Music is based on reoccurring groups of pulses. These groups usually consist of three or four pulses.
The time signature tells us how many pulses or beats are in the basic pattern and which note value represents one beat.
The denominator in a time signature tells us which note value represents one pulse.
The numerator in a time signature tells us how many pulses per pattern.
Rhythmic Notation indicates when to sound a note and when to remain silent. Silence is indicated by "rests" found on the left side of the graph, and sound by the "notes" on the right.
Using a system of note/rest durations, musical rhythm is written in "Bars". A "Bar" refers to a recurring amount of pulses such as 3 or 4.
Bar-lines separate the reoccurring groups. Within the bar-lines, all beat must be accounted for whether sounded or silent.
A composer may combine or divide beats by using different combinations of note/rest durations; however each bar must represent the exact amount of pulses indicated with the time signature and may not contain more or less.
3/4 must have exactly three beats in every bar; 4/4 must have four.
The note durations are related by ratio based on 4/4 time. Regardless of the time signature, a whole note will always represent 4 pulses, a half note 2 et cetera.
whole bar 1:1
half bar 1:2
quarter bar 1:4
eighth bar 1:8
sixteenth bar 1:16
The tempo or speed of the music determines how many pusles per minute.
The time signature assigns how many pulses per group, and which note duration represents one pulse.
The most common used music metres are 3/4 and 4/4.
3/4, 6/8, 9/8
one 2 3 | one 2 3 | one 2 ...
Notice the difference in "feel" or the accent between groups of 3 (3/4) and groups of 4 (4/4)
2/4, 4/4, 6/8, 12/8
one 2 3 4 | one 2 3 4 | one ...
America The Beautiful
Pulses per minute
60 = quarter note
This means that in one minute, there will be 60 pulses, and the quarter note duration represents one pulse.
The speed of the music is not determined by the note duration.
A melody written in whole notes can be the same speed as the same melody written in sixteenth notes.
60 = Sixteenth note
60 = Whole note
Music speed only and solely depends of the tempo which may be set to any note duration.
A triplet is to play three notes in the space two.
The change in feeling between two notes and three notes is equivalent to using squares versus triangles and it has a pronounced impact on the human ear.
Consider 6/8 and 9/8 time signature.
In 6/8, there are three main pulses with two subpulses (2x3 = 6 total pulses)
In 9/8 time, there are three main pulses with three subpulses (3x3 = 9 total pulses).
If the pulses were set to the same tempo; then 6/8 would have two subpulses per beat, and 9/8 would have three subpulses per beat.
With your left hand snap once per second. This is tempo=60.
With your right hand, snap twice for every snap with your left hand.
Your right hand is tempo=120 (2x60)
Now snap thrice (three times) for every snap with your left hand.
Your right hand is tempo=180 (3x60)
Notice the difference between duple (two) and Triple (three).