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How Surround Sound Works?

written by: M.S. Smith•edited by: Lamar Stonecypher•updated: 7/14/2009

Surround sound greatly increases the depth of any film, be it in a home theater or at the movies. Creating the stunning audio effects associated with surround sound requires some interesting technology. This intro to surround sound breaks down what it is and how it works.

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    It's Everywhere

    We've all experienced the sudden sense of euphoria and excitement that can come from a great surround sound system. Suddenly reality seems suspended and a new world seems to drop into place. The senses of sight and sound come together to overwhelm the brain, tricking it into momentarily thinking that the theater may have come crashing down, replaced by the scene playing out in front of the audience. Achieving full suspension of disbelief is difficult without surround sound as even the most realistic and detailed audio recording can seem flat and distant if played through an old-fashioned two-speaker setup, and the recreation of theater-quality surround sound is a goal which many home theater enthusiasts pursue with open wallets.

    But how does surround sound work? It seems like a simple enough question, as one would (correctly) assume that surround sound systems operate by surrounding the audience with multiple sources of audio. This is basically true, but there is much more at work. The best surround systems are technological works of art, and the experience they create goes beyond simply placing a few speakers in a circle around an audience.

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    The Basics

    Surround Sound systems direct sound from multiple sources A person listening to a standard stereo is hearing a multi-channel recording which is created (ideally) by placing two different microphones in a recording area to replicate two human ears. This is a decent form of recording for music in particular, as the concert experience tends to focus on facing towards on specific area in a large venue. For movies, however, stereo sound cannot suspend disbelief and trick the audience into feeling the sounds are real. In life, after all, sounds come from all directions. Stereo sound is flat and vague in comparison.

    As one might expect, recording surround sound is simply an extension of the stereo concept. Rather than trying to replicate human ears, however, special surround sound recording equipment is used to record a full range of sounds coming from numerous different areas. This is an effective method recording for certain kinds of music such as symphonies taking place in a concert hall. In such a venue the acoustics of the concert hall are extremely important, and recreating the experience requires the ability to record more than the sounds coming straight from the stage. Of course, in today's age of digital media, the idea of recording a movie and presenting it in surround sound by simply using some sort of specialized microphone is fairly quaint. This is particularly true in films that use a lot of CGI or animated elements. There is, of course, no Optimus Prime and so no Optimus Prime sounds to record.

    In either the case of a surround sound recorded using a special microphone or fabricated in a sound studio, all surround sound is delivered through the use of channels. Each channel consists of audio that can be mapped to a specific speaker or set of speakers. A stereo set up is usually two-channel because each speaker can deliver different sound than the other. A 5.1 channel system has left and right speakers in the front and rear and one center front speaker. The .1 stands for the Low Frequency Effects channel, a channel which is developed to deal with sub-bass effects. This channel is not dedicated to any particular speaker.

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    How Surround Sound Works: Channels and Other DetailsSurround Sound is a complex technology, but understanding how surround sound works only requires knowing a few key points. Channels, for example, a very important concept to understand how surround sound functions. Each channel represent a different audio stream with a specific surround sound speaker placement. Having more channels allows for different audio to come from different speakers. However, the number of channels a surround sound system supports is NOT the only mark of its quality.
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    Channels Tell (Almost) All

    This surround sound system could provide 7.1 channel sound, but it may provide less Channels are the building block of all surround sound systems. Once they make sense, most any surround sound system should make sense. Adding more channels means adding more speakers. That said, it should be noted that while home theaters often follow a one-channel, one-speaker format, many theaters do not. They will instead use multiple channels with multiple speakers. An old theater might simply have a 4-channel system with one channel for the left front speakers, one for the right front speakers, one for the center, and one for all of the speakers in the rear and the sides of the theater.

    This does mean that the number of channels, perhaps the most touted statistic for audio systems both in home and movie theaters, can be somewhat deceiving as to the quality, quantity, and volume of the overall arrangement. A 5.1 surround system at home and a 5.1 surround system in a theater are likely going to sound much different and have far different capabilities. Understanding the channel is important, but it unfortunately does not indicate anything about the physical layout of the surround sound system, and there is no firm standard available at this time. Monikers like Dolby TrueHD and DTS-HD are supposed to describe certain kinds of arrangements and equipment, but there is no way to prevent a user from deviating from the standards.

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    Beyond Speaker and Subwoofers

    An important and often forgotten aspect of surround sound is that it ultimately requires the cooperation of the media and the physical devices producing the sound. The media itself is the source, and it can be anything from an MP3 file to a Blu-Ray movie. The kinds of media available are massive, and many of them are limited in terms of the audio quality they can produce. For example, the popular (if now outdated) MPEG-2 video standard supports encoding up to 5.1 channels, but no more. MP3s are usually restricted to two channels. Blu-Ray, on the other hand, can support up to 8 channels.

    What this means is that the source of the audio is often just as important as the system it is played on. Although some more expensive receivers and other forms of audio equipment provide features to try and simulate extra channels in audio which do not support encoding all of the channels an expensive home theater system is capable of handling, it is by and large not possible to get the most out of an 8.1 sound system without playing some form of high-definition media.

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    Recommended Sound Systems

    Surround sound is a great addition to any home theater. It goes a long ways towards recreating the true movie theater experience. In addition, those theaters which are new enough to use latest sound equipment can produce some ear-popping sound effects. There is more to surround sound then is listed here, but this brief tutorial lists all of the basics. Those looking for advice on good surround sound systems for their home would be wise to check out our recommended surround sound systems.