Andrew York and William Kanengiser, two members of the Los Angeles Guitar Quartet, lean toward one another, sliding their fingertips down the neck of their guitars in short swipes to create percussive whispers of sound.

Throughout yesterday night's performance, the members of the LAGQ demonstrated how far four acoustic guitars can go toward sounding like a quartet of very different instruments. The sounds of cello, flute and djembe drum all made appearances in the quartet's music. The audience was alternately left awash in the sounds of classical guitar and drawn into musical brainteasers, as the four men (York, Kanengiser, John Dearman and Scott Tennant), now 25 years into their collaboration, served up Bach fugues and Indonesian gamelan music alike.

The group's long history was evident in the feeling of calm that pervaded the LAGQ's live performance. Usually each member seemed deeply engrossed in his own instrument, merging his sound seamlessly with that of his fellow guitarists. Although this assurance surely speaks to the group's mastery of their craft, the quartet's practiced air lacks the spark of tension that should ignite live performances.

If the quartet tends toward cerebral rather than intuitive play, at least they make their intellectual projects explicit. WK explained the concept behind "Turn to the Sea," a piece from the Grammy-winning quartet's new CD, Spin.

"All this tuning between pieces is sort of boring, but it started me thinking about a piece incorporating that tuning. You'll see this piece beings with Andy (York) literally turning his B string to C."

The audience, now in on the joke, murmured appreciatively when the quartet twisted their tuning pegs to conclude the piece.

You have to see the LAGQ's claim to fame, their innovative reworkings of musical standbys, to believe and appreciate them fully. The quartet's clever manipulations are often more subtle than the ear alone can detect. But it's certainly an engaging frustration.

The payoff of this method comes in live performance. Bach's "Prelude No. 1," written for keyboard, is a long arpeggio, a repetition of a chord with each note played in succession rather than all together. The undulating line of notes seemed, strangely, to hover in the air around the guitarists, with no discernable source. Each guitarist, it turned out, was playing one of the notes in the arpeggio, with such perfect precision and effortless focus that the musicians seemed not to be playing their instruments at all.

Listening to the LAGQ's rich music, much of which was either written or arranged specifically for the group, can be an experience either of easy listening or of something close to scholarship. It comes down to a choice of the listener, and judging by the scene in the Rackham lobby where the LAGQ's CDs were selling like hotcakes, the guitar virtuosi have more eager listeners at the start of their second quarter-century than ever.