Physical Modeling

The strangest synthesis method of all doesn't imitate an instrument's sound: it imitates its physics. Instead of oscillators, physical modeling builds a mathematical toy version of the vibrating object itself and lets it ring.

The most famous model is beautifully simple. A plucked string is just a wave bouncing back and forth along a wire, losing a little brightness on every round trip. In code, that's: a burst of noise (the pluck) trapped in a feedback delay loop (the wire, one round trip per vibration), with a low-pass filter inside the loop (the energy loss). That's the Karplus–Strong algorithm, and it's what you're about to play. There is no oscillator anywhere in this instrument.

String Lab · Karplus–Strong
Waveform · time
Spectrum · frequency
4.0 kHz
Damping
70 %
Sustain
A
S
D
F
G
H
J
K
L

There is no oscillator here at all, just a burst of noise trapped in a feedback loop. Low Damping = muted nylon; high Damping = bright steel string.

Try this: set Damping low (~1 kHz) and it's a soft nylon string; push it high and you get bright steel. Sustain controls how much energy survives each bounce, at 100% the note rings almost forever, like plucking a piano with the sustain pedal down. Notice how each note starts with a burst of noise that instantly "becomes" pitch: that's the loop doing its magic.
Checkpoint
In the Karplus–Strong string model, what sets the pitch of the note?
Challenge · Match the string

One pluck, two hidden physics settings: how bright is the string, and how long does it ring?

3.0 kHz
Damping
50 %
Sustain
← Granular SynthesisComplete & continue →