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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.

IMG 1208 300x225 The Future of Surround Sound from MIT

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.

IMG 12041 225x300 The Future of Surround Sound from MIT

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.

IMG 1209 225x300 The Future of Surround Sound from MIT

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