Dolby Pro Logic
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Dolby Pro Logic is a surround sound processing technology designed to decode soundtracks encoded with Dolby Surround. Dolby Surround was originally developed by Dolby Laboratories in 1976 for analog cinema sound systems as Dolby Analog SR (Spectral Recording). The Analog SR format was adapted for home use in 1986 as Dolby Surround which was then replaced by the newer and improved Pro Logic system. However, the term "Dolby Surround" is still used to describe the encoding technology or matrix-encoded soundtrack, whereas Pro Logic refers to the decoding technology/processor.
Dolby Surround/Pro Logic is based on basic Matrix technology. When a Dolby Surround soundtrack is created, four channels of sound are matrix-encoded into an ordinary stereo (two channel) sound track by using phase shift techniques. A Pro Logic decoder/processor "unfolds" the sound into the original 4.0 surround—left and right, center, and a single limited frequency-range mono rear channel—while systems lacking the decoder play back the audio as standard Stereo.
Although Dolby Surround was introduced as an analog format, all Dolby Digital decoders incorporate a digitally implemented Dolby Surround Pro Logic decoder for digital stereo signals that carry matrix-encoded Dolby Surround.
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[edit] Dolby Pro Logic II
In 2000, Dolby introduced Dolby Pro Logic II (DPL II), an improved implementation of Dolby Pro Logic. DPL II processes any high quality stereo signal source into "5.1"—five separate full frequency channels (left, center, right, left surround and right surround) plus one low-frequency-effects (deep bass) channel. Dolby Pro Logic II also decodes 5.1 channels from stereo signals encoded in traditional four-channel Dolby Surround. DPL II implements greatly enhanced steering compared to DPL, and as a result, offers an exceptionally stable sound field that simulates 5.1 channel surround sound to a much more accurate degree than the original Pro Logic.
Because of the limited nature of the original DPL, many consumer electronics manufactures introduced their own processing circuitry, such as the "Jazz", "Hall", and "Stadium" modes found on most common home audio receivers. DPL II forgoes this type of processing and replaces it with simple servo (negative feedback) circuits used to derive five channels. In addition to five full range playback channels, Pro Logic II introduced a Music mode which would not add any processing to the left and right channels, but will still extract a centre channel and two surround channels, providing a net effect of a wider center channel.
The Pro Logic II system also features a mode designed specifically for video gaming, and it is frequently used in game titles for Sony's PlayStation 2, Microsoft's Xbox, Xbox 360, Nintendo's GameCube and just recently the Wii as an alternative to digital technologies like Dolby Digital.
[edit] Dolby Pro Logic IIx
A newer Dolby Pro Logic IIx system is also now available, which can take stereo and Dolby Surround (sometimes called Dolby Stereo Surround) source material and up-convert it to 5.1, 6.1, or 7.1 channel surround sound.
[edit] Software Encoding
As of 2006, there is only one Dolby Pro Logic software implementation, the one by Minnetonka Audio.
[edit] Pro Logic Vs. Dolby Surround
Dolby Surround is the encoding counterpart to Dolby Pro Logic's decoding technology, but early home implementations of Dolby Surround decoding went by the name Dolby Surround which can cause some confusion. Dolby Surround and Dolby Pro Logic decoders are similar in principle, as both use matrix technology to extract extra channels from stereo-encoded audio. However, Pro Logic uses advanced algorithms, superior to the earlier home Dolby Surround system and similar to the original cinema Dolby Stereo processors, in order to not only extract the extra channels, but to also improve steering and discreteness between the channels.
[edit] Dolby Surround At A Glance
| DeCoder | EnCoder | Year | Description | Channels |
|---|---|---|---|---|
| Dolby Analog SR (Spectral Recording) | 1976 | Cinema use | ||
| Dolby Surround | 1986 | First Home use. Analog | ||
| Dolby Pro Logic | > 1986 | Improved Dolby Surround. 4.0 | FL FR C RearMono | |
| Dolby Digital | Adaptive Transform Coder 3 (AC3) | 1992 Film 1995 Laser Disc |
Pro Logic Decoder for digital stereo inputs | FL FR C SL SR SUB |
| Dolby Digital EX | 6.1 and 7.1 | FL FR C SL SR SUB RearMono(x2) | ||
| Dolby Digital Plus | High bitrate. Currently uses 7.1 channels with support for more | |||
| Dolby TrueHD | Lossless encoder for High Definition Video Sound. Higher Bitrate than DD-Plus | |||
| Dolby Digital Live | On the Fly 5.1 encoder for Games | |||
| Dolby Pro Logic II | 2000 | 5.1 And can also upmix Dolby Surround 4.0 | FL FR C SL SR SUB | |
| DPL II Movie | 5.1 Dolby Surround Decoding for Movies | |||
| DPL II Music | Upmix Plain Stereo into 5.1 from sources such as CDs. | FL FR C SL SR SUB | ||
| DPL II Game | 5.1 Dolby Surround Decoding for Games | |||
| DPL II Matrix | Upmix Mono to Surround | |||
| DPL IIx | Upmix Stereo or Surround to 5.1, 6.1, or 7.1 in either Movie, Music, or Game mode. | FL FR C SL SR SUB RearMono(x2) | ||
| Jazz, Hall & Stadium | Extra Decoders implemented by manufacturers. These add effects like echo and delay to change sound. |
[edit] Dolby Encoding Matrices
| Dolby Surround | Left | Right | Center | Surround |
|---|---|---|---|---|
| Left Total | 1.000 | 0.000 | 0.707 | j0.707 |
| Right Total | 0.000 | 1.000 | 0.707 | k0.707 |
j = + 90º phase-shift , k = - 90º phase-shift
| Dolby Pro Logic | Left | Right | Center | Rear Left | Rear Right |
|---|---|---|---|---|---|
| Left Total | 1.000 | 0.000 | 0.707 | j0.707 | j0.707 |
| Right Total | 0.000 | 1.000 | 0.707 | k0.707 | k0.707 |
j = + 90º phase-shift , k = - 90º phase-shift
| Dolby Pro Logic II | Left | Right | Center | Rear Left | Rear Right |
|---|---|---|---|---|---|
| Left Total | 1.000 | 0.000 | 0.707 | j0.8165 | j0.5774 |
| Right Total | 0.000 | 1.000 | 0.707 | k0.5774 | k0.8165 |
j = + 90º phase-shift , k = - 90º phase-shift
