Glossary of Home TheaterTerms K-O


Main Glossary A - E F - J K L M N O P - T U - Z

Select the first letter of the word from the list above to jump to appropriate section of the glossary.

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- K -

Kbps (sometimes kb/s)

Kilobits per second.
 
kHz

Kilohertz, or thousands of cycles per second. See also Hz.
 
Kell factor

A psychovisual phenomenon that determines how much the eye can resolve on a TV screen.
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- L -

LCD

Liquid Crystal Display. Instead of cathode ray tube (CRT) displays or CRT projection tubes, some television sets employ the LCD, which is cooler running, lighter in weight, and smaller in size. Some very small sets have direct-view displays. A few others are front-projection models that focus light through several LCD panels, with the resultant image projected to an external screen. See also CRT; Direct-view television set; Projection television set.
 
LED

Light Emitting Diode. Often used as an indicator on A/V components
 
LEDE

Live-End-Dead-End room. A room designed to attenuate speaker reflections from adjacent walls, while highlighting the more delayed, scattered reflections from the far end, behind the listeners. This keeps the recorded signals from being strongly modified by the front of the listening room and allows the longer delays from the rear to place room-generated ambience where it belongs. An LEDE room will be heavily padded at the speaker end and lined with diffusing panels at the other end. The absorptive characteristics of this room may result in recordings that are overly bright when played back on wide-dispersion speaker systems located in typical, somewhat more reflective, home-listening rooms.
 
Late reflections

In room acoustics, the sounds that arrive at the listening position after being reflected from multiple room surfaces. They are the aural clues to the size of the listening space. In DSP, they are the electrically delayed signals that a home or studio processor creates to simulate larger room spaces.
 
Learning remote

A remote control that is designed to learn commands from a variety of other (dedicated) controls, simplifying user control of multiple components.
 
Letterboxing

Video reproduction of a film that places the entire, uncropped picture on the TV screen-eliminating the pan-and-scan problems that result when a wide format is cropped to fit a 4:3-ratio (or even, in the case of extremely wide originals, a 16:9-ratio) screen. The term letterbox is supposed to have been derived by someone's impression of the view looking out through the mail slot in their door or local mailbox. It describes a view that is wide but not very tall. Letterbox is not a format, just a phrase that describes the visual appearance of the piccture on the screen. See also Matting; Pan and scan.
 
LP

Long Play. In VCR parlance, the middle recording and playback speed available on some units. In audio, the short term for the analog, long-play, 33 1/3 rpm, vinyl disc.
 
LSB

Least Significant Bit.
 
LV

LaserVideo. This is the earliest laser-read videodisc system; sometimes called the analog videodisc.
 
Line doubling

See
IDTV.
 
Line level

Low-voltage output signals available at the shielded (RCA, XLR) connections of preamplifiers, CD players, tape recorders, etc., designed to interface with the line-level inputs of amplifiers, subwoofers, tape inputs, etc. See also Speaker level.
 
Line-source loudspeaker

A line source is a tall, vertically oriented, narrow driver or line of drivers. Because of this design, the "driver" will behave like a very large source over the vertical dimension and like a smaller one over the horizontal dimension. When very tall, the resultant erratic vertical dispersion and phase cancellations will affect performance in both the direct and reverberant fields.
 
Linear audio track

The monophonic analog sound track that runs down one side of a videotape. Far inferior in sound quality to what can be obtained with hi-fi videotape, this is what you will hear if you plug your VCR (even a hi-fi model) directly into the RF input of a TV set.
 
Linear stereo tracks

These are the non-hi-fl stereo tracks that are available on some prerecorded video-tapes. They usually employ Dolby Noise Reduction to improve the S/N ratio that is sacrificed when going from a mono linear audio design to stereo, but they are still far inferior to the stereo tracks that are standard on any hi-fi-audio-equipped video recorder. This feature has fallen into disuse but may be found on some used models.
 
Liquid-cooled speaker

See
Ferrofluid.
 
Liquid-cooled tube

These are found on CRT-type projection television sets and involve a liquid solution hermetically sealed between the projection tubes and the lens assembly. The coolant prolongs the life of the tubes and keeps heat expansion from
distorting the picture.
 
Listening distance

In home audio, the subjective distance of the listener from the performers on a recording. The distance can be somewhat altered by careful use of the volume control, but the recorded sense of space around the instruments and the depth of the sound stage that result from good minimalist microphone techniques will also play a large part in determining it.
 
Lossy compression

See
Data reduction
 
Loudness compensation

A circuit available on many preamplifiers, integrated amplifiers, and receivers that attempts to compensate for the loss in low-frequency hearing sensitivity at lower volume control settings. While simplified switched versions usually are crudely effective at best and certainly less workable than simple bass tone controls, some of the more sophisticated, continuous-control versions may work well-although still no better than the bass controls.
 
Low-pass filter

Within an audio crossover network, the electronic or passive circuitry that allows the low frequencies to go to a speaker system or amplifier. See also High-pass filter.
 
Luminance

The brightness component of a television signal. See also Chrominance.
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- M -

Mbps (sometimes mb/s)

Megabits per second
 
MD

See
MiniDisc.
 
MOL

Maximum Output Level.
 
MOSFET

Metal-Oxide-Semiconductor-Field-Effect Transistor. A special, high-peak-current output transistor used in some power amplifiers.
 
MPEG

Motion Pictures Experts Group. A group that meets under the auspices of the International Standards Organization in order to generate standards for digital-video and video-audio data compression/reduction.
 
MSB

Most Significant Bit. The first bit in a binary number. In 16-bit digital-audio playback systems, it contributes 32,000 times more to the output signal than the 16th (least significant) bit. Thus, errors in MSB circuitry occurring at very low levels can cause audible distortion and nonlinearities.
 
MTS

Multichannel TV Sound. The standard stereophonic audio reception and noise-reduction process used in all true stereo television receivers not using satellite or digital decoders.
 
Macrovision

A jamming signal encoded into most prerecorded videotapes that makes it difficult to do tape-to-tape copies
 
Masking

Under ordinary conditions, the process by which the threshold of hearing of one sound is raised by the presence of another. In both digital video and digital audio, a technique that allows a system to delete superfluous (inaudible or invisible) artifacts from a data stream by means of data reduction or data compression, enabling the system to transmit or store wide-bandwidth information within a much smaller bandwidth. Four notable uses of masking involve Dolby AC-3 Digital Surround Sound, MPEG video, DCC cassettes, and the MiniDisc. See also Data reduction.
 
Matrixing

In audio, the electrical mixing of two or more channels of sound down to one or more new ones. The latter can later be "dematrixed" back to the original number. With two-channel stereo, this will involve both left-plus-right (derived center) and left-minus-right (extracted ambience) processing. Dematrixing can also be applied to two-channel stereophonic signals that were not consciously matrixed from multiple originals, with variable results. While used in FM-signal transmissions and processes to receive stereo audio signals, its most notable use is in surround-sound processors. See also Dolby Surround; Hafler circuit; Extraction processors.
 
Matting

The application of a mask to a film or video program to remove information from the top and/or bottom of a picture. Used extensively in both theater presentations and video letterboxing. A hard matte is applied to the camera during the filming or videotaping process and, like anamorphic manipulation, delivers a true wide-screen image. A soft matte is a postproduction process that is done digitally when a film is transferred to videodisc or by means of projection gates in a theater.
 
Microphone

An electroacoustic device that turns the acoustic signals that come in contact with it into electrical signals for recording. Its behavior is just the opposite of that of a loudspeaker.
 
Midbass

The part of the bass frequency range between roughly 100 and 300 Hz.
 
Midrange

The middle range of the audible spectrum, running anywhere from 300 to 500 Hz on up to 3 or 4 kHz, a total of four octaves or more. The speaker component that handles this area is called the midrange driver.
 
MiniDisc (MD)

Sony's new data-reduced, small-disc, digital format.
 
Minimalist technique

The use of very few microphones, combined with very little editing, to achieve a natural sound on an audio recording, particularly with classical or jazz music. Also called purist technique.
 
Mixing console

The piece of equipment that recording engineers use to edit the material they recorded or are in the process of recording.
 
Monaural

See
Monophonic.
 
Monitor: audio

With regard to recording, this refers to the listening the recording engineer does while "recording" and editing a program (usually music). With regard to audio playback, it refers to the speaker systems used in the monitoring and mixing room, which may be commercial models but can also be models designed for consumer use that are often better than the commercial models.
 
Monitor: video

Refers to TV sets without a tuner, which thereby require connection to a video source of some kind to produce a picture. However, many monitors designed for home use have both monitoring connections and a tuner.
 
Monophonic

A recording or sound system that has only one channel, usually with all the sound (in most cases, music) coming from just one speaker system.
 
Moving-coil cartridge

A phonograph cartridge that makes use of a moving coil attached to the internal end of the stylus assembly to excite a magnetic field in a frxed-magnet structure, producing an electrical output for amplification. Rarely available these days, except as high-end audio items, and electroacoustically no better than the moving-magnet design.
 
Moving-magnet cartridge

A phonograph cartridge that makes use of a moving magnet attached to its stylus assembly to excite a magnetic field in a fixed-coil structure, producing an electrical output for amplification.
 
Multipath distortion

In FM radio transmissions, this effect occurs when a signal, because of being reflected from some surface (building, hill, etc.), arrives slightly later than the signals arriving directly from the transmitter. Because of the nature of FM-stereo matrixing, it can cause audible problems if the antenna and/or tuner is not well designed. In video, the effect causes ghost images.
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- N -

NAB

The National Association of Broadcasters.
 
NR

Noise Reduction.
 
NTSC

The National Television System Committee. The body responsible for the color television broadcast standards in the USA. The term NTSC is often applied to the performance parameters of pre-HDTV video hardware and software in this country.
 
Near field

Technically, the region where the particle velocity is mostly out of phase with the sound pressure-meaning that it can be very close to the listener at higher frequencies. Popularly-and incorrectly-it is often considered to be any point where the direct sound is significantly louder than the reflected sound.
 
Negative feedback

In all amplifiers, a part of the output signal that is fed back and added to the input signal out of phase, somewhat reducing the gain, limiting distortion, and imparting stability. Negative feedback, when used properly, can also improve frequency response. At higher frequencies, the feedback may not be fast enough, and the result will be increased transient intermodulation distortion. Under most conditions, this will not be audible. Feedback may be used "locally," in sections of an amplifier, or "generally," to control the response of the whole unit. See also TIM.
 
Noise floor

The noise generated by an audio device in the absence of any input signal.
 
Noise reduction: audio

A blanket term to describe a variety of background-noise-suppressing systems (Dolby, dbx, CX, etc.), which are employed in audio and video sound systems. Even hi-fi video recorders have proprietary audio noise-reduction circuitry. Most digital-audio systems do not require it.
 
Noise reduction: video

On some VCRs and laser-video players, digital noise reduction is used to improve picture quality, especially as it relates to video grain and snow in dark areas.
 
Noise shaping

Digital recording techniques that take advantage of the ear's reduced sensitivity at high frequencies
 
Notch filter

In video systems, this removes a small part of the TV signal where color information is most concentrated, reducing unwanted artifacts from less-than-perfect signals. See also Comb filter
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- O -

Objective testing

The proper use of instrumentation or rigorously managed listening comparisons, rather than casual or uncontrolled techniques, to evaluate audio or video equipment. See also Subjective testing.
 
Octave

A pitch interval or frequency ratio of two to one. Thus, a jump from 50 Hz to 100 Hz is one octave, as is a jump from 5,000 Hz to 10,000 Hz (5 kHz to 10 kHz). In listening to musical programs, the interaction of ear and brain makes it difficult to resolve minor frequency-response anomalies narrower than about a third of an octave.
 
Off-axis

Any listening, viewing, measuring, or recording position that is not directly in front of the forward axis of a TV set, loudspeaker, or microphone.
 
Ohm

A basic unit of electrical resistance. See also Resistance; Impedance; Reactance.
 
Omni-directional microphone

A microphone that picks up wide-bandwidth sound equally well from all directions. A variant is the subcardioid, which has somewhat less sensitivity in one direction
 
On-axis

Any listening, viewing, measuring, or recording position that is directly in front of a TV set, loudspeaker, or microphone.
 
Open-reel recorder

A tape recorder that holds its tape in individual reels rather than cassettes. Reels vary in diameter from 5 to 10 inches
 
Output impedance

The impedance seen by an electrical load attached to the output terminals of an audio or video device. For practical purposes, the output impedance of any audio amplifying equipment should be low in comparison to what it is connected to. It should not only be low at low frequencies, where it will affect bass damping, but should also be low at higher frequencies to insure a flat frequency response. In video systems, output and input impedances should closely match.
 
Oversampling

In most digital playback equipment, the sampling frequency is increased two, four, or, in the case of bitstream devices, even hundreds of times. However, the new samples are artificially included between the originals and will not actually affect the 16-bit information. What this digital filtering technique does is reduce the need for steep analog filters to remove ultrasonic hash, saving the manufacturer and hopefully the purchaser money. Although nearly all modern CD players use this technique in one form or another, there is no evidence that oversampling markedly improves playback sound.
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Revised: June 06, 2006.
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