At times, it seems that electronic devices have become the foremost instruments in jazz. Echo units. Phasers. Harmonizers. Distortion boosters. While many musicians use these wisely, as tools for musical expression, others become the tools themselves, more like conductors in the printed circuitry of the electric effect. This situation was displayed onstage last night at the Warner Theater.

Brazillian singer Flora Purim and percussionist Airto, with their five-piece backup group, employed various devices in their show. A single trumpet became a sprightly South American brass section with the aid of a harmonizer; Purim's vocals wove their way through a dense fabric of echoed voices and noises. These were set against a background of contrasting rhythms and shifting theme lines that created an elegant tapestry of sound.

The soft intensity of Purim's singing, complemented by the fiery percussive outbursts of Airto, produced a sound that was forceful, yet also delicate and rich in musical detail.

Violinist Noel Pointer opened the show with a dismal collection of fusion-pop songs. Lacking any particular musical substance, Pointer and his group attempted to compensate for their deficiencies by using an array of electronic gadgets. The most bothersome of these was a fiendish echo gizmo that was applied to banal melody lines that became oppressive in their electrified repetition. The result was a performance by Pointer that was dull, dull, dull. . . .