Passersby of the Apex Building at Seventh and Pennsylvania may wonder where the jazz-oriented lunchtime music comes from. They'd be hard-pressed to guess that it comes from the Baltic coast via Bread and Salt, a trio of Yugoslav musicians who are providing the incidental music for the Zagreb Theatre Company, in residence at the Source Theatre through Aug. 29.

Guitarist Vlatko Stefanovski and bassist Bodan Arsovski have been together since 1976 and were recently joined by a new drummer, Dragoljub Djuricic. While there has also been an occasional keyboard player, Bread and Salt has functioned primarily in a trio format. It has put out five albums, with a sixth due out in the fall; the format sounds familiarly American -- it's a double live album.

The group, which can count on selling 30,000 albums in its homeland, has recently changed its musical approach. "We used to do more folk influeneced material, Macedonian folk music," says Stefanovski. "Now we are more jazz-rock," though it's still all original material. Even on a tape of older material, Arsovski's booming and elastic bass lines are reminiscent of Jaco Pastorius and Stanley Clarke.

Although they are involved with the art-school and theatrical communities in Yugoslavia, touring in the company of actors and actresses is a bit unusual for Bread and Salt, Stefanovski says. "What we often do is create music for performances of plays but we do not perform it live, we put it on tape and give the tape to them. It's like film. This is a tour that we made together, but we just used the possibility to come here."