Dolby Audio Coding for next-gen HD optical formats and HDTV

Since its invention by Thomas Edison more than 100 years ago, 35 mm film—and the picture and audio experience it produces—has been revitalized countless times. Without a doubt, the introduction of the 1976 hit A Star Is Born in multichannel Dolby Surround sound redefined the big screen experience. And with its effective use a year later in the blockbusters Star Wars and Close Encounters of the Third Kind, surround sound brought a new degree of realism to the cinema experience. Soon after, Dolby Surround would quickly find its way into the world of home entertainment.

Digital video delivery and projection technologies have progressed to the point where it is now commercially viable to display movies in theatres with a quality level that is better than that of 35 mm film. Just as Dolby Digital enabled 35 mm movies to sound better and gave improved audio consistency over the life of the print, digital delivery of movies will do the same for the picture side of the equation, eliminating dirt, weave, blurry prints, scratches, and lumpy splices. For cinema purists, the first or the 1,000th playback of the motion picture will present quality on par with a pristine film print being played on a well-tuned projector. For most consumers, the experience will be essentially as it has always been—only cleaner, with fewer visible distractions.

Once freed from the physical constraints of film, we’ll begin to see interesting developments such as the use of higher frame rates for more fluid motion, or kinds of 3D imaging never before possible. And who knows what else might come once creative minds are turned loose to explore the reaches of the high-bandwidth infrastructure being established to deliver movies to digital cinemas via satellite. We’ve seen how high-speed Internet access has changed the way consumers obtain their entertainment. Imagine what can happen when every major cinema in the world is tied to a huge, secure data delivery pipe.

Expanded Audio in D-Cinema
One obvious direction for D-cinema is for more audio channels to drive existing or additional speakers; precedents for this supposition already exist. Dolby Digital Surround EX™ promoted the concept of dividing the surround speaker array into three zones instead of two (as is the case with 5.1-channel formats). Other specialty-venue film formats such as Imax have used an additional speaker located at the top of the screen to enhance the sense of vertical movement. In 1940, Disney’s Fantasia premiered in New York’s Broadway Theatre with more channels than today’s cinemas.¹ There’s always been a desire to explore the use of more audio channels in cinemas, but with Dcinema it finally becomes practical to do it.

The Society of Motion Picture and Television Engineers (SMPTE) formed the DC28 Digital Cinema Technology Committee, which is defining the range of new channels and speaker locations that may be applied in future digital cinemas. Of the 20 total channels described in SMPTE 428M,² seven are those of the current Surround EX 6.1-channel configuration, and 13 provide additional capabilities. Four of the 13 new channels drive speakers that expand upon existing surround arrays, providing more directional control to the back and sides of the theatre. Another pair flanking the center speaker has been used before in SDDS and 70 mm formats. The remaining seven channels drive totally new speaker locations: a wide pair at the front, four vertical channels for an added sense of height, and even a second LFE channel.

No one expects all these channels will be used at the same time, but then again no one has mixed a movie using any of the new locations yet, nor has a commercial cinema been built to support their use. It will probably take a special event—like the release of Star Wars: Episode I—The Phantom Menace, which introduced Dolby Digital Surround EX—to motivate theatre owners to retrofit their speaker systems and take advantage of a new audio mix. Depending on the type of movie, the film mixer may wish to use different subsets of the speaker array to achieve specific effects, so cinemas will need further flexibility to automatically reconfigure their speakers accordingly.

Bringing the D-Cinema Experience Home
Dolby’s participation in the DC28 committee led us to the conclusion that it would be important to ensure a future pathway for bringing the expanded capabilities of D-cinema soundtracks to home playback systems. Two actions have occurred as a result. The first is that Dolby’s next-generation audio codecs were designed to carry several additional channels. In addition, Dolby proposed not only that these codecs be adopted in next-generation high-definition (HD) disc formats (HD DVD and Blu-ray Disc), but that they should also incorporate the standard SMPTE 428M naming conventions for the new channels. We are pleased to say that both new high-definition optical formats have adopted this proposal. While they are currently limited to a maximum capacity of eight channels, that may serve perfectly well for the foreseeable future. However, should there be justification to expand channel offerings in the future, there is no technological barrier preventing such expansion, as Dolby’s audio codecs are designed with compatible extensibility.

Dolby’s codec offerings for HD disc formats are based on extensions of the well-proven Dolby Digital and MLP Lossless™ technologies, which are worldwide standards for DVD-Video and DVD-Audio, respectively.