Transposing instrument
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ja:移調楽器 A transposing instrument is a musical instrument whose music is written at a pitch different from that pitch that it sounds when played, the written note being a transposition of the actual sounding pitch (often called concert pitch). Being a transposing instrument is not an actual physical property of the instrument, but entirely a matter of convention.
Transposing keyboards such as transposing harmoniums or electronic keyboards with a transposing function can have a similar effect, but are not usually called transposing instruments in this sense.
One of the great inventions of western music is a notation that describes the sound that is required (pitch, duration, volume) rather than what you have to do with the instrument to produce the sound (for example, "stop the E string with your second finger on the third fret"). This means that the same piece of music can be picked up and played fairly easily on a whole range of instruments: violin, flute, oboe, piano, voice, marimba. This facilitates the ensemble playing that is such a feature of western music, and means that you can look at music written for any instrument and know roughly what it will sound like when played, without having to know the details of how to play the instrument. It is more difficult to learn to read this sort of music, however, because the player has to learn a mapping from the pitch notated to the physical movements required to produce that pitch on the instrument.
Transposition at the octave
Some instruments have a range which does not lie within the tessitura of standard clefs. In this case the music is written either an octave higher or lower than it sounds, in order to avoid ledger lines. These are technically transposing instruments, but in common usage speakers sometimes exclude these types of transpositions from the class of transposing instruments. A double bass can play cello music, and the fact that it sounds an octave lower just feels like part of the different 'sound' of the double bass.
Examples of instruments which transpose at the octave:
- 1 octave higher:
- 2 octaves higher:
- 1 octave lower:
Other transpositions
The other principal use arises when there is a family of instruments with differing ranges. For example, the standard concert flute has a range from middle C up about 3 octaves. The alto flute is a very similar instrument, but longer, and hence pitched lower, with a range starting from the G below middle C. The fingering that would on a normal flute would produce a C produces a G a fourth lower on the alto flute. If alto flute music were written at actual pitch, flute players wishing to learn to play alto flute would have to re-learn the mapping from written pitch to required fingering. The alto flute is not in common enough use to make this worthwhile.
Instead, the music for the alto flute is tranposed up a fourth so that the player may play the alto flute using the same fingering for the written notes, but the resulting pitches are a fourth lower. The net effect is that the flute player can easily learn the new instrument, and can easily switch back and forth between the two (a common requirement in orchestra music) without risking confusion between two different fingering systems. The alto flute is thus a 'transposing instrument in G', sounding a fourth lower than written.
A similar thing happens in other instrument families. For example, clarinets come in various sizes and hence pitches (A, Bb, C, Eb), but the music is transposed appropriately for each size of instrument so that the player can easily move from one to the other. Expert clarinet players often use a different instrument than the transposition of their parts calls for, transposing the parts at sight instead; expert trumpet players may do this also.
In some families of instruments, the non-transposing C version has fallen into disuse; the clarinet family is one example, where only the B-flat and A members are common. Horns are another example.
Some families containing tranposing instruments:
- the clarinet family (clarinet in A and Bb; high clarinet in D and Eb; bass clarinet in Bb; contrabass clarinet in Eb and Bb)
- some members of the oboe family (oboe d'amore, cor anglais)
- the saxophone family
- most brass instruments, notably the trumpet and French horn.
French horns are a particularly interesting case. Before valves became common about 1800, horns could only play the notes of the overtone series from a single fundamental pitch. However, this fundamental could be changed by inserting one of a set of crooks into the instrument, shortening or lengthening 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 the crooks was a time-consuming process, so it only took place between pieces or movements. The introduction of valves made this process unnecessary, but Richard Wagner (1813-1883) wrote horn parts as if crooks were still in use. Furthermore, even though an F tranposition became standardized in the early 19th century, composers were inconsistent in whether they expected the instruments to transpose down a fifth or up a fourth, especially when written in treble clef.
There are a few families of instruments which have instruments of various sizes and ranges, but whose music is rarely or never transposed. The recorder family is one of these.
In conductors' scores, most often the music for transposing instruments is written in transposed form, just as in the players' parts; but a few publishers, especially of contemporary music, provide conductors with music which is all at concert pitch. The argument for the latter practice is that it makes the pitch relationships of the entire sound easier for the conductor to read. The advantage of traditional practice is that it facilitates spoken communication in rehearsal since conductor and player are looking at the same notation.