Introduction
In the first segment of Understanding Computer Audio, we looked at the basics of digital audio and some of specifications and standards users may see when looking at a computer system or audio peripherals. For Part II in the series, we look into the mysteries and complexities of surround sound and how it relates to computer audio.
Surround Sound Basics
The earliest form of surround sound came when audio was moved from a single channel source to stereophonic recordings. Later surround sound standards were developed by the movie industry to allow for a more immersive experience. Of course, the level of immersion by the listener is very dependent upon the number of speakers used and the number of channels in the surround sound encoding.
The most basic of surround sound configurations consists of at least four speakers. Two speakers are in front of the user and two behind. This gives the spatial appearance of audio in front of and behind the listener. Most modern systems also use a fifth speaker directly in front of the listener. This is typically used for dialog during movies to give the listener the sense that the dialogue is coming directly from the screen. Another common element in surround sound is a subwoofer. This is a large speaker that only puts out low frequency or bass audio that is non-directional. This also can give the loud booming effect.
The speaker layouts are denoted in a very specific manner when referring to surround sound. Typically it will be in the form of a dotted notation such as 5.1. The first number represents the number of distinct full range audio channels or speakers. The number after the dot represents the presence of a low frequency effect (LFE) or subwoofer channel.
Surround Standards
There are a variety of surround standards that have been developed over the years by the movie industry and are supported by computer audio processors for delivering surround sound. For those interested in surround sound with their computer system, the support for these different standards may be very important.
Dolby Pro Logic is a simple form of surround sound. This is actually a two-channel source that has encoding for certain frequencies to be played in a set of rear speakers. This allows the Dolby Pro Logic stream to be compatible with two speaker systems or to utilize a second set of rear speakers for a more immersive experience. A newer version called Dolby Pro Logic II was developed recently, but it is not very common.
AC-3 or Dolby Digital was developed by Dolby Labs as one of the first truly digital forms of surround sound for movies. It features 5 discrete channels (2 front, 2 rear, 1 center) plus a low-frequency effects channel. The primary benefit of this format is that it uses compression to take all this data and fit it in a very compact format with very little loss in quality. In order to playback sources with Dolby Digital (such as DVD movies), the computer audio processor will need to support this as well as have 5 speakers plus subwoofer. Audio processors require at least 16-bit 96KHz processing ability for true Dolby Digital.
DTS or Digital Theater Systems was a competing standard to Dolby Digital for 5.1 surround sound for movies. It also has five distinct speakers (2 front, 2 read, 1 center) plus a subwoofer. It uses a different encoding scheme than Dolby Digital that provides less loss in audio quality but at a larger audio stream. A newer standard called DTS-ES was recently released that supports a 6.1 speaker configurations and is backward compatible with the DTS 5.1 equipment.
Direct3D is an audio standard that is used by the Microsoft DirectX engines for generating 3D positional sound from the computer system. This is primary used in computer games to simulate the 3D environments that players are traveling through. This is not necessarily an encoding format more than a set of software standards that allows for the hardware manufacturers. It can support anything from two speaker configurations all the way up to 7.1 and 8.1 speaker configurations as long as the software programs will render the audio to that number of speakers.
Do You Need Surround?
For the majority of consumers, the answer to this question is no. Unless the computer is going to be used to watch movies or play 3D video games, the extra cost is not justified. Also, the environment that many computers exist in is not very conducive to listening to music or movies. The fans used for cooling the components of the computer will generally cause background noise that disrupts the listening experience.
For those who do plan on watching movies in surround sound or playing video games, it is generally best to make sure that the sound solutions you purchase fully support the Dolby Digital, DTS and Direct3D standards. This will ensure that whatever media you are likely to playback on your computer will work properly for surround sound.
