Time signatures define the meter of the music. Music is “marked off” in uniform sections called bars or measures, and time signatures establish the number of beats in each. This is not necessarily intended to indicate which beats are emphasized, however. A time signature that conveys information about the way the piece actually sounds is thus chosen. Time signatures tend to suggest, but only suggests prevailing groupings of beats or pulses.
– Alla Breve or Cut time
– Common time
This symbol is a throwback to fourteenth century rhythmic notation, when it represented 2/4, or “imperfect time”. Today it represents 4/4. Also referred to as simple common time as in below:
– Simple time signatures
The bottom number represents the note value of the basic pulse of the music (in this case, the 4 represents the crotchet or quarter note). The top number indicates how many of these note values appear in each measure. This example announces that each measure is the equivalent length of three crotchets (quarter notes). You would pronounce this as “Two-Four Time”, “Three-Four Time”, “Four-Four Time”, and is referred to as a “perfect” time.
– Compound time signatures
The bottom number represents the note value of the subdivisions of the basic pulse of the music (in this case, the 8 represents the quaver or eighth note). The top number indicates how many of these subdivisions appear in each measure. To derive the unit of the basic pulse in compound meters, double this value and add a dot, and divide the top number by 3 to determine how many of the pulses that appear in each measure. This example announces that each measure is the equivalent length of two dotted crotchets (dotted quarter notes). You would pronounce this as “Six Eight Time.”
– Metronome mark
Written at the start of a score, and at any significant change of tempo, this symbol precisely defines the tempo of the music by assigning absolute durations to all note values within the score. In this particular example, the performer is told that 120 crotchets, or quarter notes, fit into one minute of time. Many publishers precede the marking with letters “M.M.”, referring to Maelzel’s Metronome.