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?

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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.

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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.


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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.

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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.

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HIGH-DEFINITION AUDIO FORMATS
Uncompressed:

PCM
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.

Lossless:

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.

Lossy:

Dolby Digital Plus

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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.

TOP FIVE AUDIO SCENES ON FILM:

The Dark Knight

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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

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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

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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

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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

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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
SusannaGrant
Thu, 01 Jul 2010 09:57:02 GMT

Jun 212010
 

Sign me up!

IMG 1205 300x225 The Future of Surround Sound from MIT

The Opera of the Future group is an MIT Media Lab Research Group led by Society of Sound Fellow Tod Machover. It explores concepts and techniques to help advance the future of musical composition, performance, learning, and expression. Through the design of new interfaces for both professional virtuosi and amateur music-lovers, the development of new techniques for interpreting and mapping expressive gesture, and the application of these technologies to innovative compositions and experiences, the group seeks to enhance music as a performance art, and to develop its transformative power as counterpoint to our everyday lives. The scope of our research includes musical instrument design, concepts for new performance spaces, interactive touring and permanent installations, and “music toys.” It ranges from extensions of traditional forms to radical departures, such as the Brain Opera, Toy Symphony and Death and the Powers.

Ambisonics is one of its current research projects, and here Ben Bloomberg explains a concept that could very well be the future of surround sound….

Ambisonics

Anyone who has gone through the process of designing a home theater understands the difficulties associated with locating speakers. Unless the theater is designed and built from the ground up, it is seldom possible to put speakers in perfectly ideal positions. Ambisonic encoding provides an abstraction layer, which allows one to place speakers independently of sound. It is an elegant method of representing audio such that the locations of ‘virtual sources’ are represented in the most accurate way given any possible speaker configuration.

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At Opera of the Future, we strive to create spectacular next generation live performance systems that are realistically usable in harsh environments such as touring productions. Systems must be flexible enough to fit into any venue, ranging from small offices to concert halls, and extremely simple to setup and configure. Using Ambisonic encoding, it is possible to arrive at a venue, place surround sound speakers wherever it is most convenient and have a fantastic, consistent surround sound field.

Although Ambisonic encoding is a well-known technique for reproducing pre-recorded content, it is not often used as live tool because latency associated with encoding and decoding is too great. For our latest production, Death and the Powers, we have developed an AppleCoreAudio AudioUnit DSP engine, which is capable of processing 128 channels of ambisonics at a staggering 32 samples of delay. This allows us to take ambisonics to new heights in live entertainment and sound reinforcement.

Existing theatrical surround sound processors cost upwards of $120,000. This system can run on hardware ranging from a small FPGA-based 8-channel system ($60) to a 128 channel MacPro based system ($5,000). It can be automated using industry standard OSC and uses any CoreAudio compatible audio interface for audio I/O.

How does it work?

Ambisonic encoding uses 3rd order spherical harmonics to represent virtual sources with 16 directional coordinates that function equivalently to X, Y and Z coordinates. Using a 16 axes, instead of 3, to specify the location of a virtual source allows greater “perceived resolution” in the surround sound field. Thus adding more speakers can produce a more detailed result rather than a ‘blurrier’ field.

Bowers & Wilkins to the Rescue!

We have been developing ambisonic systems at Opera of the Future for 3 years now. Until the present, we were unable to find a speaker that was small enough and sufficiently detailed to justify use in large quantities for testing in our lab and studios. It should be mentioned that we spend our days using our 800D and 805s speakers in the studio for production work, so we were extremely picky when it came to finding a speaker that would work well for our large-scale ambisonic tests.

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Just when production for Death and the Powers was beginning to reach its peak, Bowers & Wilkins introduced us to the M-1, a four inch speaker with a one inch aluminum nautilus tweeter. Needless to say, it seemed like the perfect speaker for us to use. In a flurry of emails and phone calls, we managed to obtain 24(!) of them for some testing and experimentation.

The results could not be more positive. After some time testing and tweaking decoder weightings and crossover points, we found that paired with two of our 800Dʼs and an ASW-855 subwoofer, the system sounds incredible!

The first debut of the system was during the open house for the grand opening of our new building, but it has since been the centerpiece of many demos, including one for Gustavo Dudamel, conductor of the LA Philharmonic.

The System

The DSP rig consists of a MacPro loaded with AULab and MOTU Digital Performer running in real-time mode (a fantastic resource) and a MADI-based Solid State Logic 128 Channel PCI- express card. The system clock is generated on board a separate SSL AlphaLink SX and sent over MADI fibre-optic cable to the computer. The DSP runs at 96Khz and the converters are 24-bit.

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The M-1s are spaced evenly at 15 degree increments with two 800Ds in front at 30 degrees and an ASW-855 Subwoofer in the rear. The M-1s have a 1st order high pass filter at 140Hz and the subwoofer is crossed over at 100Hz and 180 degrees out of phase. The 800Ds run full range.

System Specs:

MacPro 8-core 2.26Ghz w/6GB RAM SSL MadiXtreme128 SSL Alpha-link MADI SX MOTU Digital Performer 7.1

Apple AULab 2.1 (19) B&W M1 Speakers (2) B&W 800D Speakers (1) B&W ASW-855 Subwoofer (2) Rotel 1512 Amplifier (2) Rotel 1091 Amplifier.

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Whatʼs next?

The M-1s will play an important role in Death and the Powers as part of a 128 channel surround-sound system! Stay tuned for more information on the design and implementation of that system.

Ben Bloomberg is an undergraduate at the Massachusetts Institute of Technology who has been obsessed with audio since age 9. Currently he designs surround sound infrastructure for live entertainment at the Media Lab. His systems have been featured internationally in productions such as the world premier of Tod Machover’s Skellig, and more recently, Death and the Powers at the American Repertory Theater in Cambridge, Massachusetts.

Death and the Powers will premier for the public at the Salle Garnier Opera House in Monaco on September 24, 2010, and then tour to the United States in the spring of 2011. For more information on the production, visit http://powers.media.mit.edu.

The Future of Surround Sound from MIT
SusannaGrant
Wed, 19 May 2010 14:54:46 GMT