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Karplus Strong is a fun and interesting technique for generating pluck-like string and percussion sounds from a synthesizer. The routing is fairly easy in a modular synth, whereas other instruments may not be as flexible. Using a very short delay set to a high feedback amount, the effect can be excited by a noise burst to create a metallic “twang”. When routed through a VCA, the amplitude of the regenerating feedback can be controlled, resulting in a more identifiable string sound.
Here’s a great video clip of Chris Randall from Audio Damage explaining the concepts behind Karplus Strong to Sonic State at Superbooth…
Karplus Strong was refined to a computer algorithm in the 1980s, to control some of the less stable elements of this loose signal flow. Pitch tracking is one of the less predictable functions in such a routing, with the pitch of the output tone determined by the delay time. Controlling the frequency of the resulting tone is not as simple as using a 1 Volt per Octave keyboard or sequencer, as we see in our example.
With the Warps Parasite delays, the delay times are are more volatile than a normal oscillator, so we get closer to a 1 Volt per 2.5 Octaves. Using a keyboard may be a fruitless endeavor, however unquantized pitch sources like sequencers and stored voltage sources can be used to dial in musical passages.
Every delay is going to be slightly different, in terms of delay length ranges, internal coloration and feedback amounts. As Chris Randall mentions, a number of companies have begun making self-contained Karplus modules, which generally adhere to more traditional tuning standards but limit the ways that the feedback may be manipulated. Try making one yourself with an available delay!
What delay modules are you using? Let us know in the comments!
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