What is a Transposing Instrument?

It is easier for musicians to play together, talk to each other about music, and share written music with each other, if everyone agrees on the same names for each pitch. The most widely used standard is called concert pitch. Used in most genres of Western music, concert pitch is usually defined by saying that a pitch that sounds at 440 hertz is an "A", with all other pitches related to that A using equal temperament tuning.

Even though concert pitch is defined by the sound of an "A", instruments that read music at concert pitch are called C instruments. This is because the key of C is the "natural" key, the major key that has no sharps or flats, only natural notes. (You may wonder why A is not the natural key. As is true for so many aspects of music notation and theory, there is no logical reason; it is just a happenstance that arose out of the history of Western music.)

Many instruments are C instruments. For example, piano, organ, oboe, violin, guitar, and trombone are all C instruments. A pianist who sees a written C will play a note that the violinist would agree is a C. This may seem obvious, but a clarinet player who sees a C on the page will play a note that does not sound like a C to the other players. This is because the clarinet is a transposing instrument. The music for transposing instruments is not written or read at concert pitch. The clarinet player, for example, seeing a C on the page, will play a note that sounds like a B flat. The clarinet is therefore called a B flat instrument. A French horn player, seeing a C on his "horn in F" or "F horn" part, will play a note that sounds like an F. So the name of the instrument ("B flat clarinet" or "F horn") tells you which concert-pitch note the instrument plays when given a written C.

Transposing does not just change the written C, however; it changes every note. For example, a B flat instrument plays every note a whole step lower than written, not just the C. This means that if you want the clarinet player to play particular concert-pitch notes, you must write those notes one whole step higher than you would for a non-transposing instrument.

Figure 1

Since every note of the scale is changed, the result is a different scale. This means that the part for the transposing instrument will be in a different key and have a different key signature than the parts for C instruments. Changing music to put it into a different key is called transposing the music. Music for transposing instruments must be properly transposed in order for most players to be able to read it. (There are musicians who can "transpose at sight," for example horn players who can read concert-pitch music and play it at concert pitch, but this is unusual.)

Transposing and Non-transposing Instruments

A complete list of all the transposing instruments would be very long. Many are very rare. I will list here only the most common ones. Then I'll discuss a couple of issues that sometimes cause confusion: octave-transposing C instruments and non-C, non-transposing instruments.

Some transposing instruments do not change key, but play an octave higher or lower than written.

Why are there Transposing Instruments?

Things do run more smoothly when everyone agrees on the same name for the same sound. So why are there transposing instruments? The instruments that transpose an octave have either a very high or very low range. Transposition puts their written parts comfortably in the staff and avoids using too many harder-to-read ledger lines.

Figure 2

Some transpositions are for the convenience of the player. Someone who has learned to play C trumpet, for example, associates a particular note with a particular fingering. If he switches to a B flat trumpet, he can use the same fingerings for the written notes, as long as the part has been appropriately transposed. If it has not (and some modern composers do not bother with transposition), he must learn to associate the same fingerings with different written notes, which can be confusing.

Other transpositions used to be for the convenience of the player, but are now mostly accidents of history. For example, there was a time when French horns, like harmonicas, came in every key, and could only play well in that key or closely related keys. French horn players could switch between different instruments playing what looked like the same set of notes, but which actually sounded in whatever key was needed. As the horn became capable of playing all notes equally well, the horn in F was the one that was chosen as having the nicest sound, so players still read parts in F.