Hot-Swap Tuning

After grumbling a couple of days ago about the dearth of tunable software synthesizers, I belatedly remembered … hey, wait a minute. I have a synthesizer that will do most of that. I built it myself.

I used Native Instruments Reaktor. Reaktor doesn’t seem to get as much buzz these days as it did five years ago (or maybe I’m just not paying attention). It’s an extremely powerful DIY environment for developing your own visionary synthesizers. The main limitation is that for other people to use your instruments, they have to own Reaktor too. There’s no run-time-only version.

I built this synth about five years ago, and I’ve never used it, other than for a little noodling around. Sometimes just building an instrument is the fun part — but also, I have more impetus now than I did then to actually finish new pieces of music.

My tunable synth has a couple of features I’ve never seen on any other instrument. Its pitch-bend depth is defined in key steps, which means the bend will tend to have a different depth depending on what note you’re bending from and to. To facilitate steel-guitar bends, bending can be switched on or off independently for each of the 12 notes on the keyboard.

Because the raison d’etre of this instrument is just intonation, it doesn’t do vibrato. Instead, it does trills whose depth is calibrated in terms of the base frequency of the tuning. The oscillators have a linear frequency offset knob, which again is calibrated to the base frequency.  These features can produce some very rich (and unexpected) harmonies.

It has separate tuning controls for each of the 12 notes on the keyboard. Limiting the scales to 12 notes per octave is perhaps not ideal, but it makes keyboard performance ever so much easier — and in most musical situations, it’s hard to imagine needing more than 12 pitches from a single instrument in a single phrase. A bank of buttons for each key gives quick access to some of the more useful ratios, and each key also has a pair of number knobs (numerator and denominator), so the key can be tuned to any harmonic ratio you happen to want.

Last night’s experiments suggest that these features can indeed be controlled during sequence playback using MIDI CC messages. While the UI is not quite as slick as what I was fantasizing about, it works. I can change the tuning on the fly. Reaktor is kind of a CPU hog, but there are ways to manage that.

As soon as I finish my current music project, I think maybe I’ll write a few pieces using my Reaktor instrument.