Dolby digital to dolby pro logic surround?

Whats the dif between Dolby Pro Logic, Dolby Digital and Dolby surround?

• Answer:

  While there are exceptions, surround sound generally implies separate amplified signals from more than 2 channels/speakers (Most commonly, so called 5.1 or 6.1 sound ... where the first number refers to the number of "normal" speakers and the latter to a subwoofer (bass only). For example, a 5.1 system requires 4 speakers for the right and left front and surround channels plus a front centre channel speaker and a subwoofer). Dolby Surround includes all flavours of Dolby surround processing (where Dolby refers to a number of standards for how sound is processed/decoded), and is therefore a general term. See the link provided by an earlier respondent for Dolby Labs for details. Dolby Digital is a term for a specific standard form of digital (vs analogue) sound processing and may or may not mean surround processing. For example, there is Dolby Digital stereo, and various surround (multiple channel) formats. The number of channels is encoded in the original program material. Dolby Surround can also be achieved by matrix processing of a stereo signal. One of the oldest standards is Dolby ProLogic. While Doby is one of the most common standards for sound processing, others, such as Digital Theatre Sound (DTS) are also common. DVD players generally have built in Dolby Digital and DTS decoders, and A/V Receivers usually include more, plus a number of preset sound processing "standards" to "shape" the decoded sound (e.g. adjust reverberation and enhance or depress high or low frequencies) further to, for example, sound like a church, hall or jazz club.