Smyth Research Virtual Surround Technology


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SVS Headphones

Originally conceived by Drs. Michael and Stephen Smyth of Smyth Research of Camarillo, CA as a home theatre adjunct, the Smyth Virtual Surround™ or SVS™ 6.1 Headphone Processor received considerable attention and interest from many pro audio mavens at a recent CES show.

What Is It?
Smyth Virtual Surround replicates the sound of up to an eight-channel surround sound speaker system over any pair of stereo headphones. This is not like Lake Technology's Dolby-licensed headphones or any other systems with multiple drivers and/or attendant electronic matrices. The Smyth Virtual Surround system accomplishes this feat in an extremely accurate, scientific and natural manner that yields satisfying and realistic results. It's especially impressive when you consider that it works in any small room with any existing system and without expensive, complicated equipment and/or intricate setup procedures.

I found the system completely 'fooled' me. Apart from the headphones having a little more super high frequency content than the speakers and obviously knowing when the phones were on or off, I would be hard pressed to tell any differences. The sound in the phones was just like the sound of the speakers. The phones' sound had the same 'distance' (from me to the speakers), the same localization cues and image size, same volume (adjustable of course), and an overall identical presentation and feeling of sonic immersion. I sampled DVD movies with 5.1 surround soundtracks, DTS discs and even stereo CDs without adjusting or reconfiguring anything but the volume control. All sources perfectly translated back and forth from phones to speakers. Regular stereo recordings, especially classically recorded orchestras, sounded unbelievably realistic and expansive on the SVS-realized phones!

The first step in setting up SVS is for the listener to be measured. All people hear differently and all playback/speaker systems produce sound differently in different rooms. Measurement is an automated process and takes about two minutes. No special training is required and anybody can accomplish it--even to himself or herself.

Whilst sitting comfortably in the "sweet" spot of a 6.1 surround speaker array (or 5.1 or 7.1), both of my ear canals were fitted with microphones encased in foam--much like earplugs. The microphones were very small electret condenser models and were connected to the SVS unit. Placed as deep as possible to include the shape and influence of both the canals and pinnas of my ears, the microphones are aimed outward.

SVS Blcok

While I kept my head still and aimed forward towards the center-channel speaker, each speaker/channel of the system was swept separately with a tone that went from 20Hz to 20kHz. I was measured again while turning my head towards the left speaker and again when aimed towards the right speaker. Afterwards, with the mics still in my ears, a pair of Stax SR-202 Basic electrostatic 'earspeakers' were placed on my head and also swept to record their response curves.

Using all these measurements, the SVS unit generates datum--a digital profile that contains binaural room impulse response information, my hearing curves, the response of the entire surround sound reproduction system including the receiver/power amp signal chains, and the Stax's response.

This digital profile or "personalization" information is stored as a single digital file of about 1MB size and the files of eight different listeners can be held in memory with any number of additional personalizations off-loaded and recalled to/from a SD memory card plugged into the SVS unit.

Once this information is obtained, it is used in a special, patent-pending "audio virtualizing" algorithm running inside the SVS unit that conforms a conventional input audio signal--be it 5.1, 6.1 or 7.1 or stereo format to sound the same over the measured headphones as if it was played on those speakers, in that room, to my ears.

Currently, the consumer SVS model can simultaneously feed two different users each with their own unique, personalization. This makes it possible for each person to wear their own phones and always be in the perfect "sweet spot". Originally designed for small rooms or home living spaces, plans are already underway to scale up the SVS's computation/storage power to enable measurement of larger rooms such as studio control mix rooms, theatres, dubbing stages or auditoriums.

Head Tracking
Although not directly part of the SVS technology or required for using it, headphone head tracking makes the whole experience even more accurate and realistic. The Smyth Personalized Head-Tracking™ (SPHT™) system starts at the top of the pair of the headphones where an infrared optical head-tracker module is mounted. It links to a positional reference transmitter center-mounted on top of the HD-TV theatre screen. This system locates and tracks my head position at all times.

SVS Tracker For purposes of my demo, a special extra tracking feature was added. If I took off the phones, the speaker system automatically unmuted and allowed me to instantly A/B the sound of the speakers to the phones. The phones became active when I put them back on and the speakers muted.

With the phones on and just like when listening to loudspeakers in a room, because of head tracking if I turn my head towards the left or right speakers the sound coming from the center speaker channel stayed locked to that position while the channel I'm aimed at grew in focus. This is not a subtle sensation--it sounds the same as if you were listening to a surround speaker system and moved your head off-center.

Pro Audio Utilization
What started as a way for home theatre owners to watch movies in true 5.1 surround sound at realistic volumes without breaking their leases or disturbing others, the Smyth Virtual Surround Technology has the potential to become a valuable tool for pro audio work.

One of the struggles in film post-production audio work is the marrying of 5.1 music, effects and dialog created, edited and processed on workstations in small rooms to match in size, ambience, EQ, relative volume etc. to what the director and mixer demand to match picture on the much larger dubbing stage. The SVS system could solve this dilemma by measuring the small room workstation operators at the mix position on the dubbing stage. Once measured and back in their small rooms and over a SVS personalized headphone system, they could hear and adjust their elements to sound correct before the mixer ever hears them.

What About the .1?
Michael Smyth reports: "Normally we would simply consider the subwoofer as a separate channel, and run a test signal through it as any other channel. However it's also possible to simply feed the subwoofer into the main left and right channels, which would be virtualized anyway. A third approach that we have tested is to use a 'butt-kicker type' device running off the subwoofer. This would be set to give a somewhat similar tactile sensation that a real subwoofer would generate. However, we have found that the low-frequency performance of the Stax headphones is excellent, and few people ever mention the lack of low-end during the demos."

In music recording, a producer or engineer could bring to the mix room his personalization file measured on his favorite home listening system and hear his mixes on headphones as if he were in his own environment. Conversely, a personalization measurement could be made at the studio and taken home where you could enjoy the same sound as the studio and its control room monitor speakers. For surround mixing, the producer and mixer could have the same sweet spot no matter where they sit in the actual mix room.

Since the SVS conveys surround sound using only two channels, personal stereo gear like an iPod (or any stereo system) could benefit from SVS. Full 5.1 surround sound could be heard and, if you're lucky enough to be measured in a superb surround mix room complete with multi-thousand dollar monitor system, you'll get the same sound as the mixer and producer heard when mixing.

Although still a home theatre unit you can buy now, I would envision a pro version to store many personalizations; have full +4dBm analog and AES/EBU digital I/O; at least 96kHz/24-bit support; and many head tracking options. Smyth Research LLC at 1270 Avenida Acaso Unit A, Camarillo, CA. 93012. 805-482-5630 or

Barry Rudolph is an L.A.-based recording engineer. Visit his Web site at:

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