This is a filter that optimizes the signal-to-noise ratio of your playback, to remove sound distortion and make the overall sound 'cleaner'. This is usually an automated process built-in to the head unit's playback system.
removing unwanted noise from a signal. For video this is accomplished with filters such as blur, mean, or median. Uniform noise reduction applies one filter equally to each pixel. Adaptive noise reduction applies different filters to different kinds of noise.
The difference in sound level between the source (talker) and receiver (listener) locations in a room or between rooms. The NR is dependent on the distance between each, the absorptive materials in the space, and the intervening acoustical barriers such as furniture panels or wall partitions.