The last few nights at the JVC Jazz Festival this year were dominated by trios and quartets at Carnegie Hall. On Thursday, at a show called “Two Times Three,” the main attraction was the trio of Paul Motian, Bill Frissell, and Joe Lovano. On Friday the two quartets were those of Dave Brubeck and John Pizzarelli. The evening was titled, appropriately, “Always Welcome.”

The Motian Trio performs regularly at the Village Vanguard, but it was illuminating to hear it at Carnegie. I have said too many times that the hall’s acoustics are bizarre for jazz. In a goofy way, however, Carnegie’s excess reverb added a level of interest to the Motian Trio – almost becoming, in effect, a fourth player. The reverb made Mr. Frissell’s surreal guitar soundscapes sound even more far out, and it added vibrato to Joe Lovano’s already-juicy tenor tone. The group was brilliant on a program of three originals and three standards, “I Wish I Knew,” “Mysterioso,” and “Love Is Here To Stay.”

Mr. Motian’s ensemble was followed by a second trio: Bela Fleck on banjo, Jean-Luc Ponty on violin, and Stanley Clarke on bass. These three instrumentalists normally work in electronic contexts but here played acoustically. They are also generally regarded as fusion players, and though they were unplugged Thursday, their music was still fusion, blending traditions of folk music and jazz. The music was pleasing as a kind of postmodern hoedown music – not to mention toe-tappin’ fun – but the performance illustrated why the Lovano-Frissell-Motian group is so strong.

The Fleck group used riffs, themes, and variations just the way the opening act did, but they lacked the distortion, the distinct intonation, the personality that three master players develop by working together for decades. Mr. Fleck, Mr. Ponty, and Mr. Clarke often found their way into long grooves in which they just seemed to be playing the same phrase repeatedly, without much variation. Rather than create a cohesive flow from beginning to end, as we expect of most jazz (even free jazz), the Fleck trio just offered a lot of middle. Nothing seems to be going anywhere, and the music seems to be designed for semiambient (or semi-stoned) listening.

Dave Brubeck, the last of many great pianists to take the stage at JVC 2005, has been leading his quartets since almost before anybody in the Fleck trio was born (and Mr. Clarke is 53). The interplay between him and his key collaborator, saxophonist Bobby Militello, continues to amaze me. (As does their rapport with bassist Michael Moore and drummer Randy Jones). Mr. Militello is an enormous bear of a man, and in his hands the diminutive alto looks like a toy instrument.

The chief attraction of the quartet is the contrast between Mr. Militello’s soulful, expressive playing and Mr. Brubeck’s classically based, though lively piano playing. The opener, “Gone With the Wind” recalled the earlier days of the Brubeck Quartet, when the emphasis was on mostly swinging, boppish-treatments of standards. Their second piece, an excerpt from Mr. Brubeck’s brother Howard’s “Dialogues for Jazz Combo and Orchestra,” was a reminder of the Brubeck family’s classical proclivities: Mr. Brubeck introduced this work at Carnegie with Leonard Bernstein and the New York Philharmonic in 1960.

Most of the set consisted of blues and bop numbers, including the title track of his new album “London Flat, London Sharp” (Telarc 83625), which showcased Mr. Militello’s effusive playing. The group wound up with its biggest hit, Paul Desmond’s “Take Five,” but for me the climax was “Sleep,” a 1923 standard employed equally by vaudevillians and swing bands – the kind of theme plate-spinners used to work to on “Ed Sullivan.” Mr. Militello couldn’t have been more entertaining or compelling if he had started tap-dancing or turning cartwheels.

John Pizzarelli – another gregarious, in-your-face entertainer, both when playing guitar and singing – realized that Carnegie demanded something more ambitious than his usual trio. Rather than bring his full-sized big band, however, he used his trio plus a revolving array of instrumental and vocal guests. Old familiars Ray Kennedy and Tony Tedesco played piano and drums, respectively, and his brother Martin played bass. But Mr. Pizzarelli filled out the roster with two additional keyboardists, Larry Goldings (mostly on organ) and Cesar Camargo-Mariano (on Brazilian specialties), as well as the marvelous tenor saxophonist Harry Allen.

Mr. Pizzarelli drew his set list mostly from his new album, the excellent “Knowing You” (Telarc), and nearly everything worked. He continues to sing charmingly and play brilliant guitar solos, and he now scats in unison with his guitar riffs even more effectively than did George Benson, who originated that idea. He reveled in his Nat Cole roots (“It’s Only a Paper Moon”), threw a nod to Mel Torme (“Pick Yourself Up”), and drew from other wellsprings of inspiration in “The Shadow of Your Smile” and Lew Spence’s “That Face.”

About the only thing that didn’t work as well were the vocal duets. Dave Frishberg’s “Quality Time,” on the album, has Mr. Pizzarelli and his wife, the fine cabaret singer Jessica Molaskey, making like Blossom Dearie and Bob Dorough. But the song’s references, both lyrical and musical, are just too intimate and too specific to translate well to Carnegie’s capacious cavern. Likewise Mr. Pizzarelli’s old chum, singer Grover Kemble, who sounded fine on the guitarists’ “Live at Birdland” double CD, came off like an overbearing busker at Carnegie.

At least the last number, “Headed Out to Vera’s,” gave Harry Allen, who had hitherto been confined to mostly obligatos, a chance to take charge and show what he could do on a blues – and that’s plenty.