As part of this year’s Fidelity Forum conference, Dolby Labs invited a group of home theater writers to the company’s headquarters in San Francisco for a tour of the facility and a look at some of its latest and greatest tech. The highlights of this two-day event were demonstrations of two new products. As I described in yesterday’s post, I wasn’t entirely sold on the need for 96k upsampling. However, the unveiling of the new Dolby Atmos theatrical sound format is considerably more exciting and easier to appreciate.
Ever since the resurgence of 3D video, both in theaters and at home, industry professionals have been actively discussing ways in which to upgrade and enhance movie soundtracks to bring a similar “3D” experience to audio. But wait, isn’t surround sound already “3D” in a sense? That’s a fair question. After all, sounds come at you from all around the listening space, both in front of and behind your seating position. While that’s all well and good, the modern standard for movie soundtracks is currently limited to only 5.1 or (more recently) 7.1 discrete channels of sound. That may seem like plenty enough for most viewers, but the formats have their drawbacks and limitations.
For example, the space between channels often leads to a “ping-pong” effect as sounds bounce from speaker to speaker. Take the case of a movie soundtrack with an airplane sound that’s supposed to travel from the front of the room to the back. In a 5.1 or even 7.1 configuration, the sound will jump from in front of a viewer to behind, with a gap in the middle. The larger the listening space, the more unnatural this sounds. Sure, the mixer will attempt to compensate for this by fading the sound out of the front channels and fading it into the rear channels, as well as applying phase effects to mask the transition, but there’s still a hole in the middle of soundstage. Professional theaters try to fill this hole with speaker arrays along the side walls, but all of the speakers on one wall are tied to a single surround channel, which means that what you hear directly to the side is exactly the same as what you hear behind you at the same time. The pan from one end to the other will be choppy, rather than smooth. There’s also a huge void overhead, which is logically where the sounds of an airplane should come from.
So, what can be done about this? The natural instinct is to add more speakers and more channels. In theaters, IMAX and some other premium venues implement proprietary sound formats and speaker configurations. To properly benefit from these, a movie will have to be mixed for the specific formats. (Any movie that plays in an IMAX theater must have a dedicated IMAX sound mix). This of course puts an extra burden on the mixer to prepare multiple soundtracks for each movie, some of which will never be used again after the theatrical run.
In the home theater environment, many A/V receivers now incorporate Dolby ProLogic IIz, DTS Neo:X or Audyssey DSX processing that will upmix a standard 5.1 or 7.1 soundtrack to as many as 11.1 channels (which would entail a 5.1 base with two surround back speakers, two height speakers above the front soundstage, and two width speakers on the sides of the room). This processing is done in real time and, aside from some phase and steering cues that can be embedded in the tracks, takes a degree of control over the soundtrack away from the original creators and sound mixers. This isn’t ideal either.
When trying to figure out just how many channels should be implemented as a new surround sound standard (NHK in Japan recommends 22.2 channels as the new Ultra High Definition Television standard), audio specialists across the industry (not just at Dolby) decided to throw out the rule book and devise a whole new process known as object-based sound mixing. This represents an entirely new paradigm in sound design.
How so? In a traditional movie soundtrack, sounds are tied to specific channels. If you want to pan a sound from left to right, you have to lower the volume and ultimately remove it from the left channel, raise and then lower it in the center channel, and finally raise it in the right. The more channels you work with, the more difficult this becomes. This process also commonly results in situations where particular sounds get isolated to a specific channel when they should more naturally radiate out further into the room.
Object-based sound design, on the other hand, models the entire listening area as a three dimensional space. Sounds are tied as metadata to specific objects within that space. As the object moves, the sound moves with it towards whatever the nearest speaker happens to be. In this way, a single sound mix can accommodate as many channels as are in the room, fully scalable from a simple stereo pair up to 64 discrete speakers or possibly more – in the front, back, along the sides, and even up above. During installation, the processor will determine the number and position of speakers, and perform the necessary calculations in real time to place sounds where the original mixer wants them to be.
Perhaps the easiest way to think of this is the same way that the visuals in CG animated movies or videogames are similarly rendered as objects in a three-dimensional space, through which a virtual camera can maneuver to pick and choose camera angles. In fact, the sound design for videogames has employed a version of object-based rendering for years. (Notice the way that the sounds of other characters speaking or explosions near you will swing from channel to channel as you change your own character’s direction and point-of-view.) Yet this has not been used for movies until now.
As I said, more companies than just Dolby are working on this. However, Dolby is first to market with a new product called Atmos that will debut in about 15 specially-installed theaters with the release of Pixar’s ‘Brave’ in June. According to company reps, the average cost for a theater to upgrade to Atmos will be about $25k to $30k, depending on what equipment is currently installed. This entails a new sound processor, new speaker amps, and potentially additional speakers. While Atmos is designed to configure to whatever speakers are already in place, it requires discrete amplification to each (as opposed to the array configurations that most theaters currently use). For the best experience, ceiling-mounted speakers above the audience are also recommended. Most of the initial theaters to receive Atmos will be upgraded from the AMC chain’s “ETX” auditoriums, which already have a speaker layout that’s well suited to Atmos integration.
How does it sound? Dolby gave us a demo in the facility’s main screening room, which we were told was outfitted with a 26.3 sound system. Six of those channels were overhead. (In larger auditoriums, Atmos can go up to 64 discrete channels.) We listened to a variety of content that included audio clips of a rainstorm, a musician walking all around the room, and dialogue from ‘The Dark Knight’. We then watched Dolby’s new Atmos trailer (which has sound design from the mixers of the ‘Transformers’ movies, and sounds very similar to the opening credits of the last one of those), the climax of ‘Rise of the Planet of the Apes’, and a lengthy scene from a very famous and popular animated movie that I’m not allowed to disclose due to some ridiculous licensing restrictions that the Dolby reps apologized profusely for.
Needless to say, they all sounded great. Specifically, the pinpoint directionality and seamless panning of sounds as they dashed around the room (including overhead) was very impressive. This created an incredibly precise sense of localization and immersiveness. Essentially, Atmos conveys the feeling that you’re standing (or sitting) right in the middle of the movie’s space. This also allows for heightened clarity of individual sounds. For example, one of the clips came from a scene in a restaurant where two different sets of background characters were having conversations audible in the surround channels. In standard 5.1, the dialogue muddled together and was largely overwhelmed by the foreground action and other ambient sounds in the location. But in Atmos, both conversations were clear and distinct. That’s a benefit that could apply to any sort of film, whether an intimate character drama or a bombastic action blockbuster.
For the time being, Atmos is only planned as a premium theatrical experience, though I expect that Dolby surely has long-term plans for a home version that could be integrated into A/V receivers. Doing so may require a new compression codec and a revision to the Blu-ray spec, though.
One thing that all of the Dolby reps were insistent upon was that Atmos (or object-based audio in general) is a “ground up” approach to sound design, and is not intended to be used to upmix existing movie soundtracks into multi-channel. All of the clips we listened to were remixed specifically for Atmos from the original sound elements. However, once an Atmos mix is created, the processor can easily downmix and render out any standard stereo, 5.1 or 7.1 format as desired. This sort of elasticity makes it both backwards-compatible with legacy equipment and future-proof for sound systems with as many speakers as someone wants to install.
Whether it be Dolby Atmos or a competitor product from another company (we’ll get to that later in the week), object-based sound design represents a revolution in the way that movie soundtracks are created. No longer will filmmakers need to create dedicated stereo, 5.1, 7.1, 9.1, 11.1, or IMAX, etc. sound mixes. There will only be one fluid soundtrack, adaptable to any playback configuration needed now or in the future. This will have major ramifications for the filmmaking industry.