- A key signature is the set of
sharps or flats
that is written at the beginning of a piece of music to indicate the
key of the piece.
- The key signature may be "null" (no sharps or flats), or it can be from one to seven flats, or from one to seven sharps; it cannot be a mixture of sharps and flats.
- The key signature is always written immediately after the clef but before the time signature.
- Here are the most complicated examples. Any possible key signature will be a "subset" of one of these examples, with some of the sharps or flats removed from the right. So any key signature you see will have the sharps or flats in this order and in these positions on the stave:
- The key signature says which notes are always altered, and therefore exactly which
notes make up the scale of the key
of the piece.
- The key signature is really a short-hand method to save writing lots of
accidentals (sharps or flats) throughout a piece.
- However, there are scope differences between an accidental
and the change to a note specified in a key signature:
- An accidental only applies to the note it specifies, at that octave, for that
bar or measure.
- A change to a note in a key signature applies to every occurence of that note on
the stave, at any octave, until the end of the piece, or the key signature is changed.
In this example, the key signature is one sharp.
The sharp is on the F line, so all Fs played in this piece should be sharpened
(although there aren't any Fs in this very short piece!).
In this example, the note G above the number 1 is sharp, because the key signature specifies that all Gs are sharp (although it is specified at the octave above).
The note C above the number 2 is also sharp, because the key signature says all Cs are sharp.
The note D above the number 3 is specified as sharp in the key signature, but the accidental overrides it, making it a D natural.
The note C above the number 4 is a C natural for the same reasons.
The note D above the number 5 is a D sharp, because the key signature specifies all Ds to be sharp, and the previous D natural only applied for that one bar or measure.
- A key signature can also appear at other places in a piece of music
where the key of the music changes.
- When the key of a piece of music changes (that is, a real change to that
new key for a period of time, not just a
few notes or part of a modulation), a new key signature is written.
- In old scores, the old key signature is always cancelled before
the new one is written.
- This is normally done at the end of a line, after a single
barline, so that the new line starts with the new key signature.
- Nowadays, this is unusual, the new key signature is just written
after a double barline.
- However, there are cases when a cancellation is still normally
- When changing from a major key to the minor key of the
same key note, or vice versa
- When changing to a key with no sharps or flats (i.e.
C major or A minor
- There are only a limited number of keys that a piece can be in,
therefore there are a limited number of key signatures. There
is a great deal of pattern about the relationships between
keys, the pattern of sharps or flats that they have, and the way
that they are written on the stave in a key signature.
- The order (left to right) in which the sharps or flats are written is
governed by their "commonness".
- This key signature indicates the key, which gives a piece
its feeling of "home". In both examples above, the pieces start and finish on the key note.
- The number of
sharps or flats indicates that the
key is one of two possibilities: a major or its
- Keys signatures with a small number of sharps and flats tend to be the most
common. There are several reasons for this:
- it is easier to play a piece with a small number of sharps or
flats (this is true on most instruments, and certainly keyboard instruments)
- it may be easier for some composers to think in a very familiar key
- the tuning of some instruments means that simple keys are more
in tune than keys with many sharps or flats
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