Writer-director Ian Tuason’s feature debut, the sonic-driven horror “Undertone,” has, at least at the outset, an appealingly stripped-down quality. The 30-something Evy Babic (Nina Kiri) lives with her dying, comatose mother (Michèle Duquet). The movie never leaves their small, two-story home. Upstairs, Evy’s mother lies wordlessly in a bed. Downstairs, Evy, at 3 a.m. puts on headphones, sits in front of a microphone and calls up her paranormal podcast co-host Justin (Adam DiMarco’s voice) to