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AC-3 (Dolby Digital)

AC-3, also known as Dolby Digital , is a perceptual digital audio coding technique that reduces the amount of data needed to produce high-quality sound. Perceptual digital audio coding takes advantage of the fact that the human ear screens out a certain amount of sound that is perceived as noise. Reducing, eliminating, or masking this noise significantly reduces the amount of data that needs to be provided. Dolby Laboratories developed two other perceptual coding systems, AC-1 and AC-2. Building upon Dolby's two previous coding systems, AC-3 was the first coding system designed specifically for multichannel digital audio. AC-3 is the sound format for digital television ( DTV ), digital versatile discs ( DVD s), high definition television ( HDTV ), and digital cable and satellite transmissions.

AC-3 is a 5.1 format, which means that it provides five full-bandwidth channels, front left, front right, center, surround left, and surround right. A low-frequency effect (LFE) channel is included for 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. AC-3 also has a downmixing feature that ensures compatibility with devices that do not support the 5.1 format.

This was last updated in January 2011

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What is the difference between Dolby D and Dolby E?
The LFE channel is more normally referred to as "low-frequency extension."


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