Basic Rhythm & Its Notation

Rhythm is represented in written music by notes of varying shapes. The notes specify time values, relative durations for which the notes are held, or sustained.

time value	semibreve	minim	crotchet	quaver	semiquaver
note

Although it is possible for any note to represent a single beat, in the early stages of learning to read music a single beat is usually represented by a crotchet (also known as a quarter-note in North America). The American terminology makes the relative values of the notes very clear - 16 sixteenth notes will take up the same amount of time as a whole note, as will 8 eighth notes, or 4 quarter notes, or two half notes. A note typically has a note-head and a stem, and may also have one or more flags (also called tails). [In the chart above, a semibreve has a note-head but no stem or flag; a quaver has one flag and a semiquaver has two.]

Beats
The vast majority of music has some sort of pulse, or beat, that you can clap or tap your foot to. Usually you can hear that some of the pulses are stronger than others; we say that these stronger pulses are accented. The number of pulses from one accent to the next divides the music into bars, or measures. If the accent comes every two beats, like in a march, then the music is in 'two time' - one two one two. If the accent comes every three beats, as in a waltz, then the music is in 'three time' - one two three one two three.

Bars & Barlines
The grouping of regular accents and the notes between them into bars is shown by placing a bar-line before each accent. That is, the first note after every bar-line is always the first beat of the bar, and is therefore accented. (Composers sometimes break this rule in order to create a special rhythmic effect called syncopation.)

Time Signatures
Written at the start of a piece of music, the 'time signature' looks much like a fraction. The top number (numerator) tells us how many beats are in each bar - that is, whether the piece is in 'two' or 'three' time (or 'four', etc.); and the bottom number (denominator) tells us the type (duration) of note that gets one beat. As mentioned above, in the early stages of learning to read a crotchet will represent one beat and the denominator for this is 4.

Common time is a frequent alias for ⁴/₄

Split common time is a frequent alias for ²/₂

Simple vs. Compound Time
In a simple time signature each beat may be divided evenly by two. For example, in a bar of 2 crotchets each crotchet may be divided into two quavers. Hence ²/₄ is simple duple time.

In a compound time signature each beat is a dotted note, and may be evenly divided by three. For example, in a bar of two dotted crotchets each dotted crotchet may be divided into three quavers. Hence ⁶/₈ is compound duple time.

Irregular times are unusual; these may have any number of either simple or dotted beats per bar.