What Is Pro Logic II?
While today’s Dolby Digital and DTS systems deliver the finest audio possible for home video, a processing technology called Dolby Pro Logic II can give older stereo audio tracks a bigger, better sound. According to Alan Lofft, writing for Axiom Home Theaters, Pro Logic II not only creates realistic multi-channel surround mixes for old stereo-based soundtracks, it can also turn two-channel music performances into surround-sound experiences.
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Technology
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Dolby Pro Logic II uses a technology known as surround-sound matrix decoding. According to Secrets of Home Theater and High Fidelity, Dolby created the first surround-sound matrix for the 1977 film "Star Wars." Dolby encoded information for left, right and center channels into the standard right and left audio tracks of the film. When decoded, three separate audio channels would result from the two audio tracks. Pro Logic II, and later Pro Logic IIx, expanded on this matrix technology to yield additional channels of audio from two-channel sources.
Development
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Dolby Pro Logic II improves on its ancestor, Dolby Pro Logic. Pro Logic could only offer full-range sound reproduction across its three front speakers, sending its fourth channel to two rear speakers as a divided mono channel. Dolby Pro Logic II improved the channel separation and the realism of the sound field while adding full-range independent rear audio channels for better surround effects and music reproduction.
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Features
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Pro Logic II offers a variety of features, depending on the individual audio receiver, that allow listeners to customize the system to their room acoustics or personal preferences. The "center width" settings, for instance, give the listener the option of running most or all of the front-channel audio through the center speaker, or directing most or all of it to the front left and right speakers. The "panorama" setting extends the front left and right audio channels into the rear speakers as well, while the "dimension" setting adjusts the ratio of front channels to rear channels.
Compatibility
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Pro Logic II works with any two-channel stereo audio source to create the impression of multi-channel sound. Lofft notes that it yields particularly convincing results with jazz, classical and other forms of acoustic music. It also works well on Dolby Surround videotapes and laser discs of films made before Dolby Digital mixes became available, effectively “remastering” these audio tracks into full-range 5.1 audio. Many leading manufacturers include Pro Logic II as a standard feature set on their home theater audio receivers.
Considerations
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Pro Logic II delivers five channels plus a subwoofer channel, while the newer Pro Logic IIx offers up to seven channels plus subwoofer, according to Yamaha Electronics. Not every home theater receiver, however, includes all the features available to these systems. Music mode, for instance, does not come with every Pro Logic II-equipped device, nor does the center width feature. Shoppers should make sure that the receiver they purchase includes all the features they want for their music and home theater needs.
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References
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- Photo Credit loudspeakers image by Alexander Oshvintsev from Fotolia.com
