Dolby Digital Sound

• Dolby Digital Sound Card

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, 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.

1. 7.1 Channels - Dolby Digital Plus is a high definition digital-based surround sound format that supports up to 8-channels of surround decoding, but also contains a standard Dolby Digital 5.1 bitstream that is compatible with standard Dolby Digital-equipped receivers.
2. Enter Dolby's newest creation, Dolby Digital (DD). For the first time, a fully discrete digital 5.1 channel surround format was created for both the theaters and home audio marketplace. When the consumer-electronics industry DVD Working Group (DVDWG) sought the best audio coding technology for the new format back in 1995, Dolby Labs jumped at.

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.

The Technology Dolby Digital Plus is an audio technology based on Dolby Digital 5.1, the established standard for cinema, broadcast, and home theater surround sound.

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 that 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.

More on Dolby Atmos

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, including 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.

Dolby Digital Sound Card

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. This is known as “pass-through.” 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 (Plex, Netflix, iTunes, Firecore Infuse etc.) must also be able to pass through 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 pass through Atmos over Dolby TrueHD, nd 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 pass through Dolby Atmos at all.

If you’re playing an Atmos-encoded Ultra HD Blu-ray on an Ultra HD Blu-ray player that’s connected to an Atmos-capable TV, soundbar, or 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 an Apple TV HD (4th gen, non-4K) connected to an Atmos-capable A/V receiver. In this scenario, the Apple TV is the weakest link: It 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+ that’s attached to a Dolby Atmos capable 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 pass through Atmos, but because you’re using an optical cable instead of HDMI-ARC, the 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.

• Using the built-in Plex client on an LG OLED TV to play a movie encoded with Dolby TrueHD and Dolby Atmos, 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 the Plex client on the LG TV isn’t yet optimized to handle TrueHD/Atmos, it down-converts the audio to Dolby 5.1 — even though both the TV itself and the connected soundbar could have easily handled the TrueHD/Atmos track.

HDMI-only?

Yes, unfortunately, HDMI is a requirement for Atmos. Whether your Dolby Atmos content is coming from a Blu-ray disc, 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. If you’re still not sure if your setup gets an Atmos passing grade, check out our Dolby Atmos cheat sheet diagram above. Good luck, and happy listening!

Editor’s note: A previous version of this article suggested that Dolby Atmos TVs, like LG’s line of 2016 and newer OLED TVs, can’t convert a Dolby Atmos/TrueHD audio track to the HDMI-ARC-friendly Dolby Atmos/Dolby Digital+ format. This is incorrect. Any TV that is certified for Dolby Atmos can accept Dolby Atmos/TrueHD from an HDMI-connected device, and perform the conversion to Dolby Atmos/Dolby Digital+ (without any loss of Atmos data) for the purpose of transmitting it over HDMI-ARC to a Dolby Atmos soundbar or A/V receiver.

Home Audio Amplifiers and Preamps

Whether you're setting up a home studio or want superior sound while listening to music, amplifiers and preamps can help you get the results you want. Preamps clean up and sometimes add detail to raw voice and digital music files. Amplifiers then increase sound volume and intensity, creating a richer, fuller audio experience.

As noise-cancelling devices, preamplifiers can provide a necessary step before amplification or other output. They take the initial audio signal, clean it up, and modulate it for you. Without preamps in place, you may wind up with feedback in your recording, lessening their quality. The type of equipment you need will depend largely on input type and desired results.

• Mic Preamps: Microphones tend to pick up considerable amounts of white noise, even in a quiet room. While recording voice, singers may breathe or sigh, creating distortion. Instrument microphones may pick up interference from neighbors. Mic preamps are designed to filter out these unwanted inputs for a cleaner signal.
• Color: Some options may add color, or modifications, similar to the acoustics that come from being in a small or large room.
• Integrated: Many amplifying devices come with integrated preamps designed to filter noise prior to amplification. Models in this category include the Yamaha A-301 and the Marantz PM7005.
• Standalone: Designed to clean up sounds from a variety of input sources, preamps act as a buffer between source and output. This option is a good choice if you want to be able to swap equipment.

Here, choices will depend largely on the number and type of outputs, because each one will need a different channel.

• Power Rating: In order to amplify speaker power, look for at least double the wattage of the speaker or output device. For example, 50-watt speakers need at least 100-watt amplification. The higher the wattage, the greater the amplification.
• Stereo: Because each side of stereo counts as a separate channel, you will need at least 2-channel amplification for stereo.
• Zoned Systems: Many home audio setups use separate zones where you can arrange for different areas to play different music and audio. In this situation, remember to consider each zone separately. Some zones may require multi-channel signal amplification for complex audio. Others may not need any at all.
• Home Recording Studios: If you're recording music or audio at home, consider a high-performance, multi-channel amp. This way, you can account for all vocal ranges, sound effects, and musical instruments.