Scat singer

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.

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.

The deliberate choice of scat syllables also is a key element in vocal jazz improvisation. Syllable choice influences the pitch articulation, coloration, and resonance of the performance. Syllable choice also differentiated jazz singers' personal styles: Betty Carter was inclined to use sounds like "louie-ooie-la-la-la" (soft-tongued sounds or liquids) while Sarah Vaughan would prefer "shoo-doo-shoo-bee-ooo-bee" (fricatives, plosives, and open vowels). The choice of scat syllables can also be used to reflect the sounds of different instruments. The comparison of the scatting styles of Ella Fitzgerald and Sarah Vaughan reveals that Fitzgerald's improvisation mimics the sounds of swing-era big bands with which she performed, while Vaughan's mimics that of her accompanying bop-era small combos.

...
Wikipedia