Home Theater Glossary
DVD Glossary
Speakers Glossary
Home Networking and WLAN Glossary

Home Theater Glossary

Audio Code 3. The previous name for Dolby® Digital, the digital audio industry standard for DVD.

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.

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

Low frequencies; those below approximately 200 Hz.

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.

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

Combining two channels of an amplifier to make one channel that's more powerful.

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.

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

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.

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.

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.

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.

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!

DVD Glossary

A signal that contains digital data in its undecoded state. An example is the signal that's fed through a DVD player's digital output(s), which carries either Dolby Digital or DTS information.

The color portion of a video signal. The chrominance channel carries the color signal that is laid on top of the luminance information when creating a picture.

The process of converting an interlaced-scan video signal (where each frame is split into two sequential fields) to a progressive-scan signal (where each frame remains whole). De-interlacers are found in progressive-scan DVD players and HDTV-ready TVs. More advanced de-interlacers include a feature called 3-2 pulldown processing. De-interlacing is sometimes referred to as "line-doubling."

Digital output
All DVD players include at least one digital audio output for sending the Dolby Digital or DTS bitstream to a compatible decoder (it's usually built into an A/V receiver). Digital data transfer offers extremely wide bandwidth, immunity to RF interference, and an easy one-cable connection. The two most common types of digital output are coaxial and optical. Both types require a special cable to connect to the digital input of your Dolby Digital/DTS-equipped receiver.

Digital-to-analog converter (DAC)
An electronic circuit that converts a series of digital "words" into a continuous analog signal. DVD players include separate DACs for audio and video.

DVD-Audio (DVD-A)
A music-oriented DVD format that can carry up to 6 channels of 96kHz/24-bit audio (music for 5.1-channel home theater systems), or 2 channels of ultra high-resolution 192kHz/24-bit audio. Most DVD-Audio discs also carry Dolby Digital or stereo soundtracks for playback on DVD players that lack DVD-Audio decoders. A DVD-Audio disc may also contain liner notes, lyrics, menus, and still pictures that display on your TV

A recordable DVD format that combines high-quality audio/video recording and tape-free convenience. A DVD-RAM disc can be erased and re-recorded up to 100,000 times. DVD-RAM discs are only compatible with DVD players which are specifically designed to play them

HDCD® (High Definition Compatible Digital)
An enhanced method of audio recording for CDs developed by Pacific Microsonics. HDCD claims to be able to capture 20-bit resolution. Although the HDCD-enhanced information can only be heard using a DVD or CD player with built-in HDCD decoding, HDCD discs are still playable on regular DVD and CD players.

The brightness component of a color video signal. Determines the level of picture detail.

The digital video signal compression standard used for DVD. This adaptive, variable bit-rate process is able to allocate more bits for complex scenes involving a lot of motion, while minimizing the bits in static scenes. The average data rate for DVD is 3.5 Mbps (million bits/second). Some DVD players can display an on-screen "bit rate meter" — a visual measure of data flow in the form of a bar graph. MPEG stands for Moving Picture Experts Group.

Multi-language capability
DVD is designed to make it easier for movies to be distributed in multiple languages. A single DVD disc can contain soundtracks in up to 8 different languages! In addition to multilingual dialogue, a DVD also has space for subtitles in up to 32 languages. Note: the number of soundtracks and subtitles will vary from disc to disc depending on the length of the movie and whether or not other special playback features are included.

PCM (Pulse Code Modulation)
The digital audio signal format used for Compact Discs. Digital outputs on DVD players are often labeled "AC-3/PCM" because they can send either the AC-3 (Dolby Digital) bitstream from a DVD, or the PCM bitstream from a CD.

Perceptual coding
A type of data compression used in recent digital audio and video formats. Audio examples include Dolby Digital and MiniDisc's ATRAC; video examples include digital satellite TV and DVD. This approach is based on sophisticated research into how we perceive sounds and images. Perceptual coding omits "imperceptible" sound and picture data which is redundant or which is judged to be masked by similar information. In the case of DVD, by "throwing away" a lot of redundant and unnecessary information, it's possible to fit multiple versions of a movie on a single 5-inch disc.

Region codes
The movie industry insisted that the DVD standard include codes which would limit playback to a specified geographical region. This was done because theater and home video releases of movies do not occur simultaneously worldwide. For example, a movie may be released on video in the U.S. just as it's first appearing in theaters in Europe. DVD players have a built-in region code lockout feature, while the DVD discs may or may not contain a code (region codes are optional on DVD software). A player will be unable to play a disc that has a different region code. Discs may contain codes for more than one region, or may not have any code, which allows them to be played on any player in any country. The region code for USA/Canada is "1".

Tech FAQ
Find the answers to the tech questions you might have on Home Theater Systems, DVDs, Speakers etc. in our Tech FAQ
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What to look for and how to choose a Home Theatre system?
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