Dolby Pro Logic
Product type | Surround sound |
---|---|
Owner | LtRt |
Markets | Worldwide |
Website | Dolby official website |
Dolby Pro Logic is a
Dolby Stereo—also known as Dolby MP (Motion Picture) or Dolby SVA (stereo variable-area)—was developed by Dolby in 1976 for analog
The Dolby MP Matrix was the professional system that encoded four channels of film sound into two. This track used by the Dolby Stereo theater system on a 35mm optical stereo print and decoded back to the original 4.0 Surround. The same four-channel encoded stereo track was largely left unchanged and made available to consumers as "Dolby Surround" on home video. However, the original Dolby Surround decoders in 1982 were a simple passive matrix three-channel decoder: L/R and mono
Later on in 1987, the Pro Logic decoding system was released to consumers. It featured virtually the same type of four-channel decoding as the Dolby Stereo theater processor with active steering logic and much better channel separation (up to 30 dB) as well as including a dedicated center channel output for the first time. Many standalone Pro Logic decoders also included a phantom center option for compatibility with earlier non-Pro Logic Dolby Surround equipped home theaters to split the center channel signal to the L/R speakers for legacy phantom center reproduction.
Dolby Surround Pro Logic is the full name that refers to the matrix surround format and decoding system in one. When a Dolby Surround soundtrack is created in post-production (Dolby MP Matrix), four channels of sound are matrix-encoded into an ordinary
A Dolby Pro Logic decoder/processor "unfolds" the soundtrack back into its original 4.0 surround—left and right, center, and a single limited frequency-range (7 kHz low-pass filtered)[3] mono rear channel—while systems lacking the decoder play back the audio as standard stereo.
Although Dolby Surround was introduced as an analog format, all Dolby Digital decoders incorporate a digitally implemented Dolby Surround Pro Logic decoder for digital stereo signals that carry matrix-encoded Dolby Surround. One of the first was the MSP400 surround sound receiver and amplifier by RCA for their high-end
Dolby Surround
Dolby Laboratories | |
Country | United States |
---|---|
Introduced | 1982 |
Related brands | Dolby Digital Dolby Stereo |
Markets | Worldwide |
Website | Dolby official website |
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
Dolby Pro Logic
Dolby Laboratories | |
Country | United States |
---|---|
Introduced | 1987 |
Related brands | Dolby Digital Dolby Stereo |
Markets | Worldwide |
Website | Dolby official website |
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)[3] 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.[3]
In addition to 5 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
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.[1]
Dolby Pro Logic II
Dolby Laboratories | |
Country | United States |
---|---|
Introduced | 2000 |
Related brands | Dolby Digital Dolby Stereo |
Markets | Worldwide |
Website | Dolby official website |
In 2000, Dolby introduced Dolby Pro Logic II (DPL II), an improved implementation of Dolby Pro Logic created by Jim Fosgate.[4] 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
Dolby Pro Logic IIx
Dolby Laboratories | |
Country | United States |
---|---|
Introduced | 2003 |
Related brands | Dolby Digital Dolby Stereo |
Markets | Worldwide |
Website | Dolby official website |
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 Laboratories | |
Country | United States |
---|---|
Introduced | 2009 |
Related brands | Dolby Digital Dolby Stereo |
Markets | Worldwide |
Website | Dolby official website |
Dolby Pro Logic IIz expands on Pro Logic IIx with the addition of a height component, creating front
Dolby Surround (2014)
Product type | Surround sound |
---|---|
Owner | Dolby Laboratories |
Country | United States |
Introduced | 2014 |
Related brands | Dolby Digital Dolby Stereo Dolby Atmos |
Markets | Worldwide |
Website | Dolby official website |
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 liba52decoder 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[6]
See also
References
- ^ a b Cohen, Simon; Hall, Parker (2023-11-10). "Ultimate surround sound guide: DTS, Dolby Atmos, and more explained". Digital Trends. Retrieved 2024-01-06.
- ^ Robjohns, Hugh (September 2001). "Surround Sound Explained: Part 2". Sound on Sound. Retrieved 2024-01-06.
- ^ Dolby Laboratories. Archived from the original(PDF) on March 26, 2014. Retrieved February 8, 2019.
- ^ Scarpelli, Paul (2015-03-03). "History of Surround Sound Processing: The Battle for Dolby Pro Logic II". Audioholics. Retrieved March 17, 2017.
- Dolby Laboratories. Archived from the originalon January 22, 2009. Retrieved January 22, 2009.
- ^ Neyrinck, Paul (February 26, 2015). "Tech Blog – TV/DVD Surround Encoding Technologies". Neyrinck. Retrieved September 15, 2017.
External links
- Dolby's official site
- Dolby's official history page 4
- Home theatre focus' history of dolby surround decoders