Wednesday, March 17, 2010

New additions to the Discombobulator

Here are two new additions to the Discombobulator:

The above is the Synth Tech MOTM-650 four-channel MIDI interface. I haven't had a lot of chances to play with it yet, but it's pretty slick. Each channel converts a MIDI Note On/Off pair to a control voltage representing pitch, an envelope gate, a control voltage representing velocity, and a fourth output which can be associated with a MIDI control number. The pitch CV reacts and responds to MIDI pitch wheel messages also.

It basically has three operating modes. It can be configured as a monophonic interface, responding to MIDI Note On/Off messages and placing the same output signals on all four channels. It can be configured to be four-voice polyphonic on a single MIDI channel -- in this mode, each output channel pitch, gate, and velocity for up to four active notes on a selected MIDI channel. It can also have the output channels divided between four MIDI channels. I believe there are some combinations of the above, but I haven't had a chance to play with that yet. There are also significant MIDI clock conversion modes and a built-in arpeggiator function, none of which I have explored yet.

The arrival of this module means that I can now dedicate my JKJ CV-5 to controlling my EML 101. EML gear uses a different scaling standard for pitch control voltages, 1.2V/octave as opposed to the now-industry-standard 1V/octave. The CV-5 is one of the few MIDI interfaces that can be scaled to this standard. Now I don't have to mess with its calibration to move it back and forth between the 101 and the modular.

I'll have more info up on the MOTM-650 after I have had some time with this module.

The second new gem, pictured above, is the Encore Electronics UEG-01 Universal Event Generator. It's been out of production for several years, as Encore has switched its focus in module design to Frac format modules, but recently Encore solicited on Muff's to see if there was any new interest in the UEG. There was, so they are now doing a reissue, and this is a new unit from the current run.

So what is a universal event generator? It's an expansion and generalization of the concept of an envelope generator. We tend to think of a conventional ADSR envelope generator as having four phases, but it's really only three, and we only have full control over one of the three:
  1. For the attack phase, we only have control over the time that this phase takes. We do not have control over what level it ends at; it always ends at the maximum level that the enveloper generator is capable of generating.
  2. We have full control over only the decay phase. We have control over its time (the decay time) and over what level it ends at (the sustain level).
  3. The sustain really isn't a phase of ADSR envelope generating, when you think about it. That's because as far as the EG is concerned, there's nothing happening; it's simply waiting for the key gate to go low.
  4. We have control over the time of the release phase. We don't have control over what level it ends at; it always ends at the zero level.
A universal even generator gives you control over the time and ending level of every phase. (In theory; it's usually the case even with UEGs that the last phase always ends at the zero level. That's true of the Encore UEG too. The only envelope generator I've come across in a hardware synth that allows the last phase to end at a non-zero level is the pitch envelope on the Roland JD-800.) The Encore UEG has eight phases, each of which has a time control sweepable from a few milliseconds to about eight seconds. The first phase is actually somewhat faster when the time control is set to full CCW, so that it can produce a nice percussive attack spike. Each phase except the last also has a knob specifying what level that phase will end at.

So what can you do with these eight phases? This is an area where the Encore UEG really stands out. There are basically three operating modes that you can select with the pair of 3-position mode switches. Putting the top switch in the GATED position and the second switch in the RELEASE position selects a "conventional" envelope generation -- but with much more flexibility. In this mode, when the gate goes high, the UEG will begin executing with phase 1, going through the times and levels as set for each phase It will continue doing this until it reaches the phase that is selected by the LOOP END switch. After that phase ends, if the gate is still high, the UEG will jump back up to the phase selected by the LOOP START switch. The steps between the LOOP START and LOOP END selections therefore constitute a sustain loop, allowing periodic variation in level during the sustain phase, and therefore a more interesting sound if you're using the UEG's output to control volume or filter setting of a patch. When the gate finally goes low, the UEG will jump to the phase following the LOOP END selected phase, and from there it will execute the remaining phases until phase 8 completes.

You can see how this can produce much more powerful and interesting envelopes. Depending on the LOOP START and LOOP END selections, you can have up to 4 attack/decay phases preceding the sustain loop, and up to 3 release phases. Or you could have a sustain loop consisting of as many as 6 phases. A further variation can be introduced by placing the second-from-the-top mode switch in the FINISH LOOP position. In this position, when the gate drops, the UEG will complete the current iteration of the sustain loop before preceding to the release. (I noticed a peculiarity in this; if the gate drops when the sustain loop is in the phase selected as LOOP END, the loop will usually run one more time before the UEG proceeds past the loop.)

The UEG interpolates between the level settings of each phase to produce slopes in the output. How it does this can be selected by the SLOPE switch. There are three settings, two of which might be conventionally used in envelope generation. In the top setting, rise and fall is exponential -- it starts rapidly and slows down as the level setting is approached. This emulates the way that most analog envelope generators work. In the middle setting, rise and fall is linear, which may be more desirable when using the UEG's output as a pitch or filter cutoff modulation envelope.

In the bottom setting of the slope switch, the UEG jumps immediately to the level setting at the start of each phase, and holds that level for the time of that phase. That can make for some interesting envelope generation, but it's intended primarily for use with the UEG's sequencer modes. Yes, the UEG can be used as a (pseudo-) analog sequencer! There are two ways of going about this. With the top mode switch still in GATED, if the second switch is set to STEP, then the UEG will advance one phase every time the gate goes from low to high. In this mode, you can input a clock signal (say from an LFO) into the GATE jack, and the UEG will act like a conventional 8-step sequencer. You set the output values with the LEVEL controls for phases 1-7; in order that step 8 doesn't have to end with zero level, in this mode only, its TIME knob becomes a level control instead. The loop switches and the phase 1-7 time knobs are ignored in this mode.

Setting the upper mode switch to LOOP ONLY turns the UEG into a self-clocking sequencer consisting of 2-6 steps, as selected by the loop start and end switches. In this mode, the selected loop runs continuously (the GATE input is ignored). The time controls are active, so that each step can occupy a different amount of time. There is no way to sync the UEG to an external clock in this mode, so instead there is a provision for the UEG to be the sync source: at the start of each loop, it will output a short trigger pulse from the TRIG OUT jack, which you can slave other modules and functions to. The rate will obviously depend on the sum of the time settings within the loop.

Finally, the UEG can be used to generate staircases or other complex waveforms by placing the upper mode switch in the ONE SHOT position. In this mode, each time the gate goes high, the UEG proceeds through all eight steps one time (the loop switches are ignored). All time and level controls are active. A trick you can use here is to trigger it with an LFO so that it generates a repeating complex waveform. You can effect the shape of the waveform with the SLOPE switch.

The TCV jack accepts a control voltage which scales up all of the time settings at the input voltage goes up. The UEG manual notes that the absolute maximum time for any stage is 8.3 seconds, so as the TCV voltage goes up, longer steps will be limited to this max time while shorter ones continue to get longer. That's a limitation, but it could also be useful. A handy manual gate button completes the panel. I've noted that the manual gate button double-hits occasionally; the manual does note that it is not debounced and is not meant as a performance control.

Both the MOTM-650 and the UEG-01 are valuable additions, although obviously much different in purpose. However, I'll note one thing they have in common: they are both microprocessor-controlled modules. There are people who will object to this, but I think that MIDI control is the gateway to (among other things) getting away from the "keyboard paradigm" of modular synth control. And the complexity of the UEG would be near-impossible in analog circuitry. It's far past time that more digital functions started showing up in modular synthesis, and the Euro format manufacturers such as Harvestman and MakeNoise have gotten ahead of the 5U world in this area. So it's good to see some large format designers approaching (or in Encore's case, re-approaching) the 5U world with a fresh eye for digital methods. Incidentally, Encore is now soliciting interest at Muff's for a revival of the 5U version of its highly regarded digitally-controlled frequency shifter. If you at all interested, chime in on that.

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