by Jeremy J. Glowacki
During my visit to Dolby Laboratories in San Francisco to learn about the company’s new TrueHD with advanced 96k audio upsampling technology, I couldn’t help but be reminded of a classic scene in This is Spinal Tap! Christopher Guest’s character Nigel Tufnel shows off his guitar amp with a volume knob custom designed to go “one louder” to 11 instead of 10. Who knew, I asked myself as I settled in at Dolby, that TrueHD lossless audio on Blu-rays could get any better than it already was? I mean it’s already lossless. How much better can it get I thought? The answer I thought was “None. None more better.” I was wrong.
But thanks to some ingenious developments inherited from Meridian’s R&D department, Dolby found a way to take lossless audio on Blu-ray Disc maybe not “just one louder” like in Spinal Tap, but at least a noticeable notch better in terms of clarity and “naturalness.”
Craig Eggers, director of content creation and playback for the home theater ecosystem division of Dolby explained it this way: “Lossless audio is a key distinguishing feature of Blu-ray content. All things being equal, you cannot improve on the quality of lossless audio coding; however, you can improve on the quality of the source PCM content prior to lossless encoding, and this is precisely what we have achieved with our advanced 96k upsampling technology. A significant amount of Hollywood content has been captured in native 48 kHz. Studios and authoring facilities that implement Dolby TrueHD with advanced 96k upsampling can elevate the quality of PCM audio prior to lossless Dolby TrueHD encoding, ensuring that consumers get the very best audio performance possible from their Blu-ray playback systems.”
Dolby Laboratories executives and engineers introduced TrueHD with advanced 96k audio upsampling technology to an small gathering of industry press here at their headquarters in San Francisco.
Depending on your ability to hear the finer details in movie soundtracks and musical performance, you may or may not be able to notice, at first, the subtle nuances added by advanced 96k. It took several passes of A/B demos of remastered and new movie clips for me to hear it. Once I had trained my ears, however, I really understood the new technology’s benefits. Movie sound effects from, say, a shattering window were more accurately reproduced with less distortion, classical music performance material from the San Francisco Symphony filled the room more with more depth and clarity, dialogue was much clearer than before, and a flurry of audio effects from a Chinese film called The Flowers of War were just as irritating to my violence-averse sensibilities, but at least much less fatiguing to my ears.
Dolby TrueHD with advanced 96k upsampling is a free software upgrade for studios, authoring houses, and mastering facilities that provide the post-production magic within the Dolby Media Producer Encoder. Dolby considers the upgrade a “value-add” for its industry partners rather than a profit play. The company hopes the coding solution simply will improve the quality of the content coming out of Dolby-badged AV receivers and Blu-ray Disc players, while adding no costs to the production or to the consumer. In other words the technology is backwards compatible with any existing TrueHD product. The advanced 96k improvements will come from the disc itself and the hope is that the studios will use it in rereleases of their catalog content as well as new productions.
The key to this new technology isn’t just what would seem like an obvious improvement from 48k to 96k; it’s about reducing the incidence of digital artifacts introduced during the content-creation process. This concept took some time for me to grasp, but here’s how I understand it: When analog audio is converted to digital, a fundamental decision is made about what sample rate to use. Higher sample rates support higher audio frequencies, but consume higher bit rates. The compact disc format chose 44.1 kHz as the sample rate, which was the lowest that could support an audio bandwidth of 20 kHz. Any A-to-D converter requires a lowpass filter to prevent sonic artifacts called aliases from being generated. In the case of the compact disc, the required anti-aliasing filter must pass all the audio up to 20 kHz, then attenuate everything above 22.5 kHz. The resulting filter shape looks a lot like a brick wall, so that became its nickname. This type of filter can have a detrimental effect on the audio but is necessary to keep the audio from going above a certain frequency. Dolby TrueHD with advanced 96k upsampling masks what are called pre-ringing artifacts from showing up in the final recording.
Movie soundtracks can comprise hundreds of sound elements captured on set, in the field, or in studios at various sample rates, and either mixed directly or converted to the 48 kHz sample rate used by digital audio workstations on dubbing stages. Each A-to-D converter and sample-rate converter includes its own anti-aliasing filter, which is designed with the intent to minimize distortion artifacts. Unfortunately each filter may leave “fingerprints” on the audio.
Upsampling audio allows DSPs and D-to-A converters to perform with reduced side effects on the audio. As a result, some higher end AV products have begun adopting such processing. As with any algorithm, there are design trade-offs to be made that can affect DSP MIPS requirements and sound quality. Meridian Audio took an uncompromising approach to the problem, devoting all the DSP resources necessary to achieve the upsampling capabilities for its flagship CD player, the model 808.2. Besides performing upsampling, the process incorporates the ability to mask the side effects of any upstream anti-aliasing filters in the chain, replacing them with a filter designed to high-sample-rate, audiophile standards. Meridian calls this an apodizing filter. By using apodizing filters, the pre-ringing that can be caused by certain brick-wall filters can be totally masked. This advanced upsampling and filtering technology is now integrated as a preprocessing feature in Dolby Media Producer.
A demo of TrueHD with advanced 96k audio upsampling technology Dolby’s new mixing room.
The apodizing filter included in Dolby TrueHD with advanced 96k upsampling technology acts as a gatekeeper to prevent undesirable artifacts introduced upstream from A-to-D conversion from intruding on the sonic perfection of lossless audio playback.
The first Blu-ray Discs to feature Dolby TrueHD with advanced 96k upsampling are The Flowers of War, and the soon-to-be-released Blu-ray Disc titles for the Joe Satriani concert film, Satchurated: Live in Montreal, and San Francisco Symphony at 100 have been premastered using Dolby TrueHD with advanced 96k.
According to Dolby, authoring houses and mixing facilities worldwide already have upgraded to Dolby TrueHD with advanced 96k upsampling within the Dolby Media Producer Encoder v2 to provide customers with the highest-quality audio experience available on Blu-ray. These facilities include United States-based Deluxe Digital Studios, Giant Interactive, Mi Casa Multimedia and POP Sound POP Sound, and Technicolor; and leading China-based companies Best & Original Production Limited, Hualu Publishing & Media Co., Ltd., and Media Asia Films.
“One of the best features in Dolby TrueHD with advanced 96k upsampling is the apodizing filter, which makes remarkable improvement in the articulation in high-frequency attacks while simultaneously cleaning up midrange mush,” Brant Biles, president and chief engineer, Mi Casa Multimedia told Dolby after using the new technology. “Upsampling with the apodizing filter on any program information, whether it is music, dialogue, or effects, delicately unveils the sound and adds an extra dimension of depth, and clarity.”
I couldn’t agree more.