|Dolby Laboratories, Inc.
|Seat||San Francisco , United States|
|Number of employees||1867|
|sales||$ 971 million|
|As of September 25, 2015|
Dolby Laboratories, Inc. is a company that previously developed compander systems for noise reduction in analog audio . The company has now specialized in digital multichannel sound systems such as Dolby Digital and Dolby Atmos for the cinema and home cinema sector. With the HDRV format Dolby Vision it is also present in the market for digital video technology. It was founded in England in 1965 by Ray Dolby , and in 1976 he relocated it to the United States of America.
Analog noise suppression methods
With the analog Dolby noise suppression method, the volume of soft sounds is compressed before the description of the tape and expanded again by the same amount during playback . This also reduces the tape noise. The first methods, Dolby A and Dolby SR , were mainly used in the professional sector, for example for the analog optical sound method in cinemas.
The most common method Dolby in commercial tape recorders called Dolby B . This is supplemented in higher-quality devices that were previously part of the standard scope of a stereo system with the further development Dolby C and sometimes Dolby HX Pro . Dolby S , released at the beginning of the 1990s, was to become the standard for higher-priced hi-fi tape decks in the home as a supplement to B and C. Due to the triumph of digital technology , however, this market segment largely broke away, so that Dolby S could no longer achieve any significant market shares.
Dolby A is the first compression system developed by Dolby for studio magnetic tape recorders from 1966. It consists of four independent compressors. Compressor 1 works below 80 Hz, compressor 2 between 80 Hz and 3 kHz and compressor 3 above 3 kHz. Compression is 10 dB. The fourth compressor works above 8 kHz and delivers an additional 5 dB in this frequency range.
Dolby B, Dolby "NR"
Dolby B, launched in 1968, works in the upper frequency range from around 1 kHz (in the case of the Dolby-compatible ANRS developed by JVC from 500 Hz) up to the treble range. During recording, the signal is amplified on the tape, depending on the frequency and level, and is weakened by the same amount as exactly as possible in mirror image during playback. During playback, the additional, annoying tape noise is also reduced. The noise reduction system must be turned on during both recording and playback. Frequency and level-dependent compression and expansion means that the degree of processing is lower in the frequency range directly above 1 kHz and more pronounced in the upper treble range. These changes only take place at medium to low levels. With Dolby B, it is particularly important that the frequency limit above which the lowering takes place shifts dynamically (sliding band). This significantly improves the lowering of the audible noise while at the same time reducing the interference effects. Other systems only change the strength of the influence in a constant frequency range. This in turn generates pumping and / or noise plumes more easily, or (in order to avoid this) necessarily requires complex processing in several frequency ranges.
Working in mirror image requires calibration . Many cassette devices have a Dolby symbol (double D symbol) on the level indicator for calibration.
Dolby insists that the system is not simply called Dolby , but rather Dolby NR (NR for Noise Reduction) . Nowadays DOLBY no longer means DOLBY B , as it did until the 1990s, but refers to Dolby Digital (television sound) or 5.1 surround (DVD).
Since compact cassettes did not achieve the quality of good reel devices even under Dolby-B-NR, and the introduction of the CD later raised the hi-fi quality requirements again, the demand for further development of this noise reduction process increased. Even if the sliding band principle largely prevented noise flags in Dolby B, the overall noise reduction was not sufficient. This is especially true when the level of the compact cassette was only moderately controlled due to the high frequency problems. The first was succeeded Dolby C . However, none of the successors achieved such global usage as Dolby-B-NR. Probably also because pre-recorded music cassettes available on the market (as an alternative to records) almost always used Dolby B.
The Dolby B method was used in particular in VHF broadcasting. Dolby FM with 25 µs pre-emphasis and adapted compander frequency response was used by a number of VHF radio stations in the USA from 1971 . There were also receivers with Dolby B expanders and cassette recorders whose Dolby B circuit could be used externally in a “pass-through” mode. The system was practically abandoned as early as 1974.
Dolby C is a further development of Dolby B that was presented to the public in 1980. It works with two cascaded compressors and an anti-saturation circuit. The first compressor corresponds exactly to the Dolby B compressor. The second works at 20 dB lower levels with a starting point that is well two octaves lower (5 dB point: 200 Hz instead of 1 kHz). The anti-saturation network improves the treble control at 10 kHz by about 4 dB and prevents oversaturation of the tape material due to excessive control of the useful signal by slightly reducing the level in the event of excessively high levels.
Dolby S is a simpler version of the professional Dolby SR, the Dolby A successor. It has three compressor levels and, compared to Dolby B and C, also works in the bass range. In addition, the three frequency bands are divided up so that recordings made with Dolby S can also be played back on devices with Dolby B in acceptable quality. The first devices with Dolby S appeared on the market in 1990. This noise suppression was initially implemented with three chips, then in 1991 a single-chip version. This resulted in a surcharge compared to Dolby C of around DM 300 in Germany.
Dolby level, Dolby calibration
The simple idea of compression and expansion is the strength of Dolby noise reduction and, at the same time, its weakness: The prerequisite for the perfect functioning of the system is the exact mirror image mode of operation during recording and playback. For this it is necessary that all compressors and expanders classify a level equally. In addition, an exact calibration to the tape material used is necessary. Furthermore, it is important to align the tape head exactly at right angles to the tape run ( azimuth ), the premagnetization (frequency response) and especially the recording level must be set precisely. This does not only mean the rough adjustment to the type of tape used, normal, chromium dioxide or metal , because there are also manufacturer-related differences within these classes.
For example, a level recorded with 0 dB can be weaker or stronger than 0 dB during playback, depending on the sensitivity of the tape material used. This leads to inaccuracies in the signal processing of the Dolby system, which can usually be expressed in the form of a dull, in rare cases too bright reproduction of the highs and slight pumping noises.
Because of this problem, the Dolby Licensing Corporation imposed particularly strict licensing conditions when Dolby S was introduced. Cassette recorders that want to use Dolby S must have a precisely aligned sound head and an externally accessible pre-magnetization setting.
To ensure that the compact cassette can be replaced, all devices must be calibrated to the same level. For this purpose, Dolby has defined a test tone with a specified tape magnetization.
Dolby HX Pro
Dolby HX Pro (HX stands for "Headroom eXtension") is not per se a noise reduction system like Dolby A , B , C and S , but a device that extends the height control. This also indirectly reduces the audibility of the noise. It was developed and presented in 1982 by Bang & Olufsen , and a year later it was marketed by Dolby as the HX Pro (Dolby had already developed a simpler circuit: Dolby HX ).
Function: A normal cassette deck has a selector switch for up to four types of tape. This switch sets (among other things) the pre-magnetization in rough steps suitable for these types of tape. Loud tones in the music signal to be recorded with a strong high frequency component also have the effect of a premagnetization. This is added to the original premagnetization. The tape is not used optimally (too much pre-magnetization significantly worsens the recording quality in the high-frequency range, on the other hand, too little increases the distortion in the lower and middle frequency range). An HX circuit now continuously measures the high frequency level in the signal from the recording head. If the proportion of high frequencies in the signal increases, the premagnetization is adjusted (Dolby HX). With Dolby HX Pro, the entire effective premagnetization is continuously regulated to a setpoint, which leads to significantly more reliable results than with the simple HX.
The dynamic pre-magnetization improves the high frequency range enormously. Improvements are possible across the entire frequency spectrum. The HX or HX PRO is particularly important for low tape speeds (small wavelengths ) such as compact cassettes . The HX Pro increases the dynamic range of cassettes and enables clearer recordings. No additional circuit is necessary in the playback device, the advantage is effective with every playback.
Together with NAD , Dolby developed the play trim control, with the help of which a faulty high frequency response of Dolby-coded cassette tapes can be approximately corrected before (important!) The dynamic expansion, so that such tapes also sound acceptable. A faulty high frequency response can result from incorrect premagnetization or frequency response equalization , overloading or non-use of the HX Pro , tape aging or azimuth errors between recording and playback and / or a poor compact cassette .
Dolby SR is a noise reduction method in use since 1987 for sound recording for analog optical sound on 35 mm film and on analog audio tapes . SR stands for spectral recording and is so called because it has a spectral compressor function that is adapted to the hearing.
The method is the most advanced audio noise reduction method and probably marks the end of the development of this method, since noise reduction is no longer required for digital systems. The dynamic range that can be achieved with this technology is mathematically roughly the same as that of a 16-bit digital recording; in practice, the properties of analog recording technology allow even better values.
Analog multichannel sound formats
- Dolby Stereo 6-Track : 6-channel magnetic sound for 70 mm films (no longer in production)
- Dolby Stereo A: Professional cinema sound system with four matrixed channels and Dolby A noise reduction
- Dolby Stereo SR: Matrix like Dolby Stereo A, but with improved Dolby SR noise reduction
- Dolby Surround : Home counterpart to Dolby Stereo
- Dolby Pro Logic : Like Dolby Surround, but with improved encoding and decoding techniques (extensions: Pro Logic II, Pro Logic IIx and Pro Logic IIz)
Digital multi-channel sound formats
Starting with Dolby Digital at the beginning of the 1990s, the company developed a number of increasingly powerful digital surround sound or multi-channel sound systems for cinemas and home theater , with which it is economically successful and with several standards or de facto standards in the digital audio technology.
Dolby Virtual Speaker
Dolby Digital was initially used as a sound format for movies and in 1995 it was chosen as the multi-channel standard sound for the then newly developed DVD . It is a digital 6-channel system (5.1) and, according to the audio coding method used, also known as AC-3 . Dolby Digital EX is an extension with one or two additional channels.
Dolby Digital Plus
Dolby Digital Plus is a further development of Dolby Digital and was introduced in 2005. It was developed with a view to use in high-definition television ( HDTV) and the then new Blu-ray Disc , and to enable digital multi-channel sound for then new media such as streaming , on-demand and download services. It is backwards compatible with Dolby Digital, so that such devices can also decode the up to eight-channel (7.1) sound of the system. Dolby Digital Plus is present on most Blu-ray Discs as one of the audio tracks that the user can choose from.
Dolby E is a digital audio format for professional use used by broadcasters , especially television companies and post-production studios . It is used for the transmission and storage of audio material with up to eight discrete audio channels in standardized data streams according to AES-3id .
Dolby TrueHD is a lossless multi-channel audio codec for Blu-ray Disc and AV receivers . It was developed by Dolby specifically for use on Blu-ray Discs as an optional, lossless surround sound format for the lossy Dolby Digital Plus. In contrast to Dolby Digital Plus, a Dolby TrueHD data stream has a significantly higher data rate with higher quality and requires more storage space on the medium. Dolby TrueHD is based on Meridian Lossless Packing as the mathematical basis for lossless compression of audio data.
Dolby Atmos is a proprietary surround format for home and cinema that was introduced in 2012. The format expands the concept of previous, purely channel-based surround sound systems - including all of the above - with additional vector-based metadata , from which the coordinates of moving objects for the respective loudspeaker setup are individually calculated when played by the AV receiver . An essential component of the system is an extension - or a partial replacement - of the existing home theater speaker system, whereby either up to four speakers are positioned on the ceiling of the listening room, or at least the front speakers are replaced by "Dolby Atmos Enabled Speakers". to be modified. If four ceiling speakers are used, a previous 5.1 system becomes a 5.1.4 system, and a 7.1 system becomes 7.1.4. The Dolby Atmos technology theoretically allows an unlimited number of sound tracks and is downward compatible with older multi-channel sound systems such as 5.1 or 7.1.
- Dolby Contrast : A video format for improved contrast in LCD devices
- Dolby 3D : A 3D projection method
- Dolby Vision : An imaging technology that delivers true-to-life brightness as well as colors and contrasts.
On February 24, 2014 Doremi Labs , a manufacturer of video editing software, was bought.
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- fonoforum.de 8/1991, test report of the Dolby S cassette deck Pioneer CT 900-S (PDF, 2 MB), accessed on April 13, 2020.
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- Dolby Debuts New Video Technologies at International CES 2008 . Dolby press release. Archived from the original on April 17, 2008. Info: The archive link was automatically inserted and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved March 28, 2008.
- Dolby Vision - More color and contrast even with 4k and UHD . Ben Mueller. Retrieved February 17, 2014.
- latimes.com: Dolby acquires Doremi Labs