Dynamic range

Dynamic range (abbreviated DR, DNR, or DYR) is the ratio between the largest and smallest measurable values of a specific quantity. It is often used in the context of signals, like sound and light. It is measured either as a ratio or as a base-10 (decibel) or base-2 (doublings, bits or stops) logarithmic value of the ratio between the largest and smallest signal values.

Electronically reproduced audio and video is often processed to fit the original material with a wide dynamic range into a narrower recorded dynamic range for easier storage and reproduction. This process is called dynamic range compression.

The human senses of sight and hearing have a relatively high dynamic range. However, a human cannot perform these feats of perception at both extremes of the scale at the same time. The human eye takes time to adjust to different light levels, and its dynamic range 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.

A human is capable of hearing (and usefully discerning) anything from a quiet murmur in a soundproofed room to the loudest heavy metal concert. Such a difference can exceed 100 dB which represents a factor of 100,000 in amplitude and a factor of 10,000,000,000 in power. The dynamic range of human hearing is roughly 140 dB, varying with frequency, from the threshold of hearing (around −9 dB SPL at 3 kHz) to the threshold of pain (from 120 to 140 dB SPL). This wide dynamic range cannot be perceived all at once, however; the tensor tympani, stapedius muscle, and outer hair cells all act as mechanical dynamic range compressors to adjust the sensitivity of the ear to different ambient levels.

A human can see objects in starlight or in bright sunlight, even though on a moonless night objects receive one billionth (10⁻⁹) of the illumination they would on a bright sunny day; a dynamic range of 90 dB. Change of sensitivity is achieved in part through adjustments of the iris and slow chemical changes, which take some time.

In practice, it is difficult for humans to achieve the full dynamic experience using electronic equipment. For example, a good quality liquid-crystal display (LCD) has a dynamic range limited to around 1000:1, and some of the latest CMOS image sensors now^[when?] have measured dynamic ranges of about 23,000:1. Paper reflectance can produce a dynamic range of about 100:1. A professional video camera such as the Sony Digital Betacam achieves a dynamic range of greater than 90 dB in audio recording.

Audio engineers use dynamic range to describe the ratio of the amplitude of the loudest possible undistorted signal to the noise floor, say of a microphone or loudspeaker. Dynamic range is therefore the signal-to-noise ratio (SNR) for the case where the signal is the loudest possible for the system. For example, if the ceiling of a device is 5 V (rms) and the noise floor is 10 μV (rms) then the dynamic range is 500000:1, or 114 dB:

$${\displaystyle 20\times \log _{10}\left({\frac {\rm {5\,V}}{10\,\mu \mathrm {V} }}\right)=20\times \log _{10}(500000)=20\times 5.7=114\,\mathrm {dB} }$$