Dolby Pro Logic

Dolby Surround is the earliest consumer version of Dolby's surround sound decoding technology. It was introduced to the public in 1982 during the time home video recording formats (such as Betamax and VHS) were introducing Stereo and HiFi capability. The name Dolby Surround described the consumer passive matrix decoding technology; the professional, active-matrix cinema technology bore the name Dolby Stereo. It was capable of decoding Dolby Stereo four-channel soundtracks to three output channels (Left, Right, Surround). The Center channel was fed equally to the Left and Right speakers. The Surround channel was limited to a 100 Hz to 7 kHz frequency bandwidth, as dialog from the center channel could leak into the surround channel—there was as little as 3 dB of separation between LCR and Surround channels. ==Dolby Pro Logic==

In 1987 the decoding technology was updated and renamed Dolby Pro Logic. A Pro Logic decoder/processor "unfolds" the sound into the original 4.0 surround—left and right, center, and a single limited frequency-range (7 kHz low-pass filtered) ==Dolby Pro Logic II==

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), while also decoding five 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 five-channel surround sound. Because of the limited nature of the original Dolby Pro Logic encoding, 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 that includes optimized channel delays and adds user controls to—for example—adjust apparent sound stage width. Pro Logic II systems also have a mode designed specifically for video games which is used in games for PlayStation 2, GameCube, and Wii as an alternative to digital surround formats such as Dolby Digital or DTS. Game mode is similar to Movie mode, except it redirects more bass to the LFE channel. ==Dolby Pro Logic IIx==

The Dolby Pro Logic IIx system, available since 2003, 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. == Dolby Surround (2014) ==

Dolby reintroduced the Dolby Surround terminology in 2014. The term now refers to a new upmixer whose purpose is to enable Dolby Atmos receivers and speaker configurations to serve non-Atmos signals. Dolby Surround is a complete replacement for Pro Logic that upmixes stereo and multi-channel inputs to play over Atmos configurations. == Software encoding and decoding ==

• The liba52 decoder library for AC3 and A52 digital sound optionally exports Lt/Rt stereo sound compatible with Pro Logic decoders. • HandBrake and FFmpeg are capable of downmixing Dolby Digital AC-3 5.1 to Lt/Rt stereo tracks compatible with Dolby Pro Logic I & II decoders. • SurCode for Dolby Pro Logic II is a Dolby-certified software encoder and decoder available in plug-in formats for DAWs and as a standalone application. == Hardware encoding ==

• Dolby Digital (AC3) compatible hardware (DVDs, TVs, Blu-ray players) downmixes the 5.1 channel tracks into Lt/Rt stereo compatible with Pro Logic decoders ==See also==