Guitar feedback can be simulated by feeding Karplus-Strong output through a nonlinear shaper back into the delay line

Guitar amplifier feedback occurs when the amplified string signal is picked up by the string again, sustaining and distorting it. To simulate this with Karplus-Strong: run one delay line per string, pass all outputs through a nonlinear shaping function (simulating an overdriven amp/fuzz), compress the output for sustain, then feed a portion back into each string’s delay line via an additional delay (simulating physical distance from amp to string). Controlling the feedback delay length controls the frequency at which the system locks into feedback oscillation; controlling feedback amount controls sustain intensity. This demonstrates that Karplus-Strong can be extended beyond simple pluck to capture complex coupled resonance behaviors.

Examples

Nord Modular patch: 6 KS delay lines → waveshaper → compressor → feedback delay → back to KS inputs. Knob 3 = ‘distance’ (feedback delay length).

Assessment

Explain why changing the feedback delay length changes the pitch of the feedback note. What physical analog does the feedback amount parameter correspond to?