With its object-based sound system, Dolby Atmos is now the high-water mark for at-home surround sound. Though it took some time to catch on, the format is now supported by Ultra HD Blu-ray discs and streaming services like Netflix, and Amazon Prime Video. So, if you’ve got Dolby Atmos speakers, and a Dolby Atmos-compatible AV receiver, and access to Dolby Atmos content, you should be hearing Dolby Atmos sound, right?
Well, as it turns out, no — at least, not necessarily. To really understand if your Atmos system is delivering true Atmos sound — and not just really, really good 5.1.2, or 7.1.2 surround — you need to understand how Dolby Atmos works with all of your media sources and components. It’s a bit technical, but we’re going to make it as simple as possible.
What exactly is Dolby Atmos?
Dolby Atmos isn’t actually a soundtrack at all. It’s metadata that is used by compatible audio gear to control which speakers are reproducing certain sounds. A good example is when a helicopter flies overhead in a movie. Without Atmos information, the sound of the helicopter is embedded in one, or many of the surround sound channels. But so are all of the other sounds you’re hearing.
With Dolby Atmos, the helicopter is treated as its own discrete object, and a Dolby Atmos receiver can use that information to separate the helicopter sound from the background sounds and move it independently from one speaker to another. The result is a very convincing 3D placement of sounds.
So if Dolby Atmos is just metadata, what am I listening to?
As we said, Dolby Atmos isn’t sound, it’s information about sound. That information piggybacks on top of existing surround sound signals. At the moment, Dolby Atmos can only do this with two types of surround sound:
- Dolby TrueHD
- Dolby Digital Plus
Dolby TrueHD is an uncompressed, very high-bandwidth format which is currently only available on Blu-ray disc. It can only be transmitted over an HDMI cable, from a Blu-ray player to an AV receiver, TV, or a soundbar that can pass through the video. The combination of Dolby Atmos and Dolby TrueHD is the best possible surround sound you can get at home.
Dolby Digital Plus is a compressed, lower-bandwidth format that has been optimized for use with streaming services, and features like B-D Live. It’s currently supported by a wide range of devices, like laptops, tablets, smartphones, and streaming boxes like Apple TV and Roku. Dolby Atmos over Dolby Digital Plus will be the way most people experience Atmos. Not only is it the format used by Netflix, and Amazon, it’s also the only version of Atmos that is compatible with HDMI-ARC (more on this later).
Files, apps, and hardware
The tricky thing about Dolby Atmos is that, for it to work, every ingredient in your home theater setup has to support Atmos. In other words:
- The movie you’re playing, whether it’s physical, downloaded, or streamed, has to be encoded with Dolby Atmos (via Dolby TrueHD or Dolby Digital Plus)
- The hardware you’re playing it on, whether it’s a Blu-ray player, streaming box, TV, or another device, has to be able to pass along Dolby TrueHD, or Dolby Digital Plus — as well as the Dolby Atmos layer — without altering it, which is known as “passthrough.” Any alteration will most likely destroy the Atmos data.
- If you’re using a streaming box, like an Apple TV, Android TV (e.g. Nvidia Shield TV), or Roku, the app on that device that you’re using e.g. Plex, Netflix, iTunes, Firecore Infuse etc., must also be able to passthrough this Dolby data.
- And of course, your AV receiver or soundbar must be Dolby Atmos compatible.
Another potential gotcha: Just because your app of choice supports Dolby Atmos on device X, that doesn’t mean it necessarily supports it on device Y. For instance, Plex running on an Nvidia Shield TV can passthrough Atmos over Dolby TrueHD, and over Dolby Digital Plus, but Plex on an Apple TV 4K will only handle Atmos over Dolby Digital Plus, and Plex on a 4th-gen Apple TV can’t passthrough Dolby Atmos at all.
If you’re playing an Atmos encoded Ultra HD Blu-ray on an Ultra HD Blu-ray player, connected to an Atmos-capable AV receiver, via HDMI, we can pretty much guarantee you’re getting the full Dolby Atmos experience. We can’t say the same about some other device combinations.
Here’s a few examples where you will not get Dolby Atmos sound:
- Playing an Atmos-encoded Netflix movie on a non-4K Apple TV, connected to an Atmos-capable receiver. In this scenario, the Apple TV is the weakest link, and doesn’t support Dolby Atmos. You’ll be limited to 7.1 Dolby Digital Plus surround sound.
- Playing any Dolby Digital Plus Atmos-encoded content on a Roku Streaming Stick+, attached to a 2018-model LG OLED TV, with an Atmos soundbar connected via optical cable. The obstacle here is the optical connection to the soundbar. You’d got Atmos content on a device that can support Atmos, on a TV that can passthrough Atmos, but because you’re using an optical cable instead of HDMI-ARC, the LG TV has to down-convert the audio to Dolby Digital 5.1 (otherwise known as EAC), because optical connections cannot cope with the higher bandwidth requirements of Dolby Digital Plus.
- Playing UHD Blu-ray disc, on a player attached to a 2018-model LG OLED TV, with an Atmos soundbar connected via HDMI-ARC. This is a really frustrating one — all of the sources and components are Atmos-capable, but because many UHD Blu-ray discs only offer Dolby Atmos with Dolby TrueHD e.g. Ready Player One, the HDMI-ARC connection can’t pass it to the soundbar. It would need to be Atmos with Dolby Digital Plus for this to work, but the Blu-ray doesn’t have that audio track, and neither the Blu-ray player nor the TV can convert the TrueHD data into Dolby Digital Plus, without losing the Atmos layer.
Yes, unfortunately, HDMI is a requirement for Atmos. Whether your Dolby Atmos content is coming from a Blu-ray disc, or a streaming box, or even from a built-in app on your TV (some TVs, like LG’s OLED series support Dolby Atmos), the only way to get that signal to your AV receiver, or soundbar, is via HDMI. Both Dolby TrueHD and Dolby Digital Plus contain more data than a digital optical connection (TOSlink) can handle. If you’re using an optical cable to connect your TV to your soundbar, or your AV receiver, these signals will be converted into a simpler surround format, like Dolby Digital 5.1, before they get transmitted. The bottom line, is that while the sound you hear will still be really good, it won’t be Atmos.
The only exception to this rule is if you’ve got a Dolby Atmos TV, with native apps like Netflix, or Amazon Video, and you’re using the TV’s internal speakers. Technically, we suppose, the full Atmos signal is being passed to these speakers. But we don’t think that built-in speakers offer even decent surround sound, let alone a convincing Dolby Atmos experience.
How do I know?
Some Dolby Digital Plus and Dolby TrueHD surround soundtracks are so good, you might not even realize you aren’t getting Dolby Atmos just by listening. The one sure-fire way to know is to check the information panel on the front of your AV receiver, or your soundbar (if it has one, or perhaps an on-screen display). It should display the kind of audio signal it’s currently working with, and if it doesn’t specifically say “Atmos,” or “Dolby Atmos,” then the odds are, you’re not getting Atmos.
Achieving proper Dolby Atmos requires a bit of diligence on your part and a wee bit of technical know-how, but it’s totally worth it. We’ll leave you with this helpful diagram, and wish you good luck, and happy listening!