Pink Floyd: David Gilmour (vocals, guitar); Roger Waters (vocals, bass instrument); Richard Wright (keyboards); Nick Mason (drums, percussion).

Additional personnel: John Aldis Choir (background vocals).

When rock operas by the Kinks and the Who were relatively new and Deep Purple was working with the Royal Philharmonic Orchestra, Pink Floyd entered the '70s with ATOM HEART MOTHER, a symphonic endeavor whose centerpieces are two long compositions divided up into movements. Starting out as a chord sequence written by Dave Gilmour, the title track became a sprawling masterpiece co-written and arranged by Scottish composer Ron Geesin. Throughout 20 minutes of movements titled "Breast Milky," "Funky Dung," and "Mind Your Throat Please," grandiose brass sections bubble over, otherworldly choruses strike a chord of impending doom, and individual Floyd contributions pop up amid all the orchestration.

The other sprawling piece, "Alan's Psychedelic Breakfast," starts out with the sounds of someone puttering about in his home and occasionally muttering to himself, broken up by either the swirling keyboards of Richard Wright or the dulcet tones of David Gilmour's acoustic guitar. The remaining three tracks are Roger Waters' folkie ballad "If," the baroque psychedelic pop of Wright's "Summer '68," and Gilmour's "Fat Old Sun." ATOM HEART MOTHER is one of the band's more overtly experimental and challenging works; yet it remains a secret favorite of die-hard fans.