Rock was already gettingheavier before Led Zeppelin emerged at the end of the ’60s, but their first LP,with the exploding Hindenburgcover,set the pace for the direction of hard rock in the ’70s and the rise of heavymetal. The band’s first three albums have been reissued as double CD sets.Remastered by Jimmy Page, that familiar music sounds as good as it ever did.The bonus disc accompanying the 1969 debut album features a good concertrecording from that year, revealing the band’s roots in The Yardbirds. Theadditional material on Led Zeppelin IIand III consists mainly of rough oralternate takes, interesting to fans but not essential. The albums themselves haveworn well over the years and are remarkable for their diversity. Amped-upblues-rock flows easily from Tolkienesque folk-rock—and it all makes sensetogether.