Dolby Analog
In the early 1970s Dolby Laboratories introduced the original multi-channel sound format to the motion picture industry that is the foundation of all modern surround
sound formats. This format encoded the soundtrack into four individual channels:
left, right, center and Mono Surround. When movies encoded in this manner were played in the theaters, the
left, center, and right channels were played back on speakers located behind the screen, and the Surround
Channel was heard through speakers located along the sides and back of the theater. The surround speakers carried only ambient and special effects sound. Due to the passive nature of the surround speakers, this original surround format lacked the directionality of modern surround formats.
Dolby Surround (more commonly called Dolby Pro Logic)
Dolby surround is the consumer version of the original Dolby analog format used to encode movies. The original four channels
are matrix encoded on two audio tracks (stereo). Matrixing is the technique of using two channels of information to carry a third or even a fourth channel, and then separating them back into the original channels. When the stereo sound is played back the Dolby Pro Logic processor decodes the information and separates it into the original four channels.
Dolby Pro Logic II
Dolby Pro Logic II added the capability to process any stereo or Dolby Surround encoded signals into five distinct channels. The speaker placements are the same with
front left, center and right speakers, and two surround speakers.
The surround speakers are sent separate signals, as opposed to a shared mono signal. Using the directional cues that occur naturally in stereo content, Dolby Pro Logic II provides superior directionality when compared to original surround format, so that you have the added dimension of front-to-back as well as side motion.
Dolby ® Pro Logic ® IIx
Dolby ® Pro Logic ® IIx extends the capabilities even further. It can process a stereo or Dolby Surround signal and separate it into as many as 7 distinct channels. In addition to the 5 speakers used in the other Dolby Pro logic standards, you can add additional back channel speakers
to your setup and a low frequency effects (LFE) channel. This allows you to create a seamless surround sound field,
even though the content is not encoded that way. There are three listening modes,
movie, music and games, allowing you to tailor the sound to handle
different programming. In music mode there are a further three settings; Dolby Center Width, Dolby Panorama and Dolby Dimension.
Although all modern programming is encoded using digital surround formats, having the analog formats available to you, will allow you the optimum experience with legacy CD’s, videocassettes and analog stereo broadcasts.
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