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Setting Up An Atmos Mixing Room

Atmos And You By Sam Inglis
Published November 2022

Many leading mix engineers are upgrading their studios to be Atmos‑capable. This is Chris Lord‑Alge’s studio in Los Angeles, recently outfitted with an Ocean Way immersive monitoring system.Many leading mix engineers are upgrading their studios to be Atmos‑capable. This is Chris Lord‑Alge’s studio in Los Angeles, recently outfitted with an Ocean Way immersive monitoring system.

Immersive audio is a massive opportunity — if you’re equipped to take it. Here’s what you’ll need to do to make your studio Atmos‑ready.

The artistic and commercial potential of Dolby Atmos is obvious. But what equipment will you need to exploit that potential? How should it be configured? Will your existing mix space work, or are you better off building a new one? And how much will it cost? To answer these questions and more, I spoke to some of the world’s leading studio design consultants.

Render Options

When you deliver your first Atmos mix, it’ll be as an ADM file. This is an extension of the Broadcast Wave format, and can be created only by the Dolby Atmos Renderer software. So the first things you’ll need are the Dolby software and a compatible computer. But which version of the Atmos Renderer?

The deluxe option is the Dolby Atmos Mastering Suite, which runs on its own Windows PC or Mac, accepting 128 channels of audio over MADI or Dante from the device doing the mixing. In a music production context, though, this is unlikely to be needed. Unless you’re working on a hardware console, it should be possible to do everything you need on one machine. However, as Pete Hofmann of Miloco points out, “Mixing in Atmos is quite CPU‑intensive, so you’ll need a relatively modern and high‑spec computer to handle everything.”

When running on the same machine, DAWs address the Dolby Atmos Renderer in different ways. If you want to work in Pro Tools (including HD, as of the 2022.9 software release) or Ableton Live, you’ll need to purchase the separate Dolby Atmos Production Suite and set up the Dolby Atmos Bridge, a virtual soundcard that pipes all the necessary audio channels into the Atmos Renderer software. In Apple’s Logic Pro X and Steinberg’s Cubase/Nuendo, by contrast, the Renderer runs as a plug‑in on your master bus, and the DAW still addresses the audio hardware directly.

To mix Atmos, you’ll need the Dolby Atmos Renderer — but which version?To mix Atmos, you’ll need the Dolby Atmos Renderer — but which version?

If your existing DAW doesn’t support Atmos, fear not: switching might not be as disruptive as you’d expect. The most common Atmos workflow is to mix the stereo master first, then export key elements as stems. The Atmos mix is then created from these stems in a separate session, and it’s only this stage of the process that requires an Atmos‑compatible DAW. The main options at present are Logic Pro X, Cubase Pro 12, Nuendo 12, Pro Tools Studio/Ultimate, Ableton Live, Merging’s Pyramix and Blackmagic Design’s DaVinci Resolve Studio. Atmos support in Logic and Cubase is streamlined in some respects compared with ‘full fat’ Atmos, but not in any way that is likely to prove limiting for music mixing.

A Room Of One’s Own

To create an ADM file that’s worth uploading anywhere, you’ll need more than just a computer. You’ll need to be able to hear what you’re doing: and it’s no exaggeration to say that pretty much all of the rest of this article will be devoted to this topic.

It is essential to check Atmos mixes on headphones, but the desirability of actually mixing Atmos on headphones is doubtful. Options are available to anyone who wants to try, and are discussed in the box. Realistically, though, if you want to create commercial Atmos mixes, you are going to need access to a suitable speaker‑based monitoring system.

To mix movie soundtracks, you will need a studio that meets Dolby’s cinema specifications, and should expect to spend a substantial six‑figure sum. If you’re ‘only’ mixing music — or “home entertainment” as Dolby call it — things are more relaxed. As studio designer and consultant Carl Tatz explains, “Since Dolby does not certify Atmos Music rooms the same way they do film stages, it’s the Wild West right now as to how they can be configured — with a general nod toward some of the Dolby specs.”

The fact that you don’t need to meet strict standards and achieve an official certification to mix music certainly means it’s more affordable, but that’s not to say you can set your room up any old way. Your first port of call should be the Dolby website: search for “home entertainment studio technical guidelines”. Dolby also make available a spreadsheet‑based Dolby Audio Room Design Tool (DARDT) that can help you optimise speaker positions and other parameters. (You will need Excel to use this, as it cannot be opened in Google Sheets, Numbers or Open Office.)

Atmos & Acoustics

The basic requirements for any mix room are simple. You’ll need an acoustically treated space, good loudspeakers appropriately positioned, and the means to feed signal to those loudspeakers and control their level. But this is hard enough to get right in stereo, and there are some additional complications with Atmos. So one obvious question is: is it practical to adapt an existing stereo control room for Atmos mixing, or should you expect to have to build a new space?

“If you’re currently planning a new studio, lucky you,” says Dolby’s Myles Clarke. “It’s a great time to consider making it an Atmos studio. If you’re not, don’t worry, you’re likely to have already made a lot of the best decisions in an existing room. Naturally you’ll probably have chosen the best orientation for the room, you’ll naturally have found your sweet spot, and importantly, you’ll already be accustomed to the room. As long as you’re willing to move a few things and make minor changes, chances are an Atmos setup will fit fairly naturally.”

“Within reason, both approaches are equally feasible,” says Dirk Noy, of studio design and build consultancy WSDG. “A properly designed stereo or 5.1 surround sound control room with sufficient ceiling height can well be modified to function as an Atmos mixing room. One thing to consider is the avoidance of reflections that may occur once additional loudspeakers are installed that point to locations where no loudspeaker has pointed to before — this may mean the modification of certain surfaces and/or relocation of equipment racks or other furniture.

Proper acoustic treatment is vital in any control room, and additional treatment may be required in converting an existing room to Atmos specs. This is Vesper Sound, a PhantomFocus room by Carl Tatz Designs.Proper acoustic treatment is vital in any control room, and additional treatment may be required in converting an existing room to Atmos specs. This is Vesper Sound, a PhantomFocus room by Carl Tatz Designs.

“In terms of reverberation characteristics, no particular data is given by Dolby, but WSDG regard it as proper to observe ITU/EBU specifications as given for stereo and 5.1 surround sound rooms (ITU‑R 1116). The primary goals of the acoustical treatments in basically any room are: reflection/echo control, where the target is a decent‑size reflection‑free zone, reverberation control, and modal behaviour control.”

“If the control room is well designed originally, an Atmos system can be quite successful,” agrees Carl Tatz. “The goal of any mix room is to have a neutral, leaning towards dead‑sounding environment. The reason being is that any sound that comes back to your ears from room reflections is going to conflict with the direct sound coming to your ears from the monitors, which causes frequency distortion, otherwise known as comb filtering.”

“In many ways, similar principles to treating a stereo mixing environment still apply,” agrees Ben Savage of Yellow Technology. “Early reflections from nearby hard surfaces between a loudspeaker and your ear will change your perception of the sound, and thus minimising these reflections with a combination of absorption and positioning is important — there are just many more speakers to consider now! Lots of people concentrate their acoustical absorption around the mix position in a small studio, so in the case of someone adding an Atmos setup into an environment like this, they may need to consider changing treatment further back in the room to minimise these reflections from the surrounds, rear surrounds and overheads. Just as with any other studio, though, care should be taken to not just add thin porous absorption such as 50mm acoustic foam without considering lower frequencies. One can quickly end up with a space that is free of early reflections (and indeed any HF reverberation!) but has a low‑frequency reverb tail that rattles on long after anything else! So, using thicker porous absorption (100mm+ absorption panels), diffusion and in some cases specialist low‑frequency absorption can be appropriate.

“SBIR (Speaker Boundary Interference Response) is the phenomenon of reflections from walls/ceilings combining with a loudspeaker’s direct sound to cause irregularities in the speaker’s frequency response, with the bumps and troughs particularly noticeable at low frequencies. SBIR remains a factor with all of the ‘new’ speakers in an Atmos setup, particularly as people tend to be tempted to push lots of the speakers towards walls, ceilings and corners. Placing appropriate absorption behind or above the speaker in these areas can reduce the inaccuracies, and ensuring that a placement doesn’t result in the speaker being equidistant from two or three boundaries is also preferable, as this makes the resulting spectral irregularities more pronounced.”

And as Pete Hofmann points out, the suitability of an existing control room for Atmos can be dependent on its layout. “Having additional side speakers often conflicts with windows, rear speakers with doors, and central speakers with screens, so all those issues have to be considered. If you think about the lengths we go to with L‑R and creating critical treatment around the mix position, you have to do that all around to create a properly immersive space.”

Pete Hofmann: "If you think about the lengths we go to with L‑R and creating critical treatment around the mix position, you have to do that all around to create a properly immersive space.”

Space Race

You may need more acoustic treatment for Atmos, then, and it may have to go in different places, but the treatment itself is the same as for stereo, and off‑the‑shelf items from manufacturers like Vicoustic, GIK or IsoAcoustics will work just as well in an Atmos room. However, a successful Atmos monitoring rig requires a decent amount of space. Dolby themselves suggest a minimum room volume of 50 cubic metres, while their other recommendations refer to the dimensions of the monitoring setup rather than the room itself. “Depending on the acoustic properties of a large room, it may sometimes work to have a smaller speaker layout within the space,” explains Myles Clarke. “For example, if a room is very long from front to back, and the mix position is naturally quite far forward in the room, it might be better to shorten the layout and have the rear speakers further forward in the room.”

“We are looking to achieve a minimum distance from speaker to mix position of 1.5 metres,” says Pete Hofmann, “so that means a room size of at least 4.5 x 4.5 x 2.6 would be a good base build.”

“We have a ‘gold standard’,” explains Myles Clarke. “A studio that follows this standard is going to give to the most accurate, powerful and flexible working experience. The more compromises you make from that gold standard, the less accurate, powerful and flexible the room becomes. This could show up in translation to other studios, and of course in translation to consumer systems. For example, the minimum recommended measurement from floor to the acoustic centre of the height speakers is 2.4m. Whilst we have seen studios coming on board with lower ceilings, the compromise in that scenario is that those speakers get closer to each other the lower they get, and therefore the sweet spot gets smaller. Too low, and that sweet spot becomes impractical. Other issues may arise when the layout becomes narrower or shorter, or when the sweet spot is much closer to the front than the rear, or vice versa.”

Equidistant Vs Orthogonal

Equidistant Atmos speaker layout.Equidistant Atmos speaker layout.Although Dolby allow the possibility of smaller setups, they strongly recommend a 7.1.4 speaker layout for Atmos music mixing, and some labels will insist on this as a minimum. This numbering convention denotes an array with seven speakers in the base or horizontal plane, at ear height, plus a subwoofer for the LFE channel, and four overhead speakers. Broadly speaking, the four height speakers are arranged in a square around and above the listener’s head and the main left and right speakers are positioned as they would be for stereo mixing, with the centre speaker between them; the surround and rear speakers are also positioned symmetrically, to the sides and to the rear respectively. Subwoofer placement follows the same principles as in a stereo mix room.

In an ideal Atmos configuration, the satellite speakers would all be located on the surface of an imaginary sphere with the listening position at its centre, so that the path length from speaker to mix position is always the same. However, this sort of ‘equidistant’ layout isn’t always practical, and if it was realised using wall‑mounted speakers, would bring the room dimensions perilously close to being cubic. In practice, thankfully, it’s not a problem to have speakers at different distances from the listener, as this can be compensated for using time alignment. What’s crucial are the mutual angles between the loudspeakers as perceived from the listening position.

Orthogonal Atmos speaker layout.Orthogonal Atmos speaker layout.For this reason Dolby also make reference to ‘orthogonal’ speaker layouts. In an equidistant speaker layout, you can imagine a straight line running from the listening position through each speaker towards the wall or ceiling. An orthogonal layout is one in which speakers are positioned at the point where these lines meet the wall or ceiling, or at some other convenient point in between. In other words, the distance between the speaker and listener is no longer the same for each speaker, but the mutual angle is retained. An orthogonal layout is often more practical than an equidistant one, especially in rooms that are being adapted for Atmos rather than specially built.

In both cases, Dolby’s guidelines provide a certain amount of leeway as to the angle of the speakers. This is lucky because implementing these angles in a real‑world space can be challenging, especially if you need to work around pre‑existing features such as doors and windows. As in a stereo monitoring system, it’s probably more important to maintain left‑right symmetry than the perfect speaker angles, but neither can be compromised too far. Note, too, that Dolby’s template for an orthogonal room has the listening position in the rear half of the room, closer to the surround and rear speakers than to the main LCR array, which may seem counter‑intuitive....

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