Key signature


Audio: key signature (0:08)

Key signature
Figure: key signature

key signature plays a melody twice on a flute using four different keys. The key signature figure shows the score:

  • Bar 1 is in the key of C major.
  • Bar 2 is in the key of G mixolydian.
  • Bar 3 repeats bar 1 in the key of C minor with a key signature of 3 flats.
  • Bar 4 repeats bar 2 in the key of G phrygian which also has a key signature of 3 flats.

A key signature is a set of accidentals (sharp or flat symbols) in a score that provides information about key.

There are 12 key signatures in 12TET, one for each note.

A key signature provides some information about key. It provides enough information to distinguish between similar modes for instance. The key signature for the first two bars of key contains no sharps or flats. This is the key signature for the C major. It determines the key as C major and not, say, G major. However, it does not enable you to decide the mode. The key could be C major, as in the first bar, or G mixolydian, as in the second bar.

A common way to signal the key of a piece of music is to make the first note the tonic note of the chosen key. This is done in key. It is a useful technique for writing music. It is not foolproof, however, you may prefer to start a piece of music on a note other than the tonic.

The only unambiguous way to signal the key is to either write it in the score or write it in the title of the piece. A title such as Heavy Rock Music In The Key Of Eb Phrygian will suffice.

You have a free hand to decide which key to write in. C major is a particular favourite and it is the simplest key signature of all. Much of the music in the guide is in the key of C. The same key signature can be used to write in the six modes related to C major: A natural minor, B locrian, D dorian, E phrygian, F lydian and G mixolydian. Many computer programmes also use C major as the default key and the added advantage of a computer is that you can write in one key then change to another key in a matter of seconds.

Live performance constrains the choice of key. Singers prefer certain keys to others because they find them easier to sing. Some musical instruments are easier to play in one key than in others. The key of C is easy to play on the piano but more difficult on the guitar because it requires a barre chord which is difficult to finger. The keys of G, D and A are easier to play on a guitar and do not require a barre chord.