Sunday started with the low point of this year’s fest (aside from the rain): the Zac Brown Band, whose “Toes” promised an hour of Jimmy Buffett-like coastal rock free from Buffett’s dogmatic moralizing and thorny political sloganeering.

A local trad jazz player told me you have to play the standards or no one will buy your CDs. That equation treats music like a can of peas, where the only thing distinguishing characteristic is the label. In that case, people will go with the familiar. But there are a host of other sales-influencing elements at play with music, and traditional jazz as smart and attractive as Tim Laughlin’s “The Isle of Orleans” is as viable if not moreso than a collection of re-re-re-re-re-re-retreads. Of course, the audience is crucial to this equation. If all you want it to sell to tourists who want a souvenir; play the standards. If you see music as art and want to reach that audience, there’s still a world of possibilities in trad jazz.

Tough food fest continues – The Cajun duck po-boy sounded great, but rather than be strips of meat forked off the bone, the duck appears to have been fed into a wood chipper and reduced to a mulch closer to the texture of canned tuna salad than a proud waterfowl. With the texture went much of the duck flavor.

Rob Walker predicted we’d hear “St. James Infirmary” during Jazz Fest in his liner notes to an imagined SJI compilation in the new issue. My first version was Shamarr Allen’s – a fine one, but not revelatory. Allen seems to continue to search for his musical voice, but a version of Gnarls Barkley’s “Crazy” that flirted with Chuck Mangione-era disco jazz might be a blind alley.

It was hard to get into the Voice of the Wetlands All-Stars set because the clouds rolling in threatened to turn the Fair Grounds into wetlands.

The rain, a better time slot and the star power/notoriety that Hamid Drake brings meant that Rob Wagner played to his largest Jazz Fest crowd (that I’ve seen, anyway). The Jazz Tent was full except for most of the Big Chief bleachers, and many had to stand in rising water or have spray from outside hit them so that the bleacher space was available in case 30 or so Big Chief members all chose to brave the monsoon mid-set.

From the start, the set was a model for what thinking artists committed to their vision can do. Rain on a tent roof is really loud, but Wagner still started quietly and when Drake took his first solo, he started on the cymbals, close to the sound of the rain. It almost seemed perverse, but it was also brilliant, drawing the ambient sound into the music. Within 10 minutes, the background din seemed to have receded, but in fact it was raining harder. Their playing focused listeners’ hearing.

Jamaican-born Roy Young has lived in England, Europe and Israel for most of his adult life, and he recently cut Memphis in Memphis with Willie Mitchell producing. His set underlined the idea that “soul” as a music and a notion is a construction. When he was at his most interesting, he was intense, that intensity manifesting itself in a vocal rasp. But then there were songs where he was less intense, where the song didn’t loan itself to seeming heartfelt, and those were just another flavor of pop. Similarly, the best song I saw – “So Strange” – expertly arranged the parts that we associate with a soul song.

Young pointed to an answer to the question I was left with the day before – why does the Ponderosa Stomp work so well? Part of it is the bands that back the stars of yesteryear, all of whom love the the sounds of the original records or the vibe of the times and work to present that, but it also has to do with the artists themselves. They either define a genre, or they’re so distinctive that they exist on the outer edges of their genre. When you imagine a ’50s rockin’ blues singer, Dennis Binder comes to mind. You hear Tammy Lynn and Roy Head and you know why neither was bigger; both are such idiosyncratic musical voices that it’s almost a miracle they had a moment in the sun at all. On the other hand, you have people like Young and Zac Brown, for whom their genres are safe, comfortable places with boundaries that don’t need to be explored or tested.

After the rain, the track was such a mess that it really wasn’t fun anymore. Food II was shin-deep, and there was a lake in the middle of the festival that I had to go around to get to Congo Square for Calle 13. “We started as a hip-hop group and kept growing and growing. Now we don’t know what we are,” rapper Residente explained. The Latin Grammy winners were pretty compelling, and the front of the stage was really into the reggaeton (though the band tries to distance itself from reggaeton, I read).

If you ever wondered why you never hear bluegrass reggaeton, it’s because they don’t really go together, as Del McCoury’s set next to Calle 13 demonstrated.

I admired Tim McGraw’s star quality as I headed for the exit. He clanked three high (but not that high) notes in 10 or so minutes, and that CPM – clams per minute – ratio wouldn’t get you into the finals of American Idol. But McGraw’s enough of a star to get away with it.