Jazz festivals have long been artistically hybrid events, free to celebrate the music's historical receptivity to whatever has been in the air musically. Listeners with the strictest notions of what jazz is may have to wait the longest to be satisfied.

That's how the Indy Jazz Fest started off Friday night, as the rain-plagued season finally seemed to take a breather and let the overcast skies say "Amen" to all the recent weather turmoil.

Despite the muddy grounds of Military Park, treacherous to hurrying feet perhaps, the scheduled sounds unfolded pretty much as planned. Only an extra-long set by Medeski Scofield Martin & Wood threw matters a little later into the evening, which concluded with audience-pleasing bluesman Buddy Guy.

Adam Birnbaum, the 2004 Cole Porter Fellow of the fest-producing American Pianists Association, provided both the balm and the authentic jazz chops of the evening in an unaccompanied mini-set just before Guy came on. The pianist assembled a charming, intricate sampler of his artistry with a couple of standards (Alec Wilder and Cole Porter), one original by himself and one by his new boss, Greg Osby, and a characteristic piece each by Thelonious Monk and Duke Ellington.

The three-day event, the 10th annual festival, was brought to attention by a kind of "in memoriam" Bo Diddley vamp introducing the first song by Hoosier blues band Mike Milligan and Steam Shovel on the WhiteLies.tv stage. Singer-guitarist Milligan headed a tight trio (with "little brother" Shaun Milligan on bass and Robert Cook on drums) through five soulful numbers, ending with the perhaps prophetic "Timing Is Everything."

The passage of time certainly seems to have been kind to Bettye LaVette, who in her 60s commands an astonishing freedom of movement, vigorous pipes and precise showmanship. Backed by an assertive quartet of keyboards, two guitars and drums, LaVette treated the audience under the tented stage (dubbed Buzzed Driving Is Drunk Driving) to a set that spanned the decades of a career dating from her teens.

The way LaVette placed quiet songs amid medium-tempo R&B and out-and-out house-rockers showed her mastery of craft. I found the balance a little too much tilted toward the band in the more energetic songs, however. That meant her style of delivery had to do most of the work and tended to obscure her sometimes trenchant message.

Guitarist John Scofield has satisfied his midlife crisis through an association with the jam band Medeski Martin & Wood. A protean stylist who nonetheless always sounds original, Scofield has narrowed his focus in this ensemble.

Despite the free-jazz interludes, loaded with woozy washes of electronic sounds out of tempo, this quartet doesn't get far from driving a groove to the nth degree.

At ear-punishing volume, MSM&W treated the fist-pumping, often smoking crowd (despite the festival's new no-smoking policy) to 75 minutes of originals that jelled around a succession of funky melodies and abstract patterns.