Ada is a guided improvisation for violin and computer based on the opening Adagio movement of Bach's first solo violin sonata. The florid ornamentation of Bach's composition evokes traditions and practices of other times and places and conjures up an ensemble that is violin-derived but far from the Baroque. The computer tracks, recalls, and matches material across time to create a responsive but unpredictable accompaniment, combining phase vocoding resynthesis of the live performance with assemblages of sampled violin and mandolin timbres.