Dolby is particularly known for its systems of reduction of noise ( Noise Reduction , for the analogical recordings), and for the reproduction of the sound in surround ( Dolby Stereo and Dolby DIGITAL to only quote most known), with the Cinéma then in our living rooms.
Dolby NR is used to attenuate the Background noise brought by the analogical supports, magnetic bands and films in particular. This background noise is generated by small variations of Luminous intensity (film) or magnetic (band). As the sounds of strong volume are not very affected, one uses a curve of amplification nonlinear, called “compression”, which consists, with the recording, on-to amplify the sounds of weak Amplitude and under-to amplify the sounds of strong amplitude. The background noise is mainly masked, without in so far as there is Saturation. After the reading of the sound, at the time of the preamplification, one corrects non-linearity by a “expansion” of the sound. The original stamp is found, and the background noise is very weakened.
In addition, the human Ear and the Cerveau are not sensitive same manner to all the ranges of Fréquence, and the parasites do not affect all the frequency bands in the same way. For this reason, the sound is initially separate in four frequency bands, and the treatment of compression/expansion is applied in a different way to each range.
It is the first system of the kind not to deteriorate, after decoding, the quality of the original stamps.
In 1966, Ray Dolby puts on the market the first apparatus of reduction of noise (known like Dolby NR-A ). It is a system reserved to the professionals. He is so much revolutionist for the time that they is since then the bands its multichannel (others that monophonic) proliferate, especially with the cinema.
In 1968, Dolby attacks the market general public and leaves the Dolby NR-B . One will find it in all the cassette players of good invoice. Moreover, the cassettes coded in NR-B can be read without decoder. The acute ones appear simply more present. Later the Dolby NRC , evolution of the precedent will leave, then the NR-S (derivative of the Dolby SR ), which still improves the principle by adding a standard to it on the material to be used (configuration of the play-back heads, etc)
One will find also recorders equipped with the Dolby HX-Pro ( Headroom Extension , developed by Bang & Olufsen), dynamic system of adjustment of skew, allowing a linear restitution of acute, even on strong level. It with the characteristic not to require a decoder (contrary to the Dolby NR ).
Dolby and the surround
In 1976, Dolby puts on the market a system invented by Peter Scheiber and who will revolutionize the cinema of the Années 1980: the Stereo Dolby . In addition to the reduction of noise, it allows the restitution of the sound in surround starting from only two tracks. Thus, one can obtain three sound ways behind the screen, and a sound way of environment. In 2006, this system is symbolized by 3/1/0: 3 ways behind, 1 way of environment and 0 optional way (which will be later detailed in the article).
The technique used is that of dieing. Very schematically, one recovers the 4 ways in the following way:
- the signals of the channels left and right-hand side are in phase (identical): they are sent on the center lane;
- the signals of the channels left and right-hand side are in opposition of phase (opposite signal of left of that of right-hand side): they are given in phase and envoys on the way of environment;
- the other signals are preserved on their respective ways.
The Dolby Stereo will be largely used by the film distributers. Indeed, it is compatible with the stereo and mono projectors (thus usable in all the rooms). The cinemas will also adopt it, because it is not very expensive to implement: it is enough to add a module of decoding, and amplifiers of sufficient number.
In 1977, when George Lucas carries out her film worship: Star Wars , it is said very disappointed sound restitution in rooms because it had enormously invested in the band its stereophony of its film.
As certain films Star Wars profited from copies 70 mm at the time of its initial exit. Since its introduction, the Format 70 mm comprised 6 audio tracks but here the tracks audios profited from a reducer of noise Dolby has . The copies 70 mm comprised a logo Dolby System with the credits of end. This system was also used on inflations of Tess.
The general public will find the Dolby Stereo in its living room with names Dolby Surround (2 ways before + surround , or 2/1/0), Dolby ProLogic (3/1/0), Dolby ProLogic II (3/2/0), and in 2006 Dolby ProLogic IIx (3/3/0). These decoders can function with any stereo source, even without to be specifically encodées.
In 1986, Dolby improves its system of reduction of noise and lance the Dolby SR (for Spectral Recording ). From there, all the sound ways are in full band. The bands of films become spectacular. Dolby adapts this system in stereophony for the general public (cassette players) with the Dolby NR-S (famous more faithful than CD).
In 1992, Dolby still revolutionizes made sound with a numerical version of the SR : the Dolby SRD ( Spectral Recording DIGITAL ). The Dolby SRD adds, beside the two tracks Dolby SR always present to guarantee compatibility, a numeric signal (AC-3) printed between the feed holes of film! Thus, one can obtain to 6 completely discrete channels (nonstamped) in configuration 2/3/1, the sixth having a reduced capacity (serious extremes, symbolized by the .1 of the 5.1 or the 1 of the 2/3/1).
A system is known as 5.1 when it uses 5 principal sound channels not-limited in band-width (restitution between 20 Hz and 20 Khz) and an optional channel (restitution between 2 Hz and 120 Hz):
- 2 channels before
- 2 channels back: surround
- 1 central channel
- 1 channel LFE ( Low Frequency Effects ) connected to a Subwoofer to reinforce the effects of low register.
The 6 channels which compose the 5.1 are independent from/to each other.
This format will change name to become the Dolby DIGITAL .
The last notable evolution is the Dolby DIGITAL EX (for Extended ), which adds a center back way, stamped in the back ways. It allows a configuration in 3/3/1 starting from a 2/3/1 source, therefore to make truly turn the sound around the listener. It remains completely compatible with the traditional decoders Dolby DIGITAL . The first film has to have used this famous DDex was Star Wars: the phantom threat of George Lucas in 1999.
The principal Dolby productsReducing of breath
- Dolby NR (has, B, C, S)
- Dolby SR (Spectral Recording) for the cinema
- : NR = Noise Reduction : this coding is intended to reduce the breath (background noise) generated by the supports of analogical recordings, such as for example the magnetic band.
Optimization of the recording (magnetic)
- Dolby HX-Pro : dynamic adjustment of the Bias
- Stereo Dolby
- Derived general public: Dolby Surround , ProLogic , ProLogic II , ProLogic IIx
- Dolby SRD ( Spectral Recording DIGITAL ), historically called Dolby AC-3 ( Audio Coding system version 3), and today Dolby DIGITAL
- and its improvements: Dolby DIGITAL EX , Dolby DIGITAL More (high-definition)
- MLP ( Meridian Lossless Packing ), format of compression without loss of a signal coded in PCM 192 Khz/24 bits maximum, on to 63 channels. Used with DVD audio to code 5 channels (+1) in 96/24, or stereophony until 192/24 (limits posed by the DVD).
- Dolby Headphone (the multichannel effect with a helmet simulates)
- Dolby Virtual Surround (simulates the multichannel effect with a pair of loudspeakers), called today Dolby Virtual Speaker
- Dolby AC1 2 3 : Dolby AC-1 is the technology of encoding introduced in 1987 during the birth of television HD.En 1989, Dolby AC-2 brings better an audio quality with a bit misses lower. Made Dolby AC-3 are public appearance in 1991 for encoder the audio tracks included in file .vob of DVD video.
- Official site
- Official site
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