Although it doesn't happen often, whenever Frank Zappa goes about the task of purging himself of his normal ration of acrimony, contempt, bile and phlegm, he sometimes comes forth with an album that is every bit the musical experience that he always claimed he could produce. With the exception of the astonishing work he and his musicians did ona couple of years ago, much of Zappa's musical output has been too malnourished to support his artistic pretensions. His excursions into jazz with the Mothers of Invention were never more than pale imitations of Miles Davis and Ornette Coleman, overlayed with effects copped from Edgar Varese, and most of his "serious" compositions contained large helpings from the glut of modern music. Originality has never been Zappa's strong point.

Waka/JawakaHot Rats, while little more than a long delayed extension of the original Hot Rats album, is one of Zappa's most enjoyable, less hypertense efforts, and while it may lack the tightness, the rock-based energy of its predecessor, it contains some of the best material he's done in years. Waka/Jawaka may well be something of a fence-mending job by Zappa after his execrable work on 200 Motels, which has got to be one of the all-time attempts by a musician and composer to discredit himself.

The musicians brought in for Waka/Jawaka are not the stellar personalities that graced Hot Rats. Captain Beefheart and Sugarcane Harris are gone, replaced by newer faces that include Tony Duran on slide guitar, Sal Marquez on trumpets, and Don Preston on Moog and piano. They comprise a tight, disciplined group.

The first song is a 17-minute extravaganza called "Big Swifty," which moves on the strength of Zappa's guitar and Marquez' horns through enough changes to add up to a solid modern jazz suite. It is something to appreciate, even though it could well be called second-rate Miles Davis, and is even leagues behind Weather Report's recent I Sing the Body Electric in inventiveness and power. And at only 17 minutes in length, "Big Swifty" seems rather light-weight for a full side piece. But that's just quibbling. It's good, it stands up to repeated listenings, and is, along with the title cut, one of the best things on the album.

Side two has "Your Mouth," a lapse back into Zappa's patented spitefulness. It's vapid and trite, a puerile exercise in sluggish swing. "It Just Might Be a One Shot Deal," is good old Mothers' music, a chaotic arrangement of acoustic, slide, Hawaiian, and pedal steel guitars, "Waka/Jawaka" rounds out the album with an 11-minute jazz improvisation.

Maybe Frank Zappa is just getting mellow for the first time in his career. Or maybe it's just a phase. Either way, while Waka/Jawaka may lack the brilliance of Hot Rats, or the capacity for irritation that existed on some of the Mothers' material, it's a distinctive album. Which, in his case, is either a sign of maturity, or evidence of exhaustion.