Originally Posted by Xanoku;14460321
Pro Logic is a technology by Dolby. It takes 2 stereo Dolby Digital Encoded Audio channels and decodes it into 6 separate channels (5.1) so you are getting 5.1 DD sound.
Dolby pro logic takes 2/4 channels and turns them into 5.1 , this is'nt a very good 5.1 and it's allso not dolby digital, the surround sound speakers are mono with the front l/r speakers but with a slight shift to create a virtual type of surround..
Dolby digital has the full audio for 5.1 which gives true to life surround sound where as pro logic just adds more channels to 2/4 channels which creates the illusion of 5.1 using tricks.
Edited by OcSlave - 8/4/11 at 7:50am
1. Dolby Pro Logic is the simplest, cheapest format. It has 4 channels that are compressed into two analog channels, so you can record it on your stereo VCR and it can also broadcasted even over analog radio or cable TV. Another advantage – Dolby Pro Logic can be easily downconverted from a Dolby Digital signal.
These are 2 discrete and 2 matrixed channels:
2 discrete, full-bandwidth channels (left front, right front),
1 matrixed full-bandwidth center channel,
1 matrixed, limited-width channel that goes to 2 surround speakers.
The Dolby Pro Logic encoder takes 4 channels (L, R, C, S) and creates two output channels (Lt, Rt). L goes to Lt and R goes to Rt without modifications, C, after a 3dB level reduction, gets divided equally between Lt and Rt. The bandwidth of S gets limited to 100Hz - 7 kHz range, it is encoded with a form of Dolby B noise reduction. After that it gets divided between Lt and Rt but with a +90 and -90 degree phase shifts.
During the playback, the surround is extracted by analyzing the difference between Lt and Rt.
Disadvantages are: both surround speakers produce the same sound from the same channel (mono sound) and are limited in bandwidth. Additionally, there is no discrete subwoofer channel specified in the standard, so subwoofer channel can extracted from other channels rather than specified explicitly.
Sources for Dolby Pro Logic include TV shows and movies, videotapes, other analog sources and downconverted signal from Dolby Digital (DVD for example).
2. Dolby Digital is a 6-channel format, referred to as “5.1-channel”. All 6 channels are discrete, 5 channels are full-bandwidth, “.1” refers to subwoofer, which supplies Low Frequency Effects (LFE).
To compress data with low loss in the sound quality, audio coding, known as "perceptual coding" is used. Dolby Digital uses a third generation audio coding algorithm (AC-3).
The channels are: front left, front right, center, surround left, surround right and subwoofer.
Advantages over Dolby Pro Logic include the fact that all channels are digital, discrete and 5 of them are full-bandwidth. Additionally, the surround speakers use separate left and right channels (stereo).
Sources include all DVDs, some DBS broadcasts and some HDTV programs.