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					Dynamic range
Dynamic range, abbreviated DR or DNR,[1] is the ratio between the
smallest and largest possible values of a changeable quantity, such as in
sound and light. It is measured as a ratio, or as a base-10 (decibel) or
base-2 (doublings, bits or stops) logarithmic value.

Dynamic range and human perception
The human senses of sight and hearing have a very high dynamic range.
A human is capable of hearing (and usefully discerning) anything from a
quiet murmur in a soundproofed room to the sound of the loudest rock
concert. Such a difference can exceed 100 dB which represents a factor of
10,000,000,000 in power. 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. Nevertheless, a
good quality audio reproduction system should be able to reproduce
accurately both the quiet sounds and the loud; similarly, a good quality
visual display system should be able to capture both shadow details in
nighttime scenes and bright areas of sunny scenes.
In practice, it is difficult to achieve the full dynamic range experienced by
humans using electronic equipment. Electronically reproduced audio and
video often uses some trickery to fit original material with a wide dynamic
range into a narrower recorded dynamic range that can more easily be
stored and reproduced: these techniques are called dynamic range
compression. For example, a good quality LCD display has a dynamic
range of around 1000:1 (commercially the dynamic range is often called
the "contrast ratio" meaning the full-on/full-off luminance ratio), and some
of the latest CMOS image sensors now have measured dynamic ranges of
about 11,000:1 (reported as 13.5 stops, or doublings, equivalent to binary
bits).[2] Paper reflectance can achieve a dynamic range of about
100:1.[dubious – discuss] Professional ENG Camcorders such as Sony Digital
Betacam currently achieves dynamic ranges of greater than 90dB in audio
recording.[3]
When showing a movie or a game, a display is able to show both shadowy
nighttime scenes and bright outdoor sunlit scenes, but in fact the level of
light coming from the display is much the same for both types of scene
(perhaps different by a factor of 10). Knowing that the display does not
have a huge dynamic range, the program makers do not attempt to make
the nighttime scenes millions of times less bright than the daytime scenes,
but instead use other cues to suggest night or day. A nighttime scene will
usually contain duller colours and will often be lit with blue lighting, which
reflects the way that the human eye sees colours at low light levels.
Audio
Audio engineers often use dynamic range to describe the ratio of the
amplitude of the loudest possible undistorted sine wave to the root mean
square (rms) noise amplitude, say of a microphone or loudspeaker.
The dynamic range of human hearing is roughly 140 dB.[4][dubious – discuss]
The dynamic range of music as normally perceived in a concert hall
doesn't exceed 80 dB, and human speech is normally perceived over a
range of about 40 dB.[5]
The dynamic range differs from the ratio of the maximum to minimum
amplitude a given device can record, as a properly dithered recording
device can record signals well below the rms noise amplitude (noise floor).
For example, if the ceiling of a device is 5V (rms) and the noise floor is
10uV (rms) then the dynamic range is 500000:1, or 114 dB:


In digital audio theory the dynamic range is limited by quantization error.
The maximum achievable dynamic range for a digital audio system with Q-
bit uniform quantization is calculated as the ratio of the largest sine-wave
rms to rms noise is:[6]


The maximum achievable signal-to-noise ratio (SNR) for a digital audio
system with Q-bit uniform quantization is


The 16-bit compact disc has a theoretical dynamic range of about 96 dB[7]
(or about 98 dB for sinusoidal signals, per the formula[6]). Digital audio with
20-bit digitization is theoretically capable of 120 dB dynamic range;
similarly, 24-bit digital audio calculates to 144 dB dynamic range.[4] All
digital audio recording and playback chains include input and output
converters and associated analog circuitry, significantly limiting practical
dynamic range. Observed 16-bit digital audio dynamic range is about 90
dB.[7]
Dynamic range in analog audio is the difference between low-level thermal
noise in the electronic circuitry and high-level signal saturation resulting in
increased distortion and, if pushed higher, clipping.[4] Multiple noise
processes determine the noise floor of a system. Noise can be picked up
from microphone self-noise, preamp noise, wiring and interconnection
noise, media noise, etc. Early 78 rpm phonograph discs had a dynamic
range of up to 40 dB,[8] soon reduced to 30 dB and worse due to wear
from repeated play. German magnetic tape in 1941 was reported to have
had a dynamic range of 60 dB,[9] though modern day restoration experts of
such tapes note 45-50 dB as the observed dynamic range.[10] Ampex tape
recorders in the 1950s achieved 60 dB in practical usage,[9] though tape
formulations such as Scotch 111 boasted 68 dB dynamic range.[11] In the
1960s, improvements in tape formulation processes resulted in 7 dB
greater range,[11] and Ray Dolby developed the Dolby A-Type noise
reduction system that increased low- and mid-frequency dynamic range on
magnetic tape by 10 dB, and high-frequency by 15 dB, using companding
(compression and expansion) of four frequency bands.[12] The peak of
professional analog magnetic recording tape technology reached 90 dB
dynamic range in the midband frequencies at 3% distortion, or about 80 dB
in practical broadband applications.[11] The Dolby SR noise reduction
system gave a 20 dB further increased range resulting in 110 dB in the
midband frequencies at 3% distortion.[13] Compact Cassette tape
performance ranges from 50 to 56 dB depending on tape formulation, with
Metal Type IV tapes giving the greatest dynamic range, and systems such
as XDR, dbx and Dolby noise reduction system increasing it further.
Specialized bias and record head improvements by Nakamichi and
Tandberg combined with Dolby C noise reduction yielded 72 dB dynamic
range for the cassette. Vinyl microgroove phonograph records typically
yield 55-65 dB, though the first play of the higher-fidelity outer rings can
achieve a dynamic range of 70 dB.[14] The rugged elements of moving-coil
microphones can have a dynamic range of up to 140 dB (at increased
distortion), while condenser microphones are limited by the overloading of
their associated electronic circuitry.[4] Practical considerations of
acceptable distortion levels in microphones combined with typical practices
in a recording studio result in a useful operating range of 125 dB.[15]
In 1981, researchers at Ampex determined that a dynamic range of 118 dB
on a dithered digital audio stream was necessary for subjective noise-free
playback of music in quiet listening environments.[16]
Since the early 1990s, it has been recommended by several authorities,
including the Audio Engineering Society, that measurements of dynamic
range be made with an audio signal present, which is then filtered out to
get the noise floor.[17] This avoids questionable measurements based on
the use of blank media, or muting circuits.
Music
In music, dynamic range is the difference between the quietest and loudest
volume of an instrument, part or piece of music. In modern recording, this
range is often limited through audio level compression, which allows for
louder volume, but can make the recording sound less exciting or live.[18]
Popular music typically has a dynamic range of 6 to 10 dB, with some
forms of music having as little as 1 dB or as much as 15 dB.[19] See
Loudness war for additional information.

				
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