"This television producer was showing me around Brno, Czechoslovakia," recalled singer Mark Murphy, "and he really put his finger on it. He said, 'You sing not the melody but the harmony.' "

Murphy, who opens tonight at Cates with Seattle pianist Marc Seales and Washington-based bassist Steve Novosel, is considered by many the quintessential jazz singer performing today. His eclectic repertoire ranges from the standards of Harold Arlen and Cole Porter to bebop, the upbeat swing of the big band era, Latin rhythms and blues. He says it's all a matter of harmony.

"I really am a harmonic singer," he says. "Because I'm very sensitive to the piano player I'm working with. When we like the same chords I can scat for hours. I also like the flow of words. So it's got to be a very astute combination and maybe that's why my favorite composer might be Cole Porter. The harmonics are there and the fantastic word thing is there."

In any given set on the bandstand Murphy might stroll through "Summertime," stretch his supple voice to fit saxophone phrases of Charlie Parker, sing a free-form tribute to John Coltrane, convert his vocal cords to the bowed strings of a bass for "It Might as Well Be Spring" and get down on a Jimmy Rushing blues vehicle.

For an encore, he likes to use his training as an actor with a stream-of-consciousness poetic tour de force based on "Here's That Rainy Day."

"My mother and father had glorious voices and Sunday afternoon we'd listen to the opera on the radio," recalls Murphy, who grew up in Fulton, N.Y. When he was about 14, a jazz-loving uncle played him a record of pianist Art Tatum interpreting Dvorak's "Humoresques."

"Tatum plays it sort of semiclassical first" -- Murphy hums it in a stately manner -- "and then he swings it. It absolutely fascinated me and I've been hooked ever since."

Murphy began checking out his uncle's record collection and paying more attention at the rehearsals of his bass-playing brother's sextet. Somewhere along the way he picked up a little piano and found himself sitting in with the band. The others knew he loved to sing and one day big brother put a microphone in front of him. People loved it.

"Our ears opened up in the right way," says Murphy of his generation's absorption of the 'popular' music available in the 1940s. "You're born and you're influenced and soon you all start selecting the Duke Ellington ballads, the best of the screen-writing songs, all the great songs."

Murphy's first influence was Nat (King) Cole, he says, and his recent album on the Muse label is devoted to tunes associated with the late singer-pianist.

"Later on I went through a period of memorizing Sarah Vaughan and Billy Eckstine and for a while I didn't listen to anyone but Peggy Lee. Then the bop era came in and I can remember listening to George Shearing whiz through a thousand notes."

"I probably will never get to know what it feels like to sell a million records," sighs Murphy, "but people do buy my albums and they keep them for years. I can be in an airplane with Gladys Knight and the Pips. Gladys is in first class and I'm back in second with the Pips. And each Pip makes more money and is better known than I am. It could get a person down, if you let it. But I'm on the plane. And I'm working."