Dolby AC-4 is an audio compression technology developed by

Dolby Laboratories Dolby Laboratories, Inc. (often shortened to Dolby Labs and known simply as Dolby) is an American company specializing in Noise reduction#In audio, audio noise reduction, Audio data compression, audio encoding/compression, spatial audio, and ...

. Dolby AC-4 bitstreams can contain audio channels and/or audio objects. Dolby AC-4 has been adopted by the

DVB Digital Video Broadcasting (DVB) is a set of international open standards for digital television. DVB standards are maintained by the DVB Project, an international industry consortium, and are published by a Joint Technical Committee (JTC) o ...

project and standardized by the

ETSI The European Telecommunications Standards Institute (ETSI) is an independent, not-for-profit, standardization organization in the field of information and communications. ETSI supports the development and testing of global technical standard ...

History

Its development started in late 2011 to create a high-quality audio format that had a certain resemblance to

Dolby TrueHD Dolby TrueHD is a lossless, multi-channel audio codec developed by Dolby Laboratories for home video, used principally in Blu-ray Disc and compatible hardware. Dolby TrueHD, along with Dolby Digital Plus (E-AC-3) and Dolby AC-4, is one of the int ...

destined for multiple uses, to be used in streaming services, future TV broadcasts, and mainly to replace the traditional

Dolby AC-3 Dolby Digital, originally synonymous with Dolby AC-3, is the name for what has now become a family of audio compression technologies developed by Dolby Laboratories. Formerly named Dolby Stereo Digital until 1995, the audio compression is lossy ( ...

, and in December 2014

approved the sound format for commercial use. On March 10, 2015, the

Advanced Television Systems Committee The Advanced Television Systems Committee (ATSC) is an international nonprofit organization developing technical standards for digital terrestrial television and data broadcasting. ATSC's 120-plus member organizations represent the broadcast, br ...

(ATSC) announced that Dolby AC-4 was one of the three standards proposed for the audio system of

ATSC 3.0 ATSC 3.0 is a major version of the ATSC standards for television broadcasting created by the Advanced Television Systems Committee (ATSC). The standards are designed to offer support for newer technologies, including HEVC for video channels of u ...

. On July 14, 2015, Dolby Laboratories announced that

Sony , commonly stylized as SONY, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. As a major technology company, it operates as one of the world's largest manufacturers of consumer and professional ...

Visual Products and

Vizio Vizio Inc. (stylized as VIZIO) is an American publicly traded company that designs and sells televisions, sound bars, viewer data, and advertising. The company was founded in 2002 and is based in Irvine, California.Lawton, Christopher, Iwatani K ...

would support Dolby AC-4. On April 14, 2016, Dolby Laboratories announced that

Samsung The Samsung Group (or simply Samsung) ( ko, 삼성 ) is a South Korean multinational manufacturing conglomerate headquartered in Samsung Town, Seoul, South Korea. It comprises numerous affiliated businesses, most of them united under the ...

would ship TVs with support for Dolby AC-4 in 2017.

Technical details

Dolby AC-4 can have up to 5.1 core audio channels which all Dolby AC-4 decoders are required to decode. Additional audio channels may be encoded as side signals which Dolby AC-4 decoders can optionally support which would allow for the delivery of 7.1.4 channel audio. Side signals may also contain audio objects. Dolby AC-4 has two different channel based encoding tools with Advanced Joint Channel Coding (A-JCC) used for low bit rates and Advanced Coupling (A-CPL) used for high bit rates. A-JCC doesn't support side signals and is limited to 5.1 channel audio while A-CPL does support side signals. Dolby AC-4 supports up to 7 audio objects with a core decoder and can optionally support additional audio objects with a more advanced decoder. The use of different decoders allows Dolby AC-4 to support lower cost devices while also allowing for more advanced decoders for

AV receiver An audio/video receiver (AVR) is a consumer electronics component used in a home theater. Its purpose is to receive audio and video signals from a number of sources, and to process them and provide power amplifiers to drive loudspeakers and ro ...

s. AC-4 uses an improved

modified discrete cosine transform The modified discrete cosine transform (MDCT) is a transform based on the type-IV discrete cosine transform (DCT-IV), with the additional property of being lapped transform, lapped: it is designed to be performed on consecutive blocks of a larger ...

(MDCT)

audio coding An audio coding format (or sometimes audio compression format) is a content representation format for storage or transmission of digital audio (such as in digital television, digital radio and in audio and video files). Examples of audio coding f ...

algorithm. Dolby states that Dolby AC-4 provides a 50% reduction in bit rate over

Dolby Digital Plus Dolby Digital Plus, also known as Enhanced AC-3 (and commonly abbreviated as DDP, DD+, E-AC-3 or EC-3) is a data compression, digital audio compression scheme developed by Dolby Labs for transport and storage of multi-channel digital audio. It is ...

. When Dolby AC-4 was tested by the DVB the

MUSHRA MUSHRA stands for Multiple Stimuli with Hidden Reference and Anchor and is a methodology for conducting a codec listening test to evaluate the perceived quality of the output from lossy audio compression algorithms. It is defined by ITU-R recommen ...

score was 90 at 192 kbit/s for 5.1 channel audio. When tested for ATSC 3.0 the bit rates needed for the required audio score was 96 kbit/s for stereo audio, 192 kbit/s for 5.1 channel audio, and 288 kbit/s for 7.1.4 channel audio. However, for 22.2 channel audio, the required bit rate may be as high as 1536 kbit/s.https://www.itu.int/dms_pubrec/itu-r/rec/bs/R-REC-BS.1196-7-201901-S!!PDF-E.pdf Dolby AC-4 is extensible and audio substreams allow for new features to be added to Dolby AC-4 while maintaining compatibility with older decoders.

Patent licensing

Dolby AC-4 is covered by patents and requires a license from Dolby Laboratories. Dolby AC-4 has a consumer royalty rate of US$0.15 to US$1.20 depending on the type of device and volume of sales. Dolby only charges for one technology per device, which means that Dolby AC-4 effectively costs nothing in devices that include existing Dolby technologies such as Dolby Digital Plus. The professional royalty rate is up to US$50 for an eight channel transcoder.

References

External links

* {{Video formats American inventions Audio codecs Consumer electronics Dolby Laboratories Film sound production Film and video technology Audiovisual introductions in 2016 Ultra-high-definition television

History

Technical details

Patent licensing

See also

References

External links