Transposing instrument

A transposing instrument is a musical instrument whose music is notated at a pitch different from the pitch that actually sounds (concert pitch). Playing a written C on a transposing instrument produces a pitch other than C, and that pitch identifies the interval of transposition when describing the instrument. For example, a written C on a B♭ clarinet sounds a concert B♭.

Rather than a property of the instrument, the transposition is a convention of music notation—however, instruments whose music is typically notated in this way are called transposing instruments. As transposing instruments is a notation convention, the issue of transposition is mainly an issue for genres of music which use sheet music, such as classical music and jazz (while jazz is an improvisation-based music, professional players are still expected to be able to read lead sheets and big band sheet music). For some instruments (e.g., the piccolo or the double bass), the sounding pitch is still a C, but in a different octave; these instruments are said to transpose "at the octave".

There are several reasons that composers, orchestrators and arrangers transpose music for certain instruments.

Many instruments are members of a family of instruments that differ mainly in size (see examples below). The instruments in these families have differing ranges, with the members sounding lower as they get larger; but an identical pattern of fingerings on two instruments in the same family produces pitches a fixed interval apart. For example, the fingerings which produce the notes of a C major scale on a standard flute, a non-transposing instrument, produce a G major scale on an alto flute. As a result, these instruments' parts are notated so that the written notes are fingered the same way on each instrument, making it easier for a single instrumentalist to play several instruments in the same family.

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