Last night's viewing: BBC4's Sound of Cinema makes you realise just how important music can be

Occasionally, a documentary comes around that manages not only to entertain and inform you, but also to change the way you look at its subject. BBC4's magnificent Sound of Cinema: the Music That Made the Movies is one such series.

Its premise is a simple one: composer Neil Brand, the regular silent-film accompanist at the National Film Theatre, guides viewers through the history of film soundtracks. Put that baldly, it sounds a dry affair. The reality is anything but, as Brand talks to the men behind some of cinema's most memorable scores (this week, the talking heads included John Barry, Martin Scorsese and Angelo Badalamenti) while demonstrating how music works its magic on film.

That sense of magic is helped by the fact that Brand is a wonderful guide: erudite, impassioned and interesting about his subject. The moments when he picks out themes on his piano, demonstrating how a composer used this change in tempo or that difference in key to suggest everything from the sultry sensuality of A Streetcar Named Desire to the effortless cool of Steve McQueen's Bullitt, were absorbing and eye- opening, forcing you to listen to those well-known scores as though hearing them for the first time.

It also makes you realise just how important music can be. While Brand touched on commerciality and how the arrival of MTV and the pop video created a whole new outlet for the movie marketing men, he also demonstrated how films such as A Fistful of Dollars owe everything to their soundtracks, the characters remaining almost silent as the music constructs a personality for them.

There were some interesting titbits, too. We learnt that Alex North, the composer on Streetcar, had to recut the famous scene where Stanley calls for his "Stell-ah", replacing the suggestive jazz with strings to appease the National Legion of Decency; that John Barry's only knowledge of James Bond came from a comic strip in the Daily Express; and that Quentin Tarantino, arch control freak that he is, wrote Reservoir Dogs with the song choices written beside each scene.

Best of all, though, was the interview with the enthusiastic Badalamenti, who talked at length about his partnership with David Lynch and in the show's highlight, demonstrated how the director got him to score Twin Peaks: "We're in a dark wood and there's a girl… these are beautiful notes, Angelo, but slower, slower, slower… yes and this girl is beautiful but she's so sad, her name is Laura Palmer. She walks out of the woods… that's it, Angelo, reach a climax. Now we're back in the woods and there's an owl…" It was a wonderful moment, both illuminating and funny, much like this understated, intelligent and unmissable show.

The makers of Peaky Blinders would agree with Brand's theory about the right soundtrack creating the right atmosphere. There are some who feel that the period crime drama's anachronistic use of the likes of Nick Cave and Jack White undermines its credibility – as though any show featuring a brave undercover colleen with a desire to avenge her dead Pa is aiming for credible – but I feel it adds another layer of swagger to an enjoyably exuberant series.

This week we finally saw those much mentioned razors in action as the Shelby brothers entered into a war with Gypsy family the Lees, in what turned out to be an unusual way of drawing racing kingpin Billy Kimber's attention.

Not content with starting any number of gang wars, Tommy also found time to ask Grace out, informing her: "You're a posh girl, get yourself a nice dress, I'm taking you to the races at Cheltenham." Be careful, Grace, the last time a young man said that to me I ended up married and living in Shepherd's Bush with two children.