She was an American jazz singer. Many[who?] place her among the greatest female jazz singers in a group that includes Billie Holiday, Ella Fitzgerald, Carmen McRae, Sarah Vaughan, Abbey Lincoln, Jo Stafford and Betty Carter. O'Day, along with Mel Tormé, is often grouped with the West Coast Cool school of jazz. Like Tormé, O'Day had some training in jazz drums (courtesy of her first husband Don Carter); her longest musical collaboration was with John Poole, a skilled jazz drummer whose career was severely curtailed by his ****** habit. While maintaining a central core of hard swing, O'Day's considerable skills in improvisation of rhythm and melody put her squarely among the pioneers of bebop; indeed, a staple of her live act in the 1950s was a smooth cover of "Four" by Miles Davis. She cited Martha Raye as the primary influence on her vocal style, although she also expressed admiration for Mildred Bailey, Ella Fitzgerald, and Billie Holiday. O'Day's soft, slightly raspy alto voice bore a strong resemblance to that of a saxophone. That unique sound, combined with her strong percussive drive, allowed her to utilize her skills in scat singing to meld seamlessly into jazz orchestras as a wordless instrument; her cover of Woody Herman's "Four Brothers" is an excellent example. Another key example of her improvisational skills and rhythmic surety is her cover of "Them There Eyes" with Canadian jazz pianist Oscar Peterson; the song is laid out at a furiously fast tempo, but O'Day pushes the lyrics out at full speed for one chorus, scats another at a Cannonball Adderley pace, then playfully paraphrases the lyrics at half-tempo for her last chorus. O'Day's song interpretations typically reflected a sly, playful sensibility (see, for example, her cover of "An Occasional Man" with Cal Tjader's band, a much more sex-kittenish interpretation than that of Peggy Lee, among others).