In jazz, live recordings not only document an artist or group's sound in its purest form but, in rare cases, herald the arrival of a musical genre. That's the case with this invaluable, two-CD collection that captures clarinetist Benny Goodman's historic 1938 Carnegie Hall concert, which exemplified the so-called "swing era." Originally released in 1950, it contains rare commentary from Goodman and music from the entire event, which was a unique mix of formality and spontaneity.