Scat
Improvised syllable singing.
What it means
Scat is a manner of singing in jazz in which not text but freely chosen syllables are sung. The voice thereby acts as a melodic instrument and improvises like a horn over the harmonic progression of a piece. The syllables are not arbitrary: their choice determines the articulation, similarly to the tongue for a wind player, and experienced singers use particular sound sequences for particular rhythmic and melodic figures.
Musical use
Scat singing makes the voice equal to the instruments in improvisation and allows lines that could not be executed with text. At the same time a peculiarity remains: the voice can change tone colour and pitch steplessly, which opens possibilities instruments lack. In the history of jazz, scat is closely connected with the development of solo playing; singers took over the phrasing and language of the horn players, just as, conversely, instrumentalists oriented themselves by the voice. The performance ranges from short interjections to extended solos over several choruses of the form.
Performance practice
First learn the form and the chord progression by heart and count along with it; without this foundation, scat becomes arbitrary. Build up a stock of syllables of your own and practise shaping articulation with them — hard initial sounds for accents, soft ones for bound lines. Sing along with instrumental solos, to learn phrasing and rhythm. Begin with short, melodic lines instead of fast runs. Listen to the rhythm section and shape in dialogue with it.
Bear in mind that the choice of syllable is not indifferent: hard initial sounds create accents, soft ones connect, and experienced singers use fixed sound sequences for particular figures. Build up your own stock and practise it deliberately. An early recorded example counts as Louis Armstrong's Heebie Jeebies of 1926. Begin with short, melodic lines instead of fast runs and shape in dialogue with the rhythm section.
Check whether a recording contains a solo you can sing along with, because that is the fastest school for phrasing.