This week's music features only the human voice: a capella music, from single voices like ultimately skilled Bobby McFerrin [left] to versatile groups like the most famous a capella singers Rockapella, hilarious singers Moosebutter, and Sweden's virtuoso Real Group [right]. The songs & artists are here.

Other featured acapella wizzes: American groups Insideout, Take 6, Spiralmouth, Moosebutter, Tonic Sol-fa, and Mosaic, Georgian (Russian) Rustavi Ensemble, Britain's The King's Singers, and acapella tracks from classic songs by Smokey Robinson & the Miracles, Marvin Gaye, and Yes.