Sharps and Flats

Thursday, October 11, 2007

We now know that notes are identified for convenience by a letter name, and that the distance from one to the other may be a tone or a half tone. Why the difference? The reason is that Western music is traditionally built on certain successions of notes known as scales, the most common of which is the major scale.

Starting on the note C this is how it looks:

In the diagram, W stands for a whole-tone interval and H for a half-tone interval.
As an example, the first phrase of the tune “Bluebells of Scotland” uses all the notes of the C-major scale.

Everything works fine using the scale of C, but what happens if we want to write the tune higher or lower to make it fit our voice range? If we just shift it up the staff it won’t sound right. Play it to see why:

The tune sounds different because the intervals have changed. To keep the same tune we want the interval from the second note to the third to be a half tone, as it was before. To do this we must raise the F by a half step, which we can do by inserting a sharp sign (#).

Because we raised the pitch to use the notes of the G scale, we are now using the key of G. We find that for the tune to come out right we must raise all the Fs to F-sharp. Instead of doing this to every F individually, there is a shorthand way to do it. The sharp sign # is placed at the beginning of the line on the F, showing that all Fs must be played sharp, like this:

An indication like this at the beginning of a line is known as a key signature because it helps identify the scale of notes used. It affects not only the note you see, but also those in other octaves:

All the Fs shown would be played sharp because of the key signature.
Finally let us change the key to use the notes of the F scale. Transferring to new keys is known as transposing.

Something sounds wrong here. Can you spot what it is by playing it through? One of the notes is wrong for the tune, and in this case it needs to be lowered rather than raised a half tone.

It is in fact the B three notes from the end, and it is a half tone too high. We can lower it by putting a flat sign beside it, like this:

We can also learn from this that in the key of F all Bs are played flat, and that the key signature looks like this:

Key of F

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