Every song has a particular beat, which is the basic time unit of music. But then there is also the pulse, more technically called tactus. And the pulse has something to do with the beat. The pulse actually is the beat, well sort of, it is a pattern of repeating beats. A repeating sequence of beats, each of the same duration. Usually the beats, that you would clap out while listening to a song. Say you’re listening to Power (Kanye West) and while doing so, you suddenly feel the urge to tap your feet, clap your hands, shake your head, you name it. If this is the case, you are likely to be tapping out beats with a, say, fairly regular interval, probably even synchronously with the hand-clapping in the song. And this underlying beatpattern is what musicians would call the pulse of the song.
This pulse is typically what listeners entrain to as they tap their foot or dance along with a piece of music (Handel, 1989), and is also colloquially termed the ‘beat,’ or more technically the ‘tactus’ (Lerdahl & Jackendoff, 1983).
Let’s look at this a bit more technical. It might be obvious that not every song has the same pulse. In one song you might be tapping your feet very fast and often, while in another you don’t even notice that you are actually tapping out a pulse. If you don’t know what I mean, watch Kanye West followed by The Gotan Project Amore Portena and try to clap along with both. See what I mean? So, how does this actually work?
First, how often you tap your feet to a song depends on its pulse rate, which musicians call tempo. And the tempo is indicated with BPM (Beats Per Minute). Imagine that we are still tapping our feet to Power, and we happen to know that this means we are tapping out beats with a rate of 154 BPM. This number tells us that in one minute Kanye makes us tap our feet 154 times exactly. Well, if it is that you actually tap out the pulse, and not only the first or some of the beats of a particular time sequence. Because that is what musicians would call the meter. The meter tells you how often you emphasize one of the beats in a particular sequence.
But wait, before we continue, let’s first explain how it is, that we can, in fact, know which beat is the first in a particular sequence. Which, subsequently, also means that we need to say a bit more about sequences. However, up to now we only learned, that in one minute we are tapping our feet 154 times. Then, how do we know, how many of such beats are being played per sequence? And how can we locate the particular beats in every repeating sequence?
Well, a more technical term for a sequence is bar. And the division of a music composition in bars is actually…a trick of our mind. An illusion. Well not really, but in a way, for the listener, it is. Our mind likes patterns. Our brains are constantly looking for patterns in its environment, in order to make sense of all the information we have to process every single day. And generally for most brains it’s just impossible to store every single bit of information separately. Which is why it needs to categorize and group things together. And the same it does when listening to music. Whenever the brain discerns some sense of structure or pattern, say Clap clap clap clap, Clap clap clap clap,…(where the capitalized ‘clap’ is emphasized) it likes to organize and store it in this way. The meter helps us to group beats in smaller sequences. Now, the meter and the pulse can help us to give us some sense of ‘location’, of knowing where we are in a song. But to know where one bar stops and the other begins we need more information. This information has something to do with the division of time of a song. It’s the time signature.
The time signature tells us two things. It gives us a number which indicates how many beats are grouped in one bar and it gives us another number. This last number tells us something about the length of the beats.
Say that Kanye mixed Power with a time signature of 4/4, then the upper number tells us that we need to tap our feet exactly 4 times to finish one bar. The lower number defines the length or duration of one such a beat. We already know that 1 beat has a duration of 154 BPM, but we don’t know yet, what this means if a note is played longer or shorter than 154 BPM. Is this note going to be a eighth note, or a sixteenth, or even a quarter? Now this is what the lower number can tell you. The lower number will usually be a 4,8,16 or other and this means that one beat of this specific length is either a quarter note, a eight note, a sixteenth etc. So now we know two more things, namely first that all beats in ‘Power’ have a duration of 154 BPM and that these beats are defined as quarter notes, and second that one bar contains 4 beats. Great!
By the way, given this tempo, we can now also infer that the greater the tempo, the more beats must be played and therefore the faster the whole piece is going to be. However, tempo is not a an infinite measure as one might assume, at least not for human perception, from 600 BMP onwards the tempo becomes a so called drone. If the tempo is a drone, the individual beats can’t be distinguished any longer and will be perceived as one.
We can now tap along with the beats of Power and we know how to stress some of the beats, we even know something about the time and the length of the beats and bars. But that’s not all. Imagine a song in which all notes would be played exactly on the beats of the pulse. That would be rather dull, very dull. I guess it would sound like the first robots trying to speak like a human, generally very monotonic, without much, say, rhythm. Every word pronounced with the same length, sounds rather odd. So the same holds for music. You really wouldn’t want to listen to a completely monotonic song. Generally what makes a song so good and intriguing is in particular the asymmetry. Some notes that fall off the beat, others that are sustained over the beat, or that crowd the gaps between the beats. And this is, apart from the meter, what avoids monotony and this is what can be called the actual rhythm.
Let’s elaborate this picture a bit more. The picture above shows the first 4 bars of the piece (listen to the excerpt above here: Kanye West “Power”). What we can immediately see is that hand clapping follows precisely every beat of the beatline, clap clap clap clap, clap clap clap clap….This is the pulse of the song. We can also see that every bar has exactly 4 of those (quarter) beats. So far, so good. But there is another line, which does not precisely follow the beats of the beatline. It rather shows a combination of long and short notes. The line, that I am talking about, is the line where the singing, the ohh eehh ohhhoo, and the notes written on top of those words occur.
Now, if I were to ask somebody, that has no training in music, to tap the first beats of this song, this person could do something like:
ohoh clap clap clap eeh heee, ohoh clap clap clap ehhhh heee,…(something like 1-and-2-3-4,1–2–,1-and-2-3-4,1–2–,..)
But if I ask a musician to do the same, the answer will rather be:
clap clap clap clap, clap clap clap clap,… (that is, with a regular 1-2-3-4, 1-2-3-4,.. pulse).
Why? Because for the musician the singing or rapping represent a pattern which is typically different from the regular pulse. The pulse is the regular repetition of beats underlying the song. The rhythm on the other hand is the asymmetrical sequence of notes. It is the storyline that actually gives the song it’s real character…