Home cinema explained

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Dolby Stereo—also known as Dolby MP (Motion Picture) or Dolby SVA (stereo variable-area)—was developed by Dolby in 1976 for analog cinema sound systems. The format was adapted for home use in 1982 as Dolby Surround when HiFi capable consumer VCRs were introduced. It was further improved with the Dolby Pro Logic decoding system after 1987.

The Dolby MP Matrix was the professional system that encoded four channels of film sound into two. This track used by the Dolby Stereo theater system on a 35mm optical stereo print and decoded back to the original 4.0 Surround. The same four-channel encoded stereo track was largely left unchanged and made available to consumers as "Dolby Surround" on home video. However, the original Dolby Surround decoders in 1982 were a simple passive matrix three-channel decoder: L/R and mono Surround. The surround channel was limited to 7 kHz. It also had Dolby Noise Reduction and an adjustable delay, for improved channel separation and to prevent dialog leaking and arriving to listeners' ears first. The front center channel was equally split between the left and right channels for phantom center reproduction. This differed from the Cinema Dolby Stereo system which used active steering and other processing to decode a center channel for dialog and center focused on-screen action.

Later on in 1987, the Pro Logic decoding system was released to consumers. It featured virtually the same type of four-channel decoding as the Dolby Stereo theater processor with active steering logic and much better channel separation (up to 30 dB) as well as including a dedicated center channel output for the first time. Many standalone Pro Logic decoders also included a phantom center option for compatibility with earlier non-Pro Logic Dolby Surround equipped home theaters to split the center channel signal to the L/R speakers for legacy phantom center reproduction.

Dolby Digital, originally synonymous with Dolby AC-3 (see below), is the name of a family of audio compression technologies developed by Dolby Laboratories. Called Dolby Stereo Digital until 1995, it is a lossy compression (with the exception of Dolby TrueHD). Dolby Digital's first use was to deliver digital audio in cinemas from 35mm film prints. It has since also been used for television broadcasting, satellite radio broadcasting, digital video streaming, DVDs, Blu-ray Discs, and game consoles.

Dolby AC-3 was the original version of the Dolby Digital codec. The basis of the Dolby AC-3 multichannel audio coding standard is the modified discrete cosine transform (MDCT), a lossy audio compression algorithm.[1] It is a modification of the discrete cosine transform (DCT) algorithm, which was proposed by Nasir Ahmed in 1972 for image compression.[2] DCT was adapted to MDCT by J.P. Princen, A.W. Johnson, and Alan B. Bradley at the University of Surrey in 1987.[3] Dolby Laboratories adapted the MDCT algorithm along with perceptual coding principles to develop the AC-3 audio format for motion pictures. The AC-3 format was released as the Dolby Digital standard in February 1991.[4][5] Dolby Digital was the first MDCT-based audio compression standard to be released, and was followed by others for home and portable use, such as Sony's ATRAC (1992), the MP3 standard (1993), and AAC (1997).

Dolby Atmos is a surround sound technology developed by Dolby Laboratories. It expands existing surround sound systems by adding height channels, interpreted as three-dimensional objects without horizontal or vertical limitations.[1][2] Following the release of Atmos for the cinema market, various consumer technologies were marketed under the Atmos brand. Early Atmos systems for cinema used in-ceiling speakers, later upward-firing speakers (e.g. for soundbars) were introduced as an alternative for consumer products.[3] Atmos is also used on some devices that do not have a height channel, such as headphones, televisions, mobile phones, and tablets.