How is it possible that a 4/4 signature corresponds to a 12/8 signature ? 4/4 is equal to 1 and 12/8 is more than 1 .
If i try to divide a 1/4 in 3 notes i get 1/12, not 1/8 as the 12/8 should be.
The time signature does not function as a fraction in mathematics. The top number serves to tell how many beats per measure, while the bottom number tells what rhythm gets counted as one beat. In 4/4, for instance, the top 4 states that there are four beats per measure, whereas the bottom 4 states that one quarter note equals one beat. Therefore, with 4/4, you'll feel a definite "one two three four, one two three four" throughout the song.
In 12/8, you'll have 12 eighth notes per measure. However, rather than feeling "1 2 3 4 5 6 7 8 9 10 11 12," you'll normally feel the eighth notes in groups of three -- "1 2 3 4 5 6 7 8 9 10 11 12". Or, to simplify, "one and a two and a three and a four and a".
This is called subdivision of the beat, this grouping of eighth notes into groups of either two or three. In 4/8, for instance, you'll feel eighth notes in groups of two (1 2 3 4), whereas in 6/8, 9/8, or 12/8, you'll feel the eighth notes grouped into groups of three.
Hope this helps!
They are related in the sense that they are both quadruple time, meaning in both instances there are four beats to a bar. 4/4 time is just Simple Quadruple time where a beat is equal to a crotchet and 12/8 is Compound Quadruple time where there are four beats of dotted crotchets.
In essence, simple time means beats without dots and compound time means beats with dots. They are both four-time the one just having regular crotchet beats and the other dotted crotchet beats.
4/4 is four quarter notes to the bar. 12/8 is four dotted quarters to the bar. Useful for music where the sub-divisions of each beat are mostly into three. Saves you writing a load of triplets (those groups of three 8th notes with a 3 bracket over the top, indicating that the three are to fit into the space normally taken by two of them).
Simple time. One-and-Two-and-Three-and-Four-and. 4/4. Or One-and-Two-and One-and-Two-and. 2/4. (Etc. That's not an exclusive list of Simple time signatures.)
Compound time. One-and-a-Two-and-a-Three-and-a-Four-and-a/ 12/8. Or One-and-a-Two-and-a One-and-a-Two-and-a. 6/8. Etc.
Whilst the time signature looks like a mathematical fraction, in a way it is, but there again, it isn't !
The top number, just like a fraction, tells how many there are, the bottom tells what they are. So, in 4/4, there are 4 of them (top), and the bottom tells they are crotchets, aka quarter beat note value, in each bar or measure. So far so good. Just like a fraction.
When we get to a time signature like 6/8, there are 6 quavers (eighth notes) in each bar. The confusing part here is that they are arranged in two lots of three. So the count is either 1--2-- or put in another way, 123456. Still with this 'fraction' - 3/4 time has the same number of 'bits' in each bar, but they get emphasised differently. 123, as there are 3 crotchets to count.
Now on to 12/8. It's pretty well double 6/8 (surprise!), but counted 1--2--3--4-- in each bar. But - those quavers can be seen in a timing manner that 3 get played in the time of two in 4/4 time sig. So, in 4/4, using normal eighth notes, there will be 8, counted 1&2&3&4& in each bar, but the equivalent timing at the same tempo for 12/8 will be 1&a2&a3&a4&a. So both can be equal in timing (bpm) but their time sigs won't be equal mathematically. It ain't easy!