Various, Brooklyn Jazz Underground, Volume 3 (BJU). If you have heard that Brooklyn is a hotbed of young jazz artists but haven’t the foggiest idea what they are about, this compilation will give you a summary. Twenty-eight musicians in combinations from a duo to a sextet stretch your ears and the definition–if there is one–of jazz. The diversity of approaches includes a viola-bass clarinet duet that sounds like French impressionism and a fine “Body and Soul” by tenor saxophonist Jerome Sabbagh.