Editing Transposing instrument (section)

===Horn crooks===
{{Unreferenced section|date=August 2015}}
Before [[brass instrument valve|valves]] were invented in the 19th century, [[Horn (instrument)|horns]] and [[Natural trumpet|trumpets]] could play only the notes of the [[harmonic series (music)|overtone series]] from a single [[fundamental frequency|fundamental]] pitch. (Exceptions included [[Slide (wind instrument)|slide-bearing]] versions such as the [[sackbut]] and finger-hole horns like the [[cornett]] and [[Serpent (instrument)|serpent]].) Beginning in the early 18th century, a system of [[crook (music)|crooks]] was devised in Germany, enabling this fundamental to be changed by inserting one of a set of crooks between the mouthpiece and the lead pipe of the instrument, increasing the total length of its sounding tube. As a result, all horn music was written as if for a fundamental pitch of C, but the crooks could make a single instrument a transposing instrument into almost any key.

Changing these lead-pipe crooks was time-consuming, and even keeping them from falling out while playing was a matter of some concern to the player, so changing crooks could take place only during substantial rests. Medial crooks, inserted in the central portion of the instrument, were an improvement devised in the middle of the 18th century, and they could also be made to function as a slide for tuning, or to change the pitch of the fundamental by a semitone or tone. The introduction of valves made this process unnecessary, though many players and composers found the tone quality of valved instruments inferior ([[Richard Wagner]] sometimes wrote horn parts for both natural and valved horns together in the same piece). F transposition became standard in the early 19th century, with the horn sounding a perfect fifth below written pitch in treble clef. In bass clef, composers differed in whether they expected the instruments to transpose down a fifth or up a fourth.