When one thinks of Dolby the immediate reaction in the mind is the phrase ’surround sound’. Despite being pioneers in other areas such as noise reduction, Dolby is probably most famous for their contribution to multichannel theatre and home cinema sound and they continue to push the limits in that arena to bring the movie goer’s experience as close as possible to actually being in the scene. Now, with Dolby Atmos, a newly developed 64-speaker theatre surround sound system, the movie goer is put in a virtual 3D realm of aural excitement. Let’s explore what Dolby Atmos is and the technology behind it. But first, to find out where we’re going we need to know were we came from, so…
…a little history.
Dolby Laboratories first appeared as a company in 1965, founded by Ray Dolby, an American engineer and inventor who devised the famed noise reduction system known as Dolby NR. He is also responsible for the co-invention of video tape recording in collaboration with Ampex. Dolby is the winner of multiple technical awards and is a fellow and past president of the AES (Audio Engineering Society) not to mention a billionaire with a place on the Fortune 400.
As mentioned, Dolby’s first pursuit was noise reduction, starting with the Dolby 301 unit which included Type-A Dolby NR. This was a “compander’ (a compressor and expander combination) based system and was intended originally for use in recording studios.
Dolby continued with noise reduction development through their B, C, S, SR and HX Pro ranges for the tape recording world and Dolby FM for radio until they eventually started seeking to improve film sound. The first film to use Dolby noise reduction on all pre-mixes and masters was Stanley Kubrick’s A Clockwork Orange in 1971. In 1972 Dolby introduced the X-Curve (eXtended Curve), which replaced the long-standing Academy Curve, an equalisation standard for cinema sound stemming from the thirties.
In 1975 Dolby Stereo, a Left, Center, Right and Surround cinema standard, was released and in less than ten years 6 000 cinemas around the world were equipped with a Dolby Stereo system. This technology later evolved into Dolby Surround for home use and eventually into Dolby Pro Logic, which is the consumer market equivalent of Dolby Stereo for cinema.
Eventually the digital age rolled around and Dolby started to foray into compression codecs for cinema sound. Dolby Stereo Digital (now called Dolby Digital) appeared in 1992 and was first featured in the film Batman Returns. It was later introduced into the home market as Dolby AC-3 in 1995 with the laserdisc release of Clear and Present Danger starring Harrison Ford. Despite initial unpopularity due to the requirement of additional hardware it was eventually adopted as part of the DVD specification. Dolby Digital is now a household name that is found worldwide in HDTV, DVD players and satellite – and cable-TV receivers.
In 2010, Dolby Surround 7.1 was released and set up in theatres across the planet. Toy Story 3 was the first film to debut with this format and a further 50 releases followed suit thereafter, culminating in over 3 600 Dolby Surround 7.1 theatres around the globe. Building on this success, Dolby Atmos was released in April 2012 which is a new cinematic audio technology and the focus of this article. There are currently over 100 theatres around the world that have this new technology, including one at the Ster Kinekor Gateway cinema complex in Durban, and the first movie mixed for the format was Pixar’s Brave.
Overview
Dolby Atmos takes the current limit in multi-channel surround technology and traditional approaches to cinema surround sound and throws them out of the window; the basic idea being to surround the audience in as many speakers as possible, eliminate traditional surround “zones’ and to deliver discrete, multichannel audio to the speakers through positional metadata. The ’Dolby Atmos Cinema Processor CP850”, the first generation Atmos cinema hardware, supports up to 128 discrete audio tracks and up to an incredible 64 unique speakers feeds.
Because there can be up to 64 discrete speakers placed throughout the theatre, sounds originating from overhead can now be experienced along with sounds emanating from discrete point sources throughout, including above the audience. These are the two main aspects that differentiate Dolby Atmos from previous surround formats in that they enable the sound designer or mix engineer to individually place sounds at any point source speaker or array of speakers behind the screen, to the side walls, the rear walls or overhead; the goal being to further immerse the audience within the scene.
It also enables panning of elements creatively into the upper hemisphere instead of just along the horizontal plane which negates the brain from having to construct an artificial phantom image. Feasibly, a missle could be launched from the rear of the theatre and it’s travel experienced and accurately followed overhead until it detonates on the screen. Also, now because of discrete feeds to the speaker arrays, if actors react to sounds happening at a specific point outside the screen, the sounds can now placed exactly where they are looking, instead of in a general surround zone as would be the case with 5.1 and 7.1.
Another step forward with the Dolby Atmos system is improved audio quality and timbre matching. In past surround systems that use “zones’ instead of discrete point sources inclined to deteriorate the quality of some sounds due to speaker array phase distortion. The ability to place these sounds in discrete speakers greatly increases their perceived localisation and eliminates any array phase artifacts. Additionally, Dolby Atmos includes improved system equalization to combat acoustical problems and surround sound bass management so that the mixer can address each speaker directly without being worried about tonal differences. Furthermore, accurate level calibration between the speaker arrays means that there are no level discrepancies when performing pans and precisely angled speakers closer to either side of the screen assure smooth transitional pans for audio events emanating from and entering the side of the screen.
Beds + Objects = Dolby Atmos
Given the relative complexity of Dolby Atmos compared to past formats, the way soundtracks are produced, mixed and played back has been changed through the implementation of audio objects and positional data in the form of metadata. But what are audio objects and beds?
Audio objects can be thought of as individual sounds or groups of sounds, such as tracks in a session, that occupied the same location in the theatre. These objects can be stationary or can be panned and panning automation is analogous to positional metadata. This metadata instructs the decoding hardware – the Dolby Atmos Cinema Processor – where the object should be at any point in time. When these objects are played back, they are manifested according to this positional metadata depending on what speakers are present, as opposed to being fed to a specific channel. This is a dramatic shift in approach compared to how soundtracks are currently produced but the upshoot is that it integrates well with the workflow of audio workstations.
All that being said, channel-based workflows are still retained. This is where “beds’ come in. Beds are simply channel-based stems or submixes that can be delivered for final playback either by combining several into a single bed or individually. They can be created in several exisiting formats such as 5.1, 7.1 or even 9.1. beds create the desired effect based on the mix of the submix and the perceptual field depth and movement within the submix.
The last noteworthy element of Dolby Atmos that it is backwards compatible and boasts simplified delivery. This means that the final mix in 64.2 (Atmos mix), and a number of other format such as 22.2, 11.1, 9.1, 7.1, and 5.1 can be delivered in a single file wrapped in the industry standard MXF (Material Exchange Format) format which is then received by the digital cinema packaging facility where it is validated before packaged into the DCP (Digital Cinema Package).
The workflow concept
As mentioned, Dolby Atmos allows up to 128 tracks to be delivered within the DCP, which consists of a combination of beds and objects. These beds and objects are mixed in the same manner as in previous formats and object audio and metadata, panning automation, etc, are recorded within the session in preparation for the dubbing theatre pre and final mix.
This metadata is integrated into the mixing console, allowing full control over the processing of both objects and beds and can be edited either by using the console surface or the workstation GUI. Monitoring is reflected in the Dolby Rendering and Mastering Unit (RMU). All metadata and the associated audio data are recorded during mastering which results in a “print master’ which includes the Atmos mix along with other formats before wrapping, as described in the previous section.
Within the single DCP framework which is delivered the cinema, the main audio mix comprises the main audio track file while the Atmos mix is part of an additional track file. This track file is ignored by systems that can not support it thus allowing the Dolby Atmos packaging scheme to be deliverable to any theatre regardless if it is equipped with Dolby Atmos hardware as it is identified as a compatible package.
Personal experience
I had the chance to see Man of Steel in Theatre 1 of the Ster Kinekor complex at Gateway Mall in Durban, which is the only theatre in Africa installed with a Dolby Atmos system. My first impression was: “Wow, that’s a lot of speakers’.
The first thing I noticed was that the film’s mixers did not depart too much from the traditional approach in film mixing by getting overly creative with the surround speaker arrays. Most of the dialogue and music was for the most part up front, which kept my attention anchored at the screen and minimised distraction. This approach is very sensible because it keeps the focus on the scene and the main elements of the film.
What I did notice, however, was that the ambience of the film was very dimensional and certain beds and effect elements were more immersive, ie. they pulled you into the scene a bit more by discrete use of the speakers within the cinema. Only the big moving audio effects moving into and out of the screen were tracked through the surround arrays and the movement was immediately perceivable and accurately followed. At one point I had to duck because it felt like a missle was flying right above my head!
As our auditory senses have evolved, humans are primarily attuned to aural perception in the horizonal plane. That is a result of most of our predators back in prehistoric times being in front, to the sides, or behind us and is why the focus of the evolution of our localisation awareness was in that plane. Our ear/brain complex is not very good at perceiving localisation above our head in the upper hemisphere, which is why when something wizzes over your head, like a low flying aircraft, you get a big fright. This is also why you don’t perceive it until the last minute. This makes the inclusion of overhead speakers a very exciting element. It is something that takes our brain by surprise. Very cool, indeed!
The wrap
Dolby Atmos is the multichannel cinema audio delivery format of the future, which is here, by the way. There’s not much more to conclude about it than that. After all, surround sound has come a long way since Disney’s Fantasia in the forties and it’s difficult to imagine what engineers and system designers may come up with next. They certainly have a lot to top with Dolby Atmos around.
