Mixing Atmos: Caroline Hilton

Caroline Hilton’s full title is Senior Director, Artist Engagement and R&D — Advanced Audio Technologies for Universal Music Group, the world’s largest music company.Photo: Nigel R Glasgow

Working in immersive audio can be intimidating even for experienced professionals. Caroline Hilton’s team at Universal Music provide the help that mix engineers need to make that transition.

Immersive audio is both a challenge and an opportunity for music professionals. It offers huge creative potential and a new revenue stream; but it’s also intrinsically complex, different from what we’re used to, and constantly evolving. Which is why Caroline Hilton’s job exists.

Hilton’s full title is Senior Director, Artist Engagement and R&D — Advanced Audio Technologies for Universal Music Group, the world’s largest music company. Her role is to provide the support that artists, engineers and producers need in working with new audio technologies. In the current climate, her main focus is therefore immersive audio, and most of her time is spent in The Garage, an annexe of Abbey Road equipped with a 7.1.4 Atmos listening setup. In a sense, it’s a return to her roots: she studied psychology and neuroscience and trained as a sound engineer before moving to artist relations at EMI.

When UMG began to explore the potential of Atmos for music, it was clear that there would be a need for someone to support audio professionals moving to the new format, and to maintain consistent technical standards. With a studio background and 20 years’ experience at record labels, Caroline Hilton was ideally qualified.

“UMG formed a strategic partnership with Dolby around six years ago, collaborating on premium experiences for the benefit of providing new opportunities for our artists — immersive audio being one of these lanes to explore. As soon as the concept of ‘immersive for audio’ became a possible consideration for delivery to the digital market, we were extremely conscious of the significant difference between music and film. Not only from a workflow perspective but acknowledging that, in most cases, there is the lack of the additional visual stimuli to help the brain process the experience. We wanted to work very carefully on understanding what this meant for our artists and the wider creative community.”

Caroline Hilton: UMG formed a strategic partnership with Dolby around six years ago, collaborating on premium experiences for the benefit of providing new opportunities for our artists — immersive audio being one of these lanes to explore.

Quality First

“We feel it is really important to walk mix engineers, who work for our artists and labels globally, through a technical quality‑control process, which predominantly includes observing overall loudness, true peak, appropriate binaural metadata and any anomalies in the audio information such as missing elements or something which may indicate a room calibration issue like excessive LFE levels that are out of balance with the rest of the mix. Once we have taken engineers through this process, they are added to our ‘UMG verified’ mix engineer list. Our label teams reference or share these mixer details when working with their artists’ teams on who to partner with on a mix. We appreciate understanding of the technology is still expanding and we find this helping hand and guidance is appreciated and a good starting point for our artists.”

This is, she emphasises, very much about helping engineers reach informed decisions themselves, rather than dictating what sort of creative judgements are acceptable. “As this is a relatively new format for music, everyone — the artist, the producer and the mix engineer — will want to experiment, and it is this experimentation that helps a technology develop. This does undoubtedly mean we are in a subjective situation of what is or isn’t a good mix. We try not to get involved or interfere with this creativity. However, we do our best to apply an objective approach on whether the mix technically meets specification.

“Even surround mixers will acknowledge that delivering an immersive project full of metadata is a huge step away from delivering a six‑channel master. For example, the age‑old debate of whether to have a dry vocal in the centre channel is a bugbear of mine, because I know how that might translate on a consumer speaker playback system, and yet not be obvious on headphones. As an artist in a previous life, I know I wouldn’t want my vocal being exposed in that way. Others may think differently, so we need to let the debate run its course and not enforce our personal feelings.”

Practices Make Perfect

“As part of our delivery requirements, we have included what we see as ‘best practices’ in working with the format. To be clear, our intention is never to mandate the creative process, but to help guide our creative community on how and why mixes may not translate in the way they intend. The beauty of Dolby Atmos audio, unlike traditional surround sound, is its ability to re‑render and virtualise to make the experience more accessible, beyond a user who may have a 7.1.4 listening environment to devices such as soundbars and headphones. However, understanding how the listeners will experience these translations can help an engineer develop their workflow and technique.”

Hilton is keen to point out that these best practices have been arrived at empirically. To the technical guidance and specifications that Dolby provide, her team at UMG are adding the fruits of real‑world experience. “We benefit from the wealth of experience across our various entities, from the content creation side through to the digital supply chain delivering tracks to streaming partners. We worked extremely closely with our mix engineers across Capitol Studios in Hollywood, East Iris in Nashville and Abbey Road in London. From that base, we were able to start exploring what worked and what didn’t. In doing so, we hope that through the years of testing we’ve put in, alongside Dolby, and by documenting it, we’ve been able to share those learnings with new mix engineers as they begin to work in the Dolby Atmos format.”

Abbey Road Studios is part of the Universal Music Group, and recently redeveloped the Penthouse as a purpose‑built Atmos music mixing space to complement the post‑production‑oriented Mix Stage.

One striking feature of immersive music releases so far is that they are almost all new mixes. Dolby Atmos includes channel‑based bed tracks in up to 7.1.4 surround, so in principle, there’s no reason why the many 5.1 album mixes that were done back in the early 2000s couldn’t be dusted off and upmixed to Atmos with minimal effort. That would probably be the cheapest way of generating a large Atmos catalogue, but it’s not an approach that Caroline Hilton or UMG are keen on. “Many of the 5.1 mixes will have been done many years ago and so the engineer and artist team may decide they want a more up‑to‑date approach to the mixing. Creatively there are differences in surround sound mixing versus Dolby Atmos mixing, especially for music. Notably, the freedom enabled by object‑based mixing versus traditional channel‑based mixing can influence that decision. Ideally, we wouldn’t want to see ‘upmixing’ from stereo or surround. Using the original session, stems or multis, will always lead to the most successful results.”

Beyond Stereo

At the other end of the scale, the differences between immersive music and stereo make it possible to deliver an Atmos mix that would be almost unrecognisable. Here, again, Caroline Hilton is happy to support the artist and producer if that is the effect they want to achieve, but more often, her role is to point out the risk of it happening unintentionally.

“When you want something new to be adopted, the approach has to be carefully considered. The artist, up until recently, in most cases has no baseline of what an Atmos version ‘should be’ because they hadn’t been exposed to the format previously. However, in many cases, there seems almost a sigh of relief when they can hear that all the essence of the creative intent in their stereo version has been retained, as the preconceptions had them thinking it would conceptually be something completely different.

“Now, there is absolutely nothing to say that it can’t be. But currently, only one [streaming] partner delivers a standalone Atmos product, whereas the other platforms ‘mezzanine’ the track with the stereo version, meaning that if the listener is not Atmos‑enabled, the track will default to the original stereo mix. So, there is a certain level of expectation of what the Atmos version should be, and as the creative community and the fans are more exposed to it, their wants and needs for the format will develop, and we may start to see these shifts in creative expression and representation.

“We may also start to see more leaning toward a traditional mix‑and‑master approach. Right now, because it’s predominantly stereo first, Atmos second, the Atmos mix engineer’s overall ethos is to retain that intent, which also means replicating the mastering of the stereo from the start. As well as this, when a mix is sent to an Atmos mastering engineer, they are still working within compatible DAWs and not necessarily being able to adopt all of their existing stereo or surround mastering tools and workflow, especially when it comes to global application of dynamics and EQ in an object‑based environment. It is the combination of these issues that can create a misunderstanding of the process. We certainly do not dismiss the importance of mastering and, with time, learning and developments, we will see the progression to a more traditional and considered workflow.”

Does she, then, foresee a time when music projects are conceived and produced immersively from the very start? “There are definitely going to be trends and fashions that develop as the technology, and learnings around it, expand. With this in mind, we are already seeing the growth in original stereo engineers upgrading to Dolby Atmos and therefore being able to deliver their mixes concurrently. It is also exciting to see artists beginning to compose for Dolby Atmos, and some engineers are exploring an Atmos‑first workflow. The advancement of the technology would support this over time.”

Affordable Atmos

One of the most persistent complaints about immersive audio is that, on the production side, the barrier to entry is too high. The minimum setup for a speaker‑based Atmos monitoring system is 7.1.4, and as well as buying lots of speakers, implementing this usually involves additional building work, acoustic treatment, and a multichannel audio interface. If you’re lucky, you might see change from £20,000. That’s a lot of money to gamble on something that might or might not deliver additional income for your studio.

Caroline Hilton: When you want something new to be adopted, the approach has to be carefully considered. The artist, up until recently, in most cases has no baseline of what an Atmos version ‘should be’ because they hadn’t been exposed to the format previously.

Caroline Hilton is keen to counter this perception that immersive audio is elitist, and says that both she and Universal Music are happy to work with artists and producers who don’t have speaker‑based setups. “There are solutions in market that could be zero cost to the engineer. You’ll be aware of Logic and Nuendo’s native integration with the Dolby Atmos Renderer, and with others exploring improving the workflow. This does create the capacity for a mixer to work binaurally without an additional cost to their setup, making it extremely accessible. We are also encouraged by the personalised HRTF development Dolby are doing with mix engineers and the creative tools. Likewise, a mixer with an existing 5.1 setup could certainly be most of the way there in terms of having less of an initial setup cost to consider.

“I will caveat this, however, as we strongly recommend that once an engineer is comfortable with where they are at in their mixes, they should go to an enabled studio to ‘finish off’ their mixes. We are just not at the stage where the technology can give you the fullest critical listening experience, when mixing, without listening back on a minimum of a 7.1.4 system. Even mixers who have been mixing for years in studios, who due to lockdowns had to rely on binaural mixing but could work on visual representations because they knew their rooms and workflows so well, would still recommend doing that final listen in‑studio before delivering.”

In other words, just like stereo, an immersive audio mix needs to work across all the possible delivery formats. And the job of Caroline Hilton and her team at UMG is to help engineers achieve that.

“One of the things we like about the format is the ability to translate across multiple environments such as headphones, home, car, venue — all via one master file. The reason we are seeing the successful roll‑out of immersive audio in the digital domain is because of this ability to translate playback across devices. We are no longer constrained to the use of Blu‑Ray and sophisticated home setups. However, there’s still a long way to go in streamlining the consumer experience, and to ensure the information is out there to make it as straightforward as possible. We work very closely with Dolby and the current streaming partners to feed back our findings, and those of the wider creative community. In time, we hope there will be a more universal approach to the experience for whichever devices or services the consumer is using.”