Alfred Hitchcock's grisly horror, which turns 65 this month, might not have become known as an-all time classic without the crucial addition of Bernard Herrmann's disturbing score.

Screaming violas that sound like they're coming out of an abattoir. Thumping bass notes, which slowly decrease in speed and seem to imitate a victim's faltering heartbeat. Take away composer Bernard Herrmann's score for director Alfred Hitchcock's Psycho, which turns 65 this month, and it's fair to say this 1960 horror film wouldn't have the same nerve-shredding impact.

Particularly key is the knives-edge music that plays when blonde bombshell Marion Crane (Janet Leigh), not long after checking in to the Bates Motel, is attacked through a shower curtain by a shadowy killer, who later turns out to be the motel's owner, Norman Bates (Anthony Perkins), dressed up as his dead mother. "That music is everything," says Rachel Zeffira, a film composer and one half of art-folk duo Cat's Eyes. "It's the birds, it's the bees, and it's the voices in the back of your head."

The project had seemed ill-starred from the start, with executives at Paramount (who had produced Hitchcock's previous five films) showing little interest, not allowing him to film it on their lot, and only distributing it rather than producing it themselves. But despite a paltry budget, Hitchcock proved everybody wrong, and for that he could partly thank Herrmann and his knack for crafting compositions that lifted scenes to new heights.

"Psycho was certainly not a bad film before it was scored, but it lacked tension," explains Steve C Smith, the author of a new book, Hitchcock and Herrmann: The Friendship and Film Scores that Changed Cinema. Herrmann proceeded to give the film a much-needed jolt by writing music for an all-string 50-person orchestra that marked a "return to pure ice water", as the composer described it to Sight and Sound.

In the case of the most famous scene, this resulted in a chorus of psychologically jarring, high-pitched squeals that meant terrified audiences no longer saw the shower as a safe space. "Before the shower scene many of the musical cues have a depressive quality and they're not really that loud," Smith says. "But suddenly with the shower scene, the mutes are off the strings, and they screech animalistically. This creates a clever link with Norman Bates, the taxidermist of birds."

Herrmann forced an initially dismissive Hitchcock to watch the shower sequence both with and without his jump-scare music. "Oh yes, we must use it!" Hitchcock concurred. "But I thought you didn't want my music here?" Herrmann sarcastically replied, before the director scoffed: "My boy, improper suggestion."

It's an anecdote that reflects the pair's fiery partnership. Their creative union consistently resulted in film scores that make the viewer feel like they are caught up in a character's murky inner dialogue, privy to both their most romantic dreams and most hopeless nightmares (see Vertigo). Zeffira describes the music that plays whenever Norman Bates is on screen as being "dejected and anxious", which she says "makes you feel sorrow for a killer. I know before writing film music, Hermann would always read the novel a movie was based on and study the literature, so his score was more empathetic. Every note Herrmann played had meaning".

An avid childhood reader, Herrmann (or Benny as he was called by friends) spent most of his downtime passionately debating whether literature or music was the greatest art form. Music ultimately won out,........

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