Dolby® Pro Logic® II is an advanced matrixing technology that delivers convincing, realistic surround sound from stereo content.

Provides compelling five-channel surround sound from any stereo program source, including TV broadcasts, movies, video games, and music

Delivers natural, realistic surround derived from spatial cues naturally occurring in stereo content; no artificial added effects

Complements Dolby Digital 5.1 decoding to ensure a surround experience on all content

Dolby Pro Logic II was developed to allow a surround listening experience from stereo content. It delivers five full-range channels (including two surround channels) derived from spatial cues that occur naturally in stereo recordings, soundtracks, and broadcasts. The result is a compelling yet entirely natural and realistic surround effect that is incorporated in virtually all home theater products, including audio/video receivers (AVRs) and home-theater-in-a-box (HTIB) systems.

Dolby Pro Logic II technology is also used by broadcasters to encode their stereo signals specifically for Pro Logic II playback. This makes it possible for them to deliver specific surround and localization effects over stereo services that are more like discrete 5.1 transmissions, without compromising regular stereo and mono playback.

Why Dolby

As PCs become multimedia hubs, consumers increasingly rely on them for entertainment, which has increased the demand for surround sound capability on the PC. Yet many PC audio sources—including streamed or downloaded audio in MP3 and AAC formats, CDs, many games, and even some DVD soundtracks—are two-channel. Dolby Pro Logic II creates realistic and natural 5.1-channel surround sound from these sources.

Dolby Pro Logic II is fully compatible with other Dolby Pro Logic technologies. It provides optimal playback for the many TV shows available online and the many PC video games that have been encoded in Dolby Surround.

Dolby Pro Logic II works especially well with Dolby Headphone to provide a personal surround sound experience. It also works with the built-in speakers on a PC, or with external speakers or component systems connected to the PC’s audio outputs.

We license Dolby Pro Logic II to PC manufacturers and also to PC soundcard manufacturers.

Dolby Pro Logic II represents a major step forward from first-generation surround decoding. In previous logic decoders, including the original Dolby Pro Logic technology, the control circuit looks at the relative level and phase between the input signals. This information is sent to the variable output matrix stage to adjust VCAs controlling the level of antiphase signals. The antiphase signals cancel the unwanted crosstalk signals, resulting in improved channel separation. This is called a feed-forward design.

Dolby Pro Logic II is a complementary encoding/decoding system. While it will generate surround sound from any two-channel source, it also allows content producers to encode the surround information for optimal playback effect. PCs and soundcards incorporating Dolby Pro Logic II can take full advantage of this content.

Dolby Pro Logic II looks at the relative level and phase between the input signals and employs a servo loop to match the levels. These matched audio signals are sent directly to the matrix stages to derive the various output channels.

Because the same audio signals that feed the output matrix are themselves used to control the servo loop, it is called a feedback logic design. Incorporating global feedback around the logic steering process improves steering accuracy and dynamic behavior.