In a conversation a few months back, Larry Coryell directed my ears to a singer I’ve had a tendency to overlook. “I rediscovered my passion for straight-ahead vocal jazz through Diane Schuur,” said the eclectic-minded guitarist, who played a pioneering role in the 1960s jazz/rock fusion movement. “There’s a bittersweet thing in her voice, but it’s overshadowed by joy, and it makes her performances all the more rich. She’s a beautiful singer and a fabulous pianist who plays great chords, and she can scat her solos on the piano. She could read the phone book and make it sound great.”

To be fair, Schuur is hardly a secret. With two Grammys under her belt and a quarter-century track record of collaborations with the likes of Stan Getz, B.B. King, Ray Charles, the Count Basie Orchestra, and Maynard Ferguson, she’s made a name as one of jazz’s most popular singers. She returns to the town where she first found fame when she headlines the Kuumbwa Jazz Center’s annual “Jazz at the Aquarium” fundraiser on Saturday at the Monterey Bay Aquarium, performing with her longtime trio featuring Jim Zimmerman on drums and music director Scott Steed on bass.

Schuur’s material might strike some jazz fans as a bit dubious; her most recent album, Midnight, is a collaboration with pop-meister Barry Manilow and his longtime creative partner Eddie Arkin. Released last August, the album is designed as a suite evoking a romantic night on the town. In addition to a concluding duet with Manilow on his tune “Anytime,” she joins forces with R & B star Brian McKnight on “I’ll Be There” and with labelmate Karrin Allyson on “Stay Away From Bill.”

For Schuur, the project with Manilow “was a natural,” she says. When Manilow signed with Concord, the label asked “who he wanted to work with and he said ‘Diane Schuur,’ so there it was. He really has a flair for jazz, so it worked out really well.”

Manilow has recorded jazz-oriented albums before, particularly Swing Street, a well-received 1987 project featuring Schuur as a guest star along with saxophonists Stan Getz and Gerry Mulligan. But Manilow’s songs haven’t found their way into the standard repertoire. Schuur is convinced that’s destined to change, and that Midnight marks the start of Manilow’s ascendance into the songwriters’ pantheon.

“All of these songs will become classic in the Great American Songbook,” says Schuur. “Every tune has a very strong lyric.”

Schuur has never limited herself to the American Songbook. At age 10, she started her career as a performer singing country music, and she continues to drop a twangy ballad or two into her shows. She’s also at home interpreting pop tunes and blues.

“I’ve always tried to stretch,” Schuur says. “I feel I’m a lot more than just a ‘jazz singer,’ but that’s what I’ve been labeled all these years. In part that’s what I am, but that’s not all I am.”

There’s no doubt that Schuur first attracted widespread attention performing in jazz contexts. In 1975, Tonight Show bandleader Doc Severinsen was in Seattle, Schuur’s hometown, auditioning singers for drummer Ed Shaughnessy’s upcoming appearance at the Monterey Jazz Festival. Schuur got the gig and it was her first big break, paving the way for her career-making 1979 Monterey appearance. Instead of appearing with a big band, she performed solo, and her wrenching rendition of “Amazing Grace” stopped Stan Getz in his tracks. He became her most effective champion and a profound influence on her sound.

“It was a very significant musical relationship,” Schuur says. “Stan always stressed to me that less is more, that you should strive for more simplicity and not be so busy in the delivery of a song.”

Over the years she has indeed become a much more nuanced singer, a performer in demand around the world. Earlier this month she opened the new Blue Note club in Milan, and she returns to Europe in the fall as part of Concord Records’ 30th anniversary tour. Whether singing Manilow, Bacharach, or Cole Porter, she’s as busy as she wants to be.

Jazz at the Aquarium features Diane Schuur, Deuces Wild, Marshall Otwell, Sadza, and others. Sat, 6/19, from 8-11pm. $75/Aquarium and Kuumbwa members, $100/general (a benefit for education programs). 648-4880.