*** T.J. KIRK, “If Four Was One,” Warner Bros.; ** 1/2 MEDESKI MARTIN AND WOOD,”Shack-man,” Gramavision; ** 1/2 DAVE ELLIS, “Raven,” Monarch; * 1/2 THE GRASSY KNOLL, “Positive,” Antilles

Backbeat and dance beats. Recorded samples and tape loops. Synthesizer technology. Electric guitars, trumpets, saxophones and drum machines. Improvisation and pop appeal.

All these elements help define “acid jazz,” one of the most widely--and loosely--applied musical terms since the invention of jazz fusion. The differences in these four recordings--which, for better or worse, have been tied to the category by promoters, critics or disc jockeys--serve to show how meaningless the acid designation can be. To borrow from Duke Ellington, it don’t mean a thing.

Still, these recordings all share one attribute: They diverge dramatically from the jazz tradition. And that’s something these musicians share with all the innovators of the past, successful or not. They’re creating something new.

The three-guitar-and-percussion combo T.J. Kirk melds the spirits of its inspirations--Thelonious Monk, James Brown and Rahsaan Roland Kirk--and comes up with sounds that satisfy on a variety of levels. The quirkiness of Monk, the funkiness of Brown and the musicality, as well as the dramatic sense, of Kirk make for interpretations that draw listeners in with familiar rhythms before taking them on varied, improvisational rides.

Of its three forebears, Brown’s influence is the most strongly felt. Covers of his “Damn Right I’m Somebody,” “Get on the Good Foot” and “The Payback” retain the rhythmic drive of the originals while allowing the guitars to compare and contrast styles.

Will Bernard plays with an electric twang and a bit of wah-wah at times. At other times, he adds country-fried touches with slide. John Schott delivers rock-powered insistence, while Charlie Hunter, who provides bass with two of the strings on his eight-string instrument, adds organ-like, R&B-flavored; touches.

Powered by Scott Amendola’s drumming, they construct tight passages of interplay and, especially in Hunter’s case, stimulating accompaniment. Medleys like the one that combines Kirk’s “Meeting at Terminis Corner,” Brown’s “I’ve Got a Bag of My Own” and Monk’s “Brilliant Corners” serve to demonstrate the brilliance of TJK’s concept.

*

Medeski Martin and Wood’s fourth album, “Shack-man” (so named because it was recorded in a hut set in the Hawaiian jungle), concentrates on grooves and funk feeling while giving a good idea of what the keyboard trio does live.

The sound, based on John Medeski’s Hammond B-3 organ and Wurlitzer electric piano, has a rough, low-tech feel that’s perfect for the rough-and-tumble rhythmic approach. While fans of their previous albums (especially the ambitious first album “Notes From Underground”) may find the new disc crass by comparison, there’s no denying the infectious beats and often amazing interplay that is sparked by drummer Billy Martin and acoustic bassist Chris Wood.

This must be acid jazz. It burns.

*

Saxophonist Dave Ellis’ first album since leaving the Charlie Hunter Trio is the most jazz-minded of this group, with tunes from Jackie McLean, Wayne Shorter, McCoy Tyner and Woody Shaw sharing space with the Lennon-McCartney tune “Tomorrow Never Knows” and Ellis’ contemporary-sounding originals.

The tenor player is a confident improviser with a round tone and a fine sense of drama. Working in a variety of instrumental backdrops, including a trio with Hunter, an electric quartet and a septet with trombone, fluegelhorn, electric bass and Fender Rhodes piano, Ellis makes a first statement solid with promise.

*

The Grassy Knoll, masterminded by guitarist-keyboardist-sampler Bob Green, may best exemplify the acid sound with its repetitive, techno beats, sampled sounds and ambient moods. Titles like “Black Helicopters,” “Roswell Crash” and “Fall of the American Empire” seem to be all of one mood, with only the occasional trumpet solo emerging from the hypnotic beats.

If one could dance in one’s sleep, this would be the music.

*

Albums are rated on a scale of one star (poor), two stars (fair), three stars (good) and four stars (excellent).