Dolby Digital and Dolby Pro Logic are both trademarks of Dolby Laboratories Licensing Corporation. They are the most common surround formats in the audio industry today.
Dolby Pro Logic
The Dolby Pro Logic signal starts out as four channels and is then encoded into two channels for transfer to your receiver. The information is encoded into two channels because it is easy to incorporate this information in medias such as satellite, videotape, or television broadcasts. When the audio is played back, the receiver will convert the two channel Dolby-encoded signal back into its original four channels.
Your receiver will detect the difference in the two tracks and send the two separate sets of information to your left and right front speakers. The stage represents the first two channels of the four-channel track. The information that is identical in each of the first two channels is sent to the center channel. Your center channel represents the third of the four channels. All identical information that is out of phase from the first 3 channels is sent to your rear surround speakers. Your surround speakers represent one channel which make the fourth and last channel for Dolby Pro Logic.
Dolby Digital
Dolby Digital is an advanced form of digital audio coding. This optimal coding makes it possible to store and transmit very high-quality digital sound for more efficient sound reproduction. This coding is a significant increase over what has been available in the past. Dolby Digital is a trademark of Dolby Laboratories Licensing Corporation which uses multiple discrete tracks for each individual channel of your home audio setup. Today's most common Dolby Digital setup has 5.1 channels with 5 full bandwidth frequencies that work through two front speakers, one center channel, and two rear-surround speaker. The .1 represent the LFE or Low Frequency Effects of the audio track. This LFE provides the resounding sound effects of explosion, thunder-like tracks of a movie.
