Make no mistake about it, the One Step Down is a listener's bar on Friday and Saturday evenings, more of a salon than a saloon, and the jazz patrons who attend generally lend respectful attention. But once in a while a performer turns up whose gift for communication is so highly developed that he commands undivided attention from the first note.

Last night the pianist John Coates Jr. held the filled club rapt for a solid hour. People hardly stretched until the mood changed toward set's end with the addition of bassist Paul Langosch, who had waited patiently in the wings during the pianist's discursive and emotion-ravaging solo performance.

Coates' approach to the keyboard, as well as his style itself, defies description. It is, in fact, a bundle of contradictions and anomalies. His skills and touch are of conservatory perfection yet he can get down on some of the funkiest alley blues this side of a juke joint. His use of dissonance and haunting motifs brought tears to some eyes, yet his audible mumbling and nonstop unison scat approaches mockery of the instrument's sounds. But along with other seeming misfits in jazz--the rasping clarinet of Pee Wee Russell and the off-center harmonics of Thelonious Monk -- Coates' pianistics cum oral sound effects reach very deep. Incidentally, judging by the final two numbers, Langosch and Coates fit like hand in glove.

The duo performs again this evening.