Audio Video Terms

3:2 Pulldown

Film is usually recorded at 24 frames per second. NTSC video (North America) is 30 frames (60 fields) per second. In order to get smooth motion, the film frames are broken into video fields in a 3-2-3 sequence. 3 fields for the first film frame, 2 fields for the second film frame, and so on. If a line doubler doesn’t compensate for the extra field during playback on a progressive-scan display, the image will have noticeable motion artifacts. A line doubler with 3:2 pulldown recognition or 3:2 inverse telecine can see this sequence in the signal and correct for it by making sure the last field in the first frame isn’t mixed with the first field of the second frame.

Aspect Ratio

The ratio of image width to image height. Common motion-picture ratios are 1.85:1 and 2.35:1. Television screens are usually 1.33:1 (also known as 4:3), which is similar to the Academy standard for films in the ’50s. HDTV is 1.78:1, or 16:9. When widescreen movies (films with aspect ratios wider than 1.33:1) are displayed on 1.33:1 televisions, the image must be letterboxed, anamorphically squeezed, or panned-and-scanned to fit the screen.

ATSC

Advanced Television Systems Committee. Government-directed committee that developed our digital television transmission system. A fancy way of saying the TV has a digital tuner.

Bass

Low frequencies; those below approximately 200 Hz.

Black Level

Light level of the darker portions of a video image. A black level control sets the light level of the darkest portion of the video signal to match that of the display’s black level capability. Black is, of course, the absence of light. Many displays, however, have as much difficulty shutting off the light in the black portions of an image as they do creating light in the brighter portions. CRT-based displays usually have better black levels than DLP, plasma, and LCD, which rank, generally, in that order.

Brightness

For video, the overall light level of the entire image. A brightness control makes an image brighter; however, when it is combined with a contrast, or white level control, the brightness control is best used to define the black level of the image (see Black Level). For audio, something referred to as bright has too much treble or high-frequency sound.

Center Channel

The center speaker in a home theater setup. Ideally placed within one or two feet above or below the horizontal plane of the left and right speakers and above or below the display device, unless placed behind a perforated screen. Placement is important, as voices and many effects in a multichannel mix come from this speaker.

Chrominance

The color portion of a video signal.

Coaxial

An audio or video cable with a single center pin that acts as the hot lead and an outer shield that acts as a ground.

Codec

Mathematical algorithms used to compress large data signals into small spaces with minimal perceived loss of information.

Component Video

A signal that’s recorded or transmitted in its separate components. Typically refers to Y/Pb/Pr, which consists of three 75-ohm channels: one for luminance information, and two for color. Compared with an S-video signal, a Y/Pb/Pr signal carries more color detail. HDTV, DVD, and DBS are component video sources, though most DBS material is transcoded to component from composite signals.

Composite Video

A signal that contains both chrominance and luminance on the same 75-ohm cable. Used in nearly all consumer video devices. Chrominance is carried in a 3.58-mHz sideband and filtered out by the TV’s notch or comb filter. Poor filtering can result in dot crawl, hanging dots, or other image artifacts.

Contrast

Relative difference between the brightest and darkest parts of an image. A contrast control adjusts the peak white level of a display device.

Crossover

A component that divides an audio signal into two or more ranges by frequency, sending, for example, low frequencies to one output and high frequencies to another. An active crossover is powered and divides the line-level audio signal prior to amplification. A passive crossover uses no external power supply and may be used either at line level or, more commonly, at speaker level to divide the signal after amplification and send the low frequencies to the woofer and the high frequencies to the tweeter.

Crossover Frequency

The frequency at which an audio signal is divided. 80 Hz is a typical subwoofer crossover point and is the recommended crossover point in theatrical and home THX systems. Frequencies below 80 Hz are sent to the subwoofer; signals above 80 Hz are sent to the main speakers.

CRT

Cathode Ray Tube. Analog display device that generates an image on a layer of phosphors that are driven by an electron gun. Old style TVs.

D-ILA

Direct Drive Image Light Amplifier. This Hughes/JVC technology uses a reflective LCD to create an image. A light source is then reflected off the reflective LCD and is directed through a lens to a screen.

Dispersion

The spread of sound over a wide area.

Distortion

Any undesired change in an audio signal between input and the output.

DLP

Digital Light Processing. A Texas Instruments process of projecting video images using a light source reflecting off of an array of tens of thousands of microscopic mirrors. Each mirror represents a pixel and reflects light toward the lens for white and away from it for black, modulating in between for various shades of gray. Three-chip versions use separate arrays for the red, green, and blue colors. Single-chip arrays use a color-filter wheel that alternates each filter color in front of the mirror array at appropriate intervals.

Dobly EX

An enhancement to Dolby Digital that adds a surround back channel to 5.1 soundtracks. The sixth channel is matrixed from the left and right surround channels. Often referred to as 6.1. Sometimes referred to as 7.1 if the system uses two surround back speakers, even though both speakers reproduce the same signal. Software is backwards-compatible with 5.1 systems, but requires an EX or 6.1 processor to obtain additional benefit.

Dolby Digital

An encoding system that digitally compresses up to 5.1 discrete channels of audio (left front, center, right front, left surround, right surround, and LFE) into a single bitstream, which can be recorded onto a DVD, HDTV broadcast, or other form of digital media. When RF-modulated, it was included on some laser discs, which requires an RF-demodulator before the signal can be decoded. Five channels are full-range; the .1 channel is a band-limited LFE track. A Dolby Digital processor (found in most new receivers, preamps, and some DVD players) can decode this signal back into the 5.1 separate channels. Most films since 1992’s Batman Returns have been recorded in a 5.1 digital format, though a number of films before that had 6-channel analog tracks that have been remastered into 5.1.

Dolby Pro Logic

An enhancement of the Dolby Surround decoding process. Pro Logic decoders derive left, center, right, and a mono surround channel from two-channel Dolby Surround–encoded material via matrix techniques.

DVD

Officially known as the Digital Video Disc, though marketers unofficially refer to it as the Digital Versatile Disc. DVD uses a 5-inch disc with anywhere from 4.5 Gb (single layer, single-sided) to 17 Gb storage capacity (double-layer, double sided). It uses MPEG2 compression to encode 720:480p resolution, full-motion video and Dolby Digital to encode 5.1 channels of discrete audio. The disc can also contain PCM, DTS, and MPEG audio soundtracks and numerous other features. An audio-only version, DVD-A uses MLP to encode six channels of 24-bit/96-kHz audio.

DVD-A

Digital Versatile Disc-Audio. Enhanced audio format with up to six channels of high-resolution, 24-bit/96-kHz audio encoded onto a DVD, usually using MLP lossless encoding. Requires a DVD-A player and a controller with 6-channel inputs (or a proprietary digital link) for full compatibility.

DVI

Digital Visual Interface. Connection standard developed by Intel for connecting computers to digital monitors such as flat panels and DLP projectors. A consumer electronics version, not necessarily compatible with the PC version, is used as a connection standard for HDTV tuners and displays. Transmits an uncompressed digital signal to the display. The latter version uses HDCP copy protection to prevent unauthorized copying. See also HDMI.

Dynamic Range

The difference between the lowest and the highest levels; in audio, it’s often expressed in decibels. In video, it’s listed as the contrast ratio.

Frequency

The number of cycles (vibrations) per second. In audio, audible frequencies commonly range from 20 to 20,000 cycles per second (Hz). In video, frequency is used to define the image resolution. Low-frequency video images depict large objects or images. Higher frequencies depict smaller objects (finer details).

Frequency Response

A measure of what frequencies can be reproduced and how accurately they are reproduced. A measurement of 20 to 20,000 Hz ± 3dB means those frequencies between 20 and 20,000 Hz can be reproduced no more than 3 dB above or below a reference frequency level.

HDCP

High-Bandwidth Digital Content Protection. Created by Intel, HDCP is used with HDTV signals over DVI and HDMI connections and on D-Theater D-VHS recordings to prevent unauthorized duplication of copyright material.

HDMI (High-Definition Multimedia Interface)

HDTV connection format using a DVI interface that transfers uncompressed digital audio and video with HDCP copy protection and multichannel audio.

HDTV (High-Definition Television)

High-Definition Television. The high-resolution subset of our DTV system. The FCC has no official definition for HDTV. The ATSC defines HDTV as a 16:9 image with twice the horizontal and vertical resolution of our existing system, accompanied by 5.1 channels of Dolby Digital audio. The CEA defines HDTV as an image with 720 progressive or 1080 interlaced active (top to bottom) scan lines. 1280:720p and 1920:1080i are typically accepted as high-definition scan rates.

High Gain Screen

Material that reflects more light than a reference material. Increases a projector’s light output at the expense of uniformity.

Home Theater in a Box (HTIB)

A complete home theater system in one box (or at least sold together as a package). Consists of five or more speakers, a subwoofer, and a receiver. May also include a DVD player.

Horn Speakers

A type of speaker that looks like a horn. These speakers have small drivers and very large mouths; the horn shape serves to transform the small radiating area of the driver into the much larger radiating area of the mouth of the horn.

IEEE 1394

Networking standard for PCs. Combined with 5C copy protection, is used as a two-way connection to transfer the MPEG-compressed digital bitstreams between consumer electronics items, including HDTV tuners and displays, D-VHS recorders, DVD players, and DBS receivers. Also called FireWire and iLink.

Interconnects

Any cable or wire running between two pieces of A/V equipment. For example, RCA terminated cables connecting pre/pros and amps.

Interlace

Process of alternating scan lines to create a complete image. In CRT displays, every second field/frame is scanned between the first field/frame. The first field represents the odd lines; the second field represents the even lines. The fields are aligned and timed so that, with a still image, the human eye blurs the two fields together and sees them as one. Interlace scanning allows only half the lines to be transmitted and presented at any given moment. A 1080i HD signal transmits and displays only 540 lines per 60th of a second. 480i NTSC transmits and displays only 240 lines per 60th of a second. Motion in the image can make the fields noticeable. Interlaced images have motion artifacts when two fields don’t match to create the complete frame, often most noticeable in film-based material.

Keystone

A form of video image distortion in which the top of the picture is wider than the bottom, or the left is taller than the right, or vice versa. The image is shaped like a trapezoid rather than a rectangle.

LCD (Liquid Crystal Display)

Liquid Crystal Display. A display that consists of two polarizing transparent panels and a liquid crystal surface sandwiched in between. Voltage is applied to certain areas, causing the crystal to turn dark. A light source behind the panel transmits through transparent crystals and is mostly blocked by dark crystals.

Letterbox

Format used widely on laser disc and many DVDs to fit wide-aspect-ratio movies (1.85:1 and 2.35:1, for example) into a smaller frame, such as the 1.78:1 area of an anamorphic DVD or the 1.33:1 area of a laser disc or video tape. The image is shrunk to fit the screen, leaving blank space on the top and bottom. This process sacrifices some vertical detail that must be used to record the black bars.

LFE

Low Frequency Effects track. The .1 channel of a Dolby Digital, DTS, or SDDS soundtrack. The LFE is strictly low-frequency information (20 to 120 Hz, with 115 dB of dynamic range) that’s added to the soundtrack for extra effect. This track does not inherently contain all the bass of the soundtrack.

Line-Level (Low Level)

A level of electrical signals too low to make the average speaker move sufficiently. Amplifiers receive line-level signals and amplify them to speaker level.

Luminance

The black and white (Y) portion of a composite, Y/C, or Y/Pb/Pr video signal. The luminance channel carries the detail of a video signal. The color channel is laid on top of the luminance signal when creating a picture. Having a separate luminance channel ensures compatibility with black-and-white televisions.

Midrange

The middle of the audio frequency range. Also used as a term for loudspeaker drivers designed to reproduce this range.

MP3

MPEG-1 Audio Layer-3. Compression scheme used to transfer audio files via the Internet and store in portable players and digital audio servers.

Multiroom Audio

System that provides audio or video to multiple areas. Usually with only one source.

Multisource

System with multiple sources. Can also be used to describe a receiver that can provide multiple different sources into different rooms.

Multizone

System that provides different sources into multiple areas simultaneously.

NTSC

National Television Standards Committee. Government-directed committee that established the U.S. color TV standard in 1953. Also known, sarcastically, as Never Twice the Same Color or Never The Same Color due to the inherent difficulty in achieving proper color calibration.

Ohm

A measure of how much something resists (impedes) the flow of electricity. Larger numbers mean more resistance.

Pixel

Contraction of picture element. The smallest element of data in a video image.

Plasma

Flat-panel display technology that ignites small pockets of gas to light phosphors.

Power Output

A measure, usually in watts, of how much energy is modulated by a component.

Pre Out

Connectors that provide a line-level output of the internal preamp or surround processor.

Preamplifier

A control and switching component that may include equalization functions. The preamp comes in the signal chain before the amplifiers.

Progressive Scanning

Each frame of a video image is scanned complete, from top to bottom, not interlaced. For example, 480p means that each image frame is made of 480 horizontal lines drawn vertically. Computer images are all progressively scanned. Requires more bandwidth (twice as much vertical information) and a faster horizontal scan frequency than interlaced images of the same resolution.

Projection System

Using a home theater projector and screen to create the perfect home theater.

RCA Connectors

Receptacles for coaxial cables carrying line-level audio, composite and component signals. Also called phono-type connectors.

Rear Projection Television (RPTV)

Display that projects an image on the backside of a screen material, usually after having been reflected off of a mirror. Usually DLP and LCD Rear Projection.

RF (Radio Frequency)

Radio Frequency. Television signals are modulated onto RF signals and are then demodulated by your television’s tuner. VCRs and DBS receivers often include channel 3 or 4 modulators, allowing the output signal to be tuned by the television on those channels. Also, laser discs used an RF signal for modulating Dolby Digital 5.1 soundtracks on some movies. This requires an RF demodulator (usually referred to as an AC3-RF demodulator) before or in the surround processor to decode the signal.

RGB

Red, Green, Blue. Can refer to an unprocessed video signal or the color points of a display device. Together these three colors make up every color seen on a display device. Also referred to a computer cable.

Ribbon Speaker

A loudspeaker that consists of a thin, corrugated, metallic ribbon suspended in a magnetic field. The ribbon acts electrically like a low-impedance voice coil and mechanically as a diaphragm.

S-Video

Video format where color and detail signals are kept separate, thus preventing composite video artifacts. tThe cable uses four-pin connector. Used with S-VHS VCRs, DVD players, Hi-8, and DBS receivers.

SACD

Super Audio CD. Enhanced audio format with up to six channels of high-resolution audio encoded using DSD. Requires an SACD player. Multichannel also requires a controller with six-channel analog or proprietary digital inputs for full playback.

Sampling Frequency

How often a digital sample is taken of an analog wave. The more samples taken, the more accurate the recording will be. You need to sample at a minimum of twice the highest frequency you want to capture. For example, the 44.1-kilohertz sampling rate of a CD cannot record sounds higher than 22.05 kilohertz.

Scan Lines

The lines drawn by an electron gun in a CRT system to make up the picture. Drawn horizontally, from left to right, starting at the top left and working to the bottom right.

Sensitivity

A measurement (in dB) of the sound-pressure level over a specified frequency range created by a speaker driven by 1 watt (2.83V at 8 ohms) of power with a microphone placed 1 meter away.

Soft-Dome Tweeter

A tweeter that uses a soft fabric or plastic dome as the radiating diaphragm.

Soundstage

The area between two speakers that appears to the listener to be occupied by sonic images. Like a real stage, a soundstage should have width, depth, and height.

Source

A component from which the system’s signals originate. DVD player, AM/FM tuners, and VCRs are sources.

Speaker

A component that converts electrical energy into acoustical energy.

Subwoofer

A speaker designed to reproduce very low bass frequencies, usually those below about 80 Hz.

THX

Certification program for home theater equipment. Uses some proprietary features, but mostly assures a base quality level for a given room size. (See THX Select or Ultra.) Is compatible with any and all soundtrack formats. Stands for either Tom Holman’s eXperiment, after the engineer who drafted the original standard, or is named after the company’s founder George Lucas’ first movie, THX 1138. Nobody agrees on which.

Tweeter

A speaker driver designed to reproduce high frequencies; usually those over approximately 5,000 to 10,000 Hz.

Universal Remote

Remote that has the commands of numerous brands stored into memory and can control several different devices simultaneously