Sound is probably the most malleable intangible, and one of the most exacting shapers is American composer Mario Davidovsky. Last night at the Terrace Theater, contemporary music specialists Speculum Musicae and an anonymous tape machine offered a four-piece survey of Davidovsky's past two decades.

He established himself during the '60s as a pioneer of mixed-media works, then reapplied what he referred to after the concert as the "protoplasmic acoustical" possibilities of electronic taped sounds to conventional instruments. "Synchronisms No. 6 for Piano and Electronic Tape," his Pulitzer Prize-winning duo from 1970, showed convincingly that the constraints a live performer, in this instance Aleck Karis, faces with a mechanical accompanist need not rob the music of feeling. Karis was forceful and precise, an ideal partner for the electronic sounds that enlarged, imitated and opposed his piano timbres.

"Chacona" (1972) for piano trio and "String Trio" (1981) each possessed abundantly energetic ideas clearly focused in the short duration of a single movement. Equally inventive was "Romancero," for soprano and chamber quartet. Judith Bettina sang the Spanish texts splendidly against a shifting canvas of strings and winds that featured such novel pairings as piccolo and high-register cello, and bass clarinet with alto flute.