"A human can see objects in starlight (although colour differentiation is reduced at low light levels) or in bright sunlight, even though on a moonless night objects receive 1/1,000,000,000 of the illumination they would on a bright sunny day: that is a dynamic range of 90 dB. A human cannot perform these feats of perception at both extremes of the scale at the same time. The eyes take time to adjust to different light levels and the dynamic range of the human eye in a given scene is actually quite limited due to optical glare. The instantaneous dynamic range of human audio perception is similarly subject to masking, so that, for example, a whisper cannot be heard in loud surroundings."