Why Can an Organ Truly Sustain a Note?

After a piano hammer strikes a string, it immediately rebounds and the sound begins to decay. An organ's long note is not an extended version of that resonance. Bellows and regulators supply pressurised air to the windchest; pressing a key opens a valve so air continues into the selected pipe. While the key remains down and the wind stays steady, the pipe keeps speaking. Releasing the key closes the valve. A pipe's material, length and scale, and whether it uses a flue or reed, help determine the pitch and colour of each stop.

This changes how a performer shapes time. An organ note does not naturally retreat into the background as a piano note does, so an overlong tone can obscure the next harmony. Direction in a long phrase therefore comes from when voices enter and leave, how stops are combined, and whether releases are clean yet breathing. In Bach's counterpoint, releasing one voice half a beat early or late can alter a harmonic boundary. Staccato is not merely an imitation of a short piano sound; it is a precise allocation of wind and silence.

The organ's sustaining power seems to offer an “unlimited” note, but it also removes the assistance supplied by a piano's natural decay. What matters is not only how a sound begins, but how long it occupies the room and when it makes space for the next one.

https://www.yamaha.com/en/musical_instrument_guide/pipeorgan/mechanism/
https://historicalkeyboards.as.cornell.edu/wind-system
https://www.kyotoconcerthall.org/en/pipeorgan/