Noise Floor

The noise floor defines the amplitude of the sum of all noise sources and other unwanted signals within a system. This could be the ambient acoustic noise in a room, or the electrical noise in a recording system or other audio equipment. In  a high quality audio system the noise floor is typically around -100dBu or better. The total dynamic range capability of a system is normally defined as the difference in amplitude between the noise floor and the highest signal that can be passed without distortion.