Surround sound

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					                                                                       Sunday, May 13, 2007
Presentation for the subject A2L:
Surround sound
Surround sound is a concept of adding additional channels to the sound stream. These
channels are reproduced by multiple speakers and create a three-dimensional sound
experience.

Surround sound systems have been developed in early 70’s after the era of dominating
stereophonic systems. Surround systems appeared first in cinemas. With the introduction of
DVD-Video format in 90’s, everyone could buy and use own home theatre with surround
sound. Today surround sound is widely used in computer games for better gaming experience.

There are two main methods to create a surround sound. Most common solution is placing
multiple speakers around the listener and sounds are coming from every direction.
But surround sound can also be created only with stereo speakers using the psychoacustic
method. The principle of this is that the sound is reproduced twice but with the different
volume, phaseshift and amplitude. That can “confuse” a brain and it seems that for example a
gunshot happened behind the listener. The problem of this method is that you have to know
the position of the listener to calculate neccesary modification of the signal. This method is
used mainly in stereophonic headphones.

In home theatres, most popular is 5.1 speaker configuration. It’s quite cheap and the 3D
experience is satisfactory. When you watch a movie, two front speakers is used mainly for
music, one center speaker for dialogs, one subwoofer for low-frequency sounds and two rear
speakers for other sounds and effects.

Nowadays there are many formats to encode a surround sound. I have prepared a short
summary about them:
Dolby Surround is older surround format. It encodes 5 channels to the stereophonic signal,
so it supports only 4.1 speaker configuration.
Dolby Pro Logic II is an upgrade of Dolby Surround. It encodes 6 channels so it can be used
in modern home theathers. This system is used in analog TV broadcasting which supports
only stereophonic sound.
Dolby Digital is the most common format of surround sound because it is a native format for
DVD-Video. Every DVD has a sound in Dolby Digital and other formats are just optional. It
supports lot of configurations; bitrate is 448 kb/s in 5.1 configuration. It uses a compression
similar to MP3.
DTS is an optional format for DVD. It uses less of compression and sound experience is
better. But the cost is a high bitrate and high size of audio files. It is almost impossible to
recognize the difference between DTS and Dolby Digital played on the normal home theather.
Dolby Digital Surround Ex and DTS Extended Surround are new formats for even better
360° audio experience. It is used mainly for 6.1 speaker configurations and higher. THX
format is created for ultimate cinema surround experience.

                                                                         Author: David Vavra