Music Theory

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Music Theory - Key Signature

    

 

Key signatures started with an understanding of which notes sound good together, either as chords or individual progression. Different notes played together make different kinds of melody. For instance, most sad songs are in a minor key. The same goes for the major keys. If you mix some major notes together, it sounds more hopeful, upbeat, or happy. 

Although not aways the practice, most songs follow a pattern of returning to one tone frequently. Some composers always end their songs on this key note. This note affects the tone of the entire song and keeps the melody consistent, rather than sounding like a bunch of random sounds played by a child on a piano. With that note comes the key signature, which is made up of other notes that sound pleasing with that key note. 

The key signature can be identified by the accidental symbols at the beginning of the measure. These show which notes should be played as sharp, which notes are played as flat, and which are natural. Placing the accidentals at the beginning eliminates the need to notate them throughout the music, making it difficult to read with little flat, natural, and sharp symbols everywhere. In addition, one just needs to look at the time signature to immediately know in which key the piece is played. 

Key signatures use the rules of the 12 major and 12 minor scales. But because there are three keys that each have two names, there are 15 key signatures. The keys of B and C-flat use the same tones, and therefore have the same sound. This also applies to the keys of D-flat and C-Sharp, and G-flat and F-sharp. 

Key signatures1All this sounds complicated, so how do we know which notes are which? By using The Circle of Fifths, which is a logical map of how each key is correctly played. Reading clockwise around the circle, each note is a perfect fifth apart. A perfect fifth is comprised of three tones and one semi-tone. If you start at the top of the Circle of Fifths, you will see a C major. On a keyboard, count up three tones and one semitone, and you get the G, which is next on the circle. 

As you progress around the circle going clockwise, you will see that each perfect fifth adds another sharp to the key. For instance, the G, being the first fifth after the top C, adds one sharp on the G line. The next note, a D, is a perfect fifth after G and it adds another sharp on the D line, totaling two sharps. Ascend by another fifth and you get the A, which adds a third sharp on the A line. Alternatively, if you go counterclockwise around the circle, you will see that the intervals are perfect fourths, which is five semitones.

The key at the very bottom can be written as a F-sharp or a G-flat, and can use either flats or sharps to achieve the same sound. At that point, going back up the left side of the circle you will see that the keys use flats only and will decrease the number of flats used until it starts again clean at the C. The bottom three keys in the circle can all be played with sharps or flats, and these are the reason there are 15 keys, rather than 12 like the scales.

Key signatures2

 

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