Latin Poetry's use of short - long syllable patterns was inherited by medieval musicians singing Latin liturgy and forms the basis of classical music's rhythmic vocabulary.
These rhythms are used as tools of the composer to convey meaning through sound.
Just as prosody has a set number of poetic feet per line, so music sets a finite number of beats per bar.
Three beats per bar is equivalent to trimeter, and four beats to tetrameter.
Groups of three or four are the most common, although other permutations are possible and used.
Once a pattern of pulses or beats is established, we expect the same pattern to continue until otherwise notated.
Each iteration of the pattern is contained in one bar and separated by bar-lines.
If the pattern is based on 4, then each bar has four beats and after the forth beat a bar-line shows the completion of the iteration and beginning of the next.
the duration of notes
Notes are presented as a visual system of rations. A half note being 1:2 of a whole note, and a quarter note being 1:4 of a whole note, and so forth.
The speed however is purely dependent upon the tempo, not the note duration used.
Just because something is written in whole note does not make it fast, and just because something is written in sixteenth notes does not make it slow.
semibreve = Whole
minum = Half
semiminum = Quarter
fusa = Eighth
semifusa = Sixteenth
The denominator in a time signature tells us which note duration represents the pulse.
A quarter note is a note duration. When the bottom number or denominator of the time signature is 4, then a quarter note will represent one beat. For each beat of time, one quarter note's worth of music is played.
If the number is 2, then a half note will represent the beat; if 8, then an eighth note.
The chart demonstrates each of the note durations representing the pulse, and there being only one pulse per bar.
1/1 = whole
1/2 = half
1/4 = quarter
1/8 = eighth
1/16 = sixteenth
The numerator of a time signature tells how many pulses or beats per bar.
If the top number or numerator is 4, then the pattern is 4. The fifth beat marks the pattern repeating.
Barlines are used to mark each pattern. If the time signature is 4/4, then after 4 beats of music a barline intersects the staff. All the beats in a bar must be accounted for, if there are no notes being played, a rest is written.
While most music is written with numerators of 2, 3, 4, 6, 9 and 12, others such as 5, and 7 are sometimes used.
Any number is technically possible, but longer numbers are divided into smaller groups of 3 or 4. Such as 12/8 which is often felt as 4 patterns of 3 notes (4x3=12), instead of 12 independent pulses.