Oscillator Calibration Guide
The steps below will guide you through the calibration process for both Mangrove and Three Sisters (or any other analog oscillator).
You will need:
- A tool to measure the frequency of the oscillator (a tuner or oscilloscope)
- An accurate voltage reference (if possible, use the module that will drive the PITCH input of your oscillator most often)
- A small flathead screwdriver.
The goal is to turn a trimpot accessed through the back of the module such that the frequency of the oscillator when 2V is sent to the v/octave input is exactly four times the frequency when 0V is sent in to the oscillators v/octave input. In other words, to make sure that the oscillator is exactly two octaves above the 0V frequency when 2V is sent in. It does not matter what you choose to tune your oscillator to for the 0V frequency, as long as you make sure to set the 2V frequency to be four times the 0V one.
- Turn your system on and wait at least 10 minutes for the module to warm up.
- Send the output of your oscillator to the input of your tuning device (use the SQUARE output for Mangrove, or turn the QUALITY of Three Sisters to max and use the LOW output).
- Select a base frequency which will correspond to 0V. The choice is arbitrary. If you choose 100Hz for 0V, then the goal is to get 2V into the oscillator generating a 400Hz oscillation. If you prefer to use a chromatic scale, then choosing C2 for 0V would mean that your goal is to get 2V to generate C4.
- Send 0V from your voltage source into the v/octave input of your oscillator (PITCH input on Mangrove, FREQ input for Three Sisters). Don't just remove the cable for 0V, actually send 0v from your source to the oscillator!
- With 0V going into your oscillator, now use the frequency control knobs to tune it to your base frequency; in this case, tune it to 100Hz. On Mangrove, this means using the PITCH (coarse) and FINE knobs, while on Three Sisters you will use the FREQ knob to tune it to your base frequency.
- Now send 2V in to your oscillator.
- Check the frequency of the oscillation. If it is precisely 4 times your base frequency (in this case, 400Hz), then you are done. If not, proceed to step 8.
- If it is flat (e.g. below 400 Hz), turn the trimpot on the rear of the module a few degrees CW for Mangrove or a few degrees CCW for Three Sisters. If it is sharp, turn the trimpot a few degrees CCW for Mangrove or a few degrees CW for Three Sisters. NB: You are *not* trying to tune it to 400Hz! You are instead changing the *scaling* of the input voltage range, and after turning need to repeat this process!
- Repeat Steps 4-9.
Keep in mind you'll likely need to repeat steps 4-9, ten or more times to have the module well tuned.