<P> In vocal jazz, scat singing is vocal improvisation with wordless vocables, nonsense syllables or without words at all . In scat singing, the singer improvises melodies and rhythms using the voice as an instrument rather than a speaking medium . </P> <P> Though scat singing is improvised, the melodic lines are often variations on scale and arpeggio fragments, stock patterns and riffs, as is the case with instrumental improvisers . As well, scatting usually incorporates musical structure . All of Ella Fitzgerald's scat performances of "How High the Moon", for instance, use the same tempo, begin with a chorus of a straight reading of the lyric, move to a "specialty chorus" introducing the scat chorus, and then the scat itself . Will Friedwald has compared Ella Fitzgerald to Chuck Jones directing his Roadrunner cartoon--each uses predetermined formulas in innovative ways . </P>

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