Anyway, enough endless blathering: let's look at what exactly Digital does!
The manual describes Digital as "True digital Synthesis". The variable caps in that description are possibly the least weird, messed-up thing about Digital.
I have very little idea what's actually going on here, but whatever it is, it's totally insane.
(I'm going to try to guess at what's happening behind the scenes in Digital, since otherwise there's little point in writing these posts, but I have zero actual information in all cases. These are all speculative conclusions based on my own limited observations. As this particular synth is so wild and weird, I might be very far off-base with some of my pronouncements -- just remember to preface everything with liberal helpings of AFAICT and IMO, and I'll understand if your thoughts tend towards WTF and STFU!)
(I guess I should stop peppering this sort of disclaimer throughout each post and just hope that people take it as given that I don't know what I'm talking about. Please let me know if you think I got it wrong -- there's a link to the comments thread on the forums at the bottom of each post)
Anyway, enough stalling: to the matter at hand.
I think that Digital is basically two oscillators, a "main" osc with variable shape and a "sub osc" with fixed shape. Some sort of cross-modulation is happening -- possibly ringmod since this is what the manual names one of the parameters -- along with a lot of really interesting distortion/aliasing/noise. Or maybe the modulation produces the distortion rather than it being a separate thing.
It's capable of some very extreme and harsh sounds, and definitely one of the most unique synth engines the OP-1 currently has to offer. If any of the synths in OP-1 are to be considered "pure evil", this is the one. It reminds me a lot of the wonderful and crazy freeware VSTis made by The Piz.
Blue ("Wave Shaper"):
This controls the shape of the main oscillator. Fully CCW it sounds like a triangle or a very soft square; turning it CW to the middle of its range it becomes brighter and more like a sawtooth with higher harmonics coming in; further CW from middle it starts to get overly bright and distorted -- blown-out sounding -- adding gritty digital noise. At the max/fully CW setting, the tone is mostly noise with a clipped/overdriven digital texture to it. There's a sweet spot near the transition from sawtooth to noise where you can get some really great ripping sounds.
I would assume from the parameter name that Blue is controlling the amount of waveshaping distortion applied to e.g a triangle oscillator, but maybe it's just an overload of high harmonics causing crazy aliasing/clipping. Or maybe it's a bit of both with some sort of lowpass filter thrown into the mix!
Graphically there are three blue particles/nodes, which move out away from each other with CW turning.
Green ("Octave"):
This controls the coarse pitch of the sub oscillator in octaves steps relative to the main osc, from -3 octaves to +3 octaves as the encoder is turned CW. The subosc sounds like a triangle or soft/filtered square.
Graphically it's a green particle which moves diagonally from bottom-left (-3 oct) to top-right (+3 oct).
White ("Detune and Ringmod. On / Off"):
This controls the fine pitch of the sub oscillator, as well as some type of ringmod between the two oscillators.
The lower/CCW half of its range has the ringmod off, with increasing CCW movement detuning its pitch downward from that of the main osc. The upper/CW half of its range has ringmod on, with increasing CW movement detuning it upward from the main osc.
Graphically, this is a white particle which moves from the top of the screen (CCW/ringmod off) to the bottom of the screen (CW/ringmod on) and left/right from the center to indicate detuning when it is up/down respectively.
This parameter is pretty complex and interacts with Green in a couple ways.
For starters, when ringmod is on (White is CW of center), and the subosc is tuned one or more octaves down (Green is CCW of center), then the subosc's signal seems to be turned off -- it only contributes to the sound via the ringmod signal.
Secondly, the range of the detuning controlled by White seems to be dependent on the current value of the Green (octave) control; as Green increases, the range of White detuning decreases: with Green at -3 octaves, the min (fully CCW) value of White sounds like it produces a full octave of detune; with Green at -2 the min value of White sounds like maybe -4 or -5 semitones; with Green at -1, min White produces between -2 and -3 semitones; Green at +0 means that min White will detune the sub osc somewhere between -1 and -2 semitones relative to the main osc. At least, this is what it sounds like to me :)
(A more concise summary of the above would be: as the value of Green is increased, the range of detuning caused by White seems to decrease.)
Values of Green above 0 render the range of White detuning very hard to hear properly, at least to my untrained ears. It sounds like the range of downward detuning becomes smaller and smaller as Green increases.
Finally, I have no idea whether the detuning values are symmetrical (i.e does turning White upward/CW produce the same range of detuning as turning it downward/CCW?) because with ringmod switched on it's impossible to distinguish the actual pitch of the subosc. Theoretically it could be done since ringmod produces the sum and difference; anyone with an oscilloscope and an abundance of patience, please feel free to let me know what's what!
The ringmod itself might be some special kind of "massaged" ringmod, because it doesn't seem to generate nearly as many inharmonic sounds as you might expect -- it's very musical.
Maybe it's just all the other distortion happening, but I'm suspicious about it: it definitely doesn't sound like any sort of ringmod I've ever heard. Then again, with all of the crazy distortion happening, and the fact that both oscillators are weird-ass shapes, who even knows what the hell is going on in here?
Orange ("Digitalness"):
This parameter is another weird one. As far as I can tell, it controls the strength or level of some sort of distortion, or some process that adds high harmonics -- maybe the distortion is fixed and Orange controls the cutoff of a lowpass filter located after the distortion.
AFAICT both the main and sub oscillators are routed through whatever insane distortion/modulator/process the Orange parameter is controlling.
Graphically it's an orange particle that moves from center (min) to right (max).
When ringmod is on, it sounds to me like Orange also controls the volume of the ringmod output. This is definitely not completely correct though, since if this was the case it would imply that with Orange at min and ringmod on, you should only be hearing the main osc and the subosc should be inaudible. However with Orange at min, turning Green still produces audible differences!
What leads me to believe that Orange has at least some sort of control over ringmod volume is that it's impossible to discern changes in subosc tuning (White CW of center) when Orange is at min value. Well, there are very slight differences but in general it's inaudible -- whereas if you turn Orange up even slightly, the beating produced by the detuned subosc and the main osc swells in volume very obviously. It just sounds a lot like the ringmod being brought into the mix.
Regardless, Orange definitely affects the entire/final signal of the synth, munging and distorting both oscillators with increasing ferocity as it's turned CW until the whole thing sounds insanely overdriven and blown out and both oscillators are mashed into unrecognizable bits. (Binary pun!)
Summing Up
Anyway, this concludes our whirlwind tour of Digital. Coming up next: everything that's wrong with Digital! (Spoilers: it's mostly just the UI!)
Comments, criticisms, corrections, complaints? Hit up the forum thread here: http://ohpeewon.com/discussion/228/op-101-digital
