Surround sound

Surround sound is a sophisticated audio technique used to increase the depth and fidelity of sound. It works by using multiple audio channels played through an array of loudspeakers. These speakers are positioned to encircle the listener, known as the surround channels. This setup creates a sensation of sound moving in any horizontal direction around the person. The goal is to enhance sound spatialization, which is the way we perceive the location of audio.

This relies on sound localization, the human ability to identify the direction and distance of a sound source.

To achieve this effect, engineers use many discrete audio channels. Most systems have a specific listening area called a sweet spot. At this location, the audio effects work most effectively for the listener. The system presents a fixed or forward perspective of the sound field to the person in that spot.

By routing different sounds to different speakers, the technology can make a listener feel like they are inside the environment. This transforms a simple recording into a three-dimensional experience.

One of the most common setups is the ITU 5.1 standard. This configuration requires six specific components to function. It includes a center channel (C) placed directly in front of the listener. There are also left (L) and right (R) speakers positioned at 60-degree angles. Two surround speakers, left (LS) and right (RS), are placed at angles between 100 and 120 degrees.

Finally, a subwoofer is used for low-frequency effects, and its exact position is not critical.

More complex systems, like 7.1, add two more rear speakers to create a 360-degree sound field.

The history of this technology is filled with experimental breakthroughs. The first documented use was in 1940 for Disney's film Fantasia. Walt Disney used a system called Fantasound to make a bumblebee sound as if it were flying around the theater. This early system used about 54 loudspeakers to diffuse sound.

In 1967, the rock group Pink Floyd performed the first surround sound concert at London's Queen Elizabeth Hall. They used a custom quadraphonic speaker system and a control device called the Azimuth Co-ordinator. This device is now part of the collections at the Victoria and Albert Museum.

Engineers use several different methods to create these immersive environments. One way is through specific recording techniques, such as using an augmented Decca tree. Another approach uses psychoacoustic methods to simulate a 2-D sound field using headphones. Some advanced systems use Huygens' principle to reconstruct sound wavefronts, creating an "audio hologram."

One version of this is wave field synthesis, or WFS, which requires many speakers and high computing power. Another common method is Ambisonics, which is widely used by musicians and in computer music. Ambisonics provides an exact sound reconstruction at the central listening point.

Surround sound is applied across many different industries and media types. In cinema, formats like Dolby Digital and DTS are standard. High-definition media like Blu-ray use lossless audio, such as Dolby TrueHD, to match the studio master.

Beyond movies, it is used in video games and personal computers to create synthetic noises that react to the user. It is even used in museums to enhance exhibits with ambient sounds like birds or machines. In the military, these techniques can help improve situational awareness for public safety.

Finally, surround sound allows for new forms of artistic expression in music. While quadraphonic audio failed in the 1970s, multichannel music returned in 1999 through formats like SACD and DVD-Audio. Some modern devices even use digital signal processors to perform "upmixing." This process takes a standard stereo recording and uses software to parse individual sounds into a five-channel field. This allows older music to be experienced in a more modern, spatial way.