[1] Da Vinci describes a mechanism using a wire or thin rod to link finger-operated buttons to remote keys or pads, allowing tone holes to be in their acoustically correct positions without having to be covered directly by the fingertips.

[3] However further research has revealed many conflicting records, accounts, and details of surviving instruments that attest to its simultaneous independent invention in several places within a short period, such that the very first inventor may never be known with certainty.

The very first designs of keyed trumpet were intended to correct the intonation of the notes in the harmonic series, rather than to extend its capabilities to a full chromatic scale.

[6] Eric Halfpenny found that each key corresponds to one of the four crooks and raises the pitch by a fifth, providing a fuller range of notes by allowing the player to switch between two harmonic series as required.

[10] This fate was shared by many other historical brass instruments that were replaced by their valved improvements, such as the serpent, early cimbasso, ophicleide, and keyed bugle.

Nevertheless, the combination of wide-flared bell and cylindrical bore introduces inherent acoustical problems when using tone holes, especially compared its conical-bore equivalent the keyed bugle.

It was once said to have sounded like a "Demented Oboe... despite Haydn's efforts, the keyed trumpet had no real success- the explanation may be that the holes detracted from the brilliant tone of the instrument.

"[11] The keyed trumpet has a different, weaker tone on open-keyed notes, due to the inability of the bell to support the harmonics produced when shortening the cylindrical air column.