Editing Dolby Pro Logic (section)

==Dolby Pro Logic==
{{infobox brand
|name           = Dolby Pro Logic
|logo           = Dolby-Surround-Pro-Logic.svg
|logo_size      = 120px
|image          = 
|type           = Surround sound
|currentowner   = [[Dolby Laboratories]]
|origin         = United States
|introduced     = 1987
|discontinued   =
|markets        = Worldwide
|website        = [https://www.dolby.com/ Dolby official website]
|related        = [[Dolby Digital]]<br>[[Dolby Stereo]]
}}
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&mdash;left and right, [[center channel|center]], and a single limited frequency-range (7&nbsp;kHz [[low-pass filter]]ed)<ref name="dplii"/> mono rear channel.

A Pro Logic decoder also uses 'Steering Logic', which drives amplifiers to raise or lower the output volume of each channel based on the current dominant sound direction. For example, while a mono signal is played, the strong correlation to the center channel triggers the output volume of the left, right and surround channels to be lowered. This increases the channel separation achievable to around 30 decibels between channels. By careful tuning of the response of the amplifiers, the total amount of signal energy remains constant and is unaffected by the operation of the channel steering. Additionally, the response time of the system to changes in sound direction is important as too fast a response results in a twitchy feel, while too slow a response leaves sounds coming from an inappropriate direction.<ref name="dplii" />

In addition to 5&nbsp;dB of noise reduction, the surround channel is slightly delayed, so that any front channel sounds that leak into the surround channel arrive at the listener after the front channels. This takes advantage of the [[Haas effect]]—audio that is present in the front speakers but delayed in the surround speakers will have the psychoacoustic effect of emanating from the front of the sound stage.

Dolby Surround and Dolby Pro Logic decoders are similar in principle, as both use matrix technology to extract extra channels from Dolby Stereo stereo-encoded audio. The terms Dolby Stereo, Dolby Surround and Lt/Rt are all used to describe soundtracks that are matrix-encoded using this technique.<ref name=":0">{{cite web |last1=Cohen |first1=Simon |last2=Hall |first2=Parker |date=2023-11-10 |title=Ultimate surround sound guide: DTS, Dolby Atmos, and more explained |url=https://www.digitaltrends.com/home-theater/ultimate-surround-sound-guide-different-formats-explained/ |access-date=2024-01-06 |website=[[Digital Trends]]}}</ref>
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