Modular Mojo: More About Pitch

After struggling a bit earlier today (see the previous post) with intonation in my modular synth, I felt I should do a few more tests. There’s some good news to report, and some bad news.

Bad news first: The output of the Toppobrillo Quantimator simply doesn’t match the desired 1v/oct input of my analog oscillators across more than an octave or so. Nor does there appear to be a calibration trimpot on the Quantimator’s circuit board. At least, if there is, I haven’t found a document where it’s mentioned. The quantizer for the Make Noise Rene is pretty much the same. Across three octaves, it just doesn’t produce a reliable 8:1 increase in frequency.

The only oscillator in my system that produces perfect octaves is the Mutable Instruments Braids. This is a digital oscillator, and does its own quantizing of the input CV internally. No surprise that it’s perfect; digital audio is all numbers. The Intellijel Cylonix Shapeshifter, on the other hand, is also a digital oscillator — yet it suffers the same problem as the analog oscillators. Its pitch input isn’t even labeled as 1v/oct, but it’s as close to that ratio as the analog oscillators. It doesn’t have internal quantization of its primary oscillator, however. (The secondary oscillator can be quantized to the pitch of the primary oscillator, but that’s not helpful in this case.) It just converts the analog input to numbers and then assumes that whoever sent the signal to the analog input knew what they wanted.

Now for the good news: There’s a workaround. I have three Intellijel Triatt modules in my system, which can remedy the problem in a couple of ways. A Triatt has three inputs and three outputs, and the third output can perform as a sum of the inputs. Each section can be either positive-going, bipolar, or negative-going. By patching the quantized output of the Quantimator or Rene into Triatt stage A and then jumpering it also into the input of stage B, I can boost the voltage slightly. Boosting it is necessary because a single Triatt stage doesn’t quite produce unity gain at its output. By combining two stages, I can produce nicely in-tune octaves across five octaves. With three Triatts in the system, I can get four nicely in-tune oscillators (including the Braids).

The other Triatt method is to patch the quantized signal to the 1v/oct input of a Rubicon oscillator, which will produce slightly sharp octaves, and also into the input of a Triatt stage. The Triatt stage is then switched to its negative-going mode, and its output is sent to the Rubicon’s exponential FM input. With the Triatt knob at about 11:15 (on a clock dial) and the Rubicon’s exponential FM input knob at about 8:15, I can get the Rubicon to play in tune across five octaves. This method is more efficient, in that it uses only a single Triatt stage, leaving the other two free for other purposes, but I couldn’t get it to work with the Dixie oscillator’s linear FM input. Possibly something about the difference between linear and exponential FM.

Maybe this is all a wild goose chase. Maybe I should think of the modular as being an instrument played by the hillbillies of Ganymede, for whom making sure the banjo is in tune with the harmonica is not a priority. Now that I think of it, Hillbillies of Ganymede is not a bad name for a synthesizer band.

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