Key signatures are one of those things in sheet music that many people have difficulty understanding. But really key signatures are very simple to understand, you just have to know a few tricks. But this begs a question first, what exactly is a key signature for?
The Purpose of Key Signatures
Key signatures, as you may have guessed, are used to indicate the key of a piece. When you are playing a piece of music, not just any note will do. Generally speaking, the piece will be in a particular key. I this key there will be eight notes that make up a scale. It is generally these eight notes (and their counterparts in the other octaves) that make up your song. The songwriter may throw in other notes that are not one of those 8 notes (called accidentals) but, in general, those are the notes you will find.
Reading Key Signatures
Now, the key the major scale is made up of all white keys is the key of C. In this key, no black keys would be played at all, unless they where accidentals. For this key, there would be no sharps and no flats in the key signature, because, as I have said, there are no black keys to play.
Now, when you add a sharp, it indicates that you need to always play a sharp on a certain note, instead of the normal white key. The way you know which is which is very simple (although, if you have no experience reading music, I suggest you go check out Reading Sheet Music 101. Just look at where the sharps or flats are in the staff. In the key signature above, the sharps are in the F, G, and C space. This means that, when ever you see an F, G or C (no matter what octave) you should play a sharped note instead, unless you should see a natural sign.
But How do I Tell What Key it is in?
Now this is the point that most people get confused. Because how exactly do you tell what the key is.
Well, I hate to break it to you, but the best way to do it is just to memorize. That way you can look at one and just know right of the bat. But obviously we cant to that instantly. There is a way to do it.
Now, just so you know, for any key signature there are two possible keys a major, and a minor. The major is fairly easy to find. For sharps, look at the very last sharp in the key, and just move up a half step. So, for the example above, the very last sharp is a G sharp, if you move up a half a space you will get A (which is the key).
For flats, all you do is look at the second to last flat in the key, and that is your name. If you only have one flat the key is F. Note, whenever you have more then one flat, you will get a key that has a flat in its name.
I sure hope this helped you further your understanding of key signatures. If you have any questions, feel free to leave a comment.