Answer:

inaudible

AnswerCrossword Clue
INAUDIBLEImpossible to pick up
INAUDIBLELike sound frequencies above 20 kHz or so, to humans
INAUDIBLEToo soft to hear
INAUDIBLEOpposite of deafening.
INAUDIBLESilent, or almost so
INAUDIBLENot picked up
INAUDIBLELike many a whisper