Woodwind pitch is changed by tone holes that selectively reflect low frequencies and transmit high frequencies

In real woodwinds, pitch is changed by opening and closing tone holes, not by changing bore length. Each open tone hole acts as a partial reflector: typically low frequencies are reflected (continuing down the bore) and high frequencies are transmitted (radiating as sound). To model this, each tone hole can be implemented as a pair of filters — lowpass for the reflected signal, highpass (input minus lowpass) for the transmitted/radiated signal. A simplified version uses switches: open = all energy reflected, closed = all energy transmitted. In multi-note instruments, the first open tone hole closest to the mouthpiece effectively terminates the bore for the low frequencies, setting the pitch. Smooth transitions between notes require careful treatment of delay line reconfiguration to avoid transient discontinuities (audible clicks).

Examples

Nord Modular clarinet with 6 tone holes: 6 NoteDetect modules → Pan modules routing energy to reflection or transmission paths. Smooth module eliminates click artifacts during note transitions.

Assessment

Explain why a tone hole’s lowpass reflection characteristic means low-pitched notes require all holes closed. Describe the click artifact that occurs when switching tone holes and how to mitigate it.