This is, by the way, one of the ways that popular music has wandered down a path towards being less interesting musically than it used to be: too much importance placed on the visual element. Try a little experiment: the next five popular songs you listen to, don't watch the video. I think you will see what I mean.
But back to music as a time art. This is true on every level. Take a single musical note:
article on acoustics is a good introduction. But this inherent quality of music: vibrations in time, is one that exists on all levels. All the different pitches are just different frequencies of vibration. But on a different scale, all rhythm is also just different frequencies of vibration. For example, that note above, in 4/4 meter, is held for four beats which are measured according to how many beats there are per minute. This is the often seen Metronome Marking such as quarter note equal to 60 beats per minute. This is the basic pulse of a piece and it is simply a slow vibration rather than a fast one. Rhythms are just subdivisions of the pulse. So melody (composed of notes in sequence), harmony (composed of notes sounded together) and rhythm (how notes are distributed within the pulse), the three basic elements of music, are all different kinds of vibrations in time.
This is all pretty obvious but I thought it was worth underlining because where I want to go next is less obvious. Pieces of music are conceived on different time scales. There are short pieces of music and long pieces of music. Well, that's pretty obvious too! But the consequences and implications are interesting. Can we tell from the first few notes how long a piece might be? Is there something in the music that signals to us either that it will be over soon or that we should settle in for the long haul?
Some of the shortest complete musical compositions we have are the themes that accompany the opening credits of television shows. Here is one example that is a mere thirty seconds long:
Here is a longer, more complex one, at a minute in length:
Both of these feature a lot of percussion with electronic sounds layered above. Here is one with a more traditional musical texture:
Voice, violin, guitar, bass and drums. In all three cases we hear nearly all of the complete texture right from the beginning. In the case of the first two, there are secondary ideas introduced. In the Homicide theme, for example, a new harmony and a quicker percussion track is introduced at the 34 second mark. But in all of these the sense we get right from the beginning is that this is what we get. We are experiencing a moment, not a journey.
These short kinds of themes are what we are used to nowadays as most of what we hear everyday is short duration. Pop songs are a little longer, about three to five minutes. But a real contrast with these brief themes would be a musical composition that was much, much longer. A journey, not just a moment. I'm going to choose three examples of pieces that all have the same title: Symphony No. 5. The first one is Beethoven:
This is pretty dynamic at the beginning, with the whole of the strings in unison, but what they are playing is pretty simple: three eighths and a quarter, falling a third, then the same thing one step lower.
But there is a tremendous sense of direction signaled by the harmonic tension. So this is one way to indicate length: set up a lot of harmonic tension that will need to be developed and resolved. This first movement is about eight minutes long, but the whole symphony is about thirty-five minutes long. Here is another Symphony No. 5, this time by Mahler:
The first movement is a funeral march that begins, interestingly, with almost the same motif as the Beethoven but while the rhythm is the same, this motif first has all repeated notes, then instead of descending, it ascends. Altogether a more complex theme. We have the strong impression at the beginning of breadth. It just feels as if this is going to take longer than Beethoven because the theme seems to want to go somewhere, but at the same time, is in no hurry to do so. This movement, about eight minutes long, is a kind of introduction to the second movement and the whole symphony is about an hour and ten or fifteen minutes long. Finally my third Symphony No. 5, this time by Shostakovich:
Again this movement is about eight minutes long and the symphony as a whole is about fifty minutes long. The mood here is entirely different. While the Beethoven was full of compressed energy and the Mahler with a broad vision, the Shostakovich is taut, on edge, but at the 45 second mark changes mood completely to one of enforced calm. We can tell even this early that there will be a psychological complexity to this piece that will perhaps not be found in the two previous ones.
There are a thousand other examples I could have chosen, but I thought it was interesting to compare three similarly numbered symphonies. In each case, the listener is given clues about the nature and extent of the music they are about to hear.
I don't think this is the kind of thing they do in theory courses much these days. But they probably should!