Because of the tremendous impact electric blues guitarists like Muddy Waters, B.B. King and Albert King have had on rock 'n' roll, many pop fans have come to think of the blues in fairly narrow terms. It's almost a formula: The verses are built on a 12-bar, I-IV-V chord progression, the melody relies heavily on flatted fifths and augmented ninths, and the lyrics use an AAB rhyming pattern. Toss in a string-bending guitar solo over a heavy backbeat, and voila! Instant blues.

The truth is that the blues offers more a vocabulary than a set of rules, and sticking to the Chicago model is as silly as assuming all jazz bands should sound like King Oliver's Band. The Texas trio ZZ Top, for example, has outfitted its new album with an array of electronic instruments, but that doesn't keep the music on "Afterburner" (Warner Brothers 25342-1E) from exhibiting the same bluesy spirit as the band's earlier successes.

Longtime fans, in fact, will barely bat an eyelash at the band's technological trappings. For one thing, this is no sudden shift in ZZ Top's sound; guitarist Billy Gibbons has been experimenting with electronics since 1979, and many of the treatments on the new album were presaged by last year's hit, "Legs."

But the band's ability to go high-tech ultimately has less to do with its track record than with its integrity, for the new equipment hasn't changed ZZ Top's approach, only certain aspects of its sound. "Sleeping Bag," for example, is basically the same sort of minor-key boogie the band has been cranking out for more than a decade. The difference is that instead of playing a funky shuffle, drummer Frank Beard pushes the beat in strict lockstep with the drum machine.

The synthetics, by and large, are fairly subdued; aside from some Fairlight flourishes on "Sleeping Bag" and a bit of Vocoder in "Delirious," the keyboards generally just throb in tandem with Dusty Hill's bassline. Nonetheless, the added color can make a big difference, for it's hard to imagine "Stages," a lovely midtempo ballad, working so well without the synthesizers to soften its sound.

On the whole, ZZ Top remains a guitar band, and given Gibbons' command of the instrument, it's not hard to understand why. Although he's tremendously capable, there is seldom much flash to his solos; rather than play a lot of notes, Gibbons concentrates on simply getting the right ones. On "Woke Up With Wood," for instance, his solo is lean but searingly effective as he navigates the straits between melodic grace and blues raunch, while "Velcro Fly" finds him growling contentedly over Beard's pounding tom-tom. Only "Rough Boy" seems less than perfect, and then largely because Gibbons plays with too much grit to pull off a "pretty" solo.

Not every guitarist subscribes to the theory that less is more. Stevie Ray Vaughan, for example, shows off with solos that are fleet-fingered and verbose. That has gone a long way toward making him something of a guitar idol, but Vaughan seems increasingly uneasy with the open-ended jamming that built his reputation.

Perhaps that's why "Soul to Soul" (Epic FE 40036), Vaughan's latest, puts more emphasis on song structure than solos. That's not to say that the guitarist lays out much, for he solos on every tune here. But the close attention to form adds clarity and focus to his playing, whether with the psychedelic soul of "Come On (Part III)" or the rock 'n' roll basics behind "Look at Little Sister." Most promising of all, though, is the nod to jazz offered in "Gone Home," a move that may well provide Vaughan with an outlet for his virtuosity that simultaneously reins in his excesses.

Still, much of Vaughan's playing merely refines the work of white blues players since the '60s. Far more interesting is the Robert Cray Band's "False Accusations" (Hightone 80005), an album offering an angle on the blues that's contemporary but uncorrupted, suggesting what might have happened had the Chicago school developed in parallel with the soul sound.

Cray is an able guitarist, with an efficient, slicing attack that owes as much to Steve Cropper as to B.B. King, but it's his strength as a singer that stands out most clearly. Hand him a song that describes love on the sly as ably as "Porch Light" or "Playin' in the Dirt," and Cray can convey those guilty pleasures with seductive ease. But he shines brightest on songs like "Change of Heart, Change of Mind" or the title track, wherein he handily returns soul singing to its blues roots. By grounding his music in both the past and the present, Cray sets up resonances few pop performers can match.