A transposing instrument is a musical instrument whose music is recorded in staff notation at a pitch different from the pitch that actually sounds (concert pitch). A written middle C on a transposing instrument produces a pitch other than middle 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 musical notation. 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 type of 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".
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.
Instruments that transpose this way are often referred to as being in a certain "key", such as the "A clarinet" or "clarinet in A". The instrument's key tells which pitch will sound when the player plays a note written as C. A player of a B♭ clarinet who reads a written C will sound a B♭ while the player of an A clarinet will read the same note and sound an A. The non-transposing member of the family is thus called a "clarinet in C".
Examples of families of transposing instruments:
Examples of families of non-transposing instruments:
Recorders are either untransposed or in some cases transposed at the octave. In the early 20th century, however, instruments with basic scales other than C were sometimes written as transposing instruments.
Examples of families with both transposing and non-transposing instruments:
The euphonium, with its close relative the baritone horn, may be played as either a treble clef instrument or a bass clef instrument because it is often played as a second instrument: trumpet or cornet players who double on the euphonium are used to playing in treble clef, while trombone or tuba players who double on the euphonium are used to playing in bass clef. In both cases, the instrument plays in the same range as the trombone, i.e., it produces the same pitches. However, in treble clef, the euphonium is a transposing instrument, i.e., its music and fingering are set up as if it is a B♭ instrument (transposing), while in bass clef, its music and fingering assume that it is a C instrument (non-transposing). Musicians who play both bass- and treble-clef euphonium must learn to use different fingerings for the written notes: e.g., a B♭ in treble clef requires that the first valve be depressed, whereas a B♭ in bass clef is open.
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Before valves were invented in the 19th century, horns and trumpets could play only the notes of the overtone series from a single fundamental pitch. (Exceptions included slide-bearing versions such as the sackbut and finger-hole horns like the cornett and serpent.) Beginning in the early 18th century, a system of 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.
In the music of Germany during the Baroque period, and notably in the music of Johann Sebastian Bach, instruments used for different purposes were often tuned to different pitch standards, called Chorton ("choir pitch") and Kammerton ("chamber [music] pitch"). When they played together in an ensemble, the parts of some instruments would then have to be transposed to compensate. In many of Bach's cantatas the organ part[clarification needed] is notated a full step lower than the other instruments. See pitch inflation.
A few early-music ensembles of the present day must do something similar if they comprise some instruments tuned to A415 and others to A440, approximately a semitone apart. Modern builders of continuo instruments sometimes include moveable keyboards which can play with either pitch standard. The harpsichord has a single string for each note, plucked by a plectrum and the difference in pitch between the Baroque A at 415 Hz and the "modern" A at 440 Hz is one half step. Moving the keyboard mechanism right or left causes the A key to play the next string, namely the A♯ at 440 Hz or the A♭ at 392 Hz respectively. Movement of the keyboard allows one to play higher or lower, though the topmost or bottommost key will not produce sound unless the builder has provided extra strings to accommodate the transposition feature.
If an instrument has a range too high or too low for composers to easily write its music on bass or treble clef, the music may be written either an octave higher or an octave lower than it sounds, in order to reduce the use of ledger lines. Instruments that "transpose at the octave" are not playing in a different key from concert pitch instruments, but sound an octave higher or lower than written. Music for the double bass is written an octave higher than it sounds. Thus, when cellos and basses are reading exactly the same part (a common practice by composers from the early Classical period), the basses' bassline is an octave below the cellos'.
Most woodwind instruments have one major scale whose execution involves lifting the fingers more or less sequentially from the bottom to top. This scale is usually the one notated as a C scale (from C to C, with no sharps or flats) for that instrument. The note written as C sounds as the note of the instrument's transposition: on an E♭ alto saxophone, that note sounds as a concert E♭, while on an A clarinet, that note sounds as a concert A. Clarinets are one exception, in that they actually have two different scales in the first and second registers, nominally an F scale and a C scale, but treated by the performer as sounding "at pitch" for a C clarinet. The bassoon is another exception; it is not a transposing instrument, yet its "home" scale is F (like the low register of the C clarinet).[dubious ]
Brass instruments, when played with no valves engaged (or, for trombones, with the slide all the way in), play a series of notes that form the overtone series based on some fundamental pitch, e.g., the B♭ trumpet, when played with no valves engaged, can play the overtones based on B♭. Usually, that pitch is the note that indicates the transposition of that brass instrument. Trombones are an exception: they read at concert pitch, although tenor and bass trombones are pitched in B♭, alto trombone in E♭. Double horns are another exception, in that they combine two different sets of tubing into a single instrument, most characteristically in F and B♭. The horn part is nevertheless transposed uniformly in F (and indeed seldom if ever specifies whether a double or single horn is to be used), with the player deciding when to switch from one side of the instrument to the other. Single B♭ horns also normally read from parts transposed in F.
In general, for these instruments there is some reason to consider a certain pitch the "home" note of an instrument, and that pitch is usually written as C for that instrument. The concert pitch of that note is what determines how we refer to the transposition of that instrument.
In conductors' scores and other full scores, music for transposing instruments is generally written in transposed form, just as in the players' parts. Some composers from the beginning of the 20th century onward have written orchestral scores entirely in concert pitch, e.g. the score of Sergei Prokofiev's Piano Concerto No. 1 in D♭.
Transposing instruments' names almost always use flats instead of sharps (thus there are instruments in E♭ or in B♭, but these are never today[clarification needed] called instruments in D♯ or in A♯). In practice the actual transposition in the score may (for the convenience of the player) depend on the key of the music. For example, in a section in C major an E♭ alto saxophone part will appear in A major (three sharps). But in a section in concert B major it would be impractical to notate the sax part in G♯ major part (a key with eight sharps, i.e. six sharps and one double-sharp). Instead, their part would appear in A♭ major (four flats), just as if they were playing a D♯ instrument.