An In-depth Look at Sony Technology

360° of Full Surround Sound with Only Two Front Speakers? --- That’s S-Force Front Surround!

Always Having the Best Seat at the Theater without Leaving the Comfort of Your Home

What if you could experience at home the kind of three-dimensional sound you enjoy at the theater while avoiding the clutter and hassle of wiring speakers to every corner of your room? Sony has developed the ideal solution --- S-Force Front Surround --- virtual surround technology which delivers a 360° sound experience with only right and left front speakers. How is it possible that only two front speakers can deliver sound all around and even behind? This issue of “Sony Tehnology” uncovers the secret by taking an in-depth look at S-Force Front Surround which makes the seemingly impossible an exciting reality.

What is S-Force Front Surround?

Imagine you’re at home on the couch watching a scene from an action-packed thriller where the hero is hiding in the jungle while a helicopter slowly circles overhead. Facing your TV, you hear the helicopter in front of you and then slowly the sound begins to circle behind as if you were the one hiding in the jungle! But how is this kind of three-dimensional surround sound possible with nothing more than right and left front speakers? That’s the beauty of Sony-developed virtual surround technology called “S-Force Front Surround.”

Normally with a 5.1 channel home theater system you would need to place speakers throughout your room to experience surround sound. However, the S-Force Front Surround system emulates a three-dimensional sound field naturally and realistically (as if sound were actually being projected from the blue areas as shown by the "System Concept" figure below) and yet does this using only two front speakers (as shown in red).

S-Force Front Surround is founded on two unique Sony technologies. One is an acoustic technology called “Digital Cinema Sound” designed to reproduce sound the way it is experienced in theaters and concert halls. The other is sound middleware technology called “S-Force” that Sony created for software developers developing games for the “PlayStation 2” platform so that their games would deliver dynamic, three-dimensional sound. Through this convergence, Sony created an entirely new unique virtual surround sound technology.

How Does it Work?

Sound waves reach our right and left ears separately. The brain uses this information (differences in volume, time lag between the right and left ears, and changes in sound waves) to correlate the location of the sound source and its relative distance. The “head-related transfer function” (HRTF) is a database expressing the difference in sound wave spectrum and arrival time at each ear. S-Force Surround mimics the way the brain correlates the source of a sound by virtually recreating the source using reverse logic. In other words, HRTF is used as the basis for precise Digital Signal Processing (DSP) to create proper volume, sound time lag and sound wave spectrum to deliver (with only two front speakers) an audio experience which, to the listener, seems to emanate from various locations throughout a room.

What Makes S-Force Front Surround Unique?

Indirect Sound Characteristics are Digitally Packaged Within Direct Sound, Giving Listeners Full Surround Without the Unnatural Feel

While there are numerous virtual surround products on the market, many of these rely on the ability to bounce sound off surrounding walls to create a virtual surround effect. S-Force Front Surround, however, does not rely on bouncing sound off walls. With S-Force Front Surround, the sound coming directly from the two front speakers alone creates a three-dimensional sound field. Another key to Sony’s unique DSP technology is that indirect sound characteristics are digitally packaged within direct sound, giving listeners full surround sound without the unnatural feel typically experienced with conventional virtual surround systems, thus enabling listeners to enjoy natural, truly immersive full surround sound. Typically, the physical shape of a room and related options for positioning speakers place limitations on the user. However, S-Force Front Surround opens up a world of new possibilities making it easy for anyone to enjoy the true excitement of home theater.
HRTF Data Compiled by Measuring Over 10,000 Points

S-Force Front Surround technology is founded on the “head-related transfer function” (HRTF) and in developing this technology Sony independently compiled its own HRTF data. To compile data, the upper body of a mannequin was constructed using human head and chest measurements to create a composite. Each ear of this mannequin was fitted with a highly sensitive microphone. The mannequin was then placed inside an anechoic chamber (an echoless room) and used to measure, at over 10,000 points, changes in both the position of the sound source and sound wave spectrum. This data was then combined with Sony’s rich storehouse of movie theater and concert hall acoustic data. This ultimately led to the development of a new surround algorithm providing the basis for a sound experience which completely envelops the listener.

The image is of the mannequin used for sampling sound data in movie theaters and theatrical venues in creating Digital Cinema Sound. This same type of mannequin was also used for sampling within an anechoic chamber (as mentioned above) in developing S-Force Front Surround. The size of the mannequin’s head, position of the ears and body shape represent the human average. It can be horizontally rotated 360° and can be vertically tilted up to 90° enabling the mannequin to sample sound from numerous angles.

Ideal Listening Position

Listening position is important in taking full advantage of S-Force Front Surround’s virtual surround experience. The ideal position is for the listener to face the right and left front speakers (which should separated more than 60cm apart from one another) so that the listener approximates an isosceles triangle by sitting at the apex --- enabling them to fully enjoy the excitement of virtual surround sound.

Products Featuring S-Force Front Surround

As part of efforts to enhance differentiation, S-Force Front Surround is finding its way into an increasing number of Sony products. (Please note that the following information is specific to the Japanese market)

-----This article has been translated as it originally appeared in the March 2006 issue of "Sony Family"-----

Copyright 2006 Sony Corporation. All rights reserved.