Album: Sia - Music

It’s difficult to know where to start with Sia’s Music. The album is billed as a collection of songs “from and inspired by” the film of the same name – so not a soundtrack, except for when it is.

It tracks range from candy coated to overly earnest; liberated to sexless; pop fun to cinematic; oblique storytelling to big-name co-writes – and yet, as delivered in the Australian singer’s distinctive, powerful voice, have a tendency to blur into one.

The album starts strongly with “Together”. Co-written with star producer Jack Antonoff, it’s a huge pop number that taps into both artists’ strengths, combining irresistible hooks with theatrical flair. Its references to the powers of music and self-love – rainbows, Stevie Wonder and, um, “The Lion Sleeps Tonite” – mesh well with the theme and colour palette of the film, the trailer of which it has already soundtracked. A full-length music video features frequent collaborator Maggie Ziegler in character as the titular Music, the non-verbal autistic woman whose story the film purports to tell – the bright colours and uplifting melody at odds with the hostility with which Sia, who co-wrote and directed the film, responded to autistic critics of her decision to cast a neurotypical actor in the role.

The title track – performed by Kate Hudson in the film – is at the opposite end of the scale: a cinematic power ballad with a grand orchestral backing and lyrics that, could, I suppose, be read as serenading either Music the character or music as art form and life blood. The problem, though, is Sia’s vocal: what floats and bounces above the collection’s poppier numbers drags on the slower tracks, leaving lyrics frequently indecipherable and nuance lost.

As the line between pop song and musical theatre grows increasingly blurry, it’s easy to see the temptation to conflate the two – but a comparison of Sia’s “Beautiful Things Can Happen”, choking in unresolved dramatic tension, with Hamilton star Leslie Odom Jr.’s version in the film is a masterclass in reasons to resist. In the absence of the full track list for the film’s soundtrack (note to self: typing “music” into the search field on Spotify was never going to get you anywhere) you can’t help but wonder if the same could be said of the other weaker tracks: “Floating in Space” which, when combined with a washed-out vocal, manages to make the riff from “Cheap Thrills” sound tired; or “Eye To Eye”, which strings together cliches about “letting it go” and “feeling it all” over a wishy-washy electropop backdrop. Then there’s “Courage To Change” with its dreary, repetitive chorus – although, given that one’s a re-do of Sia’s co-write on the last P!nk album in all but name, you could definitely be forgiven for thinking you’ve heard that one before.

Sia’s way with a pop banger remains unmatched, and there’s evidence all over Music. It’s in the "all the single ladies” schtick of “Hey Boy”; so good that a second version, featuring Nigerian reggae star Burna Boy, closes out the album. It’s in “Saved My Life”, a stadium-sized slow burner co-written with Dua Lipa. It’s just a shame that there aren’t enough of them.

• More new music reviews on theartsdesk