Modular Mojo: Tuning & Melody

We will begin with a brief digression.

Yesterday a friend brought his hurdy-gurdy over to my house and let me play a bit on it. The hurdy-gurdy, for the benefit of those among my readers who don’t attend outdoor strolling Renaissance fairs, is a stringed folk instrument that sounds a bit like bagpipes, though perhaps not as pleasant.

hurdy

You make sound by turning a crank, which rotates a rosined wheel. The wheel rubs across the strings. One or more of the strings produces a constant drone — a pitch that never changes. Melodies can be played on one or two other strings by pressing keys that force a little wedge up against the string, shortening it. It’s quite a sophisticated concept, if you’re living in the 17th century and don’t have enough money to buy a musical instrument, so you have to build one yourself using scraps of wood you find lying out behind the barn.

Also, it’s portable. You can wear it on a strap around your neck and play it standing on a streetcorner, at which point people will pay you to go away.

Be that as it may, there’s a very long tradition of music in which melodies are played over an unchanging drone. The Indian raga is perhaps the finest example of this. Also, many musical traditions get along perfectly well with a limited set of pitches for melodies. Pianists will cringe, but you don’t actually need 88 keys to play a complete musical idea.

I found myself wondering if I could patch up my modular synthesizer to transform it into an electronic hurdy-gurdy on steroids. This led to several discoveries that may be of interest to devotees of euro-rack and other analog modular gear. Or not, but it’s my blog, so I’m going to tell you anyway.

Setting up a drone is easy. A third-grader could do it. Playing melodies over a drone, though — that’s where Sam and Frodo don their backpacks and set out for Rivendell.

I’ve become very sensitive to small pitch differences, both because I play the cello, which has no frets, and because I’ve done a fair amount of composing of microtonal music using the all-digital plug-in synths in my computer. Actually, “very sensitive” doesn’t quite describe it. I’m fussy about pitch.

It’s a given that an analog synth is never perfectly in tune. When you turn it on, the oscillators need a few minutes to warm up. During that period, their pitch will drift slightly, but after ten minutes or so, the temperature should stabilize, and so should the pitch. More or less. One hopes.

Oscillators typically have pitch control inputs that are calibrated to a one-volt-per-octave (1v/oct) standard. When the incoming control voltage increases by 1 volt, the pitch of the oscillator should rise by an octave. More or less. One hopes.

I wanted to use the touch-pads on my Make Noise Pressure Points + Brains (PP+B for short) to play melodies. That’s what the pads are designed for. Each pad is associated with three knobs. Each row of knobs has its own voltage output. Touch a pad, and the voltage levels set by that pad’s three knobs appear at the three outputs. Simple enough, in concept — turn the knobs to tune your scale, patch the row output to an oscillator’s 1v/oct input, and you’re in business.

More or less. One hopes.

Twiddling eight knobs so as to produce eight in-tune notes is not easy. A very slight knob movement causes a perceptible change in pitch. If you nudge the knob while lifting your fingers off of it, you have to grab it again, twist it ever so slightly, and then let go of it more carefully.

A quantizer module addresses this problem in a neat and efficient way. And providentially, I have two of them — two Toppobrillo Quantimators. (In what follows, I mean no disrespect to the Quantimator, which is a very nice module with some slick features.) When the output of a knob row is sent to a quantizer, small changes in the positions of the knobs make no difference. The quantizer reads the incoming voltage and sends out the nearest 1/12 volt step. Patch this to the 1v/oct input of an oscillator, and you have in-tune equal-tempered half-steps.

Two issues, however, quickly presented themselves. If I hadn’t been playing over a drone, I might not have noticed them at all, or I might have been happy to shrug and ignore them. After all, this is an analog instrument. You can’t expect perfect intonation. But when a drone is providing an unchanging pitch reference, the resemblance to a hurdy-gurdy became a little more palpable than I wished.

First, my melody oscillator was not staying in tune across even one octave. If I tuned it perfectly to the drone on knob 1 and turned knob 8 up to produce the quantizer output an octave higher, the higher octave was several Hz out of tune. I don’t know whether this was because the Quantimator’s output is not calibrated well, or whether the 1v/oct input of the Intellijel Rubicon is to blame. Or both.

Even if the calibration had been perfect, the other issue would have been unavoidable. Equal-tempered fifths and thirds simply aren’t in tune with a drone. This is not a defect of an analog instrument, it’s a limitation in our equal-tempered tuning system. (Indian ragas are not played in an equal-tempered tuning, by the way.)

The solution to both problems is to get the quantizer out of the signal path entirely, and tune each knob by hand. In fact, I have to tune 24 knobs, not just 8, because I’m using a Doepfer A-152 and a trigger button to switch from one row of knobs to the next. This patch gives me three different 8-note “keyboards,” and I can switch from one to another by pressing the button. Tuning 24 knobs is extra work, but the results are all that my ear could desire.

But we’re still not out of the woods. Having tuned the knobs, I confronted the thorny question of legato. If I press my finger against one of the PP+B pads and then slide it smoothly over onto the next pad, the PP+B doesn’t notice that I’ve changed pads. It keeps right on sending out the voltage set by the knob on the old pad, rather than switching to the voltage of the new pad. In order to get the new pad sensed, I have to lift my finger briefly, so that no pad is being touched.

This articulates the new note, however. The PP+B has a very nice touch-gate output, which is typically used in this scenario to open an envelope generator. When I lift my finger, the gate signal stops and the envelope goes into its release segment. The result: no legato.

Yes, there’s a way to get quick legato pitch inflections, up or down by a scale step (or up and down across several scale steps). The way to do that is, patch the quantizer back into the signal path. The Quantimator has a choice of scales, so it can easily be set to limit its output to a major scale, skipping the black keys. Now I can wiggle a knob while holding a single pad and get little melodic flourishes without retriggering the envelope.

They won’t be in tune, but they’ll be legato. In tune or legato melody ornaments, take your pick. You can’t have both. Unless — how about smooth pitch-bending? You don’t want to do this with the knobs on the PP+B, because if you turn one you’ll have to stop playing the melody while you get it back where it belongs. In preliminary tests, however, the Intellijel Triatt voltage processor appears to work as a pitch-bender. I patched the sequencer output into Triatt input A, the sum output into the melody oscillator, and set Triatt’s B and C knobs to positive and negative outputs, respectively. As long as B and C are turned down, only the A input is being passed on to the sum output. The B knob can now be used for sharp pitch-bends and the C knob for flat ones, and turning B or C back to its fully CCW position will reliably restore the original pitch.

Maybe I won’t have to buy a wooden hurdy-gurdy after all.

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3 Responses to Modular Mojo: Tuning & Melody

  1. 0netwo0netwo says:

    very interesting read ive come across here

    isnt it that users in the modular world are just enjoying the sounds their personally designed systems can create, must we always need the “perfection” of equal temperament tuning?

    i’d like to see a picture of your modular if you still have it and it has grown

    also interested in more modular writings you have published

    thanks again!

    • midiguru says:

      There are a couple of entries over on my music-specific blog, synthage.wordpress.com. One of them has a not-quite-current photo. I’m still puzzling about what sort of music the instrument is good for. I love fiddling with it, but a coherent compositional aesthetic has so far proven elusive. I could just give up and record four-on-the-floor techno with it, but … well, maybe I’ll have time this summer to get deeper into it. As Richard Boulanger once said of Csound, “It’s a musical instrument. But to master any musical instrument, you must practice!”

  2. 0netwo0netwo says:

    yes indeed

    these lil suckers require a lot of time and practice, i just love how specific they allow you to be when designing your own sound and the many “happy accidents” you come across

    for me i just press record and then go back later and edit everything up as best i can

    thanks for the reply!

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