Editing Transposing instrument (section)

== Reasons for transposing ==
=== Ease of switching instruments ===
Some instruments are constructed in a variety of sizes, with the larger versions having a lower [[Range (music)|range]] than the smaller ones. Common examples are [[clarinets]] (the high E{{music|flat}} clarinet, soprano instruments in C, B{{music|flat}} and A, the alto in E{{music|flat}}, and the bass in B{{music|flat}}), [[flutes]] (the [[piccolo]], transposing at the octave, the standard concert-pitch flute, and the [[alto flute]] in G), [[saxophones]] (in several octaves in B{{music|flat}} and E{{music|flat}}), and [[trumpets]] (the common instrument in B{{music|flat}}, instruments in C, D and E{{music|flat}}, and the [[piccolo trumpet]] transposing at the octave). Music is often written in transposed form for these groups of instruments so that the [[Fingering (music)|fingerings]] correspond to the same written notes for any instrument in the family, even though the sounding pitches will differ. A musician who plays several instruments in a family can thus read music in the same way regardless of which particular instrument is being used.

Instruments that transpose this way are often said to be in a certain "key" (e.g., the "B{{music|flat}} clarinet" or "clarinet in B{{music|flat}}"). This refers to the concert pitch that is heard when a written C is played on the instrument in question. Playing a written C produces a concert B{{music|flat}} on a B{{music|flat}} clarinet, a concert A on an A clarinet, and a concert C on a C clarinet (this last example is a non-transposing instrument).

===Horn crooks===
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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.

=== Reconciling pitch standards ===

In Germany during the Baroque period, instruments used for different purposes were often tuned to different pitch standards, called ''Chorton'' ("choir pitch") and ''Kammerton'' ("chamber [music] pitch"). When playing together in an ensemble, the music of some instruments would therefore be transposed to compensate. In many of [[Johann Sebastian Bach|Bach]]'s cantatas, the organ part is notated a full step lower than the other instruments.<ref>{{cite book|author=Laurence Dreyfus|author-link=Laurence Dreyfus|title=Bach's Continuo Group|year=1987|publisher=Harvard University Press|location=Cambridge, Massachusetts|isbn=0-674-06030-X|page=11}}</ref> See [[Concert pitch#Pitch inflation|pitch inflation]].

Some present day early-music ensembles combine instruments tuned to A415 with instruments tuned to [[A440 (pitch standard)|A440]]. Since these pitches are approximately a [[semitone]] apart, the music for one set of instruments may be transposed to match the pitch of the others. Modern builders of [[Basso continuo|continuo]] instruments sometimes include [[Organ console#Keyboards|moveable keyboards]] which can play with either pitch standard.<ref>{{cite web|url=http://www.hpschd.nu/tech/kb/trans.html|title=CBH Global Harpsichord Technology|author=Carey Beebe Harpsichords Australia}}</ref> Some harpsichords are made with a mechanism that shifts the keyboard action right or left, causing each key to play the adjacent string. If A4 is tuned at A415, that key can then play either the A{{music|#}} at 440&nbsp;Hz or the A{{music|b}} at 392&nbsp;Hz. The top or bottom key on the instrument will not produce sound unless the builder has added extra strings to accommodate this transposition.