Shadings of Procol Harum : Rock music: Singer Gary Brooker says he’s optimistic about the future of the band, which plays Irvine tonight, despite personnel changes, disasters and disappointments.

Procol Harum, which plays tonight at Irvine Meadows, has always been an anomaly. When screaming, guitar-driven rock began to dominate the music scene in the late ‘60s, these Brits rose to prominence with “A Whiter Shade of Pale,” an organ-driven largo ballad adapted from Bach. While many songwriters of the day espoused the virtues of peace, free love and social revolution, Procol Harum sang of disease, slow death and rotting corpses.

But if the music was usually against the grain and unusually morbid, it also was consistently intelligent, intriguing and unique. Many consider such Procol releases as “A Salty Dog,” “Home” and “Broken Barricades” to be among the finest albums of the ‘60s and ‘70s, and such singles as “Whiter Shade,” “Whiskey Train,” “Conquistador” and “Simple Sister” are still played on classic-rock radio.

Creative exhaustion, personnel changes and a string of commercial failures caused Procol Harum to disband in 1977. Its members went their separate ways until the late ‘80s, when they started thinking about getting together again.

“There was a bit of a lull in what was going on in rock music,” pianist/singer Gary Brooker recalled during a recent phone interview. “We began thinking, ‘Hang on--there’s a space for Procol amongst all this, a space for melodic tunes.’ ”

Another catalyst, Brooker said, was that drummer B.J. Wilson was in the hospital suffering from a massive drug overdose, and it was hoped that the prospect of a reunion might improve his will to recover. But Wilson died in 1990 after three years in a vegetative state.

“We sent him the demo tapes we were making with a horrible drum machine on it because he hated that sort of thing,” Brooker said. “But sadly, he’d suffered catastrophic damage which was never going to right itself.” After Wilson’s death, Brooker, lyricist Keith Reid, organist Matthew Fisher (who had left in 1969) and guitarist Robin Trower (who quit in 1971) forged ahead, recording “The Prodigal Stranger” in 1991 for the Zoo Entertainment label with support from a new group of sidemen.

But the album was an artistic and commercial disaster, an uninspired attempt to play it safe that lacked the idiosyncratic sound and vision of the band’s glory days.

The material was bland, corporate rock, with lightweight synthesizer washes all but replacing the piano/organ attack that had been the group’s hallmark. Precious little space was given to Trower’s buzzing guitar licks, and Reid’s lyrics, which once had come off like Edgar Allan Poe on hallucinogens, now were meaningless, feel-good twaddle. The album’s only redeeming quality: Brooker’s still muscular, soulful vocals.

Despite its glaring shortcomings, Brooker has defended “The Prodigal Stranger” and expressed surprise that it didn’t fare better. But on the phone, he also hinted at a belief that Zoo (which since has dropped the band from its roster) had been responsible for “Stranger’s” homogenized sound.

“We felt we’d done a good work there,” he said. “Looking back, it’s easy to reflect on things and see what we’d done wrong, but I think we were with a record company which made some wrong choices on the songs.

‘ “Prodigal Stranger’ was an album in which to say, ‘Here we are; we’re still alive; we can do what we want to do.’ It’s the first album of another series, really--at least it is in our view. Procol Harum has always made a lot of mistakes in the past, but we’ve always tried to make each album different than the one before. Even if we were successful, we never tried to repeat a formula. It was a difficult album to make because it was like, ‘Hang on, we’re Procol Harum; what does that mean to anyone out there now?’ ”

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The reunion was also difficult on a personal level. Brooker expressed disappointment and perhaps a little anger that Trower, who has enjoyed a successful post-Procol career, didn’t stay on to tour with the band.

“There were two separate experiences,” Brooker said. “One was a happy one and one a not-so-happy one. Rob Trower, although he played on some of the record, wasn’t really interested in coming out on the road, whereas the opposite was true of Matthew Fisher. You can’t force people to do things. I saw Rob in 1991, but before that I hadn’t seen him since 1971 despite the fact that we went to school together, started in music together. It’s never really been more than a musical relationship. We never cross paths.”

Trower told The Times in an interview last spring that there wasn’t enough room for his playing in Procol Harum to keep him happy or interested.

In any case, Brooker, winding up a tour he feels has gone exceedingly well, remains enthusiastic about Procol Harum’s future.

“I think we’re sitting in the lap of the gods,” he said. “I think we’ve got a lot to offer, and no one in this group is ever going to stop playing. We’ve been performing for many thousands of people every night, and the response has been fantastic. So with the band and the fans, there’s no problems.”

* Procol Harum opens for Jethro Tull tonight at 8 at Irvine Meadows, 8808 Irvine Center Drive, Irvine. Tickets: $27.25, $22.25, $17.25. (714) 855-4515.