soundbytes ks symp

A Virtual String Instrument based on the Karplus Strong Algorithm.


  • Overview
  • Description of modules and controllers
  • Version History


An exitation signal is triggered by a note on event or a continous controller. This Signal is fed into a Karplus-Strong oscillator. The outcome is then filtered to simulate a resonating instrument body. Part of the original waveguide signal and of the filtered signal is fed into a system of 12 sympathetic strings that is simulated by a cluster of Karplus Strong oscillators.

The Synth supports alternative tunings for Midi Note input. These are accessible from a seperate Panel. The Sympathetic Strings can also be retuned.

The Modules:


The 'Pluck' is created here as a mix of filtered noise and an (optionally filtered) saw/triangle signal.

  • [Pluck/Cont] - Fades between continous(Bow)and plucked Excitation. Pluck can be used for Plucked strings and percussive patches while Bow is appropriate for bowed, breathy and lead sounds.
  • [Breath/Mod/AT] - switch to select the continous controller for the bowed excitation. Choices are Breath (CC2) Mod Wheel and Channel Aftertouch
  • [Noise/Saw] - Blends between filtered noise and a Triangle/Saw signal
  • [Tri/Saw] - Blends between a Triangular and a Saw Waveshape.
  • [Filter Saw] - Switches the filtering on for the Tri/Saw oscillator.
  • [Color],[Amt] - Filterfreqency is
    [Color] x [Note on frequency]. The Amt Parameter controls the influence that the note on velocity (pluck) or the Continous controller (bow) has on the filter frequency.
  • [Body] - The Body Knob blends between 2 Pole Bandpass and Lowpass filter
  • [Q] - Filter quality
  • [Att(Cont)],[Re(Cont)] - Attack and Release of the Excitation Envelope (only for the Bowed Excitation)
  • [Pluck] - Pluck volume
  • [Intensity],[Amt] - Excitation amplitude.

OSC (Voice):

Defines the characteristics of the virtual string:

  • [Mute],[Key] - dampens the sound.
  • [brilliance] - changes the sound from Nylon to Steel (or maybe from pure Nylon to Brasswound nylon ;)
  • [Threshold],[Release] - Controls for the Limiter
  • [Att],[Dec],[Rel] - Envelope controls
  • [Voice Level] - Output level (This has no influence on the voice amount that is fed into the Voice or Symp oscillators)


Controls for the Sympathetic cluster.

  • [Tune] - The cluster is tuned in a diatonic scale in the key of C major. Use the Tune knob to transpose the sympathetic strings.
  • [Mute],[Key] - dampens the sound.
  • [brilliance] - changes the sound from Nylon to Steel (or maybe from pure Nylon to Brasswound nylon ;)
  • [Threshold],[Release] - Controls for the Limiter
  • [Symp Level] - Output level (This has no influence on the symp amount that is fed into the Voice or Symp oscillators)
  • [FB S>S] - will feed each Symp string output back into itself.


Here the Excitation is mixed with a number of Feedback signals. Sources are: The voice output, the sympathetic cluster, and the final filtered output (body). This composed signal is then compressed to minimize the risk of feedback resonance.

  • [FB B>V] - The filtered 'Body' Signal contains the whole mix
  • [FB S>V] - The input from the sympathetic cluster.
  • [FB V>V] - The Amount of the Voice Signal
  • [Threshold],[Release] - Controls for the Limiter


  • [FB S>S] - The output of the whole cluster is fed back into all the oscillators.
  • [FB V>S] - The Amount of the Voice Signal.
  • [FB B>S] - The filtered 'Body' Signal contains the whole mix
  • [Threshold],[Release] - Controls for the Limiter


Some edge can be added to the Voice output.

  • [Buzz] - A simple clipper
  • [Buzz Amt] - Mix of buzzed and unbuzzed signal
  • [bypass] - switches the buzzer of


The Feedback envelope works on the Voice Signal that is fed back into itself and into the Symp Cluster.

  • [Att],[Dec/Rel],[Vol] - the Vol parameter is fully active when Pluck is selected. Vol rises to 1 as the continous (bowed) excitation is faded in.


Two cascaded Filters (2 pole LP) are used to simulate an instrument body.

  • [F1],[Q1],[F2],[Q2] - Filter controls
  • [Amt F1] - Mixes the output of Filter 1 with the unfiltered signal. The crossfade output is then fed into Filter2
  • [Amt F1/2] - Mix of the Filter 2 output with the unfiltered signal.


KS Symp4:

  • First release

KS Symp5:

  • fixed some bugs
  • Replaced Compressors with new CPU friendly Limiter modules
  • Introduced Limiters as Feedback Protection also at the output of the Voice oscillator and of each Sympathetic oscillator.
  • Panel restructured
  • reworked the Presets
  • Continous controller selection Mod/Breath/Aftertouch introduced in the excitation module (for bowed sounds)

KS Symp7:

  • Restructured the Excitation Module
  • Replaced the Bow/Pluck switch with a control. This enables fades between the two modes.
  • Added a Tuning table to the Sympathetic Cluster.
  • Added a Tuning Table to the Midi Note Input
© andreas sumerauer 2012  contact information -