Now in its sixth year, the festival served several ends. It showed off 55 bands for the attendees of the convention of the Association of Performing Arts Presenters, those who book festivals and concerts around the world. It gave the rest of us, for a $25 all-clubs, all-night ticket, a deep index of new jazz. And the attendance — 1,200 on Friday night, 2,500 on Saturday — created a mob. A mob breeds rumor; rumor off-gasses buzz.

And jazz needs buzz. There are always music-school students whose lives are being overturned by some saxophonist they saw somewhere; given the chance they’ll tell you about it. So will club owners, promoters, spry neighborhood sages and the odd obsessive-compulsive or critic. But jazz, frustratingly, is still not quite right for MySpace and MP3 listening — it’s too performance-oriented and makes teenagers gag — so on-the-street buzz remains in short supply. Sometimes, given the economy and the shortage of middlemen, you have to find out about musicians from the musicians themselves, which makes jazz feel kind of 17th century, pre-movable type.

Not here. On Saturday especially you were in a jazz equivalent of South by Southwest, surrounded by tales of not getting in or of hearing something killer.

Le Poisson Rouge was the festival’s flagship hall this year — the biggest space with the best sound, and consequently the most overrun. The pianist Vijay Iyer’s trio, with Stephan Crump on bass and Marcus Gilmore on drums, played to roars on Saturday night; last year the group made this audience’s consensus-favorite album, “Historicity,” and its performance showed new confidence through the intricate gnashing of the rhythm section. (The trio played its jolting, stuttering cover of M.I.A.’s “Galang” for the first time live.) There were roars on the same night for Jenny Scheinman and Jason Moran’s duets, sweet gospel-folk-classical tunes empowered with some cool dirt: catarrhal bowing from Ms. Scheinman’s violin, a single violent bang from Mr. Moran’s piano keyboard.

Just as musicians like Ms. Scheinman, Mr. Crump and the drummer John Hollenbeck ran among clubs to play very different sets with very different bands, there was hybridization in the music itself. In Rudder, a quintet that included the imposing drummer Keith Carlock, jazz turned toward smart jam-band funk; in Nicholas Payton’s SeXXXtet (yeah, I know), toward slinky R&B; in Eric Lewis’s bombast-and-bloodthirst solo piano performance, toward classic rock (the guys at the Back Fence would have dug his cover of “Sweet Home Alabama”); and in Bitches Brew Revisited, a septet led by the coronetist Graham Haynes, powered by the drummer Cindy Blackman and colored by the guitarist James Blood Ulmer, jazz became whatever it was Miles Davis intended in 1969: spacious, black-magic stealth funk.

In a startling set at Kenny’s Castaways late on Saturday the saxophonist Rudresh Mahanthappa’s Indo-Pak Coalition — a trio with the guitarist Rez Abbasi and the drummer Dan Weiss — played hard, bright crisscrossings of South Asian music and jazz. Mr. Weiss was the music’s visual explanation. He sat low behind his tablas, his right leg bent up to access the foot pedal for a bass drum; gracefully shifting a limb or picking up a stick, he drifted between tala and swing, between hand drums and the basics of a trap set.

But what about jazz as jazz, the music’s marrow and main stem? There was a lot of that too. I definitely heard it in the quartet of the alto saxophonist Jaleel Shaw on Friday, in its elegant, diamond-cut theme lines, its sleek, fabulous rhythm section (Aaron Goldberg, Fender Rhodes electric piano; Ben Williams, bass; Johnathan Blake, drums) and its control over dynamics in a chatty room. I heard it in the trio of the tenor saxophonist J. D. Allen, compressing the sprawl of late Coltrane into energy bars, and in the trumpeter Ambrose Akinmusire’s quintet — controlled, ambitious and ready to find a broader audience, with a group sound not far from Terence Blanchard’s. It was there in Mike Reed’s People, Places & Things, a Chicago quartet who’d never before played in New York, making freed-up hard-bop with scrappy, scholarly intensity. And even in the guitarist Mary Halvorson’s trio, with its nervous-driver lurches, tempo shifts and furious strumming: there was an elegant, flexible, Monk-like vocabulary in all that fracture.

Over the two nights I saw 18 bands. I heard good things about the music and crowds at the Bobby Previte, Elliott Sharp and Dr. Lonnie Smith gigs but missed them. At 10 on Saturday I walked over to the Bitter End to see Mr. Hollenbeck’s Claudia Quintet, a band I know and like. But the house, all standing, was packed — for a John Hollenbeck show! — and no one else was admitted. I watched through the window for a cold 30 seconds but couldn’t see or hear much through the mob. I’m happy to say I have nothing to report.