As we try to start our video link it looks like the technology is not going to work. ‘That was the shortest interview in the history of interviews,’ says Cate Blanchett. ‘Goodbye – write what you like!’

Problem sorted, we get to talk about her new film, which tells the story of Tár, a lesbian composer, conductor and writer who lives in lavishly spacious apartments in New York and Berlin with her partner and their adopted daughter. The story is all about power struggles, particularly in the conducting world, and is unremitting in its intensity. Much of the camerawork is near claustrophobic, while the boom-heavy soundtrack makes every opening door or cup being placed on a saucer sound like explosions.

The classical music world is presented as a bear pit. Beside it the opera film Meeting Venus (István Szabó, 1991) is a lark, if ultimately more credible in its variety. TÁR carries quasi-political subcurrents, as does Fellini's wonderfully deft and daft Prova d'orchestra (Orchestra Rehearsal, 1979), but it has none of Fellini's sense of satire, seeking instead to meld melodramatic intensity with fly-on-the-wall frankness.

‘It's about process rather than outcome,’ says Blanchett. ‘It's a rehearsal film. And process, as we all know, is painstaking and often painful. I know this from my own profession as well as from the toe I've dipped into the classical music world. While searching for the islands of joy and release that can come in a performance, the rehearsal process can be quite brutal. The narrative in TÁR isn't open and closed – it's not a film about conducting – so it made me think a lot about architects, sculptors, painters and dancers, as much as I did about musicians.’

Blanchett's character Tár trained as a pianist before turning to conducting. ‘I was talking to the conductor Simone Young the other day, who said the traditional way up is to start as an accompanist because the piano is like an orchestra in its own right. So playing the piano and conducting are things my character does like breathing.’ At its heart, Blanchett says the film is about ‘what happens when you come close to unassailable power and how that can be quite a corrupting force. I don't just mean in a “cancel culture” sense, I mean how it can be a corrupting force in relation to your own creativity. The character I play is someone who has become estranged from herself and the wellspring of her creativity. It's a journey back to that in all its glory and all its humiliation.’

Coming in at 158 minutes, TÁR is a long, measured film rather in the way of Visconti's Death in Venice, which similarly follows a composer through a decline of authority, unrequited young love and incipient hopelessness towards a disappearance into the bleak. Tár also happens to be rehearsing Mahler's Fifth Symphony, the Adagietto in particular. Blanchett apparently improvised the line in which she exhorts the players not to think of Visconti, but it is hard not to spot this as an ‘in’ reference in a film that is supremely self-conscious. For her the key reference in this context is with Mahler, upon whom Visconti mapped the central character in Thomas Mann's book, following a clue in one of Mann's letters.

‘My character is nearing her 50th birthday and has come to the end of a cycle – she's about to complete her final recording of Mahler's symphonies in her lifelong ambition to match Mahler, so there are definitely some parallels. But there's also a destructive urge that comes from knowing when you've come to the end of something. You have to wrench yourself away from the glory, go down into the trench and create anew. I think that that's the mark of a genuine creative life. Look at Mahler's own life: he dominated the stage and redefined conducting in so many ways. He was absolutely in control of every action of every player, in the search for artistic perfection in every dimension, yet his own life was incredibly painful.’

Each of the film's apartments contains a piano, which become sinister, looming presences. They seem to haunt the drama like Tár's doppelgänger. ‘Those extraordinary concert grands look like coffins when they're closed, but then you exhume the body of whomever you're playing, often long dead,’ says Blanchett. For her, these instruments are ‘like a dead body – something to be reckoned with.’

Blanchett at the keyboard in TÁR © COURTESY OF FOCUS FEATURES

This is not an accidental association. ‘I learnt the piano as a girl and played with great fervour. The last time I saw my father I was playing an upright piano. He left for work when I was practising and I didn't get up to say goodbye. I was ten when he had a heart attack and died and that was my last memory of him – me sitting at the piano practising. I wonder whether that created an ambivalence in me with the instrument, because I gave up by the time I was 15 and moved into acting. I always said I must pick it up again but wonder if there was some profound resistance to it – as much as I love it.’

Blanchett says ‘it was a joy’ to return to playing the piano for TÁR. ‘I have a scene with an intractable student where I had to play the first prelude of Bach's “48” over and over again, so my ability to sit at the piano and noodle has increased. I tried to play this piece as well as possible.

‘I love the way the piano allows you to move through a series of feelings and ideas and make them manifest in a medium other than language. I love nothing better than when I can dispense with language as an actor, when something can be reduced to a gesture or a sound. Language can trick us into thinking that we understand something when we don't.’