Skywalker Sound Finds Creative Uses for the Dolby DP600

Technical Building, Skywalker Sound. Photo credit: Morten Kettle

Technical Building, Skywalker Sound. Photo Credit: Morten Kettle.

As the Dolby® DP600 Program Optimizer approaches its second year on the market, it continues to develop a widening base of users. Several users are finding unique ways to apply the powerful audio processing capabilities of the DP600 for their particular needs. While the unit’s automated file-based loudness analysis and correction makes it an ideal component in the preparation of broadcast content, it is beginning to be used for content creation, as well. To get a better idea how this is happening in real-world productions, we spoke with Doug Ford, Engineering Supervisor at the legendary Skywalker Sound facility in Northern California. He provided valuable insight into the company’s initial decision to use the DP600, and how the studio has expanded its use in productions since the acquisition.

Skywalker Sound is primarily a motion picture audio postproduction facility, and its rooms are calibrated for theatrical mixing. When it began to take on DVD projects several years ago, new mixing considerations arose, including the use of metadata. “Over the early days of DVD preparation,” said Ford, “we learned about either setting dialogue normalization and trying to mix to a number, or, alternatively, mixing like we normally would on calibrated near-field speakers and finding out what the dialnorm was. Then, hopefully, the proper dialnorm level would be encoded by the authoring house as metadata on the Dolby Digital bitstream.”

In the past year, Skywalker has taken on a number of broadcast projects, including projects solely for broadcast, low-budget features slated for both broadcast and theatrical release, and films requiring both a broadcast and a DVD mix. Simultaneously, Skywalker began to see a need for a convenient way to meet broadcasters’ various delivery specifications.

Ford continued, “Broadcasters would specify maximum permitted peak levels and average levels, and also possibly a dialogue normalization level. So this raised some additional challenges; you know, the mixers that work here are very talented, and many of them have multiple Academy Awards® to their names, but they were moving into new territory here. It's kind of like asking someone who's a rock 'n' roll mixer to starting mixing documentary films. It was a slightly different world for them.

“We began to look for tools that would allow us to produce consistent quality results with the minimum possibility of rejection from the broadcasters’ quality control department. We looked at what broadcasters were using for QC on mixes. In the past, they used a real person and they played through the show in real time. That person had some kind of level-measuring device, and they often made judgment calls on level. More and more, on a file-based workflow, people are using automated tools that basically look for whether preset parameters are met or exceeded, and they're accepted or rejected based on the automated analysis.”

Mixing a Series to Spec

Skywalker initially invested in Dolby LM100 Broadcast Loudness Meters, and more recently in the Dolby Media Meter software loudness tool. The first impetus for using the DP600 came in 2008, after Skywalker had mixed the animated TV series Star Wars: The Clone Wars. The nature of the project, combined with the need to mix for multiple markets, meant that Skywalker had to pick a mix spec early on. According to Ford, “When it was sold to Turner, we measured what we had mixed, and found that we didn't meet their spec. As we looked at how long it would take to go back to the stockpile of episodes that we had made and remix them to meet their spec, we decided it would be best to invest in a Dolby DP600 Program Optimizer.”

Because Turner has two different audio specs—5.1-channel for HD and Lt/Rt for SD—the engineers needed to process them separately. “We set up two separate profiles in the DP600: one to maintain an average level for speech content that met Turner's delivery spec for the 5.1 mix, and another to maintain a similar average speech level for stereo (but with peaks at –10 dBFS)," said Ford.

“At first, while the DP600 allowed us to meet the specs numerically, the mixers found sections in the content where they could hear evidence of extreme level processing on the signal by the DP600. Because we also had the Dolby Media Meter software loudness tool, we could quickly analyze the mix and see the areas where it was wildly away from the Turner spec. This allowed the mixer to get close fairly quickly. So the general guidance we give to mixers is that they need to get their mixes into the ballpark, and then use the DP600," Ford continued.

“The results that we got once we were past that initial learning curve on using the DP600 were great. The Dolby Media Meter software loudness tool also came in very handy; it allowed us to see troublesome spots in the mix level, and then quickly nip in and fix them before using the DP600. And the mixer on Clone Wars commented that the DP600 proved to be a tremendous time-saver over trying to mix manually to the spec. It was definitely the way to go.”

Skywalker is currently working on season 2 of Clone Wars. “A nice thing about the DP600 is that we've set up a watch folder work order for it,” said Ford. “The mixing crew works on their own schedule, so they can drop their completed mixes into the watch folder as they finish them. The DP600 can process in faster than real time, which means they can go grab a cup of coffee, and when they come back, they'll have the resulting files. It's a very easy work flow for them to deal with.”

Preparing Theatrical Releases for New Formats

A number of film studios have recently requested that Skywalker prepare special mixes to comply with British broadcaster BSkyB’s specifications. Remarked Ford, “The first one we had to do that way was The Dark Knight. We had that experience before the days of the Dolby DP600. It was very challenging, and took a very complex setup in the mix room. Toward the end of last year, we were asked to make a BSkyB compliant mix of The Curious Case of Benjamin Button. We began mixing manually without the DP600 because the primary mixer was David Parker, who is a two-time Academy Award winner and four-time nominee, and Ren Klyce, who is a sound supervisor known for his attention to all things audio.

“We talked about the DP600, but they felt they wanted to give the mix a shot manually. There were some very challenging sequences in Button; for instance, there's one where there's a big celebration taking place, with fireworks going off in the background. But there's also very important plot-developing dialogue going on in the meantime as well. David wrestled with this for quite some time, and I offered to run it through the DP600 to see how it would turn out.”

Ford performed an A/B/C comparison between the existing DVD mix of the sequence, Parker's manual mix, and a version processed using the DP600 optimized for the BSkyB spec. He said that “David and Ren were absolutely blown away. Both of them were immediately sold on the concept of using the DP600. They felt it allowed them to get the best version of the mix possible—that the mix would both be absolutely compliant and completed in a reasonable amount of time.

“These are two people who are very particular, very exacting, and very good at what they do. And they acknowledged that the DP600 made it possible to achieve an artistically acceptable result while meeting a tight technical specification. Everyone was happy at the end of Button. Previously, we'd regarded it as a matter of expediency to purchase the DP600 to help with the Clone Wars work. But with Button, all of us involved with the purchasing decision felt that we were deriving additional benefit.”

In addition to its practical applications for previously prepared audio content, Ford said it can be a useful tool during the mix process. “It doesn't replace the craft of mixing,” he said, “but it augments it and provides a very valuable tool for us. Mixers need to be able to work creatively as well as to meet technical specs. The DP600 takes the strain off of them. It's like driving on the freeway—we all try to drive at 65 mph, but if you absolutely couldn't veer from that, without cruise control you'd never be able to do it. And in effect, using a DP600 is a bit like having cruise control for your mix level."

In-House Authoring of Audio and Metadata

Ford offered another revelation Skywalker had when working on Benjamin Button, when it came time to prepare a DVD mix for Academy Award screeners. “Usually, we only deliver linear files,” he said, “and then the authoring house performs the data compression and adds the metadata, and puts those assets on the disc along with the menu items and so on. Often, we've been told that we couldn't make the Dolby Digital AC-3 file because, until the picture is encoded, the authoring house doesn't know what the bit budget is on the DVD. The reality is that there are only two data rates for the audio, but regardless, we've been barred from doing that.

“In the case of the Academy screeners for Button, we received a test pressing of the disc. It sounded horrible, so we analyzed the metadata using the SoundCode for Dolby Digital tool from Neyrinck. And we discovered that the metadata was not coded as we had asked.”

Skywalker is currently considering purchasing the UC/600 upgrade for the DP600, which adds encoding, decoding, and transcoding capability to the DP600 base unit’s loudness analysis and correction capabilities. It supports Dolby DigitalDolby Digital PlusDolby E, Dolby Pulse, and MPEG-1 LII codecs. The upgrade will allow them to author DVD and Blu-ray Disc™ audio files in faster than real time.

“What I'm thinking about for future situations like this,” Ford continued, “is that because there are only two possible data rates for the Dolby Digital stream, we could just encode a separate deliverable for each data rate. We're going to push for that, as it would streamline the process and eliminate the potential for error.”

Find more details in the DP600 Program Optimizer overview for postproduction pdf.