An Introduction To Karplus-Strong Physical Modeling Synthesis

This video offers a quick introduction to Karplus-Strong Synthesis – a physical modeling technique that’s great for creating both realistic and creative string and percussive sounds. 

In the video, Nikol of Bastl Instruments introduces the concepts of Karplus-Strong Synthesis and then creates an example patch with the Noise Kitchen Eurorack modular synth.

Karplus-strong-schematic.svg

How Karplus-Strong Synthesis Works:

  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.

Diagram via Tlotoxl

14 thoughts on “An Introduction To Karplus-Strong Physical Modeling Synthesis

  1. That was great. Very clearly explained and demonstrated. Very enjoyable and effective demo.

    Didn’t go into varying the delay time– i.e., how you would determine pitch. I imagine that might be tricky to control.

  2. It’s a great technique. What I don’t understand is how this is considered “physical modeling”? PM, as a family of techniques, usually means the technique represents the physical properties of an acoustic instrument as a computer algorithm.

    1. I think they referred to it as the crude predecessor to P.M.

      I guess in some way, we are seeing the “exciter” noise and decay as modeling the pick or bow. The delay time & feedback as modeling the pitch (tension/length) & resonance of the string.

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