Musical writing is a union of symbols between notes and rests that are inserted in a bar: the time values must coincide with the value required by the indication of time in key. The unit of measurement that makes reference to the notes is the metric speed of the song (or metric time), that can be articulated by the metronome: depending on the setting of the metronome for the song, the musical events will occur with more or less speed. The stave (also called musical line) is divided into bars (or measures) with vertical line boundaries. After the clef, is the Time Signature, which is a fractional number that serves to give some information regarding the metric course in which the song is based. The upper number indicated the number of metronome movements there are in each measure, while the lower number indicates the value of each movement.
Lets use an example to better understand the concepts just seen. In a line with a time signature of 4/4 we individualize the movements of the metronome, that are shown using a series of dots.
We can define each dot as a beat (which is the ‘’tack’’) of the metronome. Every beat is called a movement and, as explained before, will have a rhythmic value. How do you find this value? The top number tells you how many beats there are per movement, and therefore to find the rhythmic value of each movement you take the signature time (4/4) divided by the number of movements (4), which gives us 1/4, or one quarter note. We will now number the four movements and play one quarter note, that will coincide with the succession of the movements.
This is the most classic form of signature time. Basically we can obtain two indications of signature time: 2/4 and 3/4. The first form (2/4) even measures, the second (3/4) odd measures. These can be multiplied in other measures: even (2/4, 4/4, 6/4) and odd (3/4, 6/4, 9/4). You can also get composed measures, by adding the even with the odd values (ie. 5/4 obtained from 2/4 + 3/4). Times using the octaves are very common (typical 12/8 in the blues), but less common are with the sixteenth (for instance 7/16). Sometimes 4/4 is substituted with a C; when this has a slash, the time value for the notes are cut in half. Below are some examples.
At this point it is necessary to learn to recognize the relationship between the time values, that are seen in the following graph. You can see that the relationship between one time value and the next is exactly double. In one 4/4 note we find two 2/4; in one 2/4 note, we find two quarter notes, etc. It's clear that in a whole note we find two half notes or four quarter notes, eight octaves, etc.
The dot placed after a note will increase its value by half of the original. For instance, a quarter note with a dot next to it is played as a quarter note plus its half (an eighth note), for a total of a quarter and a half. Here are some examples.
If we look at the first bar, we have a quarter note with a dot (that lasts a quarter and a half) and an eighth note, for a total of two movements. If we divide these first two movements by an eighth note, we get four eighth notes: the quarter note with the dot therefore has a value of 3 eighth notes. Also the rests can use the dot following these rules.
Up to now we have seen regular rhythmic figures that can practically always be divided in two. The irregular rhythms are instead composed of an odd number of notes or when divided by two give an odd number. The most common are the triplet, the quintet and the septet. These irregular groups of notes are usually labelled with a number above those notes. Here are some examples.
Remember that in one beat the sum of the values is the total of the longest sound available in that bar. It's therefore possible to insert various rhythmic combinations in a bar (between notes and rests), using the rule that the sum of the values in the bar must coincide with the total in key.
