Transposing instruments

A pianist and a clarinettist read the same written note together, a C. The pianist plays C. The clarinettist, with the C fingering, also plays what is C to them. But what comes out of the clarinet is a B flat, a tone below the piano.

Nobody made a mistake. The commonest clarinet is a transposing instrument: the note it sounds is not the note written in its part (Blatter 2007, part 6, appendix V).

Why they exist

Transposing instruments are mostly wind instruments built in different sizes. Changing the length of the tube, the same finger position produces another pitch. For practical reasons, the note keeps the name tied to the fingering, even though the real sound does not match it (Med 1996, ch. LVII).

The advantage is for the player. A saxophonist moving from alto to tenor saxophone does not have to learn to read again: the same written note asks for the same fingering on both, and each instrument sounds at its own pitch. The work of transposing falls to whoever writes the part.

The rest of the instruments, the great majority, are in C: they sound at written pitch. That is why nobody says "piano in C" or "violin in C" (Med 1996, ch. LVII). The real pitch, the piano's, is called concert pitch or sounding pitch (Blatter 2007, part 6, appendix V).

The rule of the name

A transposing instrument is named after the note it is pitched in: clarinet in B flat, horn in F, flute in G. And the name says exactly how it sounds. Med's general rule is short: a written C sounds as the instrument is named (Med 1996, ch. LVII).

A C written in the parts of four instruments, and what each one sounds:

Hear the passage

On the violin, in C, it sounds C. On the clarinet in B flat, the B flat below. On the horn in F, the F a fifth below. On the alto saxophone in E flat, the E flat a major sixth below.

The rule gives the note, not the octave; each instrument has its own distance. The commonest:

Instrument	Written C sounds	Distance
clarinet, trumpet, soprano saxophone in B flat	B flat	major second lower
clarinet in A	A	minor third lower
flute in G (alto flute)	G	perfect fourth lower
horn in F, cor anglais	F	perfect fifth lower
alto saxophone in E flat	E flat	major sixth lower
tenor saxophone, bass clarinet in B flat	B flat	major ninth lower
trumpet in D	D	major second higher

Blatter gives the same list of the best known, and points out that the tenor saxophone and the bass clarinet, though also in B flat, sound a ninth lower, not a second (Blatter 2007, part 6, appendix V).

Med also notes that "clarinet in B flat" does not mean the music is in B flat, nor that the part has two flats in its key signature (Med 1996, ch. LVII). The name is about the instrument, not the piece.

Octave transposition does not count

Some instruments are also written at a pitch other than the real one, but only by an octave, to avoid too many ledger lines. The piccolo is written an octave below where it sounds; the double bass and the guitar an octave above. Since the octave changes neither the note names nor the key, these instruments are not classed as transposing (Med 1996, ch. LVII).

Writing the part

For a B flat clarinet to sound a passage in G major, its part has to be written a tone higher, to make up for the tone the instrument drops. A tone above G major is A major, so the part carries the A major key signature, three sharps, and every note goes up a tone (Blatter 2007, part 6, appendix V).

What you want to hear, at concert pitch:

Hear the passage

What is written in the B flat clarinet part:

Hear the passage

A practical rule for the key signature follows. The part for an instrument in B flat always has two more sharps, or two fewer flats, than the music at concert pitch. For an instrument in F, one more sharp. For one in E flat, three more sharps. For one in A, three more flats.

Med sums up the paradox: to the listener, writing for a transposing instrument transposes nothing, it only copies the same melody at the same pitch. The transposition happens in the writing (Med 1996, ch. LVII).

Reading the part at the piano

The reverse journey comes up when a pianist has to play a clarinet part, or when a conductor reads the score. To go from the written note to concert pitch, go down the instrument's distance: a tone for B flat, a fifth for the horn.

When the interval is large or awkward, Blatter suggests thinking in scale degrees. An alto flute part written in D major sounds in A major, and every note keeps its degree: what was tonic in D is still tonic in A, what was dominant is still dominant (Blatter 2007, part 6, appendix V). Instead of dropping a fourth note by note, you read "first degree, seventh, fourth" and play those degrees in A.

There is also the clef method, which Blatter describes too: reading a B flat part by mentally swapping the treble clef for the C clef on the fourth line, and fixing key signature and octave (Blatter 2007, part 6, appendix V). Notation software does this sum by itself; reading at sight still requires knowing how.

Double transposition

Sometimes the part is written for an instrument the player does not have. Classical-period horns were changed to suit the key of the piece, and a Mozart part may be written for horn in G; today's horn player plays a horn in F. So they transpose once more, from G to F: they read C, play D, and it sounds G, which is the sound the composer wanted (Med 1996, ch. LVII).

The same happens to the clarinettist playing a clarinet in A part on a B flat instrument, or the trumpeter playing a trumpet in D part on a B flat instrument (Med 1996, ch. LVII). There are extreme cases: in Berlioz's overture Benvenuto Cellini, four trumpets are written in four different transpositions (Med 1996, ch. LVII).

With or without a key signature

A transposing instrument's part can be written with the key signature of the transposition, or with the same key signature as the other instruments and the alterations as accidentals (Med 1996, ch. LVII). Horn parts, by tradition, are often written without a key signature.

And some twentieth-century composers, to make their scores easier to read, took to writing every instrument at concert pitch (Med 1996, ch. LVII). This is the so-called score in C: the conductor reads the real pitches, and only the individual parts stay transposed for the players.

What comes next

Transposing instruments close the subject of transposition: first the idea of moving everything by an interval, then clefs as a shortcut, and now the instruments that live transposed. With that, an orchestral score becomes fully readable, every staff telling you what sounds.