The Duff Clearing Process concerns more than the pitch heard at the instant of attack. It also concerns how the timpano’s modal mixture evolves through the sustain and decay.
A single stroke excites several normal modes at once. Mode (1,1) is an important principal-tone component, but higher preferred modes may also be present from the beginning. What changes over time is their relative prominence, because different modes are excited with different amplitudes and decay at different rates.
This temporal evolution means that tuning and clearing should consider:
- Attack behavior: whether the initial pitch is clear and convincing
- Sustain consistency: whether beating, shimmer, or pitch drift develops
- Decay integrity: whether the perceived pitch remains stable as the modal balance changes
A stronger stroke generally changes the excitation spectrum of the real drum. Differences in mallet compression, contact time, force profile, and membrane response can make higher preferred modes such as (2,1), (3,1), and (4,1) more audible than they are during very soft playing.
This does not mean those modes suddenly appear only after a loud stroke or emerge later from another mode. They are components of the global modal response. Their audible contribution simply changes as the note evolves.
If one of these preferred modal families is appreciably split or otherwise unstable, that problem may become more obvious during the sustain or decay even when the initial attack seems focused.
One possible reason is that nearby modal components can have different amplitudes and damping rates. As their relative strengths change, the ear may become more sensitive to beating, roughness, or a shifting pitch center.
Clearing is therefore not just about the beginning of the note; it is about whether the drum maintains a convincing musical identity throughout the life of the sound.
Practical Tip: Use both soft and stronger diagnostic strokes. Soft strokes can establish a clear principal-tone reference, while stronger strokes can broaden the audible modal probe and make residual instability easier to detect. Do not judge the drum solely by the attack. Listen through the sustain and into the decay.