trail off

verb

1. Of a phenomenon, voice, etc.: to slowly diminish in frequency, intensity, or volume; also, to diminish more quickly over time.

   ““So that’s why I’m, uh, refusing … uh, to do that …” He trailed off as he saw Mr. Winchester’s disapproving stare.”

   “Four-fifths of the way through the piece, a kind of spell breaks. Something changes in the atmosphere of the auditorium. The temperature in the huge room seems to rise by several degrees. More concerningly and noticeably, the music behind Wheeler begins to trail off. The conductor stops too.”