Now we know how to use a flat to lower the pitch, or a sharp to raise the pitch, within a measure. But what if we want a certain flat or sharp to always appear in the piece? It’s a lot of work to write it in each measure, and that would look cluttered if it is really the “default” to have the flat or sharp.
Key signatures take care of this problem! By using a key signature, the music tells us that some notes are flat or sharp every time we see them (unless changed by another accidental).
The key signature appears at the beginning of each line of music, right after the treble clef. If a time signature appears on the line, then the time signature appears after the key signature, as shown in the picture.
A key signature consists of one or more flats, or one or more sharps that are written on the line or space that they impact throughout the piece.
A key signature:
- May include flats or sharps (but not both)
- May include 0-7 flats, or 0-7 sharps
- Appears “empty” if the key signature has no flats and no sharps (nothing appears at the beginning of the line in the key signature position)
- Remains in effect until a different key signature appears (called a key change), or until the end of the piece
- Applies to every octave, not just the octave where the key signature is written (note that this behavior is different from an accidental, which only applies to the octave where it is written).
How It Works
In the example below, there are two flats in the key signature – Bb and Eb. This means that the two B quarter notes in the first measure and the B whole note in the last measure are played as Bb, and the E half note in the second measure is played as Eb, even though flats do not appear beside those notes. The flats in the key signature impact all notes in this piece.
Here is another example, this time with a key signature that has 3 sharps. Each time a C appears in the song it is played as C# because of the key signature.
Notice in this example that the F# and G# in the key signature do not seem to be used because we do not have any F or G notes in the piece. We will learn why those sharps are there as we learn about the concept of key.