Dolby Digital is multi-channel digital audio, using lossy AC-3 coding technology from PCM source with a sample rate of 48 kHz at up to 24 bits. The bitrate is 64 kbps to 448 kbps, with 384 or 448 being the normal rate for 5.1 channels and 192 being the typical rate for stereo (with or without surround encoding).
The channel combinations are (front/surround): 1/0, 1+1/0 (dual mono), 2/0, 3/0, 2/1, 3/1, 2/2, and 3/2. The LFE (subwoofer) channel is optional with all 8 combinations.
Dolby Digital is the format used for audio tracks on almost all DVDs.
DD1.0 provides a mono soundtrack, typically using just the centre (dialogue) speaker in a multi-channel setup.
DD2.0 provides either:
- a mono soundtrack, with the same signal going to both the left and right speakers
- a stereo soundtrack, using both the left and right speakers
- a Dolby Pro-Logic encoded soundtrack that can also provide audio to the 2 rear speakers in a multi-channel setup
DD5.1 usually provides a 5 speaker (plus subwoofer) surround sound. However, some budget DVDs use 5.1 to provide a mono soundtrack, with the same signal going to each speaker.