At The Guardian, author/musician Stephen Thrower — a member of Coil and Cyclobe — presents a fascinating primer on horror movie soundtracks. Links galore too. From The Guardian:
If I had to choose just one great horror soundtrack from the 1970s, I'd go for The Texas Chain Saw Massacre. Relentless, disturbing and totally "out-there", this groundbreaking work arose out of free improvisations by the film's director Tobe Hooper and his musical associate Wayne Bell. Rather than composing melodic themes for the characters, or dutifully applying motifs to particular events, Hooper and Bell approached the soundtrack like vengeful deities, raining down storms of pure nightmare. The sound design rumbles with elemental violence; it's difficult to discern precisely which musical instruments, if any, are responsible. When I spoke to Bell a few years ago he told me that a signature ingredient was "an upright bass, which we did all sorts of torturous things to during the Chain Saw sessions". There's also lots of tape manipulation (slowed-down and speeded-up gongs), and what sounds like a heavily asthmatic pedal-steel guitar (it is set in Texas, after all). Hooper and Bell smear these cues (with ad hoc titles such as Seethe and Madness) throughout the film, creating a dense, expressionist impasto into which screams, chainsaw engine noise and murderous gibbering are embedded; the effect is to completely mire you in the film's claustrophobic horror.