Speaker Buyer's Guide

by Jim Warren on September 11, 2000 12:00 PM EST

·         Surround sound: Multiple companies have developed methods to create surround sound, or the conceptive of creating an immersive environment of sound that lends both direction and positioning to the audio image.  Dolby* Laboratories has developed many of the various surround technologies used in home theatre that are now making their way into the computer realm.  In addition, Creative Labs has offered its own technology called EAX.  Surround sound technology heightens the gaming environment as designers have grasped this new creative freedom to prey on another of our senses with positional audio.  The introduction of surround sound technology to computers has also continued to merge our home theatre systems with our home computer.  Keep in mind that surround sound can only be produced off of encoded signals; however, any stereo source will play through the front stereo speakers without any problems.  Even for those that don’t choose a surround sound system, any Dolby encoded audio source will always play back over the most basic stereo system without problems, even without a decoder.

o       Dolby Surround:  The first surround technology developed based on commercial theatre system.  It consists of the playback of three channels—stereo left and right and a mono surround channel with a limited frequency response that would feed speakers behind the listener.  This was the first Dolby format available to the consumer that allowed for the playback of Dolby encoding used for cinematic playback years before.  It allows access to three of the four cinematic channels encoded in the stereo signal; it does not produce the center channel for vocal reproduction that is localized to the source.

o       Dolby Surround Prologic: The next step in the Dolby evolution was to access the center channel in cinematic surround sound.  The consumer gained this access with Dolby Prologic, which provided the stereo left and right, mono surrounds, and mono center channel.  The advantage of the center channel is that vocal frequencies are reproduced in a speaker ideally placed at the visual source, localizing the vocals in a movie to the actual faces on the screen.  The Prologic design is based in processing that “steers” the sound to the center channel if it falls within the vocal frequency range and it is present in both the left and right front channels.  However, most computing speaker systems are setup around a near field listening system—that is, the speakers are already close to the listener as well as the visual source.  So the directivity issues that Pro Logic addresses in larger systems with separated speakers is rather not an issue at the computing station.  Though if the computer were going to be used by multiple people by at once, the center channel could be useful as the sweet spot between the speakers can not be shared by all viewers/listeners.

o       Dolby Digital: This technology is centered around the 5.1 Surround standard.  It consists of six discrete channels- stereo left and right front, stereo left and right surrounds, center channel, and the low frequency channel.  The low frequency channel is the “.1” channel-- it requires one tenth of the bandwidth of the other channels because it is only reproducing one tenth of the frequencies of a full range channel.  The other 5 channels are all full range channels that allow for extensive creative use.  They combine to place the sound in a three dimensional environment around the listener.  The low frequency channel feeds a sub woofer that provides the rumble to complete the viewing experience.

o       Dolby Virtual Surround or Dolby Multimedia Surround:  This approach to surround sound is based in psychoacoustical processing.  Basically, the theory is that if an individual with two ears (sound sources) can accurately place where a sound is coming from, than there should be an algorithm that allows two speakers (again, sound sources) to create a three dimensional sound image.  Loading a speaker with directional drivers and shooting sound in more than one direction combined with electronic processing creates the surround image from only two speakers sitting on the desktop. However, the sweet spot, or ideal listening zone, is smaller due to the nature of the processing.

o       A3D:  Aureal’s role in the computer surround sound market comes under their product name A3D.  Based in the processing concepts used in virtual surround sound, A3D serves as a 3D sound solution based in either a two, or with A3D 2.0, a four speaker setup. However, A3D recommends using headphones to take full advantage of the spatialization effects.  This makes sense under the theory of virtual surround sound—two point sources close to the ears should be just liking reproducing what the ears would hear in a 3D environment.  Processing algorithms give the audio a position within a three dimensional listening field by computing how the sound would react to its surroundings.  A3D 1.0 established these hardware based algorithms; the newer 2.0 standard added on some features such as environmental audio, occlusions, and reflections.  Occlusions are how a sound is perceived when passed through a surface (closed window or brick wall) while reflections calculate how the sound is perceived as bouncing off of such surfaces.  The 2.0 standard also includes wavetracing; the graphics data describing the environment (the picture of the walls) is used to realistically calculate how that room would sound.  This data is taken directly from the data sent to the graphics card.  The A3D processing technique is based in the sound card, and requires some processing time, which may result in a performance hit.  However, this internal processing sends out the audio signal to any speakers connected to them, creating the 3D audio environment.

o       Creative Labs EAX:  EAX, or Environmental Audio Extensions, is based on algorithms developed by Creative Labs that have been implemented in their sound cards, speakers systems, and their Personal Digital Entertainment (PDE) products.  It is based in a 4.1 surround sound concept, absent the center channel for vocal range directivity.  It also is based on the concept of environmental audio, or standard processing algorithm designed to make sound characteristic of an environment.  Gaming manufacturers use the capabilities to add environmental audio to their games, such as an underwater or arena effect, through programming control over processing done by the sound card.  The user can also customize and apply these environments.  As a standard designed more for the PC gaming industry, it is geared towards computer multimedia in a near field listening situation.  The speaker format that supports this standard is based in stereo front and rear channels, as well as an added subwoofer.

Speaker Formats: From simple to surround sound Final Words
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