Once upon a time, you could turn on one radio station and hear such a variety of music that you never got bored with it. Once I was listening to KEWB, I never had to turn the dial on my transistor radio, because I knew that the next song Bobby Dale played wouldn't sound the same as the one that was playing now.

"Chapel of Love," would be followed by "Papa Was A Rolling Stone," "Classical Gas," "People" and "Drop Kick Me, Jesus." If you listened to the Top 40 countdown, you'd hear Frank Sinatra and the Kingston Trio, along with Otis Redding and the Archies.

Now even the oldies stations won't play all of that music. The music scene is so fragmented that one group never gets to hear what another group is listening to. Everything must be categorized, pigeonholed, marginalized. Each to its own box, every genre discrete and separate from the others. Even the decades are divided, 80s music an entity distinct from 70s music, which in turn has apparently nothing to do with anything recorded before or after.

All last week I watched Ken Burns' Jazz series on PBS. One of the points the series makes is that all American music is interconnected. Jazz itself is like a river, with different streams feeding it, from blues and ragtime to classical and other influences. At first, no one even knew what to call it, because it was so much a part of the landscape and grew so organically. Later, for awhile, everything was called "jazz," all the popular music of the twenties and thirties.

There would be no rock music, as we know it, if not for the development and dissemination of jazz in those years. From jazz and swing we got the beat, the melody, the improvisation that led to rhythm and blues.

Yesterday I saw O Brother, Where Art Thou? at the Rialto. Mom wanted to see it, and we both also want to see State and Main, but I picked O Brother because I wanted to hear the music in it. What's called "old-timey" music is the antecedent of what we now think of as country, as well as folk and rockabilly.

And from the freedom of R&B, and the driving rhythm of rockabilly, rock and roll was born a half-century ago. For a few golden years, it had the widespread acceptance that jazz held in an earlier era. The fact that musicians have taken it in so many different directions is not a bad thing.

The bad thing is that the labels pinned on these artists and their art sometimes discourage them from listening to each other, and collaborating, and keeping the music alive and vital. So much of what I hear on the radio is either bland or imitative.

In the days of KEWB, every week Bobby Dale would introduce the new songs on the play list ("K-E-W-B Disc-covery!"). It was exciting, because you never knew what you were going to hear. It could be a follow-up to a successful record, something so similar that you couldn't tell the difference. But it could just as easily be something amazing, unlike anything you've heard before.

I miss that. I think that's why I keep searching, up and down the radio dial, for something different. It's also why I own over a thousand CDs (a number which is not increasing, by the way). If the next big thing isn't growing in the field where I'm standing, I'll move to another field, just to keep from letting my own roots grow too deeply.

O Brother, Where Art Thou?, by the way, is a visual and musical treat, sustained by spirited performances and a meandering but pointed plot. Homer's Odyssey is credited as the basis, and the references are scattered throughout the film, but it's much more an exposition of life in Mississippi in the 1930s. Between the stylized political stump speeches and Klan rallies are some witty, tender moments.

The music is what you'd expect from that time and place, a mix of bluegrass, country blues and gospel, all performed with such enthusiasm that the most jaded listener (of which I am, of course, not one) is going to get caught up in it.

And it's funny! At the screening where we saw it yesterday, the audience was laughing heartily throughout. George Clooney is better than I've ever seen him, and most of the supporting performances are either hilariously larger than life (John Goodman as a one-eyed Bible salesman) or charmingly understated (Tim Blake Nelson as Clooney's fellow chain gang escapee).

These characters are lovingly portrayed and presented. The dialog is sharp and witty and infused with humanity. I don't do movie reviews because I tend to see only what I like about a film. But I couldn't find anything not to like about O Brother, Where Art Thou? I'd see it again.