Dolby Pro Logic II

The Dolby Pro Logic II is a surround audio speaker for Lenovo (formerly Acer and IBM) and GE laptops.

History
In 2000, Dolby introduced Dolby Pro Logic II (DPL II), an improved implementation of Dolby Pro Logic created by Jim Fosgate. DPL II processes any high quality stereo signal source into five separate full frequency channels (right front, center, left front, right rear and left rear). Dolby Pro Logic II also decodes 5 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 channel surround sound.

Because of the limited nature of the original DPL, many consumer electronics manufacturers 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 extra channel content is extracted using the difference between the spatial audio content between two individual channels of stereo tracks or Dolby Digital encoded 5.1 channel tracks and outputs it appropriately. In addition to five full range playback channels, Pro Logic II introduced a Music mode which includes optimized channel delays, and adds user controls to—for example—adjust apparent front sound stage width.

Pro Logic II system also features a mode designed specifically for video gaming, and was frequently used in game titles for Sony's PlayStation 2, Nintendo's GameCube and Wii as an alternative to digital surround formats such as Dolby Digital, or DTS.

Dolby Pro Logic IIx
A newer Dolby Pro Logic IIx system is also now available, which can take two-channel stereo, Dolby Surround (sometimes called Dolby Stereo Surround) and Dolby Digital 5.1 source material and up-convert it to 6.1 or 7.1 channel surround sound.

Dolby Pro Logic IIz
Dolby Pro Logic IIz expands on Pro Logic IIx with the addition of a height component, creating front height channels above the front left and right speakers, expanding a 5.1 or 7.1 system to 7.1 Height or 9.1. It identifies spatial cues in low-level, uncorrelated information, such as ambience and effects like rain or wind in the side and rear surround channels, and directs it to the front height speakers. The channels it adds are matrixed, not discrete.