The Velvet Underground are arguably the most important American band of the second half of the '60s, but few seemed to think so at the time. The Velvets flew under the radar of public recognition through most of their career, and no one bothered to professionally record their live shows between 1966 and 1970. There have been plenty of authorized and illicit releases of Velvets live tapes (mostly audience recordings) since the early '70s, but one thing they had in common was compromised fidelity; in terms of audio, "pretty OK" is as good as they get, and for fans, listening for the music through the murk is a frustrating challenge. In November 1969, the Velvet Underground played a two-night stand at the Matrix, a club in San Francisco that had a four-track recording rig wired into its sound system; the four sets the band played were taped, and rough mixes of those shows were featured on the fine collection 1969: Velvet Underground Live, and they ranked with the very best VU live documents despite the hiss that hovered over the music. More than 40 years after that album was released, the original Matrix four-track masters have been remixed and remastered, and the four-disc box set The Complete Matrix Tapes marks the first time this material has been released in full. Though extensive excerpts from the new mixes appeared on the expanded 45th anniversary edition of the VU's self-titled third album, and many of these performances are familiar to folks who know 1969: VU Live well, this set's fidelity is a major selling point, even if you're not an audiophile. The Complete Matrix Tapes offers over four and a half hours of the Velvet Underground playing well and recorded with unobtrusive clarity, allowing the listener to hear the details of the performances and the ambience of the room as never before, and it's a remarkably exciting listen. As four sets appear in full, several songs are repeated (each disc includes takes of "Heroin," "Some Kinda Love," and "We're Gonna Have a Real Good Time Together"), but each performance has a personality of its own, and hearing how the band reshaped the longer numbers in repeated versions is a delight for fans into the minutia. (Lou Reed also changes up the lyrics on a few numbers here.) And while conventional wisdom has it that the post-John Cale edition of the band was less fiery and inventive, this lineup -- Reed on guitar and vocals, Sterling Morrison on guitar, Doug Yule on bass and organ, and Maureen Tucker on drums -- plays with strength, commitment, and a sense of adventure that ranks with their best and most purely enjoyable work. The bulk and repetition of The Complete Matrix Tapes will scare away a few casual observers, but anyone who wants to know how this band sounded on-stage on two good nights will find this to be a revelation; it's the best and best-sounding VU live release to date.