Term	Definition	Demo
Laserdisc	An optical disc, 12 or 8 inches in diameter, that can store video in analog form along with analog and digital audio signals in stereo and multichannel formats. The analog signals are frequency modulated. See: FM, CAV, CLV
LCD	Liquid Crystal Display is one in which the reflectivity and/or transparency can be changed by the application of a voltage. It is divided into many tiny independently conrolled pixels. They are very common: digital watches, calculators, dashboards, computer screens, rear and front projection video displays, etc. Since they are used as light transmission devices in most applications, there are losses, and getting the control voltages to each of the pixels presents challenges in maximizing the aperture ratio. See: Aperture Ratio, Projector.
LCOS	Liquid Crystal on Silicon. A digital video display device using a liquid crystal surface the reflectivity of which is controlled by a pixellated solid state control device underneath it. See: D-ILA, Projector.
LED	Light Emitting Diode. An electronic component that emits light when energized. Commonly used as indicator lights on electronic equipment, and nowadays in arrays as tail lights on cars and traffic lights.
LEDE	Live End Dead End (TM). A style of recording control room design in which, among other things, the front half of the room is acoustically 'dead' - without strong reflections - and the rear half is reflective and diffusive. Conceived in the days of two-channel stereo, and loudspeakers with problematic directivity, the relevance to multichannel audio is questionable.
Letterbox	The method of displaying a widescreen image on a standard 4:3 aspect ratio display. The width of the image is the width of the display, but the height is less, meaning that there are black bars above and below - like a letterbox.
LFE	See: Low-Frequency Effects
Light Valve	A video display device in which a powerful light source is modulated by a 'valve' controlled by a much smaller, less powerful one, thus making it possible to project a very large image. The valve is a polarized liquid crystal device in which one surface reflects a powerful light in proportion to the amount of much weaker light falling on the reverse side. The contolling light can be an image created by a CRT. Three valves, red, blue and green, are necessary for color projection. Being analog, there is no pixel structure. Also known a ILA (Image Light Amplifier) by its creator Hughes/JVC. See: D-ILA, LCOS, Projector.
Line Doubler	A video processor that can double the number of lines in a scanned display, making each of the lines smaller, and therefore less visible. One common form of line doubler converts an interlaced picture into a progressively scanned picture. See: Interlace, Progressive Scan, IDTV
Line Level	A low-level audio signal. The kind of signal that is typically communicated between components using shielded interconnects with RCA type connectors. Sometimes called preamp level, to distinguish it from speaker level signals. See: Speaker Level
Linear Distortion	Changes to the amplitude vs. frequency characteristic and the phase vs. frequency characteristic of a signal. Such distortions are assumed to be constant at all signal/sound levels. See: Non-Linear Distortion, Distortion.
LNB	Low-Noise Blocking Converter. The active receiving element in a satellite dish antenna. Some systems may have two or three LNB's on one dish, each aiming at a different satellite.
Localization	Assigning a perceived direction to a sound. A full description would include horizontal angle (azimuth), vertical angle (elevation) and distance. The size of the perceived sound image may also be a consideration.
Logarithm	In common logarithms, representing a number by the power to which 10 must be raised to equal it. For example, 10 to the exponent (or power) 2 = 10 squared = 100. The log of 100 is therefore 2.
Loudness	The perceptual correlate of sound level. Subjective perception of loudness is highly non-linear. Doubling or halving loudness requires about 10 dB change in sound level at middle and high frequencies. At low frequencies, it can be as little as 4 dB. The smallest audible change in overall loudness level is about 1 dB. 3 dB is just nicely audible. Loudness also depends on the frequency, bandwidth and duration of the sound. See: Loudness Contours' class='link'>Equal Loudness Contours.
Loudness Contours	See: Loudness Contours' class='link'>Equal Loudness Contours.
Loudness Control	A separate control or, more commonly, a switch-selected addition to a volume control, that causes bass frequencies to be amplified as the overall volume is turned down. The idea is to compensate for the fact that the ear becomes progressively less sensitive to bass at low sound levels. See: Loudness Contours' class='link'>Equal Loudness Contours.
Loudspeaker	An transducer that converts an electrical signal into sound.
Loudspeaker System	A set of transducers, with a crossover network, in an enclosure. A two-way system has a woofer and a tweeter, a three-way system adds a mid-range, and so on. Up to a point, more transducers allow a designer more capability in designing a good sounding system, but there are no guarantees. More transducers should, however, allow for higher sound levels. See: Woofer, Tweeter, Crossover, Enclosure.
Low Frequency	Generally refers to sounds below about 300 Hz.
Low Frequency Effects	The 0.1 channel in 5.1-channel Dolby Digital signals. All 5 main channels are full range, so this additional channel, covering the frequency range 3 Hz to 120 Hz is there to accommodate very loud low frequency special effects sounds, such as explosions. It is included in the bass managed subwoofer outputs of surround processors and receivers, but is discarded in the two-channel downmixes of Dolby Digital that occur in many DVD players. See: Downmix, Dolby Digital, Bass Management
Low Pass Filter	An electronic or acoustical device designed to pass all frequencies lower than the design frequency, and to attenuate, or block, all higher frequencies.
LP recordings	LP = Long Playing - relative to the 78 rpm discs of the previous generation. The familiar 12-inch diameter vinyl discs, containing analogue recordings played back at 33 1/3 rpm. Almost all are two-channel stereo, although some were encoded in four channel formats during the Quadraphonic era in the late 1970's.
Lt, Rt	Left total, right total. Names given to the left and right channels of a two-channel audio signal which contains Dolby Surround encoded information. See: Dolby Surround.
Luminance	Brightness, or the black and white content of a picture. The symbol 'Y' designates the luminance signal. Combined with chrominance (C) to complete a color video picture. See: Chrominance, Chroma.