Is it art? Is it performance? Or is it just PJ Harvey being ace, in a box?

While we wait to take our turn to become a sort of strangely sanctioned voyeur as PJ Harvey records her ninth album, thinking about what’s ahead feels peculiar. Essentially, we’re going to see PJ (Polly Jean) Harvey, her band, producers Flood and John Parish, a photographer and two engineers making an album in a Something & Son-designed box, formed of glass that allows visitors to see in, while the musicians can’t see out.

The broader intention is that this becomes not just a recording session that happens to have people watching it; but to blur the lines between sculpture, musical artist and performance artist. The literature surrounding the month-long event, imaginatively titled Recording in Progress, almost pitches PJ Harvey herself as a sort of artwork, or maybe actor, if indeed she can keep up a “role” as a Marina Abramović-like durational performative piece.

Those around me as I mull all this over are a varied bunch: there’s an apparently agitated duo of middle-aged, taut-faced, blonde French women; numerous middle-aged men in glasses with black, thick rims; a token bearded 20-something (you know, the sort of booted, braced young fellow who might fund a quirky breakfast enterprise on Kickstarter); and a man in a Libertines T-shirt.

As we’re ushered in, there’s less of a feeling of voyeurism than I expected. I get the sense some of the men think she can perhaps see them, making sure everyone knows just how musical they are by giving one another appreciative looks when Polly announces chord progressions. The photographer in the box snaps away, and it all feels terribly postmodern: us, out here, watching a man watching a musician.

It also feels far less staged: while there’s a definite sense of the room being a set (there’s a PJ Harvey crest emblazoned on the wall, numerous exotic percussion instruments are laid about the place, nestled alongside paper Caffe Nero cups), the sheer normality of the interactions within suggest anything but a performance. It’s all reassuringly pedestrian – it’s no Happy Mondays recording mash-up in Barbados.

Speakers are set around the viewing area outside the box, and what comes out of them when things are actually happening is really rather beautiful. There’s a guitar line that sounds eerily similar to this David Lynch track; and the tone of the bass clarinet is velvety and sublime. What we see is that like all creative endeavours, recording an album is a wonderfully imprecise science: “that feels about right, doesn’t it?”, asks Polly when trying out the length of a reggae intro.

Polly herself cuts a diminutive figure, yet a powerful presence. Her speaking voice is almost teacherish in its intonation, and she talks in a West Country lilt sitting with one long, spidery leg draped over the other. Where this all tumbles down into what we know of PJ Harvey is in the crashing disparity between her apparent normality and her voice – the thing that’s made her PJ Harvey, and not Polly. Even just vocally sketching out ideas acapella, she sounds incredible, conveying oceans of emotion and a rawness that jars with the clinical setting.

As we watch the recording of the numerous little fragments that will soon make up an album, we’re not really seeing performance art, or a sculpture, but little shards of creativity and sound that can be slow, even tedious. We begin to get a shred of understanding on how these, coupled with the sensitivity, ecstasy, and even pain that the artist puts in go on to create something whole, strong and, in the case of PJ Harvey, often jaggedly unnerving.

This isn’t a performance at all: we’re just seeing PJ Harvey and her band making sense of the gorgeous little things that have been going on in her head, wrestling them from demo into something final. As we watch through the glass, the low lighting and large panels are like the zoo outhouses where things like chinchillas and exotically-named marsupials live. The energy is similar: the musicians are measured, slow, sleepy even. But as we settle in, the 45 minutes feels like it’s over before it’s begun. It’s transfixing seeing how making something that will surely sound so powerful can feel so pedestrian. The very odd thing is that all we’re doing, really, is watching a woman in a box. But it’s PJ Harvey in a box – and somehow, that feels quite special.