While many people think of jazz strictly in terms of brilliant soloists, the heart of jazz remains essentially an ensemble music of collective improvisation that swings and employs "blue notes."

King Oliver's band, even with Armstrong's brilliant solos, was widely known for their ensemble work—the Armstrong and Oliver-improvised duet cornet breaks mystified musical sleuths who would return night after night trying to figure out how they played like that without written music.

Armstrong ...