Channel configurations[edit]
Although commonly associated with the 5.1 channel configuration, Dolby Digital allows a number of different channel selections. The options are:
- Dolby Digital 1/0 - Mono (center only)
- Dolby Digital 2/0 - 2-channel stereo (left + right), optionally carrying matrixed Dolby Surround
- Dolby Digital 3/0 - 3-channel stereo (left, center, right)
- Dolby Digital 2/1 - 2-channel stereo with mono surround (left, right, surround)
- Dolby Digital 3/1 - 3-channel stereo with mono surround (left, center, right, surround)
- Dolby Digital 2/2 - 4-channel quadraphonic (left, right, left surround, right surround)
- Dolby Digital 3/2 - 5-channel surround (left, center, right, left surround, right surround)
These configurations optionally include the extra low-frequency effects (LFE) channel. The last two with stereo surrounds optionally use Dolby Digital EX matrix encoding to add an extra Rear Surround channel.
Many Dolby Digital decoders are equipped with downmixing to distribute encoded channels to speakers. This includes such functions as playing surround information through the front speakers if surround speakers are unavailable, and distributing the center channelto left and right if no center speaker is available. When outputting to separate equipment over a 2-channel connection, a Dolby Digital decoder can optionally encode the output using Dolby Surround to preserve surround information.
The '.1' in 5.1, 7.1 etc. refers to the LFE channel, which is also a discrete channel.
from: https://en.wikipedia.org/wiki/Dolby_Digital