Why do instruments have a key?

Question

There are many instruments that have keys other than C. For example:

• The Eb Alto Saxophone
• The Bb Clarinet
• The Horn in F

Why do these instruments have a key in the first place? Here's a more specific example:

On the alto saxophone, in order to play a concert A, you must play an F#; why isn't the F# on the alto saxophone just called and taught as an A?

At least from my perspective, the only reason why that note on the saxophone is called an F# is because that's how it is taught. However, if it was taught as an A, then the instrument wouldn't be in "Eb" - it would be in concert pitch, right?

Answer 1

There are two concepts and ideas that happen in music which, when combined, explain why this happens.

The first is that the way certain instruments are constructed affects what sounds they can produce. The E♭ alto saxophone, the B♭ clarinet, and the horn in F each can easily play in the key designated. Typically, when learning to play these instruments the scales and pieces you would play would be in the key of the instrument. Those instruments can be constructed in other keys and sometimes are, but the popular key that they are built in tends to best take advantage of the timbre and the range of that instrument.

The second is that we tend to center the basics of what an instrument can play around C. So combined with the fact that instruments are built with one key being easier to play in than the others, it's common to call the easiest key to play in "C" even though it may not actually be C.

This may seem confusing, but there is one big advantage to doing this which is that someone who can play an instrument in a transposing family like the saxophone can keep the fingering the same in the notation. Wikipedia sums it up nicely:

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.

Answer 2

Transposing instruments are so due to convention, not by a technical property. The main advantage is, that different instruments of the same family can share the same mapping of

(printed) note → fingering

and so makes it easier for the player to switch instruments. The fingering will be the same for the printed note, but a different sounding pitch will result.

The disadvantage is, that the sheet music has to be adapted to exactly the instrument used and therefore it has to be stated there. Playing an A clarinet voice on a Bb instrument without mental transposition makes a lasting impression...

Answer 3

The answer is about history and harmonic series, but it varies between Brass and Woodwind to some extent.

Historically, Brass instruments didn't have valves, but were tubes of fixed length, with additional loops of tubing call crooks that could be inserted. These would allow the player to play notes only in a particular harmonic series, which corresponds to a particular key.

By saying horn in F, you would tell the horn player to add a suitable crook such that they could play the harmonic series based on F. You could write horn in D and they would put in a slightly longer crook to play notes in that key. The key of the instrument was normally specified to match the key of the piece, or a particular passage. Sometimes extra players were added in a different key to fill in notes.

Music was transposed to match that harmonic series, so the player would always see C, E, G etc. in their music and know which harmonic was needed.

Eventually valves were invented and added, but the convention of writing in the key matching the harmonic series and musical key stuck because the players and composers writing at the time already understood this. As the length of tubing became more standardised around a particular harmonic series (F for horns, often but not always B flat for trumpets) these transpositions in scores also stuck.

Trombones have been chromatic instruments with slides for as long as they have been in orchestras and as such their parts have always just been written in concert pitch. They have been written in various clefs to make writing in their range convenient for the composer and player. Similarly, tubas were chromatic since their invention, so weren't transposed. Brass bands have sought to simplify learning many different instruments, so have brought the convention of fitting to the harmonic series, a common fingering pattern and treble clef to almost all instruments. This means that the player needs to only get used to a different embouchure or the difference between slides and valves when switching instruments.

In Woodwind, key systems are now quite advanced and allow the instrument to play well in all keys. However, this wasn't always the case, and so Clarinettists needed multiple instruments to achieve the best musical results (the instruments were fully chromatic, but I gather that some accidentals did not play quite as cleanly as others). The B flat and A Clarinet covered many keys well between them, though there are others. The overall tone between the instruments is reputed to be slightly different, though I think for the B flat and A Clarinet it is subtle. By using transposition, the fingering system for the two interchangeable instruments could be kept the same and just scaled very slightly. This starting point of keeping similar fingering systems for different sized instruments in the same family has become more useful as more instruments have joined the family. (There are many common variants of most woodwind instruments).

One difference between woodwind and brass is that woodwind instruments will often be longer that their designated key might suggest to allow extra low notes. This is because the position of the holes, which are often left open, influences the pitch more than the overall tubing length.

Answer 4

Abother reason why instruments have a key: some (mainly folk/ethnic) instruments are limited to diatonic scales and can only play in one key, with several versions of the instrument for different (concert) keys.

For example: bagpipes.