The first thing you usually notice about the Zehetmair Quartet is that, perhaps uniquely among such ensembles, they play without any music sheets in front of them. Here, however, the crispness and energy of the first bars of music grabbed the attention before that even registered. Haydn's Emperor Quartet, Op 76 No 3, is an old warhorse, but sounded like a frisky thoroughbred, especially when, after a rapt slow movement and a ballsy scherzo, first violinist Thomas Zehetmair raced away in the finale so fast the others risked being left in a cloud of dust.

Not every ensemble would thrive on the Zehetmairs' approach, but that painstaking learning of the notes clearly works for them. Bartók's Quartet No 5 offered an intriguing glimpse as to why. In order to memorise the vast score, the players must have to break down this seemingly tangled music so that rhythms and musical shapes become their memory aids. And that means the music immediately gains a sense of direction, a tautly balanced combination of freshness and inevitability. The contrast between the otherworldly stillness of the second movement and the climax of throbbing chords just before the end of the work could hardly have been greater; yet these were the two extremes of a larger, organic whole.

The playing from Zehetmair himself was not always beautiful, and the beginning of Schumann's Quartet in F, Op 41 No 2, verged on the squeaky, as had moments in the Haydn. But the slow movement had an eloquent simplicity from all four players, and their unerring focus made this rather slight but sunny work hit home. The off-the-wall encore - a spiky, skittish movement from Hindemith's Fourth Quartet - was a brave and entirely fitting choice. Rough edges and all, this concert was a refresher course in how vital and alive the string quartet as a genre can be.

· Broadcast on Radio 3 on March 12.