Music is written in measures. Each measure has a pre-defined number of beats. Remember when you walk during the Tango class and your teacher annoys you to death shouting: ''beat!, beat!, beat!, beat!...' - yes, those.
- The top number of the time signature tells you how many beats to count. This could be any number. Most often the number of beats will fall between 2 and 12.
- The bottom number tells you what kind of note to count. That is, whether to count the beats as quarter notes, eighth notes, or sixteenth notes. So the only numbers you will see as the bottom number (the denominator) will correspond to note values:
You could continue on with 32, 64, but you will hopefully never encounter them! After a while it gets a bit unwieldy. The most common bottom numbers are 4, 8 and 16.
There also exist a way to indicate the silence in music. That silence indicated by note rests also has value. Exactly like notes do.
Tango is in most cases 2/4 which means there are two beats (2). Each beat is a quarter note (4).
The fact that each beat has a value of quarter note DOES NOT mean you are limited only to quarter notes. Beats may contain half notes, quarter notes, eighth notes, rests, whatever the composer wants, but all note and rest values must combine to equal no more or less than the top number (or numerator) of the time signature.
1 Whole note = 2 Half notes = 4 Quarter notes = 8 eighth notes = 16 sixteenth notes
1 Whole note = 2 Half notes
1 Half note = 2 Quarter notes
1 Quarter note = 2 eighth notes
1 eighth note = 2 sixteenth notes
There is also a way to extend the existence of note by half by using a dot....
Now - why is this important for dancers?
In a way - it's not. You can go to Argentina without speaking Spanish and survive. I did. But there is a huge difference between simply surviving and actual participation.
In music - most people intuitively hear. Knowing the structure though helps you verbally express what you hear and understand what the music tells you. It helps you advance in interpreting the music with understanding. Also - now - you can discuss it.