LAN (local area network) A combination
of at least two computers and peripherals on a common wiring scheme,
which allows two-way communication of data and shared resources between any devices on
Laplace, Marquis Pierre Simon de (1749-1827)
French mathematician and astronomer who formulated the theory of
laser (light amplification by stimulated
emission of radiation) A device which generates coherent,
monochromatic light waves. All optical drives (CD/DVD recorders
and players) contain one or more semiconductor lasers.
LCD (liquid crystal display) A display made of material
whose reflectance or transmittance changes when an electric field
is applied. An LCD requires ambient light or back-lighting for viewing.
LEC (Local Exchange Carrier) The local phone
company, provider of local telecommunications services and access to
long distance networks.
LED (light emitting diode) A semiconductor diode
that converts electrical current to light, used to display numerical or graphical information.
Used in simple one color displays such as calculators and clocks as
well as full color, high brightness, video displays used for
outdoor signage (popular in Los Vegas and Times Square) a
leveler A dynamic processor that maintains
(or "levels") the amount of one audio signal based upon
the level of a second audio signal. Normally, the second signal
is from an ambient noise sensing microphone. For example, a restaurant
is a typical application where it is desired to maintain paging
and background music a specified loudness above the ambient noise.
The leveler monitors the background noise, dynamically increasing
and decreasing the main audio signal as necessary to maintain a
constant loudness differential between the two. Also called SPL
lift/dip Popular European term meaning boost/cut.
limiter A compressor
with a fixed ratio of 10:1 or greater. The dynamic action
effectively prevents the audio signal from becoming any larger than
the threshold setting. For example, if the threshold is set
for, say, +16 dBu and the input signal increases by 10 dB to +26
dB, the output only increases by 1 dB to +17 dBu, essentially remaining
constant. Used primarily for preventing equipment, media, and transmitter
linear PCM A pulse code modulation system in which the signal
is converted directly to a PCM word without companding, or other
linear phase response See: group
The de facto standard for professional audio active crossovers is
the 4th-order (24 dB/octave slopes) Linkwitz-Riley (LR-4) design.
Consisting of cascaded 2nd-order Butterworth
low-pass filters, the LR-4 represents
a vast improvement over the previous 3rd-order (18 dB/octave) Butterworth
standard. Named after S. Linkwitz, a Hewlett-Packard engineer, who
first described the problems and solution in his paper "Active
Crossover Networks for Non-coincident Drivers," J. Audio
Eng. Soc., vol. 24, Jan/Feb 1976, pp. 2-8. In this paper, he
credited his co-worker Russ Riley for the idea that cascaded Butterworth
filters met all his crossover requirements. Their effort became
known as the Linkwitz-Riley alignment. Linkwitz showed that a significant
weakness of the Butterworth design was the behavior of the combined
acoustic lobe along the vertical axis. An acoustic lobe results
when both drivers operate together reproducing the crossover frequency
band, and in the Butterworth case it exhibits severe peaking and
is not on-axis (it tilts toward the lagging driver). Linkwitz showed
that this results from the Butterworth outputs not being in-phase.
Riley demonstrated an elegant solution by cascading two 2nd-order
(any even-ordered pair works) Butterworth filters, which
produced outputs that were always in-phase and summed to a constant-voltage
response. Thus was created a better crossover.
lossy See: digital
audio data compression
Local Loop The communications lines between the long
distance subscriber and the LEC Switching center.
Loopback A diagnostic test where a digital signal is
transmitter over a duplex communications link or network and then
returned to the sending device for analysis. Usually involves a
testing device installed a the remote end to relay the test signal
back to the testing device.
low-pass filter A
filter having a passband extending from DC (zero Hz) to some finite
cutoff frequency (not infinite). A filter with a characteristic
that allows all frequencies below a specified rolloff frequency
to pass and attenuate all frequencies above.
LSB (least significant bit) The
bit within a digital word that represents the smallest possible
coded value; hence, the LSB is a measure of precision.
Lumen A measurement of the amount of visible light energy
that comes from a light source.
luminance That part of the video
signal which carries information on how bright each pixel in the
TV signal is to be. The luminance signal can represent any
brightness level between black and white. Luminance is often
abbreviated as "Y".