Time signatures are the numbers that are placed just after the clef symbol at the beginning of a piece of music.
The time signature tells us the exact length of each measure in a piece of music. On a deeper level it defines the meter, or the basic rhythmic pattern of the music.
The time signature consists of two numbers. These two numbers together will tell us the length of the measure.
The top number acts as the multiplier. It is the number that we will multiply the bottom rhythmic value by.
The bottom number is like the bottom number of a fraction. It defines a particular rhythmic value. In the example of 4/4 the bottom number can be thought of as begin 1 divided by that bottom number.
1 divided by 4 or 1/4 equals one quarter, a quarter note. So the time signature of 4/4 means 4 times a quarter note, or 4 quarter notes, which add up to 4 beats.
The length of a measure will be the top number times the length of the rhythmic value represented by the bottom number.
Finally, there are two special time signatures. 2/2 is often called cut time and can be replaces by the symbol of a letter C with a line through it like ¢. And 4/4 is often called common time and can be replaced with the symbol C.
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