Dolby Atmos: Why and How

Date Posted:14 February 2020 


A few years ago we posted an article about Dolby Atmos.  This was a brief introduction, and an invitation for everyone to come down and experience it for yourselves.  Many people came in and had a listen and during the intervening years many people purchased or setup a Dolby Atmos system with our assistance.  But there are still a lot of questions from people about what Dolby Atmos is and why they aren’t getting a Dolby Atmos signal on their system

Dolby Atmos is an Object-Oriented Sound Process, this means that it can track 128 objects within an audio mix.  These “objects” are anything that makes a noise, a car, bullet, Helicopter a character etc.  By tracking these “objects” individually their sound is no longer restricted to a single channel or across channels.  These “objects” can placed and moved anywhere within the sound field, including above the listener.

The main addition to a traditional 5.1/7.1 sound system is the “height” speakers.  These are added in a configuration of 2 or 4, turning a traditional system in to 5.1.4/7.1.2 for example.  These addition speakers can take the shape of in-ceiling speakers or “Atmos-modules”, which are speakers that have been designed to sit on top of your existing floor standing speakers and bounce the height channels off the ceiling.  Couple these with a Dolby Atmos capable receiver and away you go.  There are also some Dolby Atmos capable soundbars that have drivers built-in to replicate this design (Yamaha YSP-5600), and at recent trade shows some TV manufacturers have revealed “Atmos TV’s” that use some speakers at the top of the LED panel to create a “Virtual Atmos” system.  I will reserve judgment on these, however if the standard of audio from modern TV’s is anything to go by I will not be expecting these TV’s to blow my socks off.

With all that said, if you have your Dolby Atmos speakers’ setup, and your Dolby Atmos capably AVR, with some Dolby Atmos enable Content you will be hearing Dolby Atmos sound! Well, Um, not quite.  It’s a little more complicated than that.  Here is why.

Dolby Atmos isn’t a soundtrack; this is complication number 1.  Dolby Atmos is actually Metadata which means it is information about the sounds, explaining where the sound sits within the overall sound field.  Essentially allowing “objects” to be moved around this sound field separate to the background noise.

With this in mind Dolby Atmos can only work with two types of surround sound:

 

  1. Dolby TrueHD
    1. Uncompressed, High Bandwidth format
    2. Currently only available on Blu-Ray Disc
    3. Can only be transmitted of HDMI
      1. No Optical
    4. Dolby TrueHD + Dolby Atmos = Best possible surround sound available at home
  • Dolby Digital +
    1. Compressed, Low Bandwidth format
    2. Optimised for streaming
    3. This is the Dolby Atmos that most people will experience

 

Complication number 2: Every aspect of your setup needs to support Dolby Atmos;

  • Content: Disc or Streaming
    • Has to be encoded with Dolby Atmos (see above)
  • Playback Device: Apple TV, Xbox, Blu-Ray Player
    • Must be able to decode Dolby Atmos or pass through the Dolby Atmos signal without altering it
  • App being used on the playback device
    • Must be capable of delivering the Dolby Atmos data to your AVR (or Soundbar)
  • AVR (or Soundbar)
    • Must be Dolby Atmos Compatible

Complication number 3: An app may support Dolby Atmos, but only on select devices. 

  • Plex on an Apple TV 4K will do Dolby Atmos over Dolby Digital+
  • Plex on an Apple TV 4th Gen will not pass through Dolby Atmos at all
  • Plex on an Nvidia Shield TV will pass through Dolby Atmos on both Dolby TrueHD and Dolby Digital+

 

Same app, three devices, three different outcomes.  So where does this leave Dolby Atmos for the home user?  We can, almost, guarantee you are getting the full Dolby Atmos experience when you are playing Dolby Atmos enabled Ultra HD Blu-ray, on an Ultra HD Blu-ray player that is connected to an Atmos-compatible AVR (soundbar if you must) via a HDMI cable.  Any other device combination will be a hit and miss experience.

Final Note: Netflix

As mentioned previously Dolby Atmos “should” work on any device that can pass-through the Dolby Atmos data unaltered.  Unless the app is Netflix.

The Netflix app currently requires that playback devices be capable of decoding Dolby Atmos natively, instead of just passing it through to your Dolby Atmos capable AVR.

The main, streaming, devices that are capable, at this point in time are:

The Netflix app on any other streaming device, no matter its capabilities in relation to Dolby Atmos will limit you to a 5.1 surround sound signal.

 


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