Understanding Object-based Surround Sound

Object-based surround sound technologies try to encode sound of each object in the scene seperately so that when decoded and played in compatible audio device (i.e. a soundbar), it give more realistic immersive sound experience.

Example:
Let’s say we have a movie scene in which there are 3 objects - a helicopter flying on top, a person talking on left and a vihecle passing by on right side. If the audio is encoded as Dolby Atmos, sound of each of these objects (helicopter, person and vihecle) will be encoded seperately and will be reproduced seperately. Therefore, listening experience will be realistic and immersive.

Object-based Surround Sound Technologies:

• Dolby Atmos (proprietary)
• DTS X (open)

Understanding Dolby Audio

Dolby Laboratories, Inc (shortened to Dolby Labs and known simply as Dolby)

• An American company specializing in audio noise reduction, audio encoding/compression, spatial audio, and HDR imaging
• Dolby Labs was founded by Ray Dolby (1933–2013) in London. The company headquarters to the United States (San Francisco, California) in 1976

Dolby Audio Formats

• Dolby Digital (DD)
• Dolby Digital Plus (DD+ or DDP)
• Dolby TrueHD

Dolby Digital (DD)

• Formerly known as AC-3 (originally synonymous with Dolby AC-3)
• Dolby Digital is a digital audio coding technique that reduces the amount of data needed to produce high quality sound
• Dolby Digital takes advantage of how the human ear processes sound
• Dolby Digital has now become a family of audio compression technologies developed by Dolby Laboratories

Dolby Digital Plus

• Abbreviated as DDP or DD+
• Also known as E-AC-3
• Successors to Dolby Digital
• Lossy or compressed format

Dolby TrueHD

• A lossless (almost uncompressed), multi-channel audio codec
• Supports up to eight audio channels

Dolby Digital Plus vs Dolby TrueHD

What is Dolby Atmos?

Dolby Atmos is a 3D surround sound technology that allows sounds to be placed anywhere in a 3D environment. Atmos is not a audio format, rather it is metadata about audio to encode and decode object-base surround sound. An Atmos compatible audio device (i.e. a soundbar, in my case Sony HT-X8500) can recieve Atmos audio encoded as Dolby Digital Plus or Dolby TrueHD format and then process Atmos data (metadata) to reproduce object-based sorround sound mentioned that it does not matter how many physical speakers the audio device have (2.1 in case of my Sony HT-X8500).

Atmos compatible formats”

• Dolby Atmos over Dolby Digital Plus
• Dolby Atmos over Dolby TrueHD

Playing Dolby Atmos to Soundbar

To play Dolby Atmos, we need HDMI ARC or HDMI eARC:

• HDMI ARC:
  • ARC stands for “Audio Return Channel”
  • Can play Dolby Atmos over Dolby Digital Plus only
  • Most streaming platform i.e. Netflix plays Dolby Atmos over Dolby Digital Plus
• HDMI eARC
  • eARC stands for “Enhanced Audio Return Channel”
  • Can play Dolby Atmos over Dolby TrueHD

See: how to play dolby atmos and dtsx audio in a soundbar

DTS X

• DTS:X is an object-based surround-sound format that competes with Dolby Atmos
• DTS-HD MA (MA -> Master Audio) is the encoding format for DTS:X (silimar to “Dolby Digital Plus” and “Dolby TrueHD” are encoding formats for “Dolby Atmos”)