Dolby Atmos: This is how the technology works and what it needs

SPEAKER

June 30, 2022 at 2:15 p.m

Dolby Atmos offers a unique sound experience. Says the ad. But how does the technology work? And under what circumstances can the full-bodied promises be realized?

1. 9.1.4 and Co. – Dolby Atmos brings a new number into play

2. Atmos is object-based sound

3. Dolby Atmos verlangt Dolby Atmos

4. What do I need for Dolby Atmos?

5. How does Dolby Atmos sound? Just test it

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In many systems, so-called surround sound is realized by a subwoofer and several distributed loudspeakers. 9.1 means that there are a total of nine loudspeakers in the room and a woofer plays the low frequencies. The principle of Dolby Atmos is based on expanding the sound planes through loudspeakers from above. This leads to settings like 9.1.4 – including four ceiling speakers.

9.1.4 and Co. – Dolby Atmos brings a new number into play

What is that supposed to help? Viewers (and listeners) in the cinema should experience with sound how a UFO approaches from above or how a superhero disappears into the air. In both cases the sound comes from above. But does he really come?

In the home cinema and even in many cinemas, the 64 loudspeakers that are actually necessary are not installed in order to achieve real Atmos sound. This means that there is almost always a downmix to the technology. Especially with the sound from above people like to cheat – with so-called upfiring. Here, the speakers are not physically located on the ceiling, but at the same level as the others. They only aim towards the ceiling, which should then reflect the sound so that it comes from above.

Whether that works depends on many factors: the reflectivity of the ceiling, the height of the room, the position of the listeners. The fact that real Atmos sound is created when upfiring is more of a coincidence than the rule.

Atmos is object-based sound

The second difference between Atmos and “classic” formats such as Dolby Digital 5.1 starts with the production and comes into play during the playout. Traditionally, production and playback are channel-based. This means that the technology assigns a specific audio track to each channel.

Atmos, on the other h and, works object-based. The object is the sound itself, for example the noise that a jet plane taking off in a movie makes. The playback is then not channel-based, but is generated by the technology from metadata and played out depending on the equipment.

It sounds impressive, but it’s a matter of taste. Anyone who has media in Atmos production mode can already hear the effects during stereo playback, since the sound objects intended for speakers that are not present in their own set are virtualized, thus complementing the sound spatially and in its directions.

Dolby Atmos verlangt Dolby Atmos

Which also brings up the next topic: The content must be produced in Dolby Atmos. This places high demands on the sound technology, whether for the cinema film or the symphony orchestra. Or to put it another way: Atmos productions are the most expensive on the market and therefore also the rarest. But the desired 3D sound can only be created if the source supports Atmos.

Even if this is the case, it does not necessarily mean that Atmos really matters. This problem is particularly present with streaming. Only with a correspondingly high, stable data rate does the Atmos soundtrack with metadata arrive smoothly.

By the way: Not every director or musician uses the sound from above. It may be that even productions created entirely for Dolby Atmos do not offer appropriate sound reinforcement from the ceiling.

What do I need for Dolby Atmos?

As already mentioned, 64 loudspeakers would actually be necessary, including mounting on the ceiling. Then real Atmos sound is created. Alternatively, the market offers various devices that are said to be “atmos-capable”. This ability begins with the connection: HDMI 2.1 (eARC) is mandatory.

Anyone who relies on soundbars should be aware that the Atmos sound is based on virtualization. Upfiring and downsizing the number of speakers cut the authentic sound.

How does Dolby Atmos sound? Just test it

Finally, the question: is Dolby Atmos better than Dolby Digital and other formats? Basically, this can only be answered individually.

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If you want to get a feel for the matter, you can “test listen” to the Atmos sound on your existing equipment. The object-based playout is retained. Whether you like it is a matter of taste. The same applies to music in 3D quality. A difference can already be heard with normal headphones.