Mixing Atmos: Andy Bradfield

Leading mix engineer Andy Bradfield shares some of the lessons he’s learned in getting to grips with Dolby Atmos.

During more than 30 years in the business, Andy Bradfield has established himself as one of the most versatile mix engineers around. He trained at Olympic Studios and became an in‑house engineer at Olympic and Townhouse Studios before going freelance. He now works mainly from his own studio, which was recently upgraded to Dolby Home Entertainment specifications, and is seeing increasing demand for Atmos mixes. Andy’s earlier experience mixing in other surround formats has stood him in good stead here.

“I’ve seen a lot of change over my career, because I started on analogue tape and SSL consoles. Then gradually Pro Tools started coming in, and I embraced it quite early on, but it was always in conjunction with other things. And eventually, that morphed into what we have now. But also, over that same period of time, I started dipping my toe into movie soundtrack work. So, I was working on score mixing as well as traditional stereo work, and that’s continued ever since. So for me to leap into Atmos was perhaps less of a jump than for some other people, because I was already quite comfortable working in 5.1 or 7.1.”

On The Level

For a studio like Andy’s to be certified by Dolby, it has to meet fairly stringent technical requirements. Obviously, it needs a surround monitoring setup that includes ceiling‑mounted speakers. Less obviously, the output from that setup also needs to be regulated. “In the post‑production world, all the spaces are calibrated. Dolby go in regularly and check the setup, and they work at a fixed, calibrated level. For someone who’s a straight‑up music guy like me, that put my head on backwards, because I didn’t fully understand the concept initially. Richard and Myles at Dolby were really great, and enormously helpful in getting me set up and configured. Avid were super helpful too.

“I started working at a calibrated level a good few years ago now, when I was doing score mixes, and actually, I found that really helped in terms of getting things to translate to the dub stage, and also integrating with the dialogue. But the thing that I found quite early on was that I struggled to work at 85 [dB SPL], because I’m in a smaller space than most post‑production studios. Working at 85 when the speakers are 20 or 30 feet away is OK. But when they’re as close as they are in a regular music studio, that’s much harder, and if you’re not careful, without realising, you calibrate yourself. So, what happens is, you mix quieter.”

On the basis of this experience, Andy has settled on a calibraton level of 79dB SPL in his studio; and now that he’s acclimatised, he finds that his instincts as to when things are too quiet or too loud are usually sound. This is crucial when mixing for Atmos, because the specification insists that mixes should not exceed ‑18 LUFS, and any that do are liable to be rejected.

“I’m sure a lot of music people will be thinking 'why are Dolby dictating all these things?' But actually, the more you read the spec and you start to understand what they’re trying to do, the more it makes sense. It is a little bit of a steep learning curve — and you’ve still got the added complications of having the renderer.”

Andy Bradfield: ...for me to leap into Atmos was perhaps less of a jump than for some other people, because I was already quite comfortable working in 5.1 or 7.1.

Render Me Speechless

The Atmos renderer is a piece of Dolby software that integrates with the DAW and acts both as monitor controller, virtual audio interface and master recorder. In essence, the renderer maps Atmos beds and objects to the specific speaker configuration in use, and when the time is ripe, generates the ADM file that will eventually be used for Blu‑Ray authoring or sent to Apple, Tidal, and other streaming services. For Andy, most of the wrinkles associated with moving from conventional surround mixing to Atmos relate to learning the ways of this Dolby utility.

“It’s actually not too difficult once you’ve used it a bit and you’ve understood it, but initially the renderer is a bit of a shock — because although it’s a monitoring box, it’s also ultimately where you output your files to. It’s sort of half a workstation, except it doesn’t have any waveforms. It’s a bit strange to get your head around when you’re so used to working with all these different tools that have waveforms. And of course, on top of that, you’ve also then got the binaural rendering for headphones.

“I’m using the renderer the way that most people do, on the same computer as Pro Tools. You set your Pro Tools interface to be the Dolby Audio Bridge, and that gives you 128 paths out to the renderer, and then they can be a mixture of what they call beds and objects. Beds are up to 7.1.2, so if you’ve got, say, a bunch of stuff that’s already mixed in surround, and you’re not really bothered about getting that much height coverage, you can just leave it in a bed, and it will pan to all the correct places in the regular surround plane. Objects can either be mono or stereo, although you can’t send those to the low‑frequency channel.

“The Dolby Atmos panner is very clever, because it’s kind of like auto‑pan on steroids. The idea is that you put it on an object channel, and it creates the panning metadata instead of the Pro Tools panners. And you can do all sorts of crazy sequencing things which would be quite difficult to achieve with the Pro Tools panner.”

Andy Bradfield’s studio has recently undergone a revamp to meet Atmos Home Entertainment specs. The speakers in the surround array are Neumann KH120s, with the Kii 3 and good old NS10s still present for stereo mixing. Note the Dolby renderer on its own screen, top left.

Space Balls

In total, an Atmos mix can contain up to 128 channels. If 10 of these are used for a single 7.1.2 bed, that leaves 118 available for objects. “You may think 128’s quite a lot, but if you started getting really crazy, it can get out of hand quite fast. But I’ve ended up only really needing one bed, which is usually a 7.1.2. I tend to start by just putting everything into the bed. Where it becomes a little bit limiting is that the height on a 7.1.2 bed is only two channels. So, generally, if it’s something that I want to add height to, I’ll make it into an object, but it’s also good for more precise movement through the 360‑degree space that Atmos gives you to mix in.

“One of the other things that’s a bit annoying is that the numbering drives you a bit crazy. The objects are numbered from 11 upwards, yet you have to have at least one bed channel, and that uses inputs 1‑10. So, your first stereo object pair is 11 and 12. What you quickly learn is some little tricks, like you suddenly go, where’s that? So then you solo it, and if you look up on the renderer, it’s got loads of little circles, and if it’s coming in, they go green. They’re like little sort of input LEDs. So you go, ah, yeah, that’s on four, or 24. All right, cool. And then carry on. Once you route to an object you can then basically pan that anywhere in the 3D space, and it shows up on the renderer as a ‘ball’ when it’s got signal — or pair if it’s a stereo object — so you get a dynamic view of the object panning or movement while you are mixing.

“One of the things that Atmos is intended to overcome is translating to different systems, so if you play on a 5.1.2 system or a 5.1 system, the hardware decoding the file will deal with it and play it in a meaningful way, which is almost impossible on traditional surround formats. In Atmos the objects get rendered depending on the playback configuration.

“I wish Apple would make us a real‑time tool to monitor their headphone playback [the Apple Music Headphone Decoding], because their headphone rendering is slightly different than Dolby’s, and Apple’s position is like, well, you just render in QuickTime and put it on your phone. And I’m like, yeah, but mixing is real time. It’s always been real time. Whereas the Apple way is that I’ve got to print into the renderer or bounce it to an ADM file, then export it to a QuickTime MP4, I’ve got to get it on my phone, and then if I want to make a change, I’ve got to do that all again. It’s just really too time‑consuming. If Apple want to push this format, they need to give us the tools to do it, even if it was a piece of software that had to be run on another machine. Apple playback can still render a full‑speaker Atmos via an Apple TV 4K and an Atmos receiver or soundbar as well.”

Bottoms Up

Not only does mixing in Atmos mean learning the ways of the Dolby renderer and adjusting to a calibrated, loudness‑normalised mixing environment; it also involves unlearning some familiar techniques. “A lot of people, myself included, for many years have used what you would call a top‑down mixing approach. That could be as simple as having a stereo EQ on your mix bus, or it could mean having quite elaborate compression and tone‑shaping tools. And, of course, that affects how everything sounds. In this world, it’s much more difficult to do that. You can’t really heavily compress the stereo bus, because you’re dealing with discrete sources a lot of the time, as the objects are in effect not a traditional bus!

“Being someone who’s made records for a long time, I’m not adverse to using limiters, and I think used well, they’re a very good tool. But sometimes on stuff that’s perhaps a little bit more extreme‑sounding, it becomes part of the sound. Certainly on a lot of pop records, there’s a lot of detail, and part of that smacky, middly driving vibe is the processing and the limiting. And when you come to doing Atmos, it’s much more difficult to achieve that effect, because that’s something that’s put on as an overall thing, and it doesn’t work in quite the same way when some of it is separated.

“Something else that I’m aware of when mixing in surround is that I always want to try and make it sound like it’s coherent, and of course, to some degree, when you’re trying to make it immersive, you’re also splitting it apart. It’s like having a ball of dough, and then just pulling it out into loads of bits. It doesn’t look like a big coherent piece any more, you know? When you’re working in Atmos, you’ve got lots more places to put things, but also then, by definition, if you do that, sometimes you’re exposing things. And that can be good and bad, because sometimes things have artefacts, or it’s a chopped‑up sample, suddenly you can hear it. When it was in a stereo mix, there may be some masking going on of where it sits, so you don’t hear some of those things. So, some things like that have to be a consideration. But again, I think, once you’ve got an Atmos setup, you’ve got a good monitoring environment that’s very revealing, then you have to make those calls as and when they come up.

“The other thing that I’ve been very aware of is that stuff that’s been mixed in stereo, if it’s quite rhythm‑heavy, it’s quite difficult sometimes to pull it too far into the room, because what tends to happen is the energy drops, and it doesn’t have that drive. And so, you kind of almost have to pin it to the front. If you’ve got something that’s big and orchestral and very lush, you could probably spread it right out, and it would sound amazing. Whereas if it’s something much more sort of tight‑knit, like a drum & bass thing or a band, you sometimes want it to be much more focused.”

Stuck In The Middle

Lead vocals are usually the most important element of any mix, and in stereo, we nearly always position them in the centre. It seems natural to do the same in Atmos, but as Andy points out, that idea can be realised in multiple ways. A vocal routed only to the centre channel is ‘centred’ in a very different way from a vocal routed to both the left and right speakers, or to all channels equally. “In the cinematic world, they tend to want the vocal in the centre channel, as that’s where the dialogue is too. That’s partly to do with having massive theatres, and the fact that if you are over on the far right or the far left, you still get the vocal because it’s in the middle, because it’s got its own channel. And I get that, but I know that some people find that a bit uncomfortable, because they’re used to listening to phantom stereo, which is what we’re all doing when we’re mixing in stereo. So, some people tend to still use left and right and put a bit of the vocal in the middle, or you could even do the funny sort of triangle thing where you could put the vocal in the middle and the effects behind you, if you wanted to. But again, it depends on the track, because sometimes you do that, and then the vocal ends up turning dry, and it doesn’t really sound right.”

The key, for Andy, is to make these decisions in context. He cites as an example a ballad from Fish’s album Weltschmerz. “It started very small, and it was just piano and vocal, and I was like: do you know what, this would be quite cool if the vocal was kind of centre, but the effect was kind of around. So I actually used a surround reverb, because there’s a surround version of the Liquidsonics plate, and it’s fantastic. And it was absolutely the right thing, because there was enough space to have it. On a much busier track, it’s possible that that would be lost on you, because you wouldn’t really hear those back/side channels, anyway, certainly not a reverb return back there on a very dense mix. So, it depends on the arrangement and what’s going on.”

Andy Bradfield: In terms of the technical aspects and the equipment, there’s a lot to it. But it’s not insurmountable, and once you get going it’s great, and I’m really enjoying it.

Head Space

“Mixing has always been a technical exercise, but it’s also a creative, musical exercise,” concludes Andy. “And at times, those things are slightly in conflict with one another. One of the things with Atmos is that initially, it’s a bit more of a technical exercise than it is a creative exercise. Once you get past that, it’s great, but I’m always very aware that I’m trying to not let the technology dictate to me, so that I can be creative. And so, in a way, I almost have to split my brain into two parts. There’s the creative part that’s Creative Andy. ‘Let’s do a mix, let’s make it really amazing.’ And then, there’s Technical Andy that has, ‘Oh, we’ve got to print this now, and we’ve got to output it, and we’ve got to make a QuickTime so I can send it to the client.’ And those two things are very different parts of the process. But unfortunately, they’re necessary parts of the process.

“I’m certainly very excited about what Atmos has to offer, but it’s a big rabbit hole! You start going down it, and you go ‘Oh my god, what have I just started?’ And I think part of it is fear of the unknown. In terms of the technical aspects and the equipment, there’s a lot to it. But it’s not insurmountable, and once you get going it’s great, and I’m really enjoying it.”

www.andybradfield.com