Karplus

A plucked-string voice built on Karplus-Strong synthesis — a mono distillation of the Voxglitch Impulse module. It's not a sample: a Trigger fires a short burst of noise into a tuned delay-line loop, and that loop rings like a string. A damping filter in the loop makes each pluck brighten on the attack then mellow as it decays, and a feedback gain sets how long it sustains. It plays in tune across the keyboard (fractional/allpass tuning), takes an audio input so you can resonate any source through the string, and has a comb for metallic, detuned character.

Patch it

  • trig — pluck the string. Each rising edge re-excites it with a fresh noise burst.
  • pitch — 1V/oct, summed on top of the Tune knob. Play it from a keyboard or

sequencer; tuning is accurate up to ~1.5 kHz (it drifts a little in the top octave).

  • audioin — feed any signal here and the tuned string resonates it (no trigger

needed): drums become pitched, noise becomes a bowed drone, a voice gets a talk-box vowel. In Gain sets the drive.

  • dampcv / decaycv / resocv — CV for brightness, ring time, and comb resonance,

each trimmed by its attenuverter knob.

  • out — mono audio.

Controls

STRING

  • Tune — base pitch, 20 Hz – 2 kHz (log taper, so a keyboard maps evenly).
  • Pitch CV — attenuverter on the pitch input. +1 (default) = true 1V/oct;

turn down to scale, below 0 to invert.

  • Decay — ring time, 0.05 – 10 s (log taper). Short = a staccato pluck; long =

a string that blooms from bright to pure and sustains for seconds. Pitch-compensated, so high and low notes ring for a similar time.

  • Decay CV — attenuverter on the decaycv input (e.g. velocity → longer ring).

TONE

  • Damp (brightness) — the in-loop low-pass, dark/felt → bright/steel. The most

musical timbre control; sweep it with an envelope for filtered plucks.

  • Damp CV — attenuverter on the dampcv input.
  • Pick — attack hardness: low = a soft, thumb/felt pluck (dark attack), high = a

hard plectrum (bright, snappy attack). It shapes the excitation, not the sustain.

  • Inject — bow/scratch: re-injects noise into the string for a while after the

pluck, turning a clean pluck into a bowed or scraped sustained tone. 0 = a clean Karplus pluck.

COMB — a feedback comb on the output for metallic/detuned character (dormant until Mix is up).

  • Ratio — comb delay as a multiple of the string length (0.25 – 8×); which

partial it reinforces. 1× thickens the fundamental; small values ring bright/nasal.

  • Reso — comb feedback: from a gentle color up to long, near-ringing metallic tails.
  • Reso CV — attenuverter on the resocv input.
  • Mix — dry string vs comb blend. 0 = pure string.

OUT

  • In Gain — drive for the audioin excitation (0 – 2×).
  • Level — output level.

Tips

  • A clean pluck: just patch a gate into trig. Raise Decay for sustain, and

sweep Damp with an envelope for a "wah" pluck.

  • Bowed/sustained: turn Inject up for a continuously-excited, scratchy drone.
  • Resonator on anything: patch a drum loop or noise into audioin (no trigger) and

set Tune — the string rings the input at pitch. Great on hats, claps, or vocals.

  • Metallic/plucked-bell: raise Mix and Reso, then explore Ratio for

detuned, gamelan-ish partials.

  • Melodies: feed pitch from a sequencer/keyboard; it tracks 1V/oct. Keep the

fundamental under ~1.5 kHz for the most accurate tuning.