Dolby Pro Logic
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Dolby Pro Logic is an analog surround sound system developed by Dolby Laboratories in 1976 for cinema sound systems as Dolby Analog SR. The Analog SR format was adapted for home use in 1986 as Dolby Surround which was replaced by the newer Pro-Logic system.
Both Dolby Surround and Pro Logic are based on basic Matrix technology; four channels of sound are encoded into an ordinary stereo sound track by using phase shift techniques. A decoder/processor "unfolds" the sound into 4.0 sourround - left and right, center, and a limited-range mono rear channel - while systems lacking the decoder playback the audio as standard Stereo.
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Dolby Pro Logic II
In 2000, Dolby introduced Dolby Pro Logic II, essentially a redesigned version of Dolby Pro Logic. DPL II uses two stereo surround channels, an LFE (subwoofer), greatly enhanced steering logic compared to DPL, and as a result, offers an exceptionally stable sound field that simulates 5.1 to a much greater degree than the orginal Pro Logic. Because of the primitive nature of DPL, many manufactures tried to introduce thier own enhancements with extra circutry and processing, often times muddling the sound clarity with artifical tones or delays. DPL II throws out most of this processing and replaces it with simple servo (negative feedback) circuits used to derive five channels. And, unlike the synthetic "EQ" modes like "Jazz", "Hall" or "Stadium" found on many A/V recievers or mini-systems, DPL II introduces no phony delay-induced echoes, reverb, or tonal colorations. The Pro-Logic II system also features modes designed specifically for music and gaming, and it is frequently used on 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, Pro-Logic and Dolby Sourround (sometimes called Dolby Stereo Surround) source material and up-convert it to 5.1/6.1/7.1 channel surround sound.
Pro Logic Vs. Dolby Surround
Dolby's earlier Dolby Surround format and Dolby Pro-Logic 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 Decoding Matrices
| Dolby Surround | Left | Right | Surround |
|---|---|---|---|
| LeftTotal | 1.000 | 0.000 | -1.000 |
| RightTotal | 0.000 | 1.000 | 1.000 |
| Dolby Pro Logic | Left | Right | Center | Surround |
|---|---|---|---|---|
| LeftTotal | 1.000 | 0.000 | 0.707 | -1.000 |
| RightTotal | 0.000 | 1.000 | 0.707 | 1.000 |
| Dolby Pro Logic II | Left | Right | Center | Rear Left | Rear Right |
|---|---|---|---|---|---|
| LeftTotal | 1.000 | 0.000 | 0.707 | -0.866 | -0.500 |
| RightTotal | 0.000 | 1.000 | 0.707 | 0.500 | 0.866 |
External links
- Dolby's official site (http://www.dolby.com/)
- A Listener's Guide To Pro Logic II (http://www.wildwestelectronics.net/lisguidtodol1.html)