It can feel easy to cast a swift judgment on the composer Oliver Leith. First, there are his titles, such as “Uh huh, Yeah,” “Bendy Broken Telemann No.3,” and “yhyhyhyhyh.” Then, there is the inspiration for his sounds, in which everyday objects like glass bottles and cereal bowls are considered intensely, becoming weird instruments themselves.

But if Leith seems flippant, he rejects that characterization entirely.

“People talk about irony in society all the time now, and I find that a little dull,” Leith said in an interview. “It’s a very British way of looking at things. Like, ‘Oh, are you being serious or are you not?’ No; I am deadly serious when I’m doing these things. I’m just chasing this strange feeling.”

Leith’s way of talking about music is a lot like his actual music: blurry and discursive, but also precisely evocative. That strange feeling he’s chasing, for example, is one he compared to being at a wake, where “outward joy and outward sadness” are possible at the same time.

Listen to his works, and you’ll see what he means. Take his opera “Last Days,” which receives its U.S. premiere on Feb. 6 in Los Angeles as part of the Los Angeles Philharmonic’s Green Umbrella series. (The opera’s first recording will also be released on the Platoon label on April 5.) It is adapted from Gus Van Sant’s 2005 film of the same name, which fictionalizes the final days of Kurt Cobain.

During its premiere run in London, in 2022, the opera garnered a lot of attention based on the assumption that it was a biographical work. “It’s so not about Kurt Cobain,” Leith said. “It couldn’t have more distance from its subjects than it has, I think.”

Instead, Leith and the opera’s librettist, Matt Copson, wanted to write archetypes — like characters in a genre film, in which the magic lies in how far they stray from their stock expectations. Formally, “Last Days” also mirrors “the way that oral histories or myths are transmitted, where every iteration keeps the soul of a story, but changes skin,” said Caroline Polachek, who sings a prerecorded aria in the show.

Before landing on “Last Days” as a project, Leith said, he wanted to write an opera about the banal, “about somebody putting their bins out.”

“Oliver walks this impossibly contemporary tightrope,” Polachek said, “between romanticism and being quite provocatively trollish.”

Like the film, the opera “Last Days” is built around the protagonist Blake and depicts the aimless days leading up to his suicide, over a duration of about 90 minutes. “There’s many deaths in opera, but this is a particularly powerful one, because you’re not watching it happen,” said the composer Thomas Adès, who will conduct the work in Los Angeles. “I felt like you almost go through it with him. It’s very eerie.”

For Adès, “Last Days” shows “the inner psychology of a moment,” though Leith said that as a character, Blake is deliberately held at arm’s length becoming “a blank cloth to be projected on the whole way through.” Silent, except for occasional mumbled phrases, Blake drifts through the opera bereft of agency: as an idol for fans, as a cash cow for the industry, even as an everyday person caught up in the daily rigmarole of Mormons and DHL delivery drivers pestering him at his door.

But the animating tension of “Last Days” is between its visual and auditory environments, and the sound world Leith builds puts audiences very much among Blake’s blurry thoughts. “You hear what he hears, in a way,” said Adès, pointing to a scene in which Blake answers a phone call from his manager: Surtitles outline the one-sided conversation, yet all that the audience hears is the gabbling voice of a cattle auctioneer.

Leith’s score builds its world by playing with genre and expectation. Everything can sing, to varying extents: In the pit, the ensemble sings or whistles; glass bottles are precisely tuned; the pouring of cereal into a bowl becomes a crunchy texture. And all the constituent elements are selected with view of creating a heightened sense of the everyday.

The physicality of Leith’s music is linked to his formative experiences playing with recorded music as a child. With records, he said, “there’s a more physical relationship with sound. Slowing things down, speeding things up; I think that relates to every piece I’ve ever made.”

Leith, who was born in 1990, grew up in London, and as a teenager played the guitar in bands with friends. (He listened to grunge, though direct references to that fact are resisted in “Last Days”). Then, he simply stopped.

“The great mystery of my life is that I have no idea what the thing was, but suddenly I couldn’t do it anymore,” Leith said. There was something instructive in that shift, too. “I don’t want to be seen,” he added. “I don’t mind it in the peripheral, but from the front? It’s terrible.”

Yet Leith’s mind remained interested in the band sound, and in electronically enhanced sound more generally. He has released electronic music on Matthew Herbert’s label Accidental Records, and said, “In a different world I might have been a producer.”

Where other composers might imagine precisely notated, microtuned glissandos to indicate a sagging gesture, in Leith’s music, the same effect might be realized better by imagining the turning of a dial on an amp. “There’s a carefully-calibrated fuzziness in multiple musical parameters at once,” George Barton, one half of the GBSR Duo, which will perform in “Last Days,” said in an email.

“What I’m really doing,” Leith said, “is putting chorus on things.”

That thinking is reflected in the language he uses on the page of a score, too. “You don’t see many — or in fact any — ‘adagios’ or ‘allegros’ written in his scores,” said Siwan Rhys, the other member of the GBSR Duo. “Last Days” includes directions like “deflated,” “sloppy” and “Big (Puccini).” Among Rhys’s favorite suggestions in his “good day good day bad day bad day” are “fluffy and imagine spinning slowly like Alice down the hole,” and “nervous nervous feeling sick — this is the big bloody show.”

“His descriptions,” she added, “are instead uniquely and precisely his, which I think makes playing his music feel very personal.”

A moment where all these ideas fuse is in “Non Voglio Mai Vedere Il Sole Tramontare,” the aria from “Last Days.” During a rare moment in which sight and sound align, Blake sobs while listening to a highly charged recording of his favorite opera singer. What we hear is a heavily warped, Verismo pastiche, featuring Polachek singing poetic Italian over plush strings.

“The aria started by Oliver texting me what my highest note is,” Polachek said. It was a high F sharp, a semitone higher than the highest note in Mozart’s famous “Queen of the night” aria. “He said, ‘fantastic, be right back.’”

What he wrote is music that wells up for about 90 seconds, before seemingly bottled-up emotion bursts out as Polachek whooshes up the octave to the note.

“I’m very interested,” Leith said, “in the idea of being overwhelmed.”