To use this editor:

  1. Connect your Castor & Pollux to your Eurorack power supply. The module must be powered by the Eurorack power supply.
  2. Connect a USB cable from your computer to Castor & Pollux's USB port. It's located on the right side of the module on the bottom circuit board.
  3. Click the connect button, and when prompted, allow the page access to your MIDI devices.
  4. Once connected the editor will appear and load the current settings from your device.
  5. Once you're done editing, click the save button at the bottom of the editor.
  6. Saving should automatically reset your module, but, if you don't see the changes take effect then try restarting your module. You can do this by turning it off and back on or by pressing the small reset button that's right beside the USB port.


This editor uses WebMIDI to communicate with Castor & Pollux. It works in Google Chrome, Microsoft Edge, and Opera (full list of supported browsers).

If you run into issues, feel free to reach out.


The higher the brightness, the more power the module will consume. At maximum brightness, it consumes 130mA from the +12v rail.

octaves (volts)

This setting effectively determines the starting note for the module since the pitch CV input and offset knobs are added to this value to determine the final pitch CV. By default, it's 1.0.

octaves (volts)
octaves (volts)
octaves (volts)
octaves (volts)

These settings determine the pitch offset knob's range for each oscillator. By default, they have a range of about -1 to +1 octaves (volts). The value of the pitch offset knob is added to the pitch CV input. Note that because the module's analog-to-digital converter (ADC) isn't perfect, the knobs don't quite reach 100% of their range. You may need to nudge these to give the knob some headroom.


The firmware adjusts the pitch CV knobs so that it's easier to tune the oscillators. It does this by spreading the values near the center of the knob out so that the range at the center is more fine. This makes the knobs non-linear. This setting controls how "intense" that non-linearity is. 0.33% is equivalent to a linear response. Higher values make it easier and easier to tune the oscillator but sacrifices the range, values lower than 33% willmake it harder to tune and aren't recommended. This is 60% by default.


This setting controls the maximum intensity of the chorusing feature. The intensity is the amount that the internal LFO effects the pitch of the second oscillator (Pollux).


This setting controls the default frequency of the internal low-frequency oscillator (LFO). This LFO is used by the chorusing feature and the pulse-width modulation (PWM) feature. The frequency can be changed anytime by holding the hard sync button and moving the chorusing amount (Ī†) knob, this just sets the frequency at start-up.

These settings control the overall waveshape of the internal LFO. The LFO is generated by adding two indepedent waveforms together. By default, the first waveform is a triangle wave and the second waveform is turned off.

These settings control whether the internal LFO is used to modulate the pulse width of each oscillator by default. The routing can be enabled or disabled at any time by holding hard sync button and moving the oscillator's pulse width knob, this just enables or disables it at start-up.

This controls the behavior of the pulse wave when the pulse width is modulated. Smooth is almost certainly what you want, however, if you choose Classic you'll introduce some interesting glitchy/stepping behavior when the pulse width changes.
The reason this setting exists is because prior to the July 2022 firmware release, Castor & Pollux had a bug that caused the effective pulse width resolution to be far lower than intended. Some folks like the old sound, so we added this setting for nostalgia.

x multiplier

These settings control how the module filters the pitch CV inputs. Due to inherent limitations with converting analog pitch CV to a digital pitch value, such as noise and transient errors, it's necessary to basically low-pass filter (or slew limit) the readings. The module's filter is a little more sophisticated than that- it is a self-modulated low-pass filter. The initial gain setting determines the minimum effect of a new reading on the ongoing average - so if it is 0.1% then it will effect the ongoing average by 10%, if it is 1.0 then previous readings are essentially ignored because it effects the ongoing average by 100%. The sensitivity setting determines how much the low-pass filter can self-modulate. Higher settings means that the module will be more reactive to large changes in the CV input, whereas lower settings will cause the module to react very slowly to any change in the CV input.

Danger zone

These settings are calibrated during assembly and do not have default values. Changing these settings can cause your module to behave incorrectly. It's highly recommended that you write down these settings before making changes in case you need to restore them.

code points, volts

These settings controls how Pollux determines when to follow Castor. The intended behavior is that when no cable is attached to Pollux's pitch CV jack, it will follow Castor's pitch. The module detects this condition by seeing if the input jack is reading 0 volts. Sometimes due to analog conversion errors this threshold needs to be adjusted. Lower thresholds may lead to glitchy behavior as the noise measures above and below the threshold, and higher settings may lead to Pollux ignoring the pitch CV input on lower notes.

code points
x multiplier
code points

These settings determine how the module corrects for gain and offset errors in its analog-to-digital converter (ADC). We calibrate every Castor & Pollux during manufacturing and save the calibration data to the device. However, we keep a copy of it in case it somehow gets erased or corrupted. You can use the restore button below to load the values that were originally on your device. If the button is greyed out, then we don't have a copy of your module's calibration data. ☚ī¸

This allows you to re-calibrate your module's tuning. You should only do this if you absolutely know what you're doing or have been instructed to do so by support. Please write down the values for the settings in the previous section as this will overwrite them.
To use this, connect the most accurate CV source that you have to the first oscillator's pitch input. Set the CV to 1V and click "Measure 1V". Repeat for 3V. Once both measurements have been taken, it will calculate new values for tuning calibration. Click "Save" to write these to the device.

Save to device