In addition to Dolby Digital, Dolby Surround( DS) is another multi- channel technology for surround sound. This method, developed by Dolby Laboratories, is a reproduction method for surround sound in home cinema.
This surround process is relatively old and can only be called surround sound with restrictions, since it generates a signal for surround sound from a stereo signal via a special Dolby matrix. The advantage is that only two channels are needed for recording and storage and existing playback devices can be used. Technically, this process mixes the soundtracks from all four sound channels (L, R, C, Surround) and encodes them onto two sound channels for stereo sound. This stereo sound can be played back with all known recording and playback devices.
If the sound is to be played back in the original, it must be decoded in a Dolby decoder and separated into the individual sound channels from each other. There are several versions of Dolby Surround: Dolby Surround Pro Logic and Dolby Surround Pro Logic II.
Dolby Surround Pro Logic: The Dolby Surround Pro Logic system works with an improved version, which has four full channels for stereo front left and right, a coded center channel and a coded surround channel for rear left and right. Since this system had some weaknesses in terms of channel separation, it was replaced by the improved Dolby Surround Pro Logic II.
Dolby Surround Pro Logic II: In this version, the surround signal is also emitted in stereo, which was not the case with the previous version. In addition, the frequency range has been extended. In addition, stereo sound can also be played back via 5.1. 5.1 refers to the number of speakers and stands for three front speakers - left, center, right - two rear speakers and a woofer.
Dolby Surround Pro Logic IIx: This version allows stereo or 5.1 signals to be converted into 6.1 and 7.1 signals. Dolby Surround is available as 5.1, 6.1, and 7.1.