The opening of Schubert's Rosamunde Quartet is always chilling, with its restless accompaniment and wan, haunted melody, but one recent recording makes the passage even eerier than usual.

The cello and second violin enter on an urgent whisper, setting the scene like the start of a ghost story, while the lone first violin spins a silvery, sorrowful voice high above. The playing is raw and intense, immediate and utterly captivating.

This is the Chiaroscuro Quartet, a formidable group of young players headed by the Russian violinist Alina Ibragimova.

The sound of the ensemble is broadly shaped by the fact that they play period instruments, meaning that for their core repertoire of early classical music - primarily Mozart, Schubert and early Beethoven - they use the appropriate bows and bowing techniques, with slim (if any) vibrato and gut (rather than modern synthetic) strings.

None of the quartet's members is a purist; they all play modern instruments elsewhere in their careers. Together their attack and engagement is fearsome.

Another thing that is striking about the Chiaroscuros before they have even put bow to string is that (apart from the cellist) they play standing up.

"We feel more free like that," says Ibragimova, "and we are more able to project our sound and move around. When I sit I tend to feel a little restricted." Restricted, the quartet's playing is not.

As befits the name, their range of colour and contrast is astounding.

"With gut strings you can get across the real extremes," the violinist explains. "On modern instruments a lot of the detail is glossed over."

But for all the ensemble's combined interpretive vision and technical command, much of the Chiaroscuro identity comes from Ibragimova herself. At 27 she is a rare talent indeed, peerless in her depth of focus, her musical intuition, her cool virtuosity and her knack of cutting to the emotional heart of whatever she is playing.

She is an unusually versatile musician, too, with a discography ranging from concertos by the Soviet modernist Nikolai Roslavets to recitals of Schubert, Szymanowski and solo Bach.

The first time I heard her perform live was when she premiered Huw Watkins's shimmering new Violin Concerto at the Proms in 2010. She made the barn-like Royal Albert Hall feel as intimate as a living room.

And it was that instinct for stripping away the excess and revealing the essence that first drew her to historical performance practice while still a teenager studying at the Yehudi Menuhin School.

"I remember wanting to play Bach in a way that was different," she says. "Not how my teachers were telling me to play, but the way I felt it. They wanted more vibrato, more projection, bigger gestures, bigger sound.

"I wanted something more direct - less about me!" It seems daft that any teacher would discourage an inquisitive young musician from a more direct, less egoistic performance style, but Ibragimova says she "really struggled at the time. I felt that I was on my own".

She met her fellow quartet members at the Royal College Of Music, where all four were already experimenting between modern and period playing.

"The college's period performance department was funding coaching for string quartets playing classical repertoire," Ibragimova explains, matter-of-factly, "so although we had played only baroque instruments until that point we decided to give it a go. Our first performances coincided with Mozart's bicentenary in 2005, which seemed fitting."

Things have changed a bit since, with Spaniard Pablo Hernan Benedi joining as second violinist three years ago, French cellist Claire Thirion moving back to France, Swedish violist Emilie Hornlund moving back to Sweden and Ibragimova's solo career jet-setting her around the world.

It does not sound like an easy recipe for band practice - "and now there are babies in the quartet, which complicates things further," says Ibragimova. "Basically we have to be very, very organised. Rehearsal days are holy; we're not allowed to add anything into our calendars, no matter how good an offer comes along."

For a soloist like Ibragimova, whose offers come from the classiest orchestras and festivals around the world, that must be tricky.

Does she really prioritise quartet rehearsals over concerto engagements? Yes, she says, and what becomes increasingly evident during our conversation is just how integral the quartet is to her whole musical outlook.

"We've grown up together. Musically we feed off each other. Whatever we learn in the quartet we take elsewhere. Playing in the quartet, with the amount of focus and listening that it takes, is more challenging than any of my other projects."

I suggest it works both ways - that she brings the solo side of her musical personality to the quartet - but she dismisses the idea.

"To be honest, I don't really have a solo side. For me everything is about chamber music; everything is about listening and reaction."

Anyone who has heard Ibragimova play might have pre-empted the answer. Her music making, whether in duo or quartet, whether leading an ensemble like the Britten Sinfonia or as soloist with a full-sized symphony orchestra, is always about listening. It isn't that she is a shy player - her sound is incisive and commanding - but that she is always acutely attuned to what the other musicians on stage have to say.

It is what makes her a musician's musician as much as an audience favourite. It is also an approach that, shared with the other quartet members, makes the Chiaroscuros an ensemble well worth hearing.

The Chiaroscuro Quartet play at the Queen's Hall on August 12.