Brass instruments vary pitch by mechanically changing the length of their tubing

Evidence

For brass instruments, lip vibration is supported by the resonator of the brass instrument formed by a length of tubing attached to a mouthpiece. Some mechanism is provided to enable the player to vary the length of the tube, which was done originally, for example, in the horn family by adding different lengths of tubing or “crooks” by hand. Nowadays this is accomplished by means of a sliding section as in the trombone or by adding extra lengths of tubing by means of valves. The tube profile in the region of the trombone slide or tunable valve mechanism has to be cylindrical in order for slides to function. — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1243

Categorization

• XREF: Historically richer parallel to how pre-valve horns used manually added ‘crooks’ — connects to brass instrument design lineage. — connects to: Trumpets need a movable tuning slide because fixed third-valve length is inaccurate — David Howard, Jamie Angus, coustics and Psychoacoustics, 1283; Brass instruments operate acoustically as stopped-end tubes driven by lip reeds — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1234