Music Theory


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Music Theory - Beat Unit


In the time signature, the bottom number tells us which note is the beat unit, or which note gets one beat. This number represents the duration of notes, which dictates the rhythm of the music. Notes without a beat unit are just indications of pitch, but cannot be played as intended, or in any consistency of form. For instance, a quarter note has no set duration without the bottom number of the time signature. Therefore, an eighth note, whole note, half note, etc. have no duration either, unless the beat unit is indicated. Surprisingly some composers have written music with no time signature, calling it free time. It is very difficult to dance to. 

Beat Units1The time signature is one of the easier parts of music to understand. The most frequently used time signature today is 4/4 time, which is the basis of modern rock, blues, country, and pop music. This is also called common time, and is sometimes notated by a C where the time signature normally sits. Simply put, a 4/4 time signature means that there are four beats per measure, and the quarter note gets one beat. 

The bottom number sets the beat unit. A two on the bottom means the beat unit is a half note, and an eight on the bottom points to the eighth note. The beat unit can be changed at any time by a new time signature after a measure line. 

Beat Units2Another frequently used time signature is 2/2. This is also referred to as cut time, and is common in marches, fast tempo orchestral pieces, and musical theater. It can also be represented by a C with a vertical line through it. In the case of 2/2 time, the bottom number means that the half note is the beat unit, getting one beat. 

The bottom number in the time signature also affects rests in the same way. If a half note is the beat unit, getting one beat, then the half rest is also held for one beat. If the timing indicates that a quarter note is the beat unit, then the quarter rest is held for one beat.


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