POP MUSIC REVIEW : Can’t Break the Sound Barrier : A poor equipment mix and Gil Scott-Heron’s own vocal troubles conspire against the singer-songwriter during Sunday’s show at the Rhythm Cafe.

In the work of Gil Scott-Heron, the message has always been the medium. So when the lyricist, poet, singer and social commentator announced Sunday to his audience at the Rhythm Cafe that he’d lost his voice a few days back in Brooklyn, it was no cause for alarm. The message would, no doubt, get through.

Wrong. The message got buried. Because of a poor sound balance, too many of Scott-Heron’s words were just plain lost in the mix. Never a great singer (although his voice did gain polish and pitch between “The Revolution Will Not Be Televised” in 1971 and “Moving Target” in 1982), he trudged through a host of past glories with the all-important lyrics mostly obscured behind the riffing of his six-piece band. The only times you could really make out what he was saying were when there was very little accompaniment or none at all.

That was the case when he first walked out on stage and gave a 15-minute monologue--but it probably made some people wonder whether they’d stumbled into a comedy club by mistake. Scott-Heron plowed some of the same territory as George Carlin, pointing out contradictions in our language and making social statements in the process. Sample lines:

“The ‘80s was the decade of the computer, and the ‘70s was the decade we sat around and talked about the ‘60s. Now the ‘90s is the decade of ‘ologies.’ You can put an ‘ology’ on the (things) you like to do and become a consultant.”

If that kind of patter was neither funny nor particularly revealing, it did serve to introduce the musician and his band, “the Amnesia Express” (“I don’t exactly remember why we call it that”). Scott-Heron dubbed himself and the band members “bluesologists,” those who study “how you feel.” Then, with some clever hand-clapping from percussionist Larry McDonald, he launched into “We Almost Lost Detroit,” his lament on America’s penchant to put business interests above human interests.

If he made any timely changes in the more-than-a-decade-old piece, they were lost in that confounded sound mix. The same was true of his ballad-invective “Winter in America”: Although its message may be timeless, its lyrics include a number of topical references from the ‘70s that could easily be updated, but whether any were is a mystery, because exactly what Scott-Heron was singing could not be deciphered.

Some selections, it was apparent, have aged well, such as “Pieces of a Man,” but it was equally obvious that others have not. “Angel Dust,” notably, seems dated now that crack has replaced that powder as the urban jungle’s most insidious drug.

In any case, no new material was presented. And those who see Scott-Heron as one of the fathers of rap must have been disappointed. He sang all his lyrics; none was delivered in the spoken style he popularized with “The Revolution Will Not Be Televised.”

Surprisingly, it wasn’t until “Angel Dust,” some 90 minutes into the set, that the band seemed to take off. Scott-Heron left the stage and sat in the audience while saxophonist Leon Williams, guitarist Ed Brady, keyboardist Kim Jordan and bassist Robbie Gordon all took long, appropriately electric solos over the psychedelic two-chord vamp. Drummer Roderick Youngs provided solid rhythmic support throughout the evening, whether working funk, jazz or reggae beats.