Kettledrums retune by pedal over a five-semitone range

Evidence

A kettledrum has a single membrane which is stretched over a metal bowl (or kettle) that is suspended on a supporting frame. Absolute tuning of a kettledrum head is set by means of adjusting screws (usually eight) around its rim, to enable it to be tuned to the appropriate absolute pitch reference. During a performance, its tuning can be changed in semitone steps by means of a lever tensioning system operated by a pedal, which typically enables a pitch variation over five semitones. The head tension varies as the lever is moved from note to note, and, if the kettledrum is struck immediately prior to the lever being moved, a rising (or falling) pitch is heard as a glide or glissando. This is sometimes used for musical effect. — David Howard, Jamie Angus, coustics and Psychoacoustics, 1324