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).

Appearing after the sprawling, unfocused double-album set Ummagumma, Atom Heart Mother may boast more focus, even a concept, yet that doesn't mean it's more accessible. If anything, this is the most impenetrable album Pink Floyd released while on Harvest, which also makes it one of the most interesting of the era. Still, it may be an acquired taste even for fans, especially since it kicks off with a side-long, 23-minute extended orchestral piece that may not seem to head anywhere, but is often intriguing, more in what it suggests than what it achieves. Then, on the second side, Roger Waters, David Gilmour, and Rick Wright have a song apiece, winding up with the group composition "Alan's Psychedelic Breakfast" wrapping it up. Of these, Waters begins developing the voice that made him the group's lead songwriter during their classic era with "If," while Wright has an appealingly mannered, very English psychedelic fantasia on "Summer 68," and Gilmour's "Fat Old Sun" meanders quietly before ending with a guitar workout that leaves no impression. "Alan's Psychedelic Breakfast," the 12-minute opus that ends the album, does the same thing, floating for several minutes before ending on a drawn-out jam that finally gets the piece moving. So, there are interesting moments scattered throughout the record, and the work that initially seems so impenetrable winds up being Atom Heart Mother's strongest moment. That it lasts an entire side illustrates that Pink Floyd was getting better with the larger picture instead of the details, since the second side just winds up falling off the tracks, no matter how many good moments there are. This lack of focus means Atom Heart Mother will largely be for cultists, but its unevenness means there's also a lot to cherish here. ~ Stephen Thomas Erlewine

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.