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Dolby Atmos At The Ministry Of Sound

Air Play
By Hugh Robjohns

Air Play

Dolby Laboratories have been leading the development of surround-sound systems for four decades, but over the last year or so they have been piloting an intriguing surround system in a famous UK night-club...

The latest enhancement to cinema surround sound, a format called Dolby Atmos, was introduced four years ago and has already been adopted in well over 2500 screens around the world. It builds upon a technology referred to generically as ‘Digital Cinema’, which incorporates the distribution of theatrical film releases as encrypted digital files, rather than on traditional celluloid film.

Dolby’s initial foray in 2010 with this concept involved compiling all the picture and sound data into a Digital Cinema Package or ‘DCP’, which, at that time, accommodated up to 16 discrete audio channels, as opposed to the 5.1 channels available in the Dolby Digital format (or 6.1 in Dolby Digital EX) — formats which had dominated the cinema industry since the early 1990s (see box). The DCP’s greatly expanded audio resources were first put to use delivering surround in a 7.1 format, which provided three screen channels (left, centre, right or LCR) plus separate left/right side and rear arrays, as well as a Low Frequency Effects (LFE) channel.

However, as a form of virtual ‘data bucket’ this Digital Cinema concept created an opportunity to completely reinvent the whole paradigm of cinema sound in terms of the physical speaker configurations and capabilities, but without breaking the all-important backwards-compatibility with the arrangements extant in theatres all around the world. That reinvention culminated in 2012 with a brand-new format called Dolby Atmos.

Ceiling Is Believing

The most visually obvious enhancement which Dolby Atmos brings to any theatre is an array of loudspeakers installed in the ceiling, allowing sounds to be generated above the audience. This simple adaptation boosts the perceived sense of realism to a remarkable degree, but it is further enhanced by the system’s ability to precisely position separate sounds almost anywhere in the room, directing them to subsets, or even specific, individual speakers. This obviously permits far better spatial positioning and movement of sounds around the room, giving the film producers a lot more creative scope and — arguably even more importantly — giving a much more consistent experience for the audience, wherever they choose to sit in the theatre. This is truly ‘immersive audio’.

For the soundtrack creators, the Dolby Atmos system supports a total of 128 audio tracks, and these are typically allocated as a ‘bed’ of up to 9.1 channels plus 118 sound ‘objects’ — the buzz-phrase is ‘object-oriented audio’. The ‘bed’ normally includes all the traditional on-screen dialogue, the music and most of the atmospheric sound effects arranged in the usual way, with the appropriate sounds allocated to the traditional screen, side, and rear speaker channels (and arrays) as you would expect. With 10 tracks allocated to a 9.1 bed, a further 118 discrete ‘channels’ remain available for sound ‘objects’, and these individual sounds can be placed in, and moved around, any individual speaker or group of speakers as required. The positional coordinates and velocities of each sound object are stored as metadata along with the individual sound files.

In order to convey vertical positioning information, Dolby Atmos systems require the installation of a number of ceiling-mounted speakers.In order to convey vertical positioning information, Dolby Atmos systems require the installation of a number of ceiling-mounted speakers.Photo: Andy Giles Associates

This technology would be unrealistic if not actually impossible without the ubiquity of the DAW (and mixing consoles that integrate closely with DAWs), of course — it would be totally impractical to manage the spatial positions of so many individual sound elements with a traditional mixing console, for example!

So, a film soundtrack can be created in a dubbing theatre with huge multi-channel beds and dozens of individual sound objects, but how does that translate to the average cinema? Well, one of the big differences between Dolby Atmos and the previous Dolby Digital systems is the former’s complete disconnect between the source sound ‘channels’ and the destination location’s physical ‘speakers’.

In Dolby Digital, for example, the front LCR channels are always reproduced on the left, centre, and right speaker stacks behind the screen, and if the theatre happened to have inner-left and inner-right speakers as well (for a 7.1 format), they wouldn’t be used given a 5.1 source. In other words, in the legacy surround systems there is a permanent link between the format’s individual channels and the specific speakers or speaker arrays dedicated to those channels in the theatre.

Dolby Atmos breaks that direct link, and instead employs a sophisticated and customisable routing matrix called an RMU (see below) installed in each theatre; this intelligently allocates the 128 Atmos channels to the most appropriate speakers, in the most appropriate positions, available in that specific theatre. This router can manage up to 64 separate speaker channels, which can be individual speakers or complete arrays of speakers.

Essentially, then, the cinema’s Dolby Atmos processor takes the bed channels and routes them to whatever speakers are physically available and appropriate to carry those specific audio signals. Similarly, it uses the object metadata to understand where each ‘sound object’ is intended to move to or come from, and dynamically routes it to the most appropriate speaker(s) within the specific installation. In this way the film-makers’ intentions are recreated as accurately and consistently as possible, regardless of the physical number and location of actual speakers in any particular theatre (and the concept can be extended into domestic home-theatre installations, too, of course).

Dolby City

So, Dolby Atmos represents a significant step forward in creative sound design for the film industry, but what does it have to do with nightclubs and producer/DJs?

Well, for Dolby’s accountants the bottom line is that Dolby are exploring other options and avenues in which to exploit the sophisticated technology developed for Atmos. There is already a growing range of domestic home-theatre equipment from the likes of Philips, Samsung and Yamaha which is able to replay Dolby Atmos material at home. Apparently, there are already a few Blu-Ray music discs on the market encoded with Dolby Atmos soundtracks too, so could there be a burgeoning opportunity to introduce a new form of surround-sound music? The answer is probably yes, but it will require significant consumer demand, and a good way to encourage that is to employ Dolby Atmos in the live music scene, creating live experiences that people will want to recreate at home.

Dolby Product Manager Gabriel Cory puts the Atmos DJ software through its paces.Dolby Product Manager Gabriel Cory puts the Atmos DJ software through its paces.

Conventional live bands might find it tricky (although certainly not impossible) to make use of Atmos, but the club music scene actually lends itself to this format and spatial manipulation rather well — and that’s the argument a group of Dolby’s engineers (who are also musicians and DJs) took to the company bosses. As a result, Dolby agreed to fund some product development and trials to explore the idea further, and Gabriel Cory, now a Product Manager in the company’s New Products Group (and I have to say a talented producer/DJ in his own right), became the format’s champion! I’m very grateful to Gabriel for extending a business trip to the UK to explain and demonstrate to me the technology, the various producer tools, and the enormous creative potential of this exciting Atmos application.

I should also point out that this is still very much a ‘pilot system’ at the time of writing, and Dolby are still assessing the reactions of both the venue owners and the club-goers, as well as the likely support for developing this application of Atmos further. In particular, although some of the various software production tools needed for DJs to mix Atmos content are already employed in the film industry, the Dolby-DJ playback software (which also allows real-time spatial manipulation) is still in a developmental beta stage. Moreover, while the initial trials have used the standard cinema RMU hardware, there is scope to produce a more cost-effective club-specific variant if the demand warrants it.

Dolby’s initial proof-of-concept trial was held in 2014 in a private nightclub in San Francisco where the company headquarters are located, and subsequently there was an invitation-only Atmos party held at Sónar Barcelona — the Music, Creativity & Technology show — in 2015. However, the first extended public pilot has been held as a residency at the Ministry of Sound nightclub in London throughout 2016. Ten dedicated Atmos events have been held so far, involving a lot of well-known international DJs including Flux Pavilion, Mat Zo, London Elektricity, Kerri Chandler, Francois K, Sub Focus and Yousef... to name but a few. All the feedback so far has been extremely positive, and so Dolby plan to extend the Atmos experience into three or four clubs across America over the next year, and possibly set up a few in Europe, too.

Atmos Preparation

Whereas Atmos film soundtracks are often incredibly complicated, with large multi-channel beds and hundreds of separate additional sound objects, a rather simpler and more pragmatic approach has been taken for the nightclub application, partly to allow producer/DJs to reformat their own music relatively easily, but also to make live manipulation of the various elements more manageable. So instead of a filmic 9.1 bed, the core of the DJ Atmos system requires nothing more than a simple stereo track — typically comprising the core drums and bass along with other foundation elements. This approach removes any requirement for creating complex surround music mixes and avoids all the hardware resources associated with it. In the club’s Atmos system this foundation stereo bed is routed automatically to the conventional stereo PA system in the usual way, providing a familiar bedrock of sound upon which the DJ can build.

Air PlayHowever, one very obvious sign that this Atmos DJ application is riding on the coat-tails of the cinema system is that the DAW project from which the Atmos files are built must have a 48kHz sample rate — the standard rate for all film and TV material. Apparently, none of the guest DJs involved so far have had a problem with that (and nor should they, of course), but if the DJ Atmos system becomes a commercial reality there may be greater pressure to develop a 44.1kHz sample rate option for greater compatibility with standard music files (and perhaps even higher sample rates, for that matter).

Supplementing this stereo bed in the club Atmos system are up to 11 additional audio objects — the limit being set by the Dolby DJ software (for practical live management reasons) rather than the Atmos system itself. These additional audio objects can be in the form of either mono or stereo stems, and can carry any specific sound elements that the producer/DJ wants to move around the room during the performance. So that could be the lead and/or backing vocals, guitar leads, keyboard lines, effects, bass drops and uplifters, percussion accents, or whatever ‘ear candy’ might benefit from some degree of spatial treatment.

Prior to the Ministry Of Sound pilot, tracks were processed using the Dolby Atmos Panner plug-in, which was used to automate the three-dimensional panning of various musical elements.Prior to the Ministry Of Sound pilot, tracks were processed using the Dolby Atmos Panner plug-in, which was used to automate the three-dimensional panning of various musical elements.During the Ministry Of Sound pilot, the pre-production process has involved guest producer/DJs taking their tracks (generally as Pro Tools projects) into Dolby’s offices located in San Francisco, Los Angeles and London, where dedicated mix rooms have been set up with small-scale Atmos monitoring systems. (Additional mixing rooms are also available in New York and Barcelona.) Here they have been able to use the Dolby Atmos Panner plug-in in Pro Tools to experiment and decide how they want the various supplemental sound elements to be placed and moved around the room. This plug-in (available in VST, AU and AAX formats for compatibility with most DAWs) provides comprehensive tools for both manual and automated panning, allowing selected sounds to be moved around in all three dimensions and following a wide variety of straight and curved trajectories and speeds (with tempo-matched panning options too). Sounds can also be focused to single speakers or decorrelated and diverged across large parts of the speaker arrays, as desired. The plug-in panning data is passed to a software Rendering and Mastering Unit (RMU) which maps the DAW’s output channels to the physical speakers connected to the DAW, allowing the audio objects and beds to be auditioned, accurately emulating the experience in the nightclub’s Atmos system.

Once all the panning information has been stored as track automation data in the DAW, it can be converted into the required Atmos metadata using dedicated Dolby Atmos Music File Builder software, and the finished remix is then packaged into Dolby’s ‘ATM’ format for transfer to the club, where a standard cinema RMU unpacks the data and routes the audio to the available speakers as required. (For completeness, in the cinema world the soundtrack ‘print master’ created at the end of the dubbing process is ‘wrapped’ using the Material Exchange Format (MXF) and delivered to the post-production house to be merged with the film images to create a DCP, which is encrypted and distributed to the cinemas. The Dolby DJ system just avoids that unnecessary intermediate DCP stage.)

In the club, the ATM Atmos files are processed through the cinema hardware Rendering and Mastering Unit (RMU), which is a 2U rackmount computer with MADI I/O. This is the brain of the Atmos system that works out how to statically and dynamically route the beds and sound objects to the connected speakers — but to do that it has first to be configured on installation to know where all the speakers are in the specific venue; something which is done using another software tool called the Dolby Atmos Designer! Again, if the Atmos DJ system becomes a commercial venture there is a possibility of developing a more cost-effective alternative to the cinema RMU, and Dolby are currently exploring the options.

The scalable nature of Dolby Atmos means that the RMU routing matrix must be ‘told’ the number and location of all the speakers in a given system, using a software package called Dolby Atmos Designer.The scalable nature of Dolby Atmos means that the RMU routing matrix must be ‘told’ the number and location of all the speakers in a given system, using a software package called Dolby Atmos Designer.

Atmos Performance

When it comes to performing with the Atmos tracks in the club, Dolby’s developmental DJ software has been designed to integrate seamlessly with the industry-standard Pioneer CDJ-2000 Nexus decks and DJM-900 Nexus mixer, which makes the operation pretty straightforward for the DJ, using entirely familiar tools and techniques. However, at present the pre-mixed Atmos audio can only be replayed using Dolby’s Atmos DJ software on a MacBook connected directly into the RMU (via MADI) — and that might be a frustration to any DJs who normally rely on Serato or Ableton. Having said that, Atmos DJ does communicate via HID with the Pioneer hardware, allowing real-time control using the standard DJ deck and mixer facilities, so the laptop can be moved out of the way if preferred since there’s no absolute need to drive the performance through the Atmos DJ software. Most things can be done remotely, if preferred.

Of course, a very big part of the DJ scene is the ability to manipulate tracks in real time, to interact directly with the audience — and the Atmos system allows that, too. The pre-mixed Atmos tracks essentially provide a known starting point, and the Atmos DJ software displays the available tracks — with all their individual object stems — within left and right side panels on the screen. Tracks can be selected here for replay and mixing following a fairly conventional DJ player paradigm. In the middle of the control screen is a display box representing the room, and it shows multiple numbered circles that bounce around and change size in real time as the music plays. These circles indicate the movement of individual audio objects according to the panning metadata, as well as the tracks and stems they relate to, and where about in the room they are going. It probably sounds complicated, but it becomes very intuitive once you can see and hear what’s going on for yourself.

Each individual stem can be soloed, muted, or have effects applied, and the level can be adjusted too, but the fun part is that the pre-programmed panning instructions can be over-ruled simply by clicking on one of the moving circles on the screen and manually dragging it around. This facility makes for an incredibly powerful, genuinely interactive and hugely involving system. Perhaps in the future Dolby will develop some kind of physical touch-interface to make this process a little easier, but that really would be decadent ganache icing on an already very tasty patisserie!

Dolby’s Atmos DJ performance software allows for real-time surround panning, and can be controlled using industry-standard Pioneer DJ hardware, via the HUI protocol.Dolby’s Atmos DJ performance software allows for real-time surround panning, and can be controlled using industry-standard Pioneer DJ hardware, via the HUI protocol.

Impressions

The technical details of how all the various software and hardware elements of the Dolby Atmos system need to be connected and configured are, inherently, quite complex and I’ve deliberately omitted most of it here for reasons of space and clarity. Much of the complexity really only affects installing and calibrating the speakers, though (both in the pre-production room and the club itself), and in configuring the necessary I/O paths in the DAW for the appropriate Renderer and Print Master destinations.

However, once the system is configured, the creative side of using it to bounce stems and elements around the room is remarkably straightforward and intuitive — and intoxicatingly good fun. I’ve long been a fan of surround music and have amassed quite a collection of (now obsolete) DVD-As and SACDs, but the technical requirements to mix music in these ‘traditional’ 5.1 surround-sound formats can be quite onerous. In contrast, the Atmos system is really just a stereo foundation mix with some glitter sprinkled on top, which is very much easier to conceive and manage, both mentally and practically. Listening to examples of remixed music in Dolby’s Atmos pre-production room, I was impressed with just how effective the format was, combining a static stereo core of music from everywhere, decorated with individual sound elements bouncing around the room.

But club music isn’t intended for listening on compact Genelec speakers in a bedroom-sized space, is it? So Gabriel and I jumped in a taxi and headed across London to the Ministry Of Sound club to hear it in its natural environment. Now, it is quite true that the last time I frequented a nightclub it was called a ‘discotheque’ and we all wore platform shoes and flared trousers — actually, I’ve probably still got mine in the back of the wardrobe. It’s also true that this wasn’t the first time I’ve stood alone on an empty dance floor bobbing up and down to loud music with a silly grin on my face! But we should probably gloss over that, too...

The enormous speaker system at the Ministry Of Sound comprises six identical 10-foot-high stacks of Martin Audio components. Each stack is rated at 25kW, costs around £60,000, and really gets the air moving with two 21-inch drivers in big sub-bass bins sat directly on the floor. Two 18-inch drivers in the re-entrant bass units sit on top, with two W8C cabinets carrying the mids and high end on top of them, angled downwards and outwards slightly to ensure an even coverage across the dance floor. This monumental system is deliberately over-specified and under-run to guarantee a hi-fi-like clarity and headroom — and it really does sound very sweet and effortlessly powerful.

The Ministry Of Sound’s usual system comprises two 25kW Martin Audio stacks, augmented for the Atmos pilot with an additional 16 Martin Audio CDD15s mounted in the ceiling.The Ministry Of Sound’s usual system comprises two 25kW Martin Audio stacks, augmented for the Atmos pilot with an additional 16 Martin Audio CDD15s mounted in the ceiling.Photo: Andy Giles Associates

For the Atmos residency, Dolby installed an additional 16 Martin Audio CDD15 cabinets in the ceiling amongst the lights, and patched a hardware RMU into the system to feed the appropriate signals to the various crossovers and amplifiers driving the six main PA stacks, as well as to the extra active ceiling speakers. (There’s also a clever system of lights and screens controlled by the Atmos audio object metadata to help highlight the locations of the Atmos speakers for the audience, really tying the sound and lighting experience together in a cohesive way.)

It might come as a surprise, but I’m afraid my chops are a little rusty when it comes to the decks, but fortunately Cory is a dab-hand and was able to demonstrate the system extremely well, using a variety of pre-programmed demo material, remixed tracks from some of the DJs that have headlined previous Atmos events at the club, and with some material that he was able to manipulate live.

The Atmos demo track starts with a powerful voice saying, “Hello boys and girls, my name is Atmos,” and it’s followed by a drum beat which rotates around the room, the sound of crickets (or something like that) fluttering overhead, and then a sung vocal that starts at the rear of the room and flies overhead to the front before whizzing back again. All quite an unusual and impressive experience for most club-goers, I’d wager, but the thing that really struck me was the clarity and pin-sharp positions of the individual sounds, both when static and as they moved around.

As with any ‘effect’, the key to Atmos is to use the panning sympathetically and creatively to support and enhance the music, and when done well it really does raise the impact enormously — far beyond what I had expected. Drops and uplifts can really drop and rise — physically from floor to ceiling and vice versa. Elements in the mix can move around you and approach or retreat in ways that really complement the overall experience. With an interactive audience I can imagine having fun throwing sounds between different groups on the floor too. Importantly, though, the overall impression really is of being inside the music, rather than just having music played at you. I found it quite entrancing, actually.

As Gabriel was keen to emphasise, this Club Atmos format is still in a pilot stage of development: at the moment an entrepreneurial venue owner can’t just go out, buy the system, and have it working by the weekend. And although some of the necessary Atmos pre-production tools are already available, such as the Atmos Panner plug-in, the crucial Atmos DJ playback app and the RMU hardware are only available from Dolby — and they’re not for sale at the moment!

However, it seems that the Ministry Of Sound residency has proved a great success, and the road ahead looks very promising for ‘Club Atmos’. If you find yourself near a nightclub involved in the pilot Atmos programme in the near future I urge you to give it a go — it’s quite an experience!

A Brief History Of Surround Sound

The world of surround sound has largely been driven by the movie industry, starting in the early 1940s with Disney’s genuinely ground-breaking Fantasound system, developed specifically to deliver a surround-sound experience to American audiences of their Fantasia film. Unfortunately, Fantasound’s development ceased when America was drawn into the Second World War, but many of the largest premier cinemas continued with either four- or six-channel surround-sound formats throughout the ‘50s and ‘60s, using expensive magnetic tape strips glued onto the film prints to carry the separate audio channels. The most common formats at this time provided for either three or five channels driving speakers behind the screen, plus an ‘effects channel’ which was distributed around a number of speakers mounted on the side and rear walls. This arrangement proved highly effective at creating a convincing immersive sound stage, helping the audience to feel they really were ‘in the jungle’ with actors, or on a city street in a downpour.

Popular though these surround-sound formats were with the audiences, they were deemed too expensive and unwieldy for the cinema industry and so relatively few cinemas were equipped to replay them. All that changed, though, when Dolby Laboratories’ A noise-reduction system was adopted to improve the signal-to-noise ratio of a 35mm film’s optical soundtrack in 1971. It turned out that the improvement was so great it became practical to divide the optical soundtrack in two, allowing a two-channel signal to be incorporated instead of mono... and that gave Dolby an idea!

The 1970s was the decade of a wide (and largely incompatible) variety of domestic four-channel ‘Quadraphonic’ surround-sound systems, several of which employed phase-matrix techniques (much like Mid-Side encoding) to squeeze four audio channels onto a stereo medium (albeit with fairly dreadful levels of inter-channel crosstalk). Dolby essentially developed this phase-matrix idea, adding a very sophisticated active channel-steering system to minimise the unwanted crosstalk, and introduced it as a very practical format which was simple to encode on film with negligible production costs and excellent reliability — instantly negating the problems associated with the previous generations of magnetic stripe formats. The new system was marketed as Dolby Stereo (because it was carried by a stereo optical track on the film), and provided LCRS (Left, Centre, Right, Surround) channels.

In this way, Dolby Stereo maintained the traditional arrangement of three front channels behind the screen (Left, Centre and Right), plus a single Effects Channel distributed around a number of small speakers mounted on the side and rear walls of the theatre — just as with the previous expensive magnetic-stripe formats. The first big film release to use this new format was the original Star Wars: Episode IV — A New Hope, in 1977. With the advent of stereo-capable domestic video recorders in the 1980s, Dolby went on to develop a domestic version of the elaborate but essential analogue channel-steering decoder, which was launched in 1982 as Dolby Pro-Logic, kick-starting the home-theatre movement.

However, brilliantly ingenious and effective though the Dolby Stereo system is, its phase-matrix technology imposes several significant practical restrictions on the way sounds can be positioned and moved around the theatre — restrictions which completely evaporated with the introduction of Dolby Digital a decade later in 1992, with Batman Returns. The most significant practical difference between the all-analogue Dolby Stereo/Pro-Logic system and the all-digital Dolby Digital format is that the latter encodes six discrete channels onto the 35mm film (as a block of black and white data pixels located between the film sprocket holes).

Dolby have set up a number of dedicated mixing rooms fitted with small-scale Atmos speaker arrays.Dolby have set up a number of dedicated mixing rooms fitted with small-scale Atmos speaker arrays.

This discrete-channel approach completely removes the problem of inter-channel crosstalk and allows far greater control over how sounds are positioned and moved around the theatre. Moreover, the Dolby Digital format introduced separate left and right effects channels, instead of just a single overall surround channel, as well as a dedicated low-frequency effects channel to obviate the need for significant headroom in the main channels to cope with explosions, etc. At the end of the decade the Dolby Digital system was expanded further to incorporate a third, centre-rear, surround effects channel, which was marketed as Dolby Surround EX and introduced with Star Wars: Episode 1 — The Phantom Menace.

However, technology has moved on and the current state-of-the-art for surround sound in the cinema is Dolby Atmos, launched in 2012 with Pixar’s Brave. This new system builds upon the Dolby Surround EX platform with an additional array of effects loudspeakers positioned on the ceiling, introducing the option of positioning sounds with a height dimension. A sophisticated DSP-based matrix system is used to place individual sound elements almost anywhere within the auditorium, using metadata encoded in the film’s soundtrack to direct up to 118 individual ‘sound objects’ at a time to any of up to 64 separate speakers — while simultaneously distributing a 9.1-channel continuous core soundtrack to the relevant speakers and speaker arrays as well!

Published January 2017