Functional density - or what to do while waiting for your MOTM modules
2002-08-18 by pugix
While awaiting arrival of my MOTM modules, I've been meditating on functional density in modular synthesizers. I've always operated on a feeling about how much tonal richness I could get from a set of modules, which had to do roughly with the quantity of activity going on all at once. This is directly related to the number of distinct signals available. The richness also has to do with the number of voltage-controlled parameters that are being modulated simultaneously. I came up with a simple way to quantify the functional density of a module as follows. It is the number of distinct signal sources produced by a module plus the number of independently variable voltage-controlled parameters afforded by the module, divided by the panel width. Here's the breakdown for MOTM. MOTM MODULE SOURCES PARAMS WIDTH DENSITY ----------------------------------------------- 101 S&H 2 0 2 1 120 SUB 0 0 2 0 190 VCA 0 2 1 2 300 VCO 1 2 2 1.5 310 VCO 1 2 1 3 320 LFO 1 2 2 1.5 380 LFO 4 0 1 4 390 LFO 2 1 1 3 410 VCF 2 3 2 2.5 410 VCF+OMS 2 6 3 2.66 420 VCF 0 1 2 0.5 440 VCF 0 2 2 1 480 VCF 0 2 2 1 490 VCF 0 1 1 1 700 ROUTER 0 2 2 1 800 EG 0 0 1 0 820 LAG 0 2 2 1 830 MIX 0 0 2 0 850 PEDAL 0 0 1 0 890 MIX 0 0 1 0 My rational for counting sources: The 101 S&H has one noise source, plus one clock. Even though filters can oscillate, I'm not counting that as a source. I don't count multiple waveforms coming from the same oscillator. Most of this is not too surprising. The quad LFO in a 1U panel has a high functional density. Modules that do static processing, such as envelope generators and mixers have zero density, which means that when added to a system simply lower the overall density. To me that gives them a lower value. But then I seem to be obsessed with functional density! This analysis did produce a few interesting results. The 310 micro VCO has twice the functional density as its big brother, the 300, because it has the same number of sources (1) and parameters (FM and PWM), but in half the space. That's the idea, I suppose. The 410 Triple Resonant Filter has a high functional density due to the internal dual LFO, which adds two sources. The 410 also has three independent parameters: combined filter frequency (sweep), LFO rate, LFO internal modulation depth. Let's add the OMS-410. Now there are six parameters: 3 independent filter frequency controls, LFO rate, internal LFO depth, external LFO depth. This is based on the MOTM-standard option panel for the OMS-410. But wait. Now it's 3U wide. Doing the math shows that adding the OMS-410 increased the functional density only a tad from 2.5 to 2.66. But I like getting those extra three parameters to control. Notice that this analysis does not quantify the aspect of having the LFO outputs available externally. Making the LFOs available for input to other processing does not add any new sources to the system. MY WISH LIST (Hey Paul!) Being an old Serge guy, I long for the Serge dual slewing module. Now, if Paul would make a very minor modification to the 820 Lag Processor we would have this. Put a comparator with big hysteresis on the output, so that when the output level reaches maximum (+5v) the comparator puts out a -6v. Now the comparator will stay at -6v until the output goes all the way down to -5v, at which point it snaps back to +6v again. So what, you say? Well, now you now have a pulse output. Patch that output into the lag input and now you have an LFO with a voltage-controllable waveshape. Functional density goes up to 1.5. But even better, I would like to see a micro Lag Processor/LFO, fitting into a 1U panel with six jacks and three pots. Jacks: Input, Pulse Out, Lag Out, VC Up, VC Down, VC Up-Down Pots: Initial Up, Initial Down, +/- Inverting attenuator VC Up-Down input Sources 1, Parameters 2, Width 1, Functional density 3. I had about eight or so modules of different variants on this theme in my original synthesizer (which is now probably gathering dust in somebody's attic). -Richard Brewster