Dolby Digital is a digital audio coding technique that reduces the amount of data needed to produce high-quality sound. It takes advantage of how the human ear processes sound. When coding noise is close to the frequency of an audio signal, that audio signal masks the noise so that the human ear hears only the intended audio signal. Sometimes the coding noise is not in the same frequency of an audio signal and must be reduced or eliminated. By reducing, eliminating, or masking the noise, the amount of data is reduced to one-tenth of the data on a compact disk (CD). Dolby Digital is used with digital versatile discs (DVDs), high-definition television (HDTV), and digital cable and satellite transmissions. It has been selected as the audio standard for digital television (DTV).
Dolby Digital provides five full-bandwidth channels, front left, front right, center, surround left, and surround right, for true surround sound quality. A low-frequency effect (LFE) channel is included that provides the sound needed for special effects and action sequences in movies. The LFE channel is one-tenth of the bandwidth of the other channels and is sometimes erroneously called the subwoofer channel. This multi-channel scheme is known as 5.1 channels.
Because not everyone has the equipment needed to take advantage of the most commonly used Dolby Digital’s 5.1 channel sound, developers included a downmixing feature that ensures compatibility with any playback device. The decoder in the playback device delivers the audio signal specific to that particular device’s ability. For example, a 5.1 channel audio signal is delivered to a mono television. The playback device’s decoder downmixes the 5.1 channel signal to a mono signal allowing the television to use the received audio signal. Because the playback device does the downmixing, producers do not have to create multiple audio signals for each playback device.
Dolby Atmos is the name of a surround sound technology announced by Dolby Laboratories in April 2012, which was first utilized in Pixar’s Brave. The first installation was in the Dolby Theatre in Hollywood, California, for the premiere of Brave in June 2012. Throughout 2012, it saw a limited release of about 25 installations worldwide, with an increase to 300 locations in 2013. The format allows for an unlimited number of audio tracks to be distributed to theaters for optimal, dynamic rendering to loudspeakers based on the theater capabilities.
The first generation cinema hardware, the “Dolby Atmos Cinema Processor” supports up to 128 discrete audio tracks and up to 64 unique speaker feeds, the technology will initially be geared towards commercial cinema applications only, but will later be adapted to home cinema. In addition to playing back a standard 5.1 or 7.1 mix using arrays, the system will give each loudspeaker its own unique feed, thereby enabling many new fronts, surround, and even ceiling-mounted height channels for the precise panning of select sounds such as a helicopter or rain.
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