I highly recommend reading this very thoughtful essay by thoughtful essayist Alex Ross in The New Yorker:
Music can take control of the image; it can also suggest a world separate from the image, or expose the image as a lie. Shortly after sound came in, Eisenstein and other Soviet directors wrote a manifesto declaring that soundtracks should create “sharp discord” with the visual dimension, in order to cultivate critical thinking on the part of the audience. (That’s not quite what Stalin had in mind, of course.) One early illustration of the practice was Shostakovich’s 1929 score for “The New Babylon,” a story of the Paris Commune. At the end, when the Communards are killed by a firing squad, Shostakovich responds not with a tragic utterance but with a distorted version of Offenbach’s Can-Can.
When the images themselves are terrifying, music can bring about an even trickier reversal, providing ironic reassurance or genuine compassion. Stanley Kubrick’s decision to play “We’ll Meet Again” over a montage of nuclear annihilation at the end of “Dr. Strangelove” is one famous example; another is Oliver Stone’s use of Barber’s velvety “Adagio for Strings” over scenes of carnage in “Platoon.” Harold Budd and Robin Guthrie, in their score for the new Gregg Araki film “Mysterious Skin,” do something wholly unexpected: as a horrendous story of child abuse in a Kansas town unfolds, the music sways toward a state of irrational bliss, as if to numb the pain. Music, in these cases, doesn’t show the image as a lie; instead, it is itself the lie we tell ourselves in order to survive.