Jul 012010
What with all the attention give to high-definition and 3D in 2010, it’d be easy to underestimate the role of great sound in the film experience. But think about it: what was it that made the shark attack in Jaws so scary? Why did the opening scene of Star Wars leave such an indelible mark on most contemporary viewers? And why, even now, does the opening scene of Saving Private Ryan possess the power to shock so completely?

jawsfilmcover 224x300 The Definitive Guide to High Definition surround sound

Simply put, the answer is great sound. Spielberg knew that sharks were silent, stealthy killers: it took John Williams’ powerfully affecting score to heighten the terror of each attack. George Lucas was just as profoundly aware of the need for great sound: he needed it to hide the flaws in his 1970s-vintage special effects. Once the thundering engines of a Star Destroyer have screamed over your head, you’ll pay less attention to the fact that, quite obviously, it’s all being done with models. And then there’s Saving Private Ryan, that paragon of surround sound savagery, as realistic a multichannel masterpiece as any in movie history: here, the sonic intent was to both convince and terrify, and did it ever work.

So great sound counts. In fact, according to Randy Thom, one of Hollywood’s most acclaimed sound designers, it counts so much that “If you look closely at and listen to a dozen or so movies you consider to be great, you’ll realise how important sound is in many if not most of them”. Or to put it another way, while watching a great movie in stereo through bandwidth-limited television speakers has little impact on your ability to understand dialogue or follow the plot, it’s still a long way short of the complete entertainment experience the director originally intended you to have.

Randy Thom 550x367 300x200 The Definitive Guide to High Definition surround sound

All the more reason to buy a Blu-ray player and an appropriate multichannel amplifier, receiver or processor: the combination of these two (or three) components, used in harness with a good-quality surround speaker system, will get you closer than ever to the original sound of the master audio tracks created by the world’s best sound designers.

Older disc formats such as DVD are comparatively careless with the precious cargo they bear: in essence, when we talk about data compression for DVD sound, what we really mean is data ‘reduction’, because elements of the original source audio are permanently discarded during the disc-encoding process. With Blu-ray’s uncompressed and lossless audio technologies, that doesn’t happen, so the end result can be sonically identical to the original.

Identical? Really? Unbelievably, the answer is yes. For any film, sounds are first recorded and engineered as uncompressed 24-bit/48kHz PCM audio (far better than CD quality, which is 16-bit/44.1kHz PCM): this is then mixed in the studio to create an original master. After that, the finished soundtrack is usually heavily compressed to create final versions of the movie for distribution on film or, subsequently, for domestic use. This is very similar to the way MP3 works on a CD-quality piece of music: indeed, Dolby Digital, the most commonly used compression system found on DVD discs, stores audio at transfer rates very similar to a good MP3 file (384 to 448kbps, or kilobits per second).

This compromise is enforced by the technical difficulties involved in cramming surround sound on to a film reel, on to a limited-capacity data disc or, most recently, on to a DVD. DVD can only offer between 4.7 and 9.4GB of storage space for the completed movie presentation, and its video is packaged using less-efficient MPEG2 compression, which requires more space per second of video information than newer, more efficient systems. That, plus the need to accommodate numerous extra features and, in discs destined for the European market, additional soundtrack options in other languages, has meant that on many DVD releases, audio has frequently come a poor third to its two space-hungry rivals.

09   BW Custom Theater CT800 System 1 537x215 The Definitive Guide to High Definition surround sound

But Blu-ray has up to 50GB of storage capacity and often uses newer and much more efficient video compression systems compared to DVD, so there’s no need
to cram in data to fit the space available. In fact, there’s so much space on a 50GB disc that it can even accommodate a studio-quality 7.1 channel 24-bit/48kHz PCM soundtrack, if needed: the only inhibiting factors are the duration of the film, the extent of the extras included and the willingness of each studio to make the effort. As a guide, two hours of 7.1 channel, uncompressed 24/48 PCM audio would need 8.3GB of space, or less than 20 percent of the space on a 50GB Blu-ray.

That said, not all Blu-ray discs afford dual-layer 50GB capacity: many films are released as single-layer 25GB discs. Even here, it¹s possible to fit multiple channels of uncompressed PCM audio onto a 25GB disc ­ but at the same time, to do so obviously takes up a relatively larger proportion of the available capacity.

So, to create room for extras, soundtrack options and video, most studios have adopted one of two approaches. Some have preferred to down-convert the 24-bit PCM original into a 16-bit/48kHz version. This still sounds very good, because even down-converted, uncompressed PCM will deliver more dynamic range and detail than a Dolby Digital soundtrack. Two hours of 16/48 7.1-channel PCM occupies 5.5GB of disc space ­ a useful capacity saving.

However, rather than opting for a lower-quality version of PCM, an alternative is to use a ‘lossless’ packaging system, either DTS-HD Master Audio or Dolby TrueHD. These work rather like zip files in home computing: they repackage the 24-bit/48kHz PCM master (or whichever quality of master is available) into less space, rather than down-converting it. All that’s required is some way of ‘unzipping’ the data file to recover the original PCM audio, which can be done inside your Blu-ray player, or, depending on the type and quality of kit you own, inside most new surround amplifiers, receivers and processors.

10   BW CT800 System Grilles Off 1 537x215 The Definitive Guide to High Definition surround sound

Using this lossless approach, a 24/48 7.1-channel PCM soundtrack packaged using Dolby TrueHD requires 4.2GB of space, meaning it occupies about half the disc space of the same soundtrack stored as uncompressed data. Clearly, that makes lossless packaging attractive for studios releasing single-layer 25GB Blu-ray discs, and even on dual-layer 50GB discs, it’s frequently used for films with long running times.

Whichever type of lossless packaging system is used, the salient point is this: the sounds you eventually hear will be bit-for-bit identical to the original studio master, and should also sound better than a down-converted 16-bit/48kHz PCM alternative.

Which lossless system sounds best? It’s frequently asked, but it’s also fundamentally irrelevant. For starters, very few discs are encoded with both forms of lossless audio, (because studios have no vested interest in doing so), so any direct comparisons between the two systems are very difficult to carry out. But just as importantly, each form of encoding system uses variable bit rates and different data algorithms, so while DTS-HD Master Audio has a nominally superior maximum audio bitrate (24.5Mbps, as against 18Mbps for Dolby TrueHD) in practice the two technologies are far harder to separate.

Whatever the theory, the key point is this: with Blu-ray, film soundtracks can sound far more dynamic and spacious than their DVD equivalents. In fact, your favourite films can sound as good as the original studio masters, which is a giant leap forward in quality for home cinema. All you need is the appropriate electronics and loudspeaker to make the most of them.

04   BW CT700 Home Theater 1a 1 537x215 The Definitive Guide to High Definition surround sound

Pulse-code modulation, sometimes referred to as Linear PCM or LPCM, is broadly used on CD, in computer audio and on Blu-ray. In the latter context, bit depths of 16, 20 and 24-bits are used, with the latter quality, sampled at 48kHz, being the most commonly employed ‘master’ standard in film production. Every Blu-ray player must support PCM as standard, although not every disc includes a standard PCM soundtrack for the reasons outlined above. In essence, its disadvantage is solely that it demands considerable space on a disc.


Dolby TrueHD

Dolby TrueHD The Definitive Guide to High Definition surround sound

One of the two key lossless audio formats (referred to as ‘codecs’) on Blu-ray. It’s an optional rather than mandatory part of the audio specification for Blu-ray, but is widely supported just the same. Supports bit-depth of up to 24 bits and  sampling rates up to 96kHz at up to eight channels (arranged as 7.1, typically), with higher sampling rates (192kHz) available for soundtracks with fewer channels of audio. The maximum encoded bit-rate is 18Mbps, although in practice most discs use much less than that.

DTS-HD Master Audio
The other key lossless audio codec on Blu-ray. It’s also optional, but it’s more widely supported (so far) than Dolby TrueHD. Supports bit-depth of up to 24 bits and sampling rates up to 96kHz for up to eight channels (arranged as 7.1, typically), with higher sampling rates (192kHz) available for soundtracks with fewer channels of audio. The maximum encoded bit-rate is 24.5Mbps, although in practice most discs use much less than that.


Dolby Digital Plus

Dolby Digital Plus 300x105 The Definitive Guide to High Definition surround sound

Rarely used on Blu-ray, this compressed audio system offers significantly better quality than standard Dolby Digital, with the potential for data rates as high as 6Mbps, although typical usages are much lower that that (around 1.5Mbps, maximum). Up to 7.1 channels of discrete audio can be included, at up to 24-bits, although more frequently 16-bit audio is used.

DTS-HD High resolution
Another relative rarity on Blu-ray, DTS-HD HR is broadly similar to Dolby Digital Plus in that it supports up to 6Mbps datastreams, up to 7.1 channels of audio and up to 24-bit data.


The Dark Knight

The Dark Knight 300x300 The Definitive Guide to High Definition surround sound

Sound Designer Richard King won the Academy Award for Sound Editing in 2009
for his work on Chris Nolan’s second Batman film ­ hear it on Blu-ray, and you’ll immediately understand why. Presented in Dolby TrueHD, this is a masterful demonstration of deft effects placement intermixed with formidable dynamics. As with all the best soundtracks, it’s not afraid to use silence as a dramatic counterpoint to volume, either.

Saving Private Ryan

saving private ryan 204x300 The Definitive Guide to High Definition surround sound

Still one of the most celebrated surround soundtracks in film history, Gary Rydstrom’s Academy Award-winning masterpiece is as intense as modern home
cinema sound gets. Deftly intermixing furious power with astonishing attention to period detail, the DTS-HD Master Audio presentation is thrilling and terrifying in equal measure.

Sherlock Holmes

Sherlock Blu ray 216x300 The Definitive Guide to High Definition surround sound
Chris Munro’s work on the DTS-HD Master Audio presentation to Holmes disproves the myth that all the best home cinema experiences rely on action sequences to deliver thrills: while it¹s blessed with considerable dynamics, the soundtrack here works just as well at modest volumes and with apparently quieter, more subtle effects: it¹s especially effective at wrapping surround information around you.


Up 243x300 The Definitive Guide to High Definition surround sound

Want a home cinema thrill your kids can enjoy, too? Try this: its DTS-HD MasterAudio soundtrack features 6.1 audio for additional rear-speaker spaciousness, and this adds considerable extra scale to the film¹s grander scenes. There’s all the low-frequency thunder you could want, too ­especially during the film’s standout thunderstorm sequence!


Avatar 214x300 The Definitive Guide to High Definition surround sound

Yes, the film that everyone went to see at the cinema is now the film that everyone¹s going to buy on Blu-ray, but with good reason: this THX-mastered disc features not a single extra, allowing almost all its 50GB capacity to be given over to delivering the best-possible sound and vision. It¹s a purist approach, but one that delivers outstanding results in DTS-HD Master Audio.

The Definitive Guide to High-Definition surround sound
Thu, 01 Jul 2010 09:57:02 GMT