PWM option in Zebra 2 OSC...I don't get it

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mabian
KVRAF
1667 posts since 10 Jan, 2005

Post Fri May 22, 2020 1:32 am

Hello,

I am trying to get back to Zebra 2 basics because I want to learn something more about sound design.
I'm a bit scratching my head about the PWM option in OSC modules.

This is what the manual says:

"PWM
Adds an inverted copy of the waveform. Applied to a sawtooth, phase modulation cre-
ates an effect very similar to classic PWM (only the phase of the original wave is shifted
around, while that of the inverted copy remains fixed). See PHASE below."

But then, if I don't enable phase modulation, shouldn't I just get complete silence when enabling PWM (because the inverted waveform should null the original one)?
I am instead getting sound, a sort of square wave (using an oscilloscope plugin to check).
For sure I'm missing something, but what is it?

Thanks,
Mario

The unshushable Coktor
KVRist
333 posts since 18 May, 2007 from Berlin

Re: PWM option in Zebra 2 OSC...I don't get it

Post Fri May 22, 2020 2:48 am

Hi Mario,

look at the "Phase/PW" knob on the right side of the osc panel. At 100, the inverted waveforms overlap in that way that produces silence. At lower values, the phase positions between original and inverted waveform are not identical so they produce non-silent results.

Viktor
u-he team
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User avatar
Urs
u-he
24433 posts since 8 Aug, 2002 from Berlin

Re: PWM option in Zebra 2 OSC...I don't get it

Post Fri May 22, 2020 2:52 am

For convenience, at a phase setting of 0 the inverted waveform is shifted by half a wavelength.

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User avatar
EvilDragon
KVRAF
19667 posts since 7 Jan, 2009 from Croatia

Re: PWM option in Zebra 2 OSC...I don't get it

Post Fri May 22, 2020 4:17 am

ASCII to the rescue! :D

mabian
KVRAF
1667 posts since 10 Jan, 2005

Re: PWM option in Zebra 2 OSC...I don't get it

Post Fri May 22, 2020 5:10 am

Thank you for the replies, it's much clearer now!

A second question though then... how does this inverted waveform phase interact with the "reset" button?
Is its phase always reset, so retriggered from its start at each note? Or does it have a half wavelength constant offset (excluding the effect of the "phase" button)?

- Mario

User avatar
EvilDragon
KVRAF
19667 posts since 7 Jan, 2009 from Croatia

Re: PWM option in Zebra 2 OSC...I don't get it

Post Fri May 22, 2020 7:04 am

When Reset is enabled, you get the phases set up exactly how Urs showed on every new note.

User avatar
Howard
KVRAF
3909 posts since 23 May, 2004 from Bad Vilbel, Germany

Re: PWM option in Zebra 2 OSC...I don't get it

Post Fri May 22, 2020 12:37 pm

Note: The phase of the inverted copy remains fixed at 180° while the original wave reacts to the Phase setting (and modulation).

mabian
KVRAF
1667 posts since 10 Jan, 2005

Re: PWM option in Zebra 2 OSC...I don't get it

Post Fri May 22, 2020 12:46 pm

Howard wrote:
Fri May 22, 2020 12:37 pm
Note: The phase of the inverted copy remains fixed at 180° while the original wave reacts to the Phase setting (and modulation).
Thanks Howard, maybe I'm a bit dumb but still don't understand what happens with the OSC "reset" setting to this inverted copy when a new note is played...

1) Does it always retrigger at 180° no matter if "reset" is on or off?
2) Does it retrigger at 180* when "reset" is on and run free when "reset" is off, regardless of note retriggers?
3) Other?

- Mario

User avatar
EvilDragon
KVRAF
19667 posts since 7 Jan, 2009 from Croatia

Re: PWM option in Zebra 2 OSC...I don't get it

Post Fri May 22, 2020 2:26 pm

It's always at 180° he just said :)

mabian
KVRAF
1667 posts since 10 Jan, 2005

Re: PWM option in Zebra 2 OSC...I don't get it

Post Fri May 22, 2020 2:33 pm

EvilDragon wrote:
Fri May 22, 2020 2:26 pm
It's always at 180° he just said :)
He just said it mentioning the phase knob, not the "reset" button... but I'll try checking it myself more in detail.

Thanks,
Mario

User avatar
Howard
KVRAF
3909 posts since 23 May, 2004 from Bad Vilbel, Germany

Re: PWM option in Zebra 2 OSC...I don't get it

Post Fri May 22, 2020 10:28 pm

mabian wrote:
Fri May 22, 2020 5:10 am
... how does this inverted waveform phase interact with the "reset" button? Is its phase always reset, so retriggered from its start at each note? Or does it have a half wavelength constant offset (excluding the effect of the "phase" button)?
The Reset button makes no tonal difference. Its status doesn't affect the phase offset between the original and inverted copy.

mabian
KVRAF
1667 posts since 10 Jan, 2005

Re: PWM option in Zebra 2 OSC...I don't get it

Post Sat May 23, 2020 4:47 am

Wow I must say I'm amazed of having three (major) members of U-he replying to this thread, thanks!

I'm researching thoroughly with oscilloscope plugins and similar, finding what follows - mostly in agreement to what replied so far, not completely though. The reset button is not considered at all here, to make clean examination of the "phase" parameter.

At phase "100" (as mentioned by viktor) the inverted waveform nulls completely with the original wave form; so the inverted and the original are completely in phase, good.
Also, at 0, there's a strong level reduction, like the inverted and the original are almost in phase. Good again, we can speculate that phase 0 to 100 relate to full 360° turn around. This is also confirmed by the fact that when moving the phase knob end to end the change is continuous and 0 seems adjoining to 100.

Then, to have 180° offset between the inverted and the original, the phase value must be set to 50 (default value of the initialize patch) and not 0; in the example of Urs, the sawtooth becomes a square when the PWM button is activated (a sawtooth plus an inverted sawtooth shifted of 180° is a ideally a square indeed). But this happens at phase value 50.

Finally, bringing back the reset button, I found, as mentioned by Howard, that it doesn't change anything; the phase offset between the inverted and the original stays the same, the original waveform phase is simply reset to the Phase parameter value at every note retrigger, the inverted keeps its offset untouched.

So, just two little details aren't in my opinion completely right on what discussed so far:

1) The phase knob goes full circle (360°) from 0 to 100, not only 180° as mentioned in the manual:
"Phase/PW
Adjusts the oscillator phase (from 0° to 180°, but you can modulate it up to 360°). Rapid phase modulation normally affects pitch, but if the PWM switch (see above) is on, the effect is similar to pulse width modulation"

2) The 180° offset between PWM inverted waveform and original is achieved at 50.

Not wanting to be pedantic, just willing to fully understand how it works.
Am I missing something?

Thanks,
Mario

User avatar
exmatproton
KVRAF
2656 posts since 25 Apr, 2011

Re: PWM option in Zebra 2 OSC...I don't get it

Post Sun May 24, 2020 1:02 pm

Howard wrote:
Fri May 22, 2020 10:28 pm
mabian wrote:
Fri May 22, 2020 5:10 am
... how does this inverted waveform phase interact with the "reset" button? Is its phase always reset, so retriggered from its start at each note? Or does it have a half wavelength constant offset (excluding the effect of the "phase" button)?
The Reset button makes no tonal difference. Its status doesn't affect the phase offset between the original and inverted copy.
It does when using more then 1 osc ofcourse

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