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As has been posted elsewhere, the latest beta versions of Zebra have 2 new OscFX. One of these is called "PhaseDist" and it does pretty much what it says.
Download new Zebra (Mac + PC) from this thread.
Huh?
With PhaseDist the oscillator waveform acts as function of the phase of an inverse cosine waveform. Unfortunately all images I found on Google got it totally wrong. They always use sine waves (starting at a zero crossing) and that's plain crap. Even the example code on Wikipedia is wrong. Arrrgh
Nevermind. What I want to say is, Phase Distortion like in the old CZ synths is a little bit less trivial than is commonly known (mostly because of misinformation), as it's a bit abstract.
Example patches
Hence I have posted a few presets that explain the basic waveforms sawtooth, square, peak (aka impulse), double peak (aka double impulse), sawsquare (aka half sine):
http://www.u-he.com/Z2PhaseDist.zip
Additionally I'm using the existing "Ripples" OscFX to simulate the resonant waveforms of the CZs. It is however not as accurate as the other examples, and I found a little bug in Ripples that makes it a bit grainy unless one adds another OscFX
When you open the example patches, you always simply have a CZ-ish filter sweep. The sweep is always done by modulating the oscillator waveform in GeoMorph mode. Check out the Osc1 tab to see what happens.
closing the filter, sort of
In the end, the "closed filter" (or "DCW" as Casio called it) is always an upwards sawtooth waveform, resulting in a sine wave. The sawtooth basically "plays" one full cycle of the sine (ahem, cosine) waveform. To add harmonics, some points within the sawtooth move around, effectively slowing down some parts of the sine while accelerating others within the cycle. That's Phase Distortion.
You can however create different effects, the possibilities are endless. For instance, instead of morphing from saw up to anything else you can also of course modulate the OscFX depth, which simply blends the waveform with an upramping saw. That's often less spectacular, but who knows...
And of course, check out the resonant example. It's done by using the waveform as an envelope (or window) for multiple cycles of a sinewave. the higher the OscFX setting, the more cylcles of sonewave are stuffed into the thing. If beginning and end of the waveform/window are in the zerocrossing (middle), then the waveform is continuous and sounds quite smooth. I might add a "Ripples II" OscFX which uses - you get it - cosine waveforms instead of sines, and which uses the whole range of the waveform (positive + negative part) as the window area. Then we can do pretty perfect CZ stuff, without any audible aliasing.
Note though that this comes at a cost. A Osc Resolution of 8.00 is mandatory for smooth effects!
Enjoy,
Urs
