Dolby Atmos Explained Plus More First Impressions
Things are moving fast on the Dolby Atmos front. In case you’ve been living in a cave for the past few months, Dolby, working together with a number of manufacturers sure to grow in number, is bringing the commercial Atmos audio format home. You’ll also find an accompanying interview with Brett Crockett, director of sound research at Dolby Labs. While there is some overlap here with the information in that interview, I’ve elected not to edit out the areas of duplication here, since I approach the subject from a slightly different angle. And in these infant days of home Dolby Atmos, there’s no such thing as too much information.
I've had the pleasure of attending two formal demo sessions in recent weeks but before I offer up my first impressions, let's take a look at what Dolby Atmos is—and isn't. Atmos was originally designed for theatrical presentations. It first appeared in the Pixar movie Brave in 2012. Rather than just the conventional 5.1 or 7.1 channels used for conventional surround sound in the movie house, Atmos could use as many as 64 independent speaker channels.
Channels vs. Objects
But while we’re apt to refer to these extra speakers as “channels” simply because that’s a familiar term, they’re actually something very different. There aren’t 64 independent channels on the soundtrack. Instead, the sound mix is what is called “object” based. Suppose, for example, the sound designer wants to place a sound effect somewhere overhead. Instead of directing it to one of the ceiling speakers, he or she records both the effect and its desired location in the hemispherical space around the audience.
The effect can also be directed to move in a particular way. On playback the decoder, using the directional data in the mix (metadata) and an Atmos algorithm, directs the sound to the specified location. This might require that it be directed to more than one speaker, relying on the “phantom image” effect to position it properly. But the algorithm takes care of this; the mixer need only deal with the effect itself and its location and/or movement in space.
Moreover, the system doesn’t require the full possible complement of 64 speakers. For financial reasons, most Atmos-equipped theaters likely won’t go that far. No matter; the playback algorithm can be modified to the specific theater’s setup, including the number of speakers and their precise locations. Given that information, the system massages the data to fit the installation and directs the sounds to the positions in space that were desired in the original sound mix. The more speakers, of course, the more precise the effect can be, but the point is that the theatrical system can accommodate a wide range of configurations.
As you might imagine, programming every single effect in a movie for this could become exceptionally tedious and time consuming, and time is money. Most Atmos mixes will likely still make use of the usual front and surround channels and save the Atmos “object-based” steering for when it’s really needed. But the more sound mixers become comfortable and adept at using Atmos’ capabilities, the more they’ll use them. And, perhaps, abuse thembut that’s a story for a future blog!
For home theater Atmos, however, it’s very likely that the number of added speakers will be far more limited than even a modest Atmos theatrical experience will offer. In fact, Atmos for the home is limited to 34 speakers, plus subwoofer(s). But we can imagine the response of the family’s in-house interior decorator to that“You want to put 34 speakers in MY living room?” Fortunately, most of Atmos benefits in the home can be realized with the addition of four ceiling speakers to the usual 5.1 or 7.1 channels. Dolby refers to such arrangement as 5.1.4 or 7.1.4, where the last digit indicates the number of Atmos ceiling speakers.
Atmos-Enabled Speakers Save the Day
But even that can be daunting. Most folks won’t want to install even four ceiling speakers (two near the front, two further back). If that was the only way to bring Atmos home, the format would likely go nowhere. That’s where Dolby “Atmos-enabled” speakers come in. Each of these speakers will include an additional driver or drivers on the top of the cabinet, firing upward at a slight angle and driven separately from the main, forward-facing drivers. The sound from these upward-firing speakers bounces off the ceiling and appears to come from there. With this arrangement you’ll have the same number of visible speakers in the room as with a conventional multichannel setup. But Atmos-enabled speakers are not, at least not yet, compatible with in-wall or on-wall speakers, or conventional speakers shoved into a bookcase or other type of enclosed furniture.
For those who already have speakers they like and are unlikely to replace them, some manufacturers will offer upward facing modules that will sit on top of your existing speakers. Whether or not these will blend cosmetically or look like a kludge is as yet a question only a little less important than whether or not they will blend in well sonically.
Atmos at Home: Hardware You'll Need
Dolby Atmos at home will require not only new or added speakers but also an AV receiver or pre-pro equipped with the proper Atmos algorithms. You’ll also need additional amplifier channels (opening up an expanded market, perhaps, for external power amplifiers). The discs themselves must be encoded for Atmos to produce the intended effects, though the home decoding AVRs will certainly include simulated Atmos modes to serve your existing non-Atmos movie and/or non Atmos downloads. (As of now, Dolby is planning on calling such modes Dolby Surround, which will stir either nostalgia or confusion among long-time home theater fans.) And Atmos Blu-ray discs should start appearing before the end of the year as well. Over 120 feature films have been mastered in Atmos to date, so you’ll get to enjoy (and re-buy) your favorite titles all over again.
But you won’t need a new Blu-ray player. Existing players should work fine, as long as you feed your Atmos-ready AV receiver a digital bitstream from the player (PCM digital or multi-channel analog won’t do). Atmos compatible AVRs have already been announced from most of the usual suspects, though the Atmos algorithms will likely not be available before the end of this year (via a firmware update).
Atmos at Home: First Impressions
I’ve already experienced Dolby Atmos in the theater; my local AMC theater has an auditorium equipped for the format. But it’s only recently that I’ve heard a home setupnot in my home but in two formal demonstrations near Los Angeles, one by Pioneer and the other by Dolby.
Pioneer’s came first, and was held at a Pioneer facility near Long Beach, CA. Pioneer was the first manufacturer to announce both AVRs and Atmos-enabled speakers fitted with both front- and upward-facing drivers. Both top and front employ woofer/tweeter coincident drivers. Dolby recommends that the drivers covering the ceiling “channels,” whether they reflect off the ceiling or are actually located there, respond down to at least 180Hz, and Pioneer’s top-facing driver meets this requirement.
Pioneer will soon be shipping two Elite-series Atmos-enabled speakers, the SP-EFS73 floor-stander ($1400/pair) and the stand-mount SP-EBS73-LR ($750/pair). There’s also a more conventional Elite SP-EC73 center channel design ($400), also with the coincident front-facing driver but no upward facing one. The system auditioned used a pair of the floor standers and the center up front, the stand-mounts in the rear, and a single Elite SW-E10 subwoofer ($600). In the photo at the top of this blog, Pioneer speaker guru Andrew Jones is shown with the center and the floor-stander models, both of which he designed.
The demo room had a 10-foot reflective ceiling and measured roughly 17.5x23 feet (Pioneer said 16x23, but I paced the width off at about 17.5 feet, give or take a few inches). The AVR was, of course, a Pioneer.
The demo, using Atmos trailers and the first few minutes of Star Trek Into Darkness (all, of course, mastered in Dolby Atmos) was very effective. Sounds came from all around us (well, not the floor—that’s apparently, as yet, an undiscovered country). If I have to make a criticism, it would be that when the going got crushingly complex, as it did in the Trek piece, the busy mix began to sound congested, which could have had any number of causesthe room, the speakers, the mix itself, the high playback level, or some combination of these.
Later we had a chance to listen briefly to just the speakers themselves in two-channel stereo with no sub. I found the smaller stand-mounts more open-sounding, if less extended than the floor-standers. If I don’t wax eloquently about how they sounded, it’s only because I’ve been spoiled by hearing innumerable speakers designed with fewer (or no) price constraints, including TAD models running into six figures. (TAD is Pioneer’s high-end brand, and the new Pioneer Elite Atmos-enabled models sounded as good as they did largely because designer Andrew Jones also designed those TAD speakers. He knows what to listen for, even if at less than 5% of the price of the cheapest TADs he can’t quite equal them. But the affordable Elites will certainly make a lot of budget conscious audio fans happy.)
The Dolby Demo
Two weeks later came the Dolby event in Burbank, CA. It began in Dolby’s small theater (I’m guessing 40-50 seats, tops), equipped with a full theatrical Atmos system. The material was the same used in the Pioneer demo. The playback level here was excruciatingly loud—at reference level or perhaps even higher. I was amazed that everyone but me sat calmly through it all, while I had my fingers firmly planted in my ears during the loudest bits. The Trek clip was the main offender there, with edgy dialogue that was virtually unlistenableat least at the chosen playback level. But one thing was obvious to me, and I’ve noticed it before in theatrical Atmos presentations: the Atmos effects were most effective not on the explosive bits but rather on quiet material—rain, rustling leaves, the gentle whooshing of the wind. When the soundtrack becomes loud, complex, and congested the benefits of Atmos become, for me, marginal at best. Perhaps with more experience sound mixers will learn to avoid this problem.
The demo then moved to a smaller room with a more modest, home theater style 7.1.4 setup (in contrast to 5.1.4 used in the Pioneer demo). The room here was also 17.5 x 23 feet (I paced off the width again, editor Rob Sabin paced off the length), though the ceiling height was, by my estimation, about 8 feet. Significantly, that ceiling was slightly absorptivenot the best situation for Atmos. But as in the Pioneer demo the ceiling was flat.
In this room they first compared a standard 7.1 system with and without Atmos, using Atmos-enabled speakers. The program material was the same as before. The speakers and electronics were not identified, though the speakers were small stand-mounted models with upward-firing, full-range drivers for the “ceiling” channels (not coincident as in the Pioneers). The differences were clearly in favor of Atmos. They then compared these Atmos-enabled speakers with discrete ceiling speakers. I preferred the latter, finding it more precise and less congested. Others, however, preferred the diffusiveness of the reflecting setup. I later found out that the ceiling speakers may not have been timbre matched to the 7.1 system. But they worked for me, since the comparison was very brief and we were all listening more for the effects than the timbre.
In either case I actually preferred the sound in this home space to that in the “big” Dolby home theater; the level was much more tolerable so I could actually concentrate on the Atmos effects and not on protecting my ears. (If you’re wondering, I do listen at levels most would consider quite loud in my own home theatertypically 4-8 dB below reference.) Both approaches (ceiling speakers vs. Atmos-enabled reflective ones) are valid; which one works better will likely depend to a great extent on your room.
Dolby Answers Questions
In a Q&A session following the demos, Dolby representatives recommended a flat ceiling with a height of 8-14 feet for Atmos-enabled speakers. Cathedral ceilings may be incompatible with the reflected version of Atmos, though I’m sure they’d work in some situations. Dolby also recommends that the Atmos-enabled speakers be at least 3 feet from any listener. There was also the inevitable question on "acoustical ceilings." The answer: so-called popcorn ceilings should be fine (their acoustic properties are virtually nil), but other types of absorptive treatment on the ceiling would be a bad idea. If you use discrete ceiling speakers, however, neither cathedral ceilings nor acoustical ceiling treatments should be an issueas long as the latter doesn't block the sound from the ceiling speakers.
I asked the reps about how much added data space would be required to carry the Atmos soundtracks, and was told an increase of about 20%. Atmos can be used with either Dolby TrueHD or Dolby Digital+ encoding. DD+ was not originally designed to offer better sound than plain-Jane DD. Rather, it was intended to provide sound equivalent to DD but at a much lower data rate. That’s why it’s almost universally used for movie downloads, and likely will still be with Atmos downloads. It can be used at a higher rates for better results, but remains a "lossy" format. I trust (but will verify when the time comes) that Atmos releases on Blu-ray will use TrueHD, at least for their English tracks.
Atmos for Headphones
Dolby also mentioned that Atmos will also appear, though not immediately, in mobile devices. Atmos playback in a car may be a little distracting (!) but we're talking headphones here. How this will work in conventional two-channel phones will be a story in itself. It will certainly require a different playback algorithm than with multichannel speakers. Hopefully that algorithm will be offered as a firmware update to this first generation of new Atmos-equipped AVRs, rather than requiring new hardware, when it becomes available. But this application is for down the road, not this year.
Many questions remain. Will the addition of more channels, particularly if they’re discrete (not reflected) and respond down to the range where they might generate standing waves of their own, complicate bass management? If EQ in the receiver is used, will it have enough processing power to handle up to 11.1 channels (a 7.1.4 system)? (Pioneer says that its AVRs will.) And if AVRs are designed with 11 channels of full-range amplification, how might his affect the power output and quality of the amps? Finally, might Atmos-enhancements find their way onto music-only multichannel Blu-ray discs?
Atmos is one of the most exciting developments yet in home theater soundcertainly the biggest story since the advent of lossless Dolby TrueHD and DTS-HD Master Audio. Answering these questions will happen over time. And as is always the case with new developments, the discoveries are half the fun.