Resonance as Pitch
A filter with high Q rings at its natural frequency. It is a resonator. Feed it a noise burst and you get a pitched, decaying tone. You've been building resonators since Part 5 without calling them that.
The Ringing Filter
When Q is high enough, a bandpass filter doesn't just pass frequencies; it rings. Hit it with an impulse and it produces a pitched tone that decays naturally. The higher the Q, the longer the ring and the purer the pitch. This is exactly how a tuning fork works: a mechanical resonator with extremely high Q.
Resonators, Not Filters
Every physical object that vibrates is a resonator. A guitar string, a drum head, a bell. Each has resonant frequencies where it naturally vibrates. A high-Q bandpass filter behaves identically: it has a center frequency where it resonates, and energy at that frequency persists while everything else dies away. The word "filter" undersells what's really happening.
Stacking Modes
One resonator produces one pitch. Stack multiple resonators at different frequencies and you get a complex timbre. This is how physical objects work. A vibrating plate doesn't ring at one frequency; it has many resonant modes that combine into a characteristic sound. Harmonic ratios (1×, 2×, 3×) sound string-like. Inharmonic ratios sound like drums or bells.
Try it: hit Trigger to fire a noise burst through the resonator. Start with "Single Resonator" then try "Bell Modes" to hear how inharmonic mode stacking creates metallic timbres.
References
- Resonance, Wikipedia
- Normal mode, Wikipedia
- Synth Secrets series, Sound On Sound