So, when I was younger, I guess our grade school tried to expose us to different things. We had magic shows, marionette shows ... and sometimes quartets from the local symphony.

So, it'd be a brass or a string quartet. Usually, they'd go through all their instruments. "This is what the Jaws theme sounds like on a violin." "This is what the Jaws theme sounds like on a cello." "This is what the Jaws theme sounds like on a double bass." Or, if it was the other quartet, "This is what the Pink Panther theme sounds like on a trumpet."

The kids always got into those demonstrations, because they were able to recognize the melodies.

Of course, the quartets would also play songs. So, they'd sit down, and play, and I'd be getting into it, thinking, yeah, this is nice. This is good, too. Hmm, liked the other part better. Hey, that sounds like the part I liked before. Now I'm losing my place again. Then I'd zone out. And notice I zoned out. And zone out again. And come to. And then they play a part with a catchy melody again. Then, after twenty minutes or so, they'd take a break, and one of them would say, "That was blah blah blah by Mozart," and I'd think, "What the, that was ONE song???!!?"

I like some classical music, but even now I have a modern attention span. So, some good classical music for that would be The Nutcracker (short songs, very distinct songs, memorable melodies). Or The Four Seasons.

But even though pop songs tend to be short, they still average maybe 3 or 4 minutes.

I noticed, though, that a lot of Creedence Clearwater Revival songs are less than 3 minutes. Bad Moon Rising, Green River, Down on the Corner, Fortunate Son, all less than three minutes. Do they need to be longer than that?

Most Van Halen instrumentals are about 2 minutes or less. That seems about right. You have an idea, execute it, explore it a little, and wrap it up. A lot of instrumentals that go on for five minutes have a melody at first, but then they get to noodling, and I zone out. (As a contrary example, Metallica was pretty good at having long instruments (Call of Cthulu, Orion) that kept my interest.)

Sometimes when I listen to the radio, I catch myself reaching to change the channel even if a song I like is playing, maybe because I get antsy and like getting overstimulated and hearing different things.