As part of the ongoing "Impossible Music" exhibition at Tufts University Art Galleries, the Tufts New Music Ensemble — with special guest John McDonald — will perform a selection from Tom Johnson’s "Imaginary Music" series (1974-1975, 1993). Containing a total of 104 scores, these drawings of musical symbols or loose suggestions of notes promote non-linear interpretations, and Johnson used them as tools to imagine new musical possibilities. Free and open to the public with no tickets required. On view until April…