Few albums start as rowdily as Deep Purple in Rock, with a guitar caterwaul that resolves into stately church organ and then sudden, screaming heavy rock (“Speed King”). That’s the level of intensity the Purps maintain throughout this startling 1970 classic. “Child in Time” is the peak of bug-eyed drama—over 10 minutes building from nothing to everything—but this is an album of giddy confidence, whether bludgeoning everyone aside in “Flight of the Rat” or swaggering weightily through “Into the Fire.”