Glossary of Home Theatre Terms
Anamorphically Squeezed This process, which is used on few laserdiscs, a few DVDs and even fewer TV broadcasts, is used to achieve a widescreen image, where the image is considerably wider than standard NTSC fare, once it is 'unsqueezed'. The wider image is squeezed into the skinnier aspect ratio, which is usually the NTSC standard of 4:3/1.33:1. Unsqueezing can be done with a 'stretching circuits' in the TV. The end result (if left unsqueezed) is a picture with really skinny objects. Another option which has less detail, but is more widely used is letterboxing the picture. Related: Common Aspect Ratios
Aspect Ratio This describes the width of a picture to the height. The NTSC standard is 4:3. The current HDTV standard is 16:9, or 1.78:1. Modern movies range from 1.66:1 to 2.4:1. By far the most common are 1.85:1 and 2.35:1. Related: Common Aspect Ratios.
Bipole Speakers One type of surround speaker. In this instance two or more drivers are facing different directions, and their cones vibrate in phase. This causes an omni-directional sound.
Channel Leakage This occurs with matrix-surround encoded material. What happens is that sound meant to be heard from one channel is also heard from another channel. Solved with new 5.1-channel Dolby Digital and 6-channel DTS sound systems by virtue of a discrete channel sound system.
CRT Projector One type of front projector. It consists of three tubes each putting out one color: red, green, and blue. They offer brightness and detail, but are difficult to setup, and convergence is required about two times a year. Related: Front Projection Info
Digital Light Processor(DLP) Used to control Digital Micromirror Devices (DMD's) in order to make an extremely bright sharp pictures. May control one or three DMD's. Related: Front Projection Info
Digital Micromirror Device (DMD) A mirror that is very small (micromirror) that can be kept as is or tilted x amount of degrees (45?) in order to reflect light. As such, it is either on or off. It can be turned on and off at various rates per second to achieve different levels of brightness. Commonly used together to form micromirror "wafers" and are controlled by a Digital Light Processor (DLP). Related: Front Projection Info
Digital Verstaile Disc (DVD) Previously known as Digital Video Disc, this represents the latest in home theater. It is a purely digital format use MPEG-1 and/or MPEG-2 compression. This may result in artifacts such as pixellation. The format is also has the ability to have multiple aspect ratios, several different versions of a movie with several different captions as well as Dolby Digital sound. Each disc consists of two layers so that when the end of one layer is reached, the laser beam focuses down to the next layer for a seamless layer change. Be sure to see the article on DVD's for more information.
Digital Theater Systems (DTS) An 8-channel sound format used in commercial movie theaters. Only 6 are used, and the sound is run off CD's. The supposed followup for home theater is DTS Coherent Acoustics.
Dipole Speakers One type of surround speaker. In this instance two or more drivers are facing different directions (most commonly and by definition 180 degrees) and their cones are vibrating out-of-phase. This causes nulling out of the sound by the viewing area which forms a "figure-8" sound field.
Dolby AC-3 The old name for the most popular 5.1-channel home theater sound system. Is now called Dolby Digital. Consists of front left/right speakers, a center speaker, left/right surrounds, and a Low Frequency Effects (LFE) channel, usually used with a subwoofer.
Dolby Digital 1 - The new name for the most popular 5.1-channel home theater sound system. Used to be called Dolby AC-3. Consists of front left/right speakers, a center speaker, left/right surrounds, and a Low Frequency Effects (LFE) channel, usually used with a subwoofer. 2 - A 5.1-channel sound system used in some commercial movie theaters in which the sound is placed in between the sprockets on the film.
Dolby Digital Surround EX 1 - Dolby's latest surround format. It is essentially Dolby Digital with an added center rear channel. Some would call this setup a 6.1 channel setup, but that would be misleading. The rear center channel is mixed into the other rear channels, and is extracted upon playback. This is very similar in fashion to Dolby Pro-Logic and matrixed surround. It premiered with Star Wars Episode I: The Phantom Menace. DVD players are just starting to support this format. Related: THX Surround EX / DTS ES
Dolby Pro-Logic Most popular surround format. Almost any receiver nowadays has it. Uses matrixed surround in order to encode four channels of sound: left/right front channels, a center channel, and one surround channel. It is quite a common occurence to see two speakers used for the one surround channel however, as well as a subwoofer to supplement the speakers.
Dolby Surround The encoding process used to make material compatible with Dolby Pro-Logic. 2 - Another surround format that came out before Dolby Prologic. It consists of only three channels: left/right front channels, and one surround channel.
DTS Coherent Acoustics A 5.1 channel sound format for use in home theaters. The channels are left/right front channels, left/right surround channels, a center channel, and a Low Frequency Effects (LFE) channel, usually used with a subwoofer.
DTS ES Very similar to Dolby Digital Surround EX. The only difference is that the rear center channel is done digitally.
Front Projector One type of viewing device. This is a separate unit that projects the image onto a separate screen allowing screen sizes of over 300". Related: Front Projection Info
Hard-matte A filming technique where plates block out the top and bottom of the picture as it is being filmed in order to achieve a widescreen effect. The opposite is Soft-matte.
High Definition TeleVision (HDTV) The supposed 'future' of television. It is a viewing format with a supposed aspect ratio of 16:9/1.78:1. It is slated to have over 1000 lines of resolution, as well as to have Dolby Digital be the offical sound format. There are two forms in existance. There is an analog system in Japan, and a digital system proposed by the Grand Alliance for the US. This system is supposed to co-exist with and eventually replace NTSC around the year 2006. Related: Common Aspect Ratios
Laserdisc Looking like an over-sized CD, it is currently one of the best viewing mediums for home theater. It has a theoretical resolution of 425 lines. It also has 4 audio channels: 2 analog and 2 PCM digital tracks. Each laserdisc usually consists of two sides, so when the end of one side is reached, the viewer must either flip over the disc or (if the viewer has a dual-sided player) allow the laser beam to switch over to the other side. See Laserdiscs for more detailed information and more terminology related to laserdiscs.
Leakage See Channel Leakage.
Letterbox This process, which is used on many laserdiscs and some TV broadcasts, is used to achieve a widescreen image, where the image is considerably wider than standard NTSC fare. The end result is a wider picture with black bands on the top and bottom of the screen, which reduces the overall resolution of the image. Another option with greater detail, but is less widely used is anamorphically squeezing the picture. Related: Common Aspect Ratios
LCD Projector One type of front projector. It is the smallest type of them all. It is sort of like a Watchman with a magnifying glass, but more detailed. One major benefit is that convergence is not required. One drawback is that this technology results in pixellation. Related: Front Projection Info
Light-Valve Projector One type of front projector. It combines the technologies of LCD projectors and CRT projectors. They offer exceptional detail and brightness. Related: Front Projection Info
Line Doubler/Tripler/Quadrupler Doubles, triples or quadruples the number of lines that make up a picture, therefore increasing detail, and ridding the picture of scan lines. Usually used with front projectors.
Matrixed Surround Term used to describe the process to make Dolby Pro-Logic compatible material. It fits four channels of sound into a space meant for two channels. The center channel is decoded by using material common to both left/right channels, and the surround channel is decoded by extracting the sounds with inverse waveforms. This process results in channel leakage.
Monopole Speakers One type of speaker with all drivers facing one direction. Used for precise placement of sounds. Usually used in front and center speakers.
NTSC The standard by which TV is broadcast in the US. It has a theoretical maximum resolution of 525 lines. Also has an aspect ratio of 4:3 or 1.33:1. Related: Common Aspect Ratios
PAL The standard by which TV is broadcast in Europe. It has a theoretical maximum resolution of 625 lines. Also has an aspect ratio of 4:3/1.33:1, and in some places 16:9/1.78:1.
Pan and Scan A technique used in which the right and/or left edges of widescreen material is chopped off in order to fit the picture into a a narrower aspect ratio, for example the NTSC standard of 4:3 or 1.33:1. Pepople who do this select the best part of the image to scan, and then if the whole image needs to be seen, scans across the rest of the frame. Related: Common Aspect Ratios
Rear Projector One type of viewing device. It is essentially a front projector and screen rolled into one. Screen sizes range from 45" to 80".
Rear Speaker The term wrongly applied to surround speakers.
Receiver The guts of many home theaters. It has a decoder, audio/video switcher, AM/FM tuner, and an amplifier section all in one.
Refresh Rate The rate at which the picture redraws itself in one second. Usually expressed in hertz (Hz).
Resolution A term associated with the number of lines that make up the vertical portion of the picture. The higher the number, the more detailed the picture is. If the resolution is too low, and the picture size too big you get scan lines.
Screen What the picture is projected onto. The screen is more important when it comes to front projectors, when the screen must be bought separately.
Soft-matte A projection technique where plates block out the top and bottom of the picture as it is being projected in order to achieve a widescreen effect. The opposite is Hard-matte.
Sony Dynamic Digital Sound (SDDS) An 8-channel sound format used in commercial movie theaters. The 8 channels are: Left Front, Left/Center Front, Center Front, Right/Center Front, Right Front, Left Surround, and Right surround. The sound is encoded in between the sprockets on the film. No followup has been announced for home theater.
Subwoofer This is a separate speaker used to handle the bass of movie soundtracks, and can be used with the Low Frequency Effects channel in the new digital sound formats. These speakers can sometimes handle frequencies as low as 15hz.
Surround Sound The popular term used to describe an experience where the sound 'surrounds' you. This is best achieved using surround-encoded material, a receiver, and surround speakers.
Surround Speaker Buy these to best achieve the surround sound effect. This type of speaker diffuses the sound so as to make it harder to discern where the sound is coming from. Two popular types are bipoles and dipoles.
THX Rumored to stand for the Tomlinson Holman eXperience. Others say it named after George Lucas' first film, THX-1138. THX is a set of standards by which laserdiscs and video tapes are made, as well as by which home theater equipment is made. They are supposed to yield the highest quality in home theater.
THX Surround EX This is built to further extend Dolby Digital Surround EX (DD-EX). This could be considered a 7.1 channel system. As opposed to DD-EX, which has an added channel in the center rear, THX-EX puts 2 more channels in the rear, so there is a front left, front right, front center, listening position left, listening position right, rear left, rear right. It uses Dolby Digital 5.1 as a base and matrixes in the extra 2 channels into the rear channels similar in fashion to Dolby Pro-Logic and Matrixed Surround. It is going to be available exclusively in THX Ultra certified products.
Widescreen Term used to describe a picture in which the aspect ratio is wider than the NTSC standard of 4:3/1.33:1. Almost all movies made nowadays are shot in some widescreen format. To solve the problem of different aspect ratios, several different techniques can be used. Among them are anamorphic squeezing, letterboxing, and Pan and Scanning. Related: What Is Widescreen, and Should I Invest In It? / Common Aspect Ratios