Audio Damage Proton Tuned Delay Line Eurorack Module

Chris Randall of Audio Damage shared this preview of their new Proton Tuned Delay Line Eurorack module.

The ADM17 Proton module is a tuned delay line, designed for doing Karplus-Strong synthesis. It combines a capable “vintage digital” style delay line with 1V/Oct clocking, and adds an enveloped noise burst.

Starting with the delay line, which is “tuned” via the coarse and fine tune knobs, they add a low pass filter (modeled on the MS20’s LPF) and damping circuits. They’ve included a ‘Sub’ control that adds a sine at the fundamental frequency to produce ‘gut-churning low end’.

Karplus-Strong Synthesis in a nutshell:

  1. A short impulse is generated to simulate a ‘strike’ or ‘pluck’. In the original algorithm, the impulse was a burst of white noise, but other types of signals can be used.
  2. The impulse sound is output and simultaneously fed back into a delay line. The length of the delay time determines the pitch of the resulting sound.
  3. The output of the delay line is fed through a filter. The filter characteristics and settings determine the harmonics of the resulting sound.
  4. The filtered output is fed back into both the output and the delay line.


  • Proton is a DSP-based module that runs at 48kHz sample rate and 24 bit depth, via a Cirrus-Logic codec.
  • The PITCH control sets the delay time, while the FINE TUNE knob provides further control. The PITCH input responds to 1V/Oct.
  • The DAMPING control is the corner frequency of an MS20-style low pass filter in the feedback path of the delay.
  • The DECAY control is an additional feedback amount control, not normally found in KS synthesis. This enables bright tones with short decays.
  • The IMP FILTER controls a pair of filters on the noise burst impulse. At 12 o’clock there is no filtering. Anti-clockwise controls the corner frequency of a low pass filter, and clockwise the same for a high pass. This controls the timbre of the impulse, and the resulting pluck.
  • The IMP DECAY control sets the release time of the noise burst’s envelope. This results in a heavily colored pluck.
  • The SUB knob controls the level of a sine wave, the frequency of which is set by the PITCH and FINE TUNE controls. This allows a false low end, normally missing from low-pitched Karplus-Strong plucks.
  • The MIX knob controls the wet/dry mix (if using the audio input) or the level (if using the internal impulse.) Both the internal impulse and the input can be used simultaneously.
  • MANUAL and TRIGGER fire the internal impulse. CHOKE closes the DECAY value, and this is not reset until a new TRIGGER is received.
  • Proton can be used as a normal delay with the input; the DAMPING, DECAY, and MIX control the level, while PITCH sets the delay time.
  • Every control has a CV input that accepts +/-5V. Panel controls are sampled at low audio rates (approximately 35Hz), and have further internal lag processing for smooth parameter changes.
  • USB port (on the backplane) for easy firmware updates.
  • 1High-quality construction, including panel-bolted 100,000-cycle BI potentiometers and custom stamped Rogan knobs.
  • Power draw is 50ma from the +12V rail and 9ma from the -12V rail. This module has an on-board regulator and does not require +5V. Module width is 12HP. Module depth is 25mm.
  • Proton, like all Audio Damage hardware products, includes a lifetime unconditional warranty.

Pricing and Availability

The Audio Damage Proton is available now for US $325.

Leave a Reply