the silence of a voice that has gone
Silence of presence v. silence of absence, maybe. The silences on the tapes are the worst.
Context
The engineer monitoring a dead microphone distinguishes the theme's two silences: the silence of a present person choosing not to speak, and the silence of pure absence — and the second is unbearable. The damaged late-night listeners who trek into the studio to check whether the voice is still there, mutely present but withholding, are the far end of broadcast intimacy: people who cannot tell a withheld presence from a total absence, inquiring after a person who was only ever a voice and is now not even that.