Welton USA - Home Theater Glossary

Home Theater Glossary

A B C D E F H I J K L M N P R S T V W Y

3-2 Pulldown A technique for converting 24 frame per second film to 60 field per second interlaced video. Film frames are alternately converted to two or three video fields, always in odd-even field order. Every four film frames, A-D, are converted to 10 video fields (5 video frames) in AoAe AoBe BoCe CoCe DoDe order.

4:3 The aspect ratio (width:height) of conventional (NTSC) TV and computer displays.

4:3 Letterbox Format A standard definition TV format for displaying any widescreen movie aspect ratio greater than 4:3 (1.33:1) on a 4:3 aspect ratio display. Black horizontal stripes are added to the top and bottom of the active picture area to fill out a 4:3 display. One of two 720x480 DVD formats for displaying widescreen movies.

5.1 The number of channels used for encoding Dolby Digital, DTS, and most SDDS film soundtracks. The five channels are left front, center, right front, left surround, and right surround. The ".1" channel is the low frequency effects (LFE) channel.

16:9 The aspect ratio (width:height) used for most DTV display formats including all HDTV and some Standard Definition DTV formats.

16:9 Enhanced Format A standard definition TV format for displaying any widescreen movie aspect ratio greater than or equal to 16:9 (1.78:1) on a 16:9 aspect ratio display. Black horizontal stripes are added to the top and bottom of the active picture area to fill out a 16:9 display. The 16:9 display area utilizes 720x480 pixels to provide 33% more vertical resolution than the 4:3 Letterbox format.

24/96 PCM (Pulse Code Modulation) digital audio at 24-bit resolution and a 96 kHz sampling rate per audio channel.

A/D Conversion The process of converting analog signals to digital signals. Analog audio or video signals are sampled in the time-domain at a specified sampling rate, and quantized in the amplitude-domain to a specified bit resolution.

A/V Audio/Video.

Absorption In acoustics, the conversion of sound energy to heat. Absorptive materials or resonators are used in media rooms to reduce excessive audio reflection or resonances that can make dialog difficult to understand and can render musical sounds too bright (if there are excess reflections at high frequencies) or too boomy (if due to low frequency resonances). See also Diffusion.

Absorption Coefficient The ratio of sound energy that is absorbed by a reflecting surface to the sound energy incident on the surface. The coefficient is a number that varies between 0 and 1 (1 representing 100% absorption, zero representing 100% reflection).

AC Alternating Current. A signal, such as the electricity from the wall socket, in which the electrons alternately change direction.

AC-3 Original name for Dolby Digital surround sound. See Dolby Digital.

Active Subwoofer A speaker designed to reproduce only low frequencies. "Active" indicates that the speaker includes an integral power amplifier to drive the speaker.

ADSL Asymetric Digital Subscriber Line. A technology allowing high speed (up to 8Mbps) internet access over conventional phone lines. See DSL.

AES/EBU Interface Audio Engineering Society/European Broadcast Union Interface A professional standard for the transmission of digital audio signals.

AFC Automatic Frequency Control. A TV circuit that locks on to the desired frequency.

AGC Automatic Gain Control. A circuit that adjusts the average level of a signal so that the level is appropriate for the following circuit. For example, most color decoders need a level to be within a certain range to operate properly, and AGC circuits are used to accomplish this.

Ambience The particular acoustic properties of a room (concert hall, media room etc) that give it a sense of space. Also used to refer to how well an a/v system reproduces the sense of space in the original environment.

Analog A signal that varies continuously with time, rather than sampled at discrete instances of time (see and contrast with "digital").

Anamorphic A process for filming and projecting widescreen movies in cinema theaters. A special camera lens is used to squeeze the image horizontally during photography and a complimentary lens is used in the film projector to restore the image width during projection. The anamorphic process is used for many films with aspect ratios of 2:35:1, most notably Panavision today, and CinemaScope in the past. Conversely, Super 35 is a non-anamorphic process for making widescreen films.

‘Anamorphic’ is also used by some DVD manufacturers to describe the 16:9 Enhanced format. We discourage this usage because it can be confusing as to whether the film or DVD format is being described. Both anamorphic and non-anamorphic films can use either the DVD 4:3 Letterbox format or the 16:9 Enhanced format.

ANSI Lumens A standard way of measuring the brightness of a display device. ANSI stands for American National Standards Institute.

Artifacts A generic term describing various picture distortions that result from imperfect signal processing or display processes. Also used to describe various audio distortions.

Aspect Ratio The ratio of a picture or display’s width to its height. A conventional NTSC TV has a 4:3 (1.33:1) aspect ratio. HDTV and 16:9 Enhanced DVD has a 16:9 (1.78:1) aspect ratio. Many films have a 1.85:1 aspect ratio, while some (e.g.CinemaScope or Panavision) have 2.35:1 aspect ratios. Other ratios are also used. Adjusting for these differences between how films are shot and how they are displayed involves several techniques (see Anamorphic, Letterbox, Pan and Scan).

ATSC Advance Television Standards Committee. The group that developed and proposed the digital TV (DTV) standards for the United States.

Attack The beginning of a sound. Used to describe how effectively an a/v system reproduces fast, high amplitude signals (e.g. drum beats or guitar plucks).

A/V Preamplifier See digital controller.

A/V Receiver The central component of a basic home theater system; receives signal from source components (DVD, VCR, DSS, Cable, etc), selects which signal you watch or listen to, controls playback volume and balance, performs signal decoding, receives radio broadcasts, and amplifies signals to drive loudspeakers. Also sometimes called a surround receiver.

Bandwidth The range of signal frequencies that a system can process before its response falls below specified levels, usually — 3 dB. Or the difference between a signal’s highest and lowest frequencies.

Bass Sounds in the low frequency range (generally from below 20 Hz to 200 Hz).

Bass Management A combination of controls and circuits in an A/V receiver or digital controller that route bass signals to the appropriate speakers (depending on the frequency response of each speaker and the presence or absence of subwoofers). With bass management, for example, the low frequencies for the left and right front and surround speakers can be routed to the subwoofer(s) if the front or surround speakers do not have the necessary frequency response.

Bass Reflex A speaker with a port or slot in the cabinet that allows some bass sounds inside the cabinet to emerge into the listening room to reinforce sounds from the main bass driver(s).

Bipole A loudspeaker configuration in which identical drivers radiate in opposite directions and in phase. Because the sounds radiate in-phase, the sound pattern of a bi-polar speaker is approximately omni-directional. In rear channel applications, bipolar speakers are most appropriate for discrete multi-channel recordings. See Dipole and Direct Radiator.

Bit The basic unit of data in digital signals. A bit can be assigned only two values: 1 (on) or 0 (off).

Bit Rate The number of bits per second stored or transmitted by a digital audio or digital video signal. For example, the bit rate of 5.1 channel Dolby Digital audio varies from 320,000 bits per second (320 kbps) for film to 448 kbps maximum on DVD. Higher bit rates using the same processing algorithms produce higher quality. See lossless compression.

Black Level The video signal level that represents a complete absence of light output from a properly calibrated display device.

Black Level Control (Brightness Control) The Black Level Control on a TV adjusts the offset of the RGB signals that drive the CRT, which sets the signal level corresponding to black.

Blanking Interval A period from the end of each active video picture line to the beginning of the next active picture line during which the display intensity is turned fully off. Short horizontal blanking intervals are used by CRT display devices to retrace the electron beam from the right edge of the screen to left edge in preparation for the next active scan line. Longer vertical blanking intervals are used to retrace the electron beam from the bottom of the display to the top of the display after each video field or frame.

Brightness In video, the subjective visual sensation corresponding to more or less light. In audio, an excessive amount of treble that adds a shrillness to the sound.

Brightness Control (Black Level Control) The Brightness Control on a TV adjusts the offset of the RGB signals that drive the CRT, which sets the signal level corresponding to black.

Byte 8 bits.

CbCr Digital color difference signals. Cb is an amplitude scaled version of a B-Y (blue - luma) signal. Cr is an amplitude scaled version of an R-Y (red — luma) signal. See also PbPr.

Center Channel In a multichannel audio system, the audio channel that carries information that will be reproduced by a speaker placed in the center front of the viewing room (and in an A/V system near or behind the display screen).

Center Channel Speaker The speaker in a multi-channel audio or A/V system that produces center channel information.

Channel A specific path for a defined flow of information. Audio systems use multiple channels within one program to reproduce a sense of ambiance. Television uses multiple channels to present different programs.

Channel Balance The relative levels or volumes of the different channels in an audio system.

Channel Separation A measure of how well sounds in one audio channel are separated (distinct) from sounds in other channels.

Chrominance The color of a picture independent of its luminance.

Chroma Video signal or signals that carry color information as an encoded pair of color difference signals, i.e. CbCr or PbPr. See luminance.

Color Temperature The hue of white that would be produced by heating pure carbon to a specified temperature in degrees Kelvin. A color temperature of 6500 degrees Kelvin, known as Illuminant D65, is the standard white reference for current NTSC and HDTV video systems. Higher color temperatures have a bluer hue and lower color temperatures a redder hue.

Coloration A change in sound from the original introduced by a component in an audio system. A loudspeaker, for example, which is "colored", doesn’t accurately reproduce the signal fed to it.

Comb Filter A filter used to separate the luma (Y) and chroma (C) signals from a composite video signal. The quality of the comb filter affects the level of "dot crawl" and rainbow-like moiré artifacts in the image.

Component Video Signals Three separate analog or digital video signals, either RGB (red, green, and blue) or a luma signal (Y) and two color-difference signals (Pb and Pr if analog, Cb and Cr if digital). Component video signals usually carry more chroma resolution than S-video (Y/C) or composite video signals, and avoid Y/C separation artifacts from composite video signals.

Composite Video Signal A video signal in which the luma (Y) and chroma (C) information are combined into a single signal along with sync information.

Compression In digital systems, the application of techniques to reduce the amount of data required to represent a signal. In this sense, compression can be either lossy (some data is lost during the compression and decompression activity) or lossless (the compressed signal can be decompressed into an exact representation of the original digital data). In audio, reducing the dynamic range of a signal by reducing the level of loud passages.

Cone The paper or plastic diaphragm of a loudspeaker driver that moves back and forth to create sound waves.

Contrast Control (Picture Control) Adjusts the overall RGB gain (and therefore the white level intensity) of a display.

Contrast Ratio The ratio between the maximum and minimum luminance levels of a picture.

Crossover The circuit in a loudspeaker that apportions frequencies to different drivers (e.g. low frequencies to a woofer, high frequencies to a tweeter).

CRT Cathode Ray Tube. A vacuum tube device used to display video images. In a CRT, electrons strike a screen coated with phosphors that give off red, greeen or blue light.

D/A Converter A circuit that converts digital signals to analog signals.

DBS Direct Broadcast Satellite. A system for receiving A/V programming directly from satellite to home.

Decibel (db) A unit of the loudness of sounds. A greater number of db corresponds to louder sounds. Typically the background noise in a quiet room is about 40db, soft music is about 70db, loud music about 90 - 100db, a jet engine perhaps 140db. Also, a unit to express the logarithmic ratio of two quantities. It is 10x the log of power ratios or 20x the log of voltage ratios.

Diffraction The distortion of a sound wave caused by an interfering object.

Diffusion The reflection of sound waves across a variety of angles, rather than at one angle. Diffusion is useful in creating a sense of ambience in small spaces (e.g. media rooms) without reducing greatly the amount of sound energy.

Digital A numerical representation of a signal or information as 1’s and 0’s.

Digital Controller A device inserted between a source (DVD, VHS, CD, DSS) and amplifier and display. Typically handles a) processing of multi-channel signals b) conversion of digital signals to analog form, c) control of volume, balance and frequency response, d) switching and routing of signals.

Dipole A loudspeaker configuration in which identical drivers radiate in opposite directions and out of phase. Because the drivers are out of phase, sounds at the side (the surface away from the drivers) cancel out, generating approximately a "figure 8" radiation pattern. This pattern tend to excite room standing waves less at low frequencies (while also making it more difficult to generate bass power). In rear channel applications, dipole speakers can be positioned so that little sound is aimed directly at the listener (who is at the "waist" of the figure 8) and most sound is directed at walls. This leads to diffuse (non-localized) sound in the surround channels. Dipole speakers are considered (by some) ideal for film sound, as films are mixed for diffuse surround speakers. See Bipole and Direct Radiator.

Direct Radiator A speaker that produces most of its sound toward the front of the speaker. Many speaker that use cone (i.e. woofer, midrange, tweeter) drivers are direct radiators. See Bipole, Dipole.

DLP Digital Light Processing. A method of projecting images by reflecting light from thousands of tiny mirrors on a semiconductor chip. Can produce very bright, and thus very large images.

Dolby Digital A digital audio format used to encode multiple channels (typically 6 channels, 5 full range plus ".1" for low bass) of audio information. Lossy compression is used to limit storage capacity or transmission bandwidth. Commonly used for film soundtracks. Sometimes referred to as Dolby AC-3.

Driver A sound producing device used in a loudspeaker (such as a woofer or tweeter).

DSL Digital Subscriber Line. A set of related technologies, often termed xDSL, for allowing relatively high speed internet data flow over phone lines and the switched telephone network. ADSL is commonly mentioned as an important new technology because it allows high bandwidth into PCs and other devices in the home. ADSL faces some technical and economic hurdles. Therefore, IDSL (ISDN DSL) -- with up to 128kbps speeds -- HDSL (High Bit Rate DSL ) and SDSL (Symmetric DSL) — with up to 2Mbps speeds -- are more commonly being deployed. HDSL/SDSL are fast enough to support video conferencing, while ADSL and VDSL (Very High Bit Rate DSL) could allow video on demand.

DSP Digital Signal Processing. Manipulation of audio or video signals by performing mathematical functions on the digital signal.

DSS Digital Satellite System. A specific DBS system.

DTS Digital Surround Digital Theatre Systems multichannel audio encoding/decoding system.

DTV Digital TV.

DVD Digital Versatile Disc. An optical data storage medium with a capacity of about 4.5 Gigabytes (a CD can store about 640 megabytes). Used to store both audio and video information.

DVD-A DVD Audio. A set of specifications for the reproduction of multi-channel audio utlizing the DVD storage medium. DVD-A focuses mainly on audio with no accompanying video. DVD-Video also provides a set of specifications for the storage of audio, both with video and audio alone.

Dynamic Range The difference between the smallest and the largest usable signal that a system can handle.

Equalization The technique of adjusting the frequency response of a system to more closely match a desired result.

Feedback The use of a portion of the output signal of a system at an input to the system. Feedback is often used to reduce the distortion of a system.

Foley Sound effects added to a film soundtrack, such as footsteps and doors closing.

Frame One complete picture in video. The NTSC television picture, for example, is composed of 29.97 frames per second. Half a frame in this system (the odd or even lines) is called a field.

Frequency Number of repetitions of a cycle of a video or audio signal per second. Measured in Hertz (Hz), or cycles, per second.

Frequency Response The change in output of a system with frequency. Loudspeakers, for example do not generate equal output at all frequencies when presented with a signal of equal level at each frequency.

Harmonics Integral multiples of a given or fundamental frequency.

HD Downconversion Conversion of High Definition video formats (1080i, 1080p, or 720p) to a standard definition video format (480i or 480p).

HDTV High Definition Television. See SDTV.

HDTV Formats The ATSC proposed a set of 18 DTV formats including six HDTV formats. All HDTV formats are 16:9 aspect ratios, three with 1920x1080 pixels and three with 1280x720 pixels. The 1080 formats include 1080i (interlaced) at 30 frames per second (FPS) and 1080p (progressive) at 24 and 30 FPS. The 720 formats are all progressive, 720p at 24, 30, or 60 FPS.

Hertz (hz) The unit of frequency in measuring a signal. Higher hz indicate higher frequencies (eg. Treble in audio signals).

Horizontal Lines See scanning lines.

IC Integrated Circuit. A group of transistors arrayed in a circuit on a single piece of silicon.

Impedance The opposition to the flow of electrical or acoustical energy.

Interlaced Scanning A process for tranmitting and displaying video images. Commonly used for conventional broadcast TV. Interlacing refers to consecutively transmitting and displaying fields containing the odd or even horizontal lines of an image to create a single frame on the screen. Contrast with Progressive Scanning.

In-wall Speaker A speaker mounted in a wall. Often, the wall is used as a baffle for the sound.

IR Infrared. Low frequency light signals commonly used for remote control.

IR Repeater A pair of devices, called an IR sensor and and IR flasher, that together relay IR commands from a remote to components hidden from the remote control’s view.

IRE An arbitrary unit to describe video signal amplitudes. 100 IRE is defined as the peak white amplitude and 0 IRE is defined as the blanking level.

Jitter Time distortion of a digital signal.

kbs Kilo-bits per second. Thousands of bits per second. See bit rate.

LCD Liquid Crystal Display. A technology for displaying text or images. Light is projected through a grid of crystals that either pass or block light.

Letterbox See 4:3 Letterbox.

Line Doubler/Tripler/Quadrupler Also called a Upconverter or scan converter. Line doublers de-interlace interlaced signals converting them to progressive video. Triplers and Quadruplers scale the resulting progressive video to create 1.5 or 2 times the scan lines of a line doubler to reduce their visibility, particularly on large images.

LNB Low Noise Blocking converter. A device inside a satellite dish that picks up the transmitted video signal.

Localization The ability to detect the direction or placement of sounds.

Low Frequency Effects Channel A separate channel in the Dolby Digital format reserved for low bass effects, such as explosions. The LFE channel is the ".1" channel in the 5.1-channel Dolby Digital audio format.

Luma The black and white component of a video signal. Represented by the letter Y.

Matrix A method of encoding four audio channels into two channels for transmission or storage.

MLP Meridian Lossless Packing. A lossless compression scheme for multichannel audio. Specified for use on DVD-Audio discs.

MP3 A standard for compression of audio signals to allow storage with limited capacity and transmission using limited bandwidth. Part of the MPEG 1 standards.

MPEG Motion Picture Experts Group.

MPEG-2 Video Compression A video compression scheme used in DSS, DVD, and HDTV.

NTSC National Television Standards Committee. The color television standard for North America established in 1953.

Pan-and-Scan A method of converting widescreen (1.85:1, 2.25:1, etc) film images to the standard NTSC 4:3 aspect ratio without black bars at the top and bottom of the image. A telecine colorist scans and zooms over the widescreen image in each scene to recompose the picture within a 4:3 aspect ratio. Results in the left and right edges being cut off as needed.

PbPr Analog color difference signals. Pb is an amplitude scaled version of a B-Y (blue - luma) signal. Pr is an amplitude scaled version of an R-Y (red — luma) signal. See also CbCr.

PCM Pulse Code Modulation. A method of representing a signal as a series of digital samples where the amplitude of each sample is quantized and binary coded.

Perceptual Coding A lossy compression method designed to reduce the number of bits needed to encode a signal with limited audible or visual effects by utilizing human perceptual modeling.

Phantom Image The creation of an apparent sound source between two speakers.

Phase The time relationship between two signals, such as the input and output of an amplifier. Phase can vary with frequency, and thus is commonly used to refer to the time distortion of a signal.

Pixel Picture Element. The basic unit of a display image. The more pixels in an image the finer the resolution.

PLUGE Picture Line Up Generation Equipment. A test pattern for properly setting black levels.

Polarity The relative orientation of the signal leads (+ and -) in a system.

Progressive Scanning A process for transmitting and displaying video images. Commonly used in personal computers and on some HDTV and SDTV formats. Progressive scanning refers to displaying horizontal scan lines in sequence from top to bottom of a full frame.

Pressure Zone When sound strikes a surface the velocity of the air particles is close to zero and the pressure is relatively high. This high pressure layer is referred to as the pressure zone.

Radiation Pattern The way in which a speaker disperses sound in different directions.

Reflection Sound bounces from a surface as light does (or as a pool ball bounces from a bumper), as long as the wavelength of the sound is small relative to the surface (i.e. midrange and treble frequencies in most residential rooms). See also resonance.

Resonance The reinforcement of sounds when the wavelength of the sound corresponds to the dimension of a room. In most residential rooms, resonance is primarily an important phenomenon at low frequencies.

Reverberation The dropping off of sound intensity over time as reflection (and absorption) convert sound energy into heat.

RGB Red, Green, Blue video signals. Sync is carried as separate signals, either H (horizontal) and V (vertical) sync, or combined as a composite sync signal.

Scan Lines A scan line is one sweep of a beam of electrons across a video display device. NTSC video has 525 scanning lines per frame, about 480 in the active picture area.

Screen Gain A measure of a screen’s reflectivity compared with a reference material. Screen gains of more than 1.0 are possible because screens focus their reflected light over a narrow viewing area.

SDTV Standard Definition Television. A set of digital TV standards. See HDTV.

SDTV Formats The ATSC has proposed a set of SDTV formats including 640x480 pixel and 704x480 pixel formats. The 640x480 pixel formats, with 4:3 aspect ratio, include 24 frames per second (FPS), 30 FPS and 60 FPS progressive and 30 FPS interlaced scanning formats. These are unlikely to be used other than for computer applications. The 704x480 formats may be either 4:3 or 16:9 using the same 24, 30 , 60 FPS progressive and 30 FPS interlaced scanning. DVD implements a minor variation with 720x480 pixels using either 4:3 or 16:9, 30 FPS interlaced scanning.

S/PDIF Sony-Philips Digital Interface A consumer standard for the transmission of digital audio signals. Very similar to the AES/EBU professional interface.

Sound Pressure Level (SPL) A measure of loudness. Expressed in decibels (dB).

Soundstage The impression that reproduced sound comes from a specific space, with height, width and depth.

Source Components A/V components that provide audio and video signals to the rest of a system. DVD players, VCRs, CD players and DSS systems are examples of source components.

Spectrum The distribution of the energy in a signal across a frequency range.

Standing Wave A resonance in a closed space (e.g. a media room) in which sound waves travelling in one direction reinforce the energy of waves travelling in another direction.

Storage Capacity The amount of data that can be stored on a particular medium. A CD has approximately 550 megabytes (million bytes) of storage capacity. A DVD has approximately 4.7 gigabytes (billion bytes) on a single layer, or almost 10 times the storage capacity of a CD. A double layer, double sided DVD (DVD-18) has about 17 GB of storage.

Subwoofer A speaker designed to handle only the lowest bass frequencies. Typically, these would be frequencies below 80 Hz. Often applied in home theatre systems to the low frequency effects channel (the .1 in 5.1 channel).

Surround Delay A technique of delaying the signal to the surround channels to increase the sense of ambiance in the reproduced sound. Also used by Dolby Pro Logic to increase the perceptual channel separation of the front and rear channels.

Surround Sound An audio recording and playback format that uses more than two channels, and is reproduced with two or more loudspeakers behind the listener.

S-Video (Y/C Video) A video interconnect system that keeps the luma (Y) and chroma (C) signals separate. See composite video and component video.

Timbre The quality of sound that defines how accurately the original sound spectrum (frequency distribution) of an instrument or voice is reproduced.

Timbre Matching A THX technology that aims to ensure that sounds arriving from the listener’s sides have the same frequency response as those arriving from the front, in order to ensure smooth panning of sounds.

TosLink Output An optical output for transmitting digital audio.

Transient A short-lived element of a signal involving the rise and decay of the signal.

Transparency The quality of reproduced sound which encompasses the sense of listening directly to the original performance.

Video Display A device that converts a video signal into a visual image. A TV is a video display that includes a television receiver.

Watt The unit of electrical power equal to 1 volt x 1 amp.

Wavelength The distance a wave travels in the time it takes it to complete one cycle.

Widescreen Any film with an aspect ratio greater than 1.37, the full 35mm film image.

Y Luma Video Signal.

Y/C Video (S-Video) A video signal interconnect system that keeps the luma (Y) and chroma (C) signals separate. See composite video and component video.

Y/C Delay Delay time between luma and chroma video signals. Excessive delay will be seen as color fringing on the edges of objects.

YPbPr A generic term for representing any analog color-difference component video signals. Some products label analog component video inputs or outputs as YCbCr (should be reserved for digital signals only) or Y, B-Y, R-Y (technically incorrect since the color difference signals are actually scaled versions of B-Y and R-Y) or YUV. The latter should be reserved for PAL TV systems but has long been used for any color-difference component video system.

Home | Will Call Information | Warranty | Service Centers | Accessories | Manuals | How to papers | Events | Contact Us

©Copyright 2002-2008 Welton USA, Ltd., all rights reserved.