Dolby Laboratories, Inc., often shortened to Dolby Labs, is an American company specializing in audio noise reduction and audio encoding/compression. Dolby licenses its technologies to consumer electronics manufacturers.
1. Analog audio noise reduction:
Dolby A/B/C/S-Type NR: professional and consumer noise reduction systems for tapes and analog cassettes.
Dolby SR (Spectral Recording): professional four-channel noise reduction system in use since 1986, which improves the dynamic range of analog recordings and transmissions by as much as 25 dB. Dolby SR is utilized by recording and post-production engineers, broadcasters, and other audio professionals. It is also the benchmark in analog film sound, being included today on nearly all 35 mm film prints. On films with digital soundtracks, the SR track is used in cinemas not equipped for digital playback, and it serves as a backup in case of problems with the digital track.
Dolby FM: noise reduction system for FM broadcast radio. Dolby FM was tried by a few radio stations starting with WFMT in 1971. It used Dolby B, combined with 25 microsecond pre-emphasis. A small number of models of tuners and receivers were offered with the necessary decoder built in. In addition, a few cassette deck models appeared that allowed the deck's internal Dolby B decoder to be put in the line into line out "pass-through" path, permitting its use with Dolby FM broadcasts. The system was not successful and was on the decline by 1974.
Dolby HX Pro: single-ended system used on high-end tape recorders to increase headroom. The recording bias is lowered as the high-frequency component of the signal being recorded increases, and vice-versa. It does nothing to the actual audio that is being recorded, and it does not require a special decoder. Any HX Pro recorded tape will have, in theory, better sound on any deck.
2. Audio encoding/compression:
Dolby Digital (also known as AC-3) is a lossy audio compression format. It supports channel configurations from mono up to six discrete channels (referred to as "5.1"). It was first developed for movie theater sound and spread to Laserdisc and DVD. It is also part of both the Blu-ray and the now defunct HD DVD standards. Dolby Digital is used to enable surround sound output by most video game consoles.
Dolby E: professional coding system optimized for the distribution of surround and multichannel audio through digital two-channel post-production and broadcasting infrastructures, or for recording surround audio on two audio tracks of conventional digital video tapes, video servers, communication links, switchers, and routers. It is transcoded to Dolby Digital at lower data rate for final DTV transmission for home viewers.
Dolby Stereo (also known as Stereo A): original analog optical technology developed for 35 mm prints and is encoded with four sound channels: Left/Center/Right and Surround for ambient sound and special effects. It also employs A-type or SR-type noise reduction, listed above with regards to analog cassette tapes.
Dolby TrueHD: Dolby's current lossless coding technology. It offers bit-for-bit sound reproduction identical to the studio master. Over seven full-range 24-bit/96 kHz discrete channels are supported along with the HDMI interface. Theoretically, Dolby TrueHD can support 8 channels for HD DVD and Blu-ray Disc.
Dolby Pulse: released in 2009, identical to the HE-AAC v2 codec except for the addition of Dolby metadata, which is common to Dolby's other digital audio codecs. This metadata "ensures consistency of broadcast quality."
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