This programme has two parts: a performance of Tchaikovsky’s Fourth Symphony and a documentary that, in Michael Tilson Thomas’s words, tries to explain ‘how and why classical music is brought to life’. The film goes behind the scenes with the San Francisco Symphony to answer the ‘how’ part of that question. We see the conductor at home studying and marking the score; orchestra librarians patiently copying markings into the parts, wind players making their reeds, and the timpanist soaking natural skins for his drums in a baby’s pool backstage.

There are interviews with players and peeks into individual practice sessions. MTT and concertmaster Alexander Barantschik test different bowings in a pre-performance meeting, and a one-on-one between conductor and principal oboist William Bennett gives an inkling of the thought that goes into preparing a big solo.

It’s in its attempt to answer the ‘why’ part of the question that the documentary falls short. Tilson Thomas is an articulate, enthusiastic spokesman and he offers more than a few insights – as when he declares that Tchaikovsky’s genius was that he dared to go over-the-top, or talks about the composer as ‘a sonic cinematographer’. But there’s a distinct lack of depth to the discussion, as if the film-makers were afraid to venture beyond the rudimentary for fear of alienating their audience. As Tilson Thomas studies the score, for example, singing it aloud and playing it through on the piano, he tells us he’s in a search for details that will give him a new concept, a fresh perspective. Yet the discoveries that fuel this particular performance are never divulged.

That’s a real pity, given the excellence of the concert portion. The orchestra plays with visible involvement throughout and is in terrific shape. The strings sound dark and silken, the winds are full of character and the brass intone their fateful fanfares with stentorian splendour. Tilson Thomas moves from one section of the score to the next with a firm hand but no feeling of rigidity, and one feels he always has the entire structure in mind. The finale is particularly exhilarating, played with obvious panache. Indeed, if there’s a convincing answer to the ‘why’ question posed in the documentary, it’s right here where it should be – in the music itself.