Rainmaker, karplus strong, v/oct and C

I explored some karplus strong on the rainmaker today.

With nothing in v/oct and comb size all the way CCW the rainmaker outputs a slightly flat (about 20 cents) A. Is there a way (a setting somewhere or calibration) that would allow me to have a C with comb size CCW?

I solved this by applying offset on the way out of my teletype, but it would be awesome if it could be tuned so that 0V is C with comb size all the way CCW…

Anyone? I’d love to have the rainmaker output a C with 0V and combsize at some known pos (like all the way CCW)

I think pitch also depends on chosen filter type and clockdivision. Did you experiment with those parameters?

“Clarinet” is for instance lower in pitch then “Guitar” and “Sitar” (if my ears ain’t fooling me). In a way that makes sense because, a “Böhm”-clarinet is tuned in B flat.


Year, I experimented with those, and (forgot to mention) it’s also on presets, as well as my own doodlings…

Filters seems to alter the response, the frequency is the same (makes sense), Clock divisions drops in octaves and fifths (makes sense).

Is it possible to calibrate the comb v/oct input? It’s also not tracking more than decently.

Yes, it is possible to calibrate the Comb section 1v/oct input. I’ll copy/paste and adapt the instructions from our internal testing doc below. You will need a voltage source that can output 1v and then 2v. This is referred to in the instructions as the 1V/OCT tool, for which we use a voltage source like Triplatt with a quantizer like Scales with only C selected so it steps in 1v increments.

Note that this is only to determine the tracking, not to set the offset or center point of the COMB SIZE knob.


  1. Load Preset #1. Calibration can only be saved using Preset #1.
  2. Remove the Rainmaker from your case but leave it connected to power.
  3. Connect your 1V/OCT tool into the 1V/OCT input in the comb section.
  4. Turn the unit over and engage the button labelled KEY0 found furthest to the left on the FPGA. The display should now show a calibration screen that’s ready to receive a 1V signal. Feed 1V from the 1V/OCT Tool, then press KEY0 again and feed a 2V signal. When you press it a third time it should show you a value between 1600 and 1700. Once these steps are done the unit has been calibrated.

Thanks so much, sounds very promising. Will this give me a C with 0V (and 1V etc) in v/oct and comb all the way CCW?


No, this is just to make sure the pitch tracks accurately from a 1v/oct input. Your workaround of adding an offset to your voltage source is probably the best way of making the full CCW position C is probably the best option for now.

Ok, thanks!

I’ve cheated other calibrations in the past (pico vco and the mutable range) by sending something else than (in this case) 1V and 2V, any reason why this wouldn’t work with the rainmaker? Since it’s about a minor 3rd flat in my case, I guess it should be something like 0.75V and 1.75V…


Yeah that couldn’t hurt to try! Worst case scenario you just recalibrate it normally afterwards. Let us know how it goes…

Calibration went fine, the rainmaker how ever doesn’t seem to react to voltages themselves, only to difference. I tried with 0.75+1.75, 1+2 and 1.25+2.25, no difference.

So maybe this could be added to the firmware: respect the level of the calibration voltages so not only tracking but also tuning can be calibrated?

Thanks for all the pointers!

Ah… For the last hour I was trying to figure it out. The " Clarinet" seems like an octave lower. Comb CCW and clockdivision /1 seems like a very high pitched C to me. But then would /12 be a lower C and that’s not the case. Sorry I couldn`t help out!

The division is in frequency, not notes.
Let’s say /1 is a C, then /2 would be an octave lower, /4 another octave lower (two octaves lower than /1), /8 yet another octave lower (three octaves below /1) and so forth. The “odd” number in between is in between octaves, for instance /3 is an octave and a fifth below /1, so an F. I suppose it’s like the overtone series, but going down aka the undertone series https://en.wikipedia.org/wiki/Undertone_series


Thanks for the explanation. :+1:
Did not realise the dividing in in frequencies (and its a few months ago that I read the manual). But it makes sense. "Modular" is in general in frequencies and not in (western) notes. And besides that generalization, I dont think it would make sense to express values of a (comb) filter in (western) notes.