AC-3
When Dolby Digital sound was first introduced in 1995, its designator was AC-3. This term was soon discarded in favor of the more appropriate "Dolby Digital," which properly identifies the Dolby laboratories as creators of this process. We still have no idea what the term AC-3 actually signified, but nobody uses it anymore (although alert reader Kevin Smith has informed us that the "3" signifies the third level of surround sound developed by Dolby, and there's a rumor that "AC" stands for the initials of the techie primarily responsible for the development). The AC-3 logo can be found on Dolby Digital laserdiscs that were issued in 1995 and 1996.

A/V
Acronym for "Audio/Video," usually used in reference to systems which combine audio (CD players, tuners, tape-decks, etc.) with video (TVs, VCRs) systems.

Amplifier
Audio component that increases (amplifies) the electrical signal coming from a sound source (radio, CD or DVD player, etc.). Complicating things, there are power amplifiers (they drive the speakers) which have to be connected to a pre-amplifier which actually processes the sound. Most contemporary receivers are a combination of amplifier, source switcher (switching the signal from different output components like TV, VCR, CD, DVD, etc.) and tuner (i.e. radio); separate power amplifiers and pre-amplifiers are used primarily in high-end movie-theater assemblies.

Anamorphic widescreen
In cinematographic terms, the word "anamorphic" refers to a widescreen process (like Panavision) in which the camera films a wide, rectangular image through an anamorphic lens, squeezing the image onto a square film negative. If you looked at the raw negative, people would appear to be stick figures. In theaters, this squeezed film image is then projected through the same sort of anamorphic lens, restoring the image to its proper spatial dimensions (to an aspect ratio of approximately 2.35). The term "anamorphic" has also been adopted by DVD companies, referring to the process of mastering a movie onto DVD at a squeezed ratio, utilizing more horizontal lines of resolution from top to bottom and wasting less data on the thick black borders of a letterboxed title. This anamorphic process allows for widescreen televisions (the ratio of widescreen TVs is 16x9 compared to the squarer ratio of a standard TV set, which is 4x3, or simply 1.33). It is then used to extract the squeezed anamorphic image and stretch it out side-to-side to take advantage of the increased capacity for image resolution. The DVD player must be set for either widescreen 16x9 TV output or for standard 1.33:1 output. If an anamorphic image intended for 16x9 TVs is incorrectly outputted for a standard 1.33:1 TV set, you'll see a squeezed image.

Aspect ratio
It means the width-versus-height dimensions of a film image. Most movies are filmed at an aspect ratio of roughly 1.85:1, meaning the image is nearly twice as wide as it is tall. Many movies are filmed in an anamorphic widescreen process (Panavision, for example) that creates an onscreen aspect ratio of 2.35:1 – the image is almost 2½ times as wide as it is tall. Since a standard television set is nearly square (4x3, or simply 1.33:1), all movies at a wider aspect ratio must either be cropped on the sides (this process is called "panning-and-scanning") or letterboxed to contain the entire width of the image.

Bass module
Speaker dedicated to reproduce the lowest part of the audio spectrum, in other words, low-pitch sounds. Usually it's a large box and can be placed almost anywhere in a room since bass is omnidirectional (our ears cannot locate where low sounds come from). Also referred to as a subwoofer (a powered subwoofer contains its own amplifier and an electronic crossover).

CAV
A term used for laserdiscs. It means that the laserdisc spins within the player at "constant angular velocity." On a frame-for-frame basis, data on CAV discs take up more room than on the more common CLV discs. Essentially, tracks of data at the center of the disc are smaller compared to tracks of data at the outer edge of the disc, but the laser reads them at the same rate. Laserdiscs mastered in CAV mode can store only 30 minutes of information per side (compared to 60 minutes per side in CLV mode), but allow for more advanced user functions, such as crystal-clear freeze-frames, high-speed access and variable forward-and-reverse playback options.

CD changer
A CD player capable of holding 3 or more CDs. Some can hold hundreds and are also referred to as "CD Jukeboxes."

Center channel
The channel in a Dolby Digital or Dolby Surround capable system which carries dialogue.

CLV
A term for laserdiscs that means the laserdisc spins within the player at "constant linear velocity." Every track of data is the same size. Laserdiscs mastered in CLV mode can store 60 minutes per side, but freeze- frames, slow-motion, etc. aren't as clear as CAV discs and access isn't as rapid.

Compression artifact
A pixelization evident in the image that is usually the result of a lot of movement within the frame. Since the data on DVDs are compressed, the DVD player must extrapolate picture information between two data points and render the difference for a point between them that isn't, in fact, mastered onto the disc. When there's a lot of movement within the frame, DVD players can be known to "hiccup" and, as a result, the image can randomly – momentarily – break up into large digital pixels or, sometimes, jerkily skip a few frames ahead.

Contrast
The separation range between light/shadow values. The higher the contrast, the brighter the whites and the darker the blacks. If the contrast is too shallow, the image will be predominantly gray and pale.

Dolby Digital
A surround sound process that delivers 5.1 discrete channels of sound. That is, sound for 5 speakers (left, right, center, rear/left, rear/right) and a distinct subwoofer channel for very low frequencies (bass). The center speaker is devoted primarily to dialogue, hence when placed over or below the TV set it creates the sense that voices come directly from the screen. The rear/left and rear/right speakers are used primarily for ambient effects and they are in stereo.

Dolby Pro Logic
Dolby Pro Logic surround sound can output four distinct channels of audio: Left, right, center and rear. There is no separate subwoofer channel (as in Dolby Digital) and Pro Logic can support only a monaural surround channel which is heard on both the left and right surround speakers simultaneously – while there are two rear speakers, rear/left and rear/right as with Dolby Digital, they both carry the same sound channel.

Dolby Surround
Not quite as dynamic as Pro Logic, Dolby Surround has no discrete center dialogue channel. The three discrete channels of sound are left, right and rear.

Dolby
Audio technology company whose standards have dominated the industry for the last several decades.

DTS
A variation of Dolby Digital, endorsed first by Universal Studios and Steven Spielberg. Like Dolby Digital, there are 5.1 discrete channels of audio, but playback requires separate DTS-compatible equipment. The vast majority of DVD players support only Dolby Digital.

DVD
Originally stood for "Digital Versatile Disc" but is used to (or misused, as purists insist) to mean "Digital Video Disc." It was so named because data stored on a DVD can be used for both home-theater applications as well as for PC-compatible computer programs.

Full Screen
Also known as "standard" and as "full-frame," a full screen image fills in the entire nearly-square TV screen (a ratio of 1.33:1). Pan-and-scan titles are full-frame because there are no letterboxing borders; the entire TV screen area is used to show picture information.

Laserdisc
The forbearer of DVD, laserdiscs are 12-inch platters and they are double- sided. The video information is not digitally mastered and is not compressed (unlike with DVDs). Their audio portions are digital, and they are of CD quality. Depending on the mastering mode, up to 60 minutes can fit onto a single side of a laserdisc. Unlike most DVDs, laserdiscs require the viewer to flip sides in order to watch any program longer than 60 minutes (CLV) or 30 minutes (CAV).

Letterboxing
The practice of fitting a wide, rectangular image into the nearly-square television screen of most regular TV sets. When letterboxed and presented at its intended aspect ratio, the image will be fitted within black borders at the top and bottom.

Matting
See letterboxing.

Monaural
Also called simply "mono," it signifies that the audio content of a CD, laserdisc or DVD title contains only a single channel of sound.

Pan-and-scan
The process of shuttling the nearly square 1.33:1 TV viewing area of a widescreen movie image back and forth, left-to-right, focusing on the dominant action, but cropping off the sides of the image because the rectangular film image is wider than the square TV image. Most videotapes are mastered in pan-and-scan.

Platter
A term used for laserdiscs, referring to a 2-sided 12-inch disc. A movie that's longer than the 120-minute maximum for a laserdiscs requires an additional third side, thus requiring a second platter.

Receiver
The principal audio component: It acts as an amplifier, strengthening the electrical signal and driving the speakers, it switches between different audio and video signals (from TV, CD, VCR, DVD, etc.) and is a radio to boot.

Super 35
A highly confusing cinematography process whereby the camera negative records an image at an aspect ratio of roughly 2:1. This image is very flexible in that it can be slightly cropped off the top and bottom to render a wider aspect ratio (used in theaters to create an image with the same 2.35:1 dimensions as legitimate anamorphic films). Likewise, this 2:1 image requires far less panning-and-scanning for the transition to squarer TV screens than would anamorphic images: once the full top-to-bottom dimensions are "unmasked" from theater images, not as much left-to-right information is sacrificed in the transition to full screen format. The inconsistencies with Super 35 arise from the fact that the standard pan-and- scan version of a Super 35 film unmasks image information above and below the wider 2.35:1 image seen in theaters, and in many cases this is information that the director doesn't want you to see (such as intruding boom mics). Likewise, the wider 2.35:1 theatrical ratio might actually overcrop information you're supposed to see. Depending on the care with which the director and cameraman frame their shots, Super 35 films can look good either way. But more often than not, both the 2.35:1 version and the 1.33:1 version of a Super 35 film will each suffer in different ways. Most savvy directors hate this process, but some masters – like James Cameron – swear by it.

Surround sound
Refers to the audio content of a title containing a discrete channel of audio dedicated to the rear speakers, creating a fuller, more enveloping listening experience.

THX
Taken from the 1971 George Lucas film "THX-1138," THX is a Lucas-authorized quality-assurance home video standard. Consider it the "gold standard" for home video. If the specifications of a title or hardware meet Lucas's high standards of picture and sound excellence, THX will grant the right to use the logo, as an endorsement of sorts.

Widescreen
See Anamorphic Widescreen & letterboxing.

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