Dolby Audio Codecs

Dolby Digital audio compression technology was developed by Dolby laboratories for cinematic applications. Also referred to as AC-3, is an advanced audio encoding/decoding technology that efficiently delivers up to 5.1 discrete channels of rich, vibrant and enveloping surround sound for broadcasting, home theater, cinema, PC, online streaming, and video game programming.

The three front channels (Left, Center, and Right) provide crisp, clean dialogue and accurate placement of on-screen sounds, while the twin surround channels (Left Surround and Right Surround) create an immersive effect into the action for the audience. The Low-Frequency Effects (LFE) channel delivers deep, powerful bass effects that can be felt as well as heard. It delivers low-pitched sound in the range 3-120Hz to Subwoofers. This channel uses up only about one-tenth the bandwidth of each of the other channels. Dolby Digital offers a maximum bit rate of 640kbps. Both Blu-ray and HD-DVD are required to support Dolby Digital at its maximum bit rate. Because Dolby® Digital audio codec is so efficient; it has been widely adopted as a standard for DVD as well as Blu-ray Disc™. It has also been adopted as the preferred standard for Satellite SD/HDTV in US, Canada, Australia and UK.

Dolby Digital specifics

• 1.0 to 5.1, discrete
• 32–640 kbps, scalable
• DVD data rate, 5.1-channel audio: 384 or 448 kbps
• Blu-ray Disc data rate, 5.1-channel audio: 640 kbps
• Supports Dolby metadata
• Connections: S/PDIF, HDMI, IEEE 1394
• Capable of Mixing/streaming 

Dolby Digital Plus

Dolby Digital Plus is a versatile digital audio coding technology that extends the capabilities of Dolby Digital. Dolby Digital Plus delivers up to 7.1 channels of cinematic surround sound, with scalable sound delivery and a wide range of bit rates ensuring optimized sound quality and efficiency for the available bandwidth. With more channels, less compression, and higher bit rates, Dolby Digital Plus helps equipment manufacturers and content producers differentiate their products by delivering a sound experience that some reviewers have described as being “virtually transparent” to the original source.  

 

Dolby Digital Plus specifics

• 1.0 to 7.1 discrete channels
• 32 kbps–6 Mbps scalable data rate; typical range on HD optical discs is 768 kbps–1.5 Mbps
• Supports Dolby metadata
• Supported by  S/PDIF, HDMI, IEEE 1394 connections  
• Capable of streaming/mixing
• Backward Compatibility; S/PDIF to legacy A/V receivers (640 kbps data rate)

 

Dolby® Digital Surround EX™

Dolby® Digital Surround EX™ is created by introducing an additional rear surround audio channel to the 5.1 channel Dolby Digital. Adds a center rear channel to the Dolby Digital 5.1 system for increased cinema realism and creates a richer enveloping surround sound with sound effects panning from front to back. Supports 6.1-channel home audio playback.

Dolby® Pro Logic® II

Dolby® Pro Logic® II is an advanced matrixing technology that delivers convincing, realistic surround sound from stereo content. It delivers a natural, realistic and compelling five-channel surround sound from stereo program sources; namely TV broadcasts, movies, video games, and music. 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.

Dolby® Pro Logic® IIx

Dolby® Pro Logic® IIx is an extension of Dolby Pro Logic II matrixing technology that delivers enriched enveloping 6.1 and 7.1 surround sound from both stereo and 5.1 content. It enhances spatial depth and improves sound directionality. With this technology the listening area is perceptibly larger and provides soundfields tailored for movies, music and gaming.

Dolby® Pro Logic® IIx specifics 

• Ability to generate up to 7.1 channels from stereo and 5.1 sources
• Supported decoding: 
• Pro Logic mode  
• Virtual Compatible mode  
• Music mode  
• Movie mode  
• Matrix mode  
• Dolby Digital EX mode  
• Supported upmixed output configurations based on stereo sources: 
• 2 to 3 [Left, Right to Left, Center, and Right]
• 2 to 4 [Left, Right to Left, Right, Left surround, and Right surround]
• 2 to 5.1 [Left, Right to Left, Center, Right, Left surround, and Right surround] 
• 2 to 6.1 [Left, Right to Left, Center, Right, Left surround, Right surround and Center surround] 
• 2 to 7.1 [Left, Right to Left, Centre, Right, Left surround, Right surround, Left rear surround, and Right rear surround]
• Supported upmixed output configurations based on 5.1 sources with independent Ls and Rs channels: 
• 5.1 to 6.1 [Left surround, Right surround to Left surround, Right surround, and Center surround] 
• 5.1 to 7.1 [Left surround, Right surround to Left surround, Right surround, Left rear surround, and Right rear surround] 

Dolby® Pro Logic® IIz  

Dolby® Pro Logic® IIz adds front height channels to surround sound, creating a 7.1 or 9.1 playback system for home music, movies, and video games. Dolby Pro Logic IIz brings enhanced spatial effects, added depth, and an overall airiness to the listening experience. Essentially, it’s an extension of Dolby Pro Logic IIx by front height channels. It is possible to expand a 5.1 playback system to a 7.1, or a 7.1 system to a 9.1 while offering a near discreet listening experience. By adding front height channels, Dolby Pro Logic IIz creates a 7.1 or 9.1 playback system that enhances the spaciousness of music, movies, and video games, by introducing a vertical component to the horizontal soundfield of a conventional 5.1 or 7.1 surround system.  

 

Dolby® Pro Logic® IIz specifics  

The features listed above allow Dolby Pro Logic IIx to provide a true surround sound experience from a variety of sources. However, all the outputs derived by existing Dolby Pro Logic IIx decoders are located in a horizontal plane. The Dolby Pro Logic IIz extensions to Dolby Pro Logic IIx allow it to derive height channel outputs that significantly enhance the spatial experience. In addition, Dolby® Pro Logic® IIz supports the following;

• Ability to generate audio of up to 9.1 channels that include height channel outputs from stereo, 5.1, and 7.1 Back sources.
• Supported upmixed output configurations based on stereo sources:
• 2 to 7.1 Height [Left, Right to Left, Center, Right, Left surround, Right surround, Left height, and Right height]
• 2 to 9.1 [Left, Right to Left, Center, Right, Left surround, Right surround, Left rear surround, Right rear surround, Left height, and Right height]
• Supported upmixed output configurations based on 5.1 sources with independent Ls and Rs channels:
• 5.1 to 7.1 Height [Left surround, Right surround to Left surround, Right surround, Left height, and Right height]  
• 5.1 to 9.1 [Left surround, Right surround to Left surround, Right surround, Left rear surround, Right rear surround, Left height, and Right height] 

Dolby TrueHD 

Dolby TrueHD offers playback that is as close as it gets to the sound captured at a live concert. Its powerful sound is bit-for-bit identical to what is created in the recording studio or mixing stage. Dolby TrueHD brings a spacious sound stage, highly accurate effects, and unsurpassed dynamic range to home theaters, delivering a compelling “you are there” surround sound experience. It’s 100 percent lossless, bit-for-bit identical to the original studio recording. It conserves Disc space through the 4:1 compression to limit bandwidth usage. For playback through a home theater system, Dolby TrueHD is transported via HDMI® (High Definition Multimedia Interface) version 1.3 or later, a single-cable digital connection for audio and video. Dolby TrueHD content may also be introduced to a playback system via Ethernet or USB connections.  

Dolby TrueHD features 

• Dialogue normalization maintains consistent volume levels when switching between Dolby TrueHD and Dolby Digital or Dolby Digital Plus programming. 
• Dynamic range control enables reduced peak volume levels without impacting overall sound quality. It’s ideal for late-night viewing. 

• Downmixing allows the content creator to enable stereo playback from the original multichannel source or to provide an independent stereo “artist’s mix” that is incorporated into the Dolby TrueHD bitstream.
• Three presentations, one bitstream: A single Dolby TrueHD stream can contain up to three separate mixes (presentations): a 7.1-channel surround mix, a 5.1-channel surround mix, and a two-channel “artist’s” stereo mix. This gives content creators the ability to tailor each mix for optimum listening on any playback system. 

• Advanced 96k upsampling: Movie soundtracks and TV shows are often recorded using a 48 kHz (48k) sampling frequency. The brickwall filters required for 48k analog-to-digital (A-to-D) conversion in the recording process introduce artifacts called preringing, heard as an unnatural hardness or edginess. To deliver clearer, more natural playback sound from this content, Dolby TrueHD encoding now includes a proven 96 kHz (96k) upsampling process developed by Meridian Audio. It significantly improves the sound from a Blu-ray Disc in any channel configuration. The process applies higher sample rates and increased playback quality through an advanced apodizing filter that masks undesirable digital artifacts in 48k material. The upsampling takes place before Dolby TrueHD encoding.  By applying the upsampling in software, Dolby TrueHD creates content that’s compatible with all Blu-ray™ players and all A/V receivers with 96k digital-to-analog converters (DACs). It does not add any computing burden in playback. Although the upsampling increases file size and data rates, the optional Dolby Mapping (noise-shaping) feature, specifically designed for Dolby TrueHD, minimizes or eliminates these increases. Content producers can employ the upsampling feature at their discretion. The process is designed to improve 48k audio files and is not needed for native 96k material. 

• Dolby TrueHD can deliver up to 16 channels of pristine audio, so it is ready for any future HD streamed formats. On Blu-ray Disc today, it delivers up to eight full-range channels of 24-bit/96 kHz audio and supports up to 24-bit/192 kHz for stereo and 5.1 content. 

• Leverages interchannel correlations to reduce data rates for lossless matrixing and more efficient downmixing.
• Employs decorrelation to take advantage of the predictive nature of audio. 

• Allows fewer bits to be assigned for commonly occurring values within the data stream for a more efficient coding process using Huffman (entropy) coding.

• Smooths the encoded data rate with managed FIFO buffering throughout audio data transmission.

 

Dolby TrueHD Specifics 

Dolby TrueHD supports;

• 44.1 kHz to 192 kHz sampling frequency.
• Variable bit rate; CBR rendering for transport over HDMI
• Word length up to 24 bits.
• Up to eight channels of 24-bit/96 kHz Blu-ray audio; designed to be expandable should the Blu-ray Disc standard adopt additional channels.
• Two- to six-channel of up to 24-bit/192 kHz. 
• Maximum bit rate of up to 18 Mbps on Blu-ray Disc.