EMS-style rectified sine
I'm trying to model the sine oscillator with shape control from the EMS Synthi and VCS3. For the uninitiated, you can see what I'm after in the examples below. When the oscillator's shape knob is turned to the left, you get a rectified sine. When centered, a typical sine. And when turned to the right, an inverted rectified sine.
In Drambo, it's easy enough to add DC offset to a sine to get the left half. And inverting that signal gives the right half. But I can't figure out how to get both shapes out of the same rack, depending on where the knob is positioned.
Anyone have any ideas to fix it? Is it even possible in drambo?
Comments
I'd rather crossfade between the sine and its exponential'ized version, more sonically pleasing imo:
@rs2000 its nice, but x-fading doesn't behave like the VCS3/Synthi's shape knob. At least I can't get it to do it.
Here's another option, using a saw wave osc with anti-aliasing disabled.
Graphic shapers let you draw any waveform, maybe that's more like what you're looking for.
This in VCV rack, but maybe it'll give some inspiration? Or you can just use it as an AUv3? https://patchstorage.com/synthi-waveshaping-study/
My other thought was to find a wavetable of the waveform.
Offset into a shaper?
Nah thats not right yours gets more pointed.
I think there’s still a noticeable bump when you cross zero (which crosses from normal to inverted signal but I think this is close.
What about this; the knob on the left goes through the Graphic Shaper and controls the saturation amount so that +/-1 Sat is at Max, knob also controls offset.
That’s not right either is it. Gets too narrow. Sorryi I’m more enthusiastic than skilled ;)
This is very close! And I learned some new techniques exploring it. I'll need to play with it more to understand why every period contains two asymmetrical parabolic waves of different amplitude when the Value knob is set slightly offset from the center (as shown below). But this is much closer to the functionality that I was struggling to replicate — smoothly modulating from one shape to its inversion with the twist of a single knob! Thanks!
Looking at this pic:
I would now suggest the following, even simpler version:
I've skipped the right half in the Shape Control part of the manual because it just seems to be the mirrored version of "Left" which would be the same, sonically.