this matter.

When using a squarewave as a modulator the effect is like switsching the destination between two values, being the original value + mod value OR original valueu - mod value.

In this case think of it like repeatedly flipping a switch to flip between different widths of pulsewave.

The moment when this switch occurs coincides either with pulswave of VCO being 'high' or being 'low'.
When pulsewave is 'high' when the modulator decreases pulsewidth it can happen that vco reaches abrupt low. This is more or less the same effect as a very fast enveloppe: the sound is suddely cut of, what will be percieved as a pop.

Hope this explanation makes any sense  :)

 

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