At first it seems so simple, almost archetypal: saxophone and guitar; tunes and chords. Shades of Getz and Gilberto, of Clarence and the Boss. The two instruments sound great together, the melodic, vocal tones of one against the strumming, chiming timbres of the other.

When Andy Sheppard and John Parricelli play in unison, as they do in the concluding section of He Stood in His Shoes and He Wondered, there's an "odd couple" appeal in the sound. The gruff, Walter Matthau-like tenor sax rubs along with the more clipped, precise tones of the electric guitar. Yet the guitar (like Jack Lemmon's character), has a potential for barely suppressed rage: fiery outbursts, noises and power chords.

What Sheppard and Parricelli do is far from simple. Their compositions are subtle and complex, with rich harmonies, singing melodies, crafted structures and neat bridges. Each piece is orchestrated to make the most of the tonal palette: Parricelli's three guitars and accompanying electronics and Sheppard's soprano and tenor saxes.

The repertoire makes extensive use of Parricelli's high-fidelity sampling gear: a funky vamp for Say So; a chilled waltz for Reverie; a dense electronic carpet for the aforementioned Wondered.

Alfredo, a sentimental, Cinema Paradiso-inspired piece by Parricelli, uses a mind-boggling 36-bar loop. The guitarist records the long, accompanying chord sequence live into his sampler while Sheppard plays over the top; Parricelli hits a foot pedal and takes the next solo - sounding unreasonably relaxed and creative - over his own, freshly recorded accompaniment.

There's little space for error; no other musicians to cover the joins. Sheppard takes different risks: after the delicate theme of Touch, he plays a long soprano cadenza using circular breathing. Good showmanship, of course, but there's no lack of musical content.

Sheppard and Parricelli make many supposedly "edgy" performers seem tame and musically impoverished: the duo's hour of high-wire performance produces a polished and entertaining example of quintessentially British jazz.

But you have to listen: some of the best moments are the quietest. A laser-printed card on each table says: "Patrons are reminded that they are REQUIRED to keep as QUIET as possible when artists are performing." The Ronnie's crowd, wowed by the duo, appreciates every nuance.

· Until Saturday. Box office: 020-7439 0747.