1. At a given frequency, the rate at which the sound level in a room decreases after a source stops emitting sound; expressed in decibels per second (dB/s). 2. Of sound waves in an enclosed space, the rate at which the soundpressure
level of reverberation decreases; usually expressed in decibels per second.
3. Of a vibrating mechanical system, the rate at which some stated characteristic (such as the amplitude of vibration) decreases with time.