I think for the sake of brevity (or, realistically, slightly-less-book-length-ity) it would be best to split the discussion of each synth into two parts: a description of the synth -- how it works and what the knobs do -- and a critique where the interface and design decisions are discussed.
I should point out that I'm not an expert and in no way affiliated with TE -- or else I would have actual info to share here and not just rambling conjecture!
Anyway: Cluster.
(note: I'm just going to use screenshots from the manual. The manual pics are slightly out of date -- in the case of Cluster, there are currently only 4 waveforms, not 6, and they never get as large as the above pic suggests. However, the manual pics are gorgeous and likely to look much better than a picture of my OP-1. These are all property of Teenage Engineering.)
The manual has this to say about Cluster: "Multi layered oscillator cluster".
The manual tends to be rather succinct, if not sometimes overly austere and cryptic, which is definitely part of the whimsical charm of the OP-1. Having said that, not knowing how the hell things work really bugs me, so let's get to the bottom of this thing!
As far as I can tell (from here on in, pretend that every statement is prefaced with AFAICT), the basic deal with Cluster is that it's multiple detuned oscillators sent through an enveloped lowpass filter.
It's great for "string machine" type sounds, thick bass, and basically anything that lowpassed sawtooths are good at. It's also the OP-1's strongest contender for that most vital of all synth capabilities: supersaw trance lead!
Visually, it's just 4 virtual rotary dials above a set of four animated waves.
I don't know how much detail I should go into here about the visuals -- you've all seen it, so describing it seems a bit stupid. Then again, you've all turned knobs and heard the sounds it makes, so perhaps this entire enterprise is a waste of time! Regardless, I'm going to press on for the 1-2 people who have bothered reading this far.
For the sake of clarity I'll refer to parameter values using "o'clock" terminology, i.e 9 means "9 o'clock", aka dial is pointing straight left. The dials in this case sweep out 270 degrees, minimum values at 7:30 to max values at 4:30 (or should it be 7.5 to 4.5?). (Incidentally, I'll be using min/CCW and max/CW interchangeably; CW and CCW are abbreviations for clockwise and counter-clockwise just in case this isn't clear).
Let's check out all four of those sweet, sweet parameters:
Blue ("# of Waves"):
The number of oscillators varies from 1 (min) to "several" (max). The manual says "0-6" but this is clearly impossible since 0 oscs would be inaudible, yet it makes sound even at the minimum setting. Perhaps this is just one of the many mysteries of the OP-1... it's so bad-ass it can actually make sound with 0 oscillators!
Anyway, this is possibly the simplest control of any of the OP-1's synth engines: turn it CW to add more oscs to the mix, turn it fully CCW to get a single osc.
Frankly anything beyond 3-4 oscillators sounds very same-y to me, I can't distinguish between say 4 or 6 oscillators. To me the oscs sound like sawtooths, but again I might be wrong.
It seems like TE are applying some sort of normalization to try and keep the levels even regardless of the number of oscs -- adding more does not make things louder, and if anything makes the output drop as detuned waves tend to cancel each other out and dull the sound a bit compared to a single raw oscillator.
(Sadly they haven't yet applied this same sort of level control to Unison mode, which means that it's currently an unuseable "lots of clipping" mode. But let's save that for another day.)
Green ("Wave Envelope"):
The filter is a lowpass. In case it's not painfully obvious, I'm just a hobbiest, so aurally determining if its slope is 12/db or 24/db is far beyond my abilities.
It has either very little or no resonance; it sounds to me like no resonance, but again I'm just spitballing here.
The cutoff of the filter is modulated by an A/D envelope, and the Green parameter controls various combinations of Attack, Decay, and Cutoff.
This "ganging" of cutoff and env parameters into a single knob is a great idea, and very elegant solution to providing lots of control with a minimum of parameters. This is the sort of unconventional fresh approach that permeates the OP-1 and makes it such a joy to delve into.
Unfortunately this unconventional approach also makes it seriously annoying to try and succinctly document/describe the behaviour of this particular parameter -- a recurring pattern, and one suspects at least part of the reason the manual is so vague -- but I'll do my best. Basically, CCW from 12 o'clock results in an increasingly fast downward cutoff sweep, while CW produces an increasingly slow upward sweep. The details are a fair bit hairier than that though.
As far as I can tell, the modulation depth is constant, i.e the envelope will always sweep the filter up or down between some fixed minimum and maximum cutoff values.
From around 11 o'clock to around 1 o'clock, there's a big "dead zone" where Green has no effect: the filter's cutoff remains at max and the envelope depth is 0 (i.e the cutoff doesn't move).
Let's start with the right side: from 1:00 going CW to the max value at around 4:30, we get increasing attack times (slower upward cutoff sweep) coupled with decreasing initial cutoff (so that there's room to sweep upward), until at the max value the cutoff remains low forever. I guess you could think of this as attack time being infinite -- cutoff doesn't move.
On the left side it's a bit more complex: starting from 11:00 and turning CCW to 9:00, decay is introduced: the filter cutoff sweeps downward with increasing speed. There are literally only six different values for decay time, which can be slightly annoying -- but let's save the griping for later!
In the lower-left section, from 9:00 to 7:30, things get weird: the cutoff starts with a downward sweep, and then sweeps upward. Simultaneously the cutoff is being lowered a bit as you move CCW. The attack phase (downward modulation) is very subtle and decreases in time and depth until at the min value (7:30) we have just an upward cutoff sweep. This range sounds like modulation by a downward triangle, with cutoff being swept down and then up again; as you travel CCW the downward phase shortens and the upward phase lengthens. You could think of it as the bottom "point" of the triangle being pushed toward the left until it becomes a rising sawtooth.
(I'm sorry this is such a long-winded explanation for something that's so obvious -- this is definitely making me question the entire validity of this enterprise. Damn it, why didn't I start with Digital?!)
White ("Spread"), Orange ("Unitor"):
I'm going to handle these two together because they both seem to affect different aspects of the same operation: the detuning of the oscillators relative to each other.
I actually have no idea what's really going on here -- this isn't simply a fixed detune as found on most (virtual) analog synths. It sounds more like "drift" -- basically a smoothed sample+hold signal applied to osc pitch so that each osc "wanders around" a bit independently of each other. The sound is really interesting and distinct, it doesn't sound at all like the standard Moog-ish "detuned waves beating", instead it can sound harsh and nasally or diffuse and noisy.
AFAICT White controls the depth of the drift while Orange controls the rate at which the pitches wobble around. However, I suspect it's not that simple and that there are hidden modulations or multiple things being controlled by each knob -- some sort of fixed detuning in addition to the osc drift -- because there are two cases which contradict the simple "White = Depth, Orange = Rate" explanation:
1) If you set Orange to min and turn White, there is an enveloped detuning effect -- the amount of detune decreases over time until the oscs settle to a constant tone. Curiously they don't seem to be settling detuned with each other, because that would cause beating, and instead it sounds like some sort of phasing -- different harmonics are cancelled or reinforced.
Turning White CW increases the length of time it takes the oscs to drift together -- either by increasing their initial starting distance or decreasing the speed at which the drift is brought to 0, or maybe both: it's hard to tell! This sort of enveloped behaviour isn't noticeable at all if Orange is set to any value above min; possibly it's always there but it's so subtle that any amount of constant drift makes it impossible to hear a small amount of fixed detune.
2) The second special case is when White is at min and Orange is moved: as you turn it CW, it sounds like there is an increasing amount of detuning applied to the oscillators. This sort of contradicts the notion that Orange controls drift rate, since it sounds in this case like it's also controlling depth to a certain extent. This is a really weird sound, sort of like phasing sometimes.
So anyway, there is some interaction between White and Orange and it's hard to pinpoint exactly which aspects of the osc detune are controlled and how, or even whether there is some amount of fixed or enveloped detuning happening in addition to the very obvious oscillator-drift effect.
In conclusion...
Writing this, it's obvious to me that I'm in no position to speak authoritatively about any aspect of the OP-1 -- I'm clearly just fumbling around in the dark. However, unknowns really bother me, so I'm compelled to keep plugging away in the hopes that other people can fill the gaps in my knowledge. Perhaps together one day we can form a complete document of the wonders of this beautiful machine.
If you have any comments or insights into the mysteries of the Cluster, please share them on this thread at the great OP-1 forum: http://ohpeewon.com/discussion/226/op-101-cluster
