7.1 ‘ Surrounded Or Overwhelmed?
As Pictures Peg Big Expectations on Two More Channels, Here's How Mixers are Reacting
Mi Casa President and chief mixer Brant Biles notes that some standards are agreed upon – including the speaker mapping and, in the case of the DTS coefficient algorithm, speaker “re-mapping” – 7.1 is still a pioneering proposition. “The [configuration] most people, including us, seem to be using is three speakers in front, two on the sides, located at 90 degrees from the listening point, and two speakers in the rear,” he says. But there's a total of seven possible speaker configurations, including three in front and four rear, a 5.1 setup with the extra pair situated directly overhead, a 6.1 configuration with a mono directly overhead, and the same thing with the overhead moved slightly forward. In fact, Mi Casa’s mixers set up a total of 18 speakers in their Studio A to experiment with speaker mapping. However, while they have settled on the 3-2-3.1 configuration, home-theater owners may have different ideas. In that case Brant includes information on the specific speaker map he used for a given mix as part of the metadata accompanying the soundtrack. The DTS home-theater processor will note that, compare it to the speaker positions in the theater, and re-compute delay and level compensations for each speaker based on the differences in layout.
What the two extra channels give back, though, is greater consistency through front-to-back panning. This allows for slower, more expressive and definitive pans in those directions – a feature missing from 5.1, with its gap between the LCR and the surrounds, says Biles. “The side channels allow you to have a more polyphonic, more immersive and three-dimensional experience,” he says. “The void in the side is gone.”
Tim Hoogenakker, who has been mixing 7.1 titles including Ultimate Avengers, Dr. Strange and Belly at POP for the better part of a year, was skeptical at first, but now agrees with Biles. “I didn’t think much of it until I got started,” he says. “Now, [I understand] there are things you can’t do with 5.1, like hard sound effects, [or] an airplane flying from front to back, side to side. “It’s really kind of indescribable how inside the picture it puts you.” Hoogenakker says it also brings new depth to sound design, allowing it to fill in the 90-degree angle from the dialog source.
Working on an AMS-Neve DFC Gemini console with 384 signal paths connected to a Digidesign Pro Tools HD system, and monitoring through Quested H208 speakers in the LCR, JBL 8330s as surrounds and an M&K MX-5000 THX-compliant subwoofer, Hoogenakker uses a 3-2-2 (LCR-side-rear) set-up, and says he uses the side channels for niche elements as well as ambiances. In some cases, he’ll create additional sound effects for them – it's as if he suddenly finds himself with more audio closet space. “If there’s a scene with a lot of dishes clanking around, for instance, I’ll sample some of that from the effects stems and add more of it to the side channels,” he explains. “If the effects layers start to get dense in other scenes, the side channels are a good place to move the effects to so that they stay very present but don’t trip over the dialog or other elements.” (Needless to say, the technique of sampling and inserting new sound effects is subject to final approval by the director or his or her appointed sound supervisor.)
Certain elements in the additional channels also require different types of processing. “I’ll almost always change the EQ on the music,” he says. “If there are transients in the side channel, like a tambourine or a triangle, they’ll usually need to be toned down so they don’t become distracting. I’ll usually take some level off the upper frequencies with EQ and/or add some additional compression to the channels to bring them more in line level-wise with the rest of the music track.”
Hoogenakker tends to place dialog in the center, effects left and right, music in the side channels and ambiences in the rear speakers. “Every picture is different, but it’s a good starting place,” he says. “Some elements, like music, are going to overlap into other channels to an extent,” which is also inevitable when mixing for matrixed formats like DTS [HD] and Dolby [EX] where the home theater processor decodes the two surrounds into four. “Then it’s a matter of matching levels across the monitoring field.”
The encoding process for the two audio codecs on both high-definition disc formats, DTS and Blu-ray (BD), illustrate some of the more technical nuances of 7.1 The DTS-HD encoder is able to produce a 5.1 version automatically via the codec’s “core stream” algorithm, which contains a pre-mixed 5.1 soundtrack (the core) available for legacy receivers that don’t support 7.1. (Even this 5.1 mix is at a higher bit rate than standard-definition DVD audio.) The Dolby codec has certain features such as dialog normalization and dynamic range control. It offers selectable fixed levels of compression to ensure that louder sounds, such as explosions, don’t confuse the encoding process in terms of placing that element in the sound field. “It limits you a bit in certain ways, but it also acts as a check against the levels I set and keeps the final outcome in balance,” he says.
Also, SMPTE specified how to apply a standard power-preservation downmixing coefficient so that theaters presented with any of these new channels could properly and consistently downmix them to 5.1, and ensuring that any 7.1 program will play correctly in a 5.1 home system. (Every 7.1 mix carries a complete 5.1 version.)
Dolby and DTS essentially agree on the implementation of SMPTE 428M in processors for home theater and theatrical applications. “When the question of how 7.1 was to be defined in the HD DVD and Blu-ray formats came up, Dolby proposed that since these were movie formats, they should support the extension channels defined by DC-28, so the new blue formats both reference the SMPTE 428M,” states Roger Dressler, director of business development for Dolby’s consumer group. DTS’s DTS-HD algorithm uses digital delays to let the sound from any of the speakers reach the listening position at the same time they had in the mixing studio.
While 7.1 may be a home video phenomenon initially, some feel it will hit cinemas soon enough. “The Digital Cinema specification already supports 7.1 and the retrofit of two additional speakers and amplifiers isn’t that difficult for most theaters,” says Steve Venezia, Dolby’s manager of DVD and broadcast support. “History also seems to say that we’ll keep increasing the number of channels.”