Dolby Pro Logic
From Open Encyclopedia
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 playback 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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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 logic 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.
The Pro Logic II system also features modes designed specifically for music and gaming, and it is frequently used in video games for Sony's PlayStation 2, Microsoft's Xbox and Nintendo's GameCube as an alternative to digital technologies like Dolby Digital.
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.
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 almost identical in practice, as both use Matrix technology to extract extra channels from stereo-encoded audio. However, Pro Logic uses advanced algorithms, superior to the earlier Dolby Surround system, in order to not only extract the extra channels, but to also improve steering and discreteness between the front channels.
Dolby Encoding Matrices
| Dolby Surround | Left | Right | Center | Surround |
|---|---|---|---|---|
| Left Total | 1.000 | 0.000 | 0.707 | -0.707 |
| Right Total | 0.000 | 1.000 | 0.707 | 0.707 |
| Dolby Pro Logic | Left | Right | Center | Rear Left | Rear Right |
|---|---|---|---|---|---|
| Left Total | 1.000 | 0.000 | 0.707 | -0.707 | 0.707 |
| Right Total | 0.000 | 1.000 | 0.707 | 0.707 | -0.707 |
| Dolby Pro Logic II | Left | Right | Center | Rear Left | Rear Right |
|---|---|---|---|---|---|
| Left Total | 1.000 | 0.000 | 0.707 | -0.8165 | -0.5774 |
| Right Total | 0.000 | 1.000 | 0.707 | 0.5774 | 0.8165 |
