Home Theater Glossary
AC-3
Audio Code 3. The previous name for Dolby® Digital, the digital audio industry standard for DVD.
Anamorphic
A type of widescreen display format optimized for playback on a TV with 16:9 aspect ratio.
Aspect ratio
The ratio between the width and height of an image or display screen. The NTSC television standard is 4:3 (1.33:1). However, most movies are made for the wide screen of a theater, and are originally displayed at the wider ratios of 1.85:1 or 2:35:1.
DVD's huge data storage capacity makes it possible to include multiple versions of a movie on a single disc. It's not unusual for a DVD disc to feature a Standard (4:3) version on one side and a Widescreen version on the other.
For TVs with standard 4:3 screens, movies (whether on disc or tape) must be re-formatted to either "letterbox" or "pan-and-scan." If you usually rent or buy VHS movies, you're probably used to pan-and-scan.
A DVD played in pan-and-scan mode provides an image with full height, but shows a central "window" that is only 75% of the original widescreen width. What this window shows is determined by the preferences of the person(s) performing the film-to-disc transfer.
For letterbox mode the player uses a "letterbox filter" that adds horizontal black bars to the top and bottom of the picture. What you see is a short, rectangular image that maintains the movie's full original width. Letterbox has been popular for many years with laserdisc fans and other movie purists.
DVD is the first consumer video format to make "anamorphic" widescreen mode available on a significant number of movie titles. If a movie's widescreen version is anamorphic, the packaging usually says, "Optimized for 16:9 viewing" or something similar.
You should only play a movie in anamorphic mode if you're using a TV or projector with true 16:9 aspect ratio — on a standard TV, anamorphic will appear horizontally squeezed. A 16:9 aspect ratio works out to 1.78:1, which means you'll see more of the original image.
Balanced input
An input circuit whose electrical midpoint is grounded.
Bandpass
A two-part filter that cuts both high and low frequencies to leave a band in the middle. A bandpass enclosure cuts high frequencies by acoustic cancellation and low frequencies by natural physical limitations on bass response
Bass
Low frequencies; those below approximately 200 Hz.
Bipolar
Bipolar speakers are a popular choice for surround speaker application and a THX requirement. Each speaker enclosure consists of two speaker arrays facing opposite each other and wire out of phase from one another to create a more ambient or nondirectional soundfield.
Bi-wiring
Of or referring to a method of connecting the amplifier or receiver to the speaker in which separate wiring is run to the woofer and the tweeter, or in a three-way system, to the midrange driver
Bridging
Combining two channels of an amplifier to make one channel that's more powerful.
Channel
In components and systems, a channel is a separate signal path. A four-channel amplifier has at least four separate inputs and four separate outputs.
Composite Video
The standard video transmission method. Not as good as s-video or component video. Composite video utilizes one (RCA-jack type) cord to transmit all picture information.
Component Video
A video transmission method. Better than composite video and s-video, equal to RGB video. Component video uses three (RCA-jack type) cables to distribute the red, blue and green portions of a video transmission separately. Component video is typically used with DVD players and HDTV systems.
Crossover
A component that divides an audio signal into two or more parts by frequency, sending, for example, low frequencies to one output and high frequencies to another. Crossovers are sometimes built into amplifiers or equalizers
Damping
Of or pertaining to the control of vibration by electrical or mechanical means.
Dolby Digital
A discrete multichannel digital audio standard offering enhanced sonic realism. Dolby Digital is normally associated with 5.1-channel surround sound. Though this channel configuration is common, it is only one of several possible variations — a "Dolby Digital" soundtrack can mean anything from 1 to 5.1 channels.
If you're specifically looking for titles with a 5.1 soundtrack, you should carefully read each disc's packaging. Relatively few older movies with stereo or mono soundtracks will be remastered with 5.1-channel surround for DVD.
Dolby Digital 5.1 soundtracks will in most cases provide the most satisfying sound quality for a home theater system. It is referred to as a 5.1-channel system because it offers five full-bandwidth channels (including true stereo surrounds), plus a "low frequency effects" subwoofer channel.
Unless your DVD player has its own built-in Dolby Digital decoder, you'll need to connect your player to a receiver or processor that can take the digital bitstream from the disc and convert it into 6 channels of audio. Dolby Digital uses a data compression technique called "perceptual coding" to reduce the original amount of audio data by a factor of about 10:1
Downmixed audio
If you don't have a Dolby Digital system, you can still enjoy excellent Pro Logic™ or stereo sound. All DVD players have the ability to take a 5.1-channel Dolby Digital soundtrack and "downmix" it to two channels, which can then be sent to a stereo TV, a stereo receiver, or to an A/V receiver with Dolby Pro Logic decoding.
DTS (Digital Theater Systems)
DTS is an established multichannel audio format in movie theaters, but a relative newcomer to home theater. Like Dolby Digital, DTS is primarily a 5.1-channel format. The compression scheme used in DTS "throws away" significantly less audio data than Dolby Digital, so it should sound better, but so far, side-by-side comparisons have been inconclusive.
Nearly all new DVD players are DTS-compatible; some players and nearly all new A/V receivers include DTS decoding. Still, the number and availability of DVD titles with DTS soundtracks remains somewhat limited.
Field
In interlaced-scan video, each complete frame is split into 2 sequential fields, each of which contains half the scanning lines of the frame. One field contains the odd scanning lines, and the other field the even lines.
Frame
A complete, individual picture in a movie film. In a video signal, a frame contains all of the picture's scanning lines.
Frame rate
The rate at which frames are displayed. The frame rate for movies is 24 frames per second (24 fps). In regular NTSC video, the frame rate is 30 fps.
Horizontal resolution
The number of vertical lines that can be identified across the width of a TV screen, usually measured by displaying a test pattern. A bigger number is almost always better. DVD is capable of 500 lines of resolution. By comparison, laserdisc maxes out at 425 lines, Super VHS at around 400, and standard VHS at 240 lines.
Interlaced scan
An interlaced-scan video signal splits each complete picture frame into 2 sequential fields, one containing the frame's odd scanning lines, and the other containing the even lines. Interlaced scan has been an effective way to maximize our long-in-the-tooth NTSC video system, but it is prone to problems like motion artifacts, which are generally eliminated by progressive-scanning.
Letterboxing
The scaling of a widescreen image to fit a standard 4:3 aspect ratio TV screen by shrinking the image's vertical dimension so that the width fits exactly. The horizontal black bars that appear above and below the image are actually recorded with the picture, so some of the picture's vertical resolution is lost when you view it. Letterboxing is much more common on DVD movies than VHS videos.
Pan-and-scan
A technique for making a widescreen movie fit a standard TV's 4:3 aspect ratio by showing only selected portions of the original image. This is the standard practice on VHS videos ("formatted to fit your screen"), but is less common on DVDs.
Progressive scan
Instead of splitting each video frame into two sequential fields like interlaced scan, progressive scan displays the entire frame in a single sweep. So, where a standard DVD player's 480i output displays 30 frames (60 fields) per second, a progressive-scan player's 480p output displays 60 full frames per second. Progressive-scan picture quality is more filmlike, with more fine detail and less flicker. Progressive-scan viewing requires an "HDTV-ready" TV.
Signal-to-Noise ratio (video)
This ratio is a measure of the content portion of the video signal in relation to the noise in the signal. As with audio, video signal-to-noise is measured in decibels (dB). The way the decibel scale works, if component A has a signal-to-noise (S/N) ratio of 20 dB and component B has a S/N ratio of 30 dB, component B will have ten times less noise in the signal than component A.
Basically, a S/N ratio tells you how "clean" a video signal is. Because of the way they process signals, digital video formats like DVD and digital satellite TV are extremely clean. A standard VHS VCR may have a S/N spec in the low 40s; a laserdisc player, the low 50s. DVD is rated to deliver a S/N ratio of 65 dB!
Glossary
