Dolby Digital is the common version containing up to six discrete channels of sound. The most elaborate mode in common usage involves five channels for normal-range speakers (20 Hz – 20,000 Hz) (right front, center, left front, rear right, rear left) and one channel (20 Hz – 120 Hz allotted audio) for the subwoofer driven low-frequency effects. Mono and stereo modes are also supported. AC-3 supports audio sample-rates up to 48 kHz.
E-AC-3 (Dolby Digital Plus) is an enhanced coding system based on the AC-3 codec. It offers increased bitrates (up to 6.144 Mbit/s), support for more audio channels (up to 13.1), and improved coding techniques to reduce compression artifacts.
Channel configurations
Although commonly associated with the 5.1 channel configuration, Dolby Digital allows a number of different channel selections. The options are:
- Mono (Center only)
- 2-channel stereo (Left + Right), optionally carrying matrixed Dolby Surround
- 3-channel stereo (Left, Center, Right)
- 2-channel stereo with mono surround (Left, Right, Surround)
- 3-channel stereo with mono surround (Left, Center, Right, Surround)
- 4-channel quadraphonic (Left, Right, Left Surround, Right Surround)
- 5-channel surround (Left, Center, Right, Left Surround, Right Surround)
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