visual comfort probability (VCP)
this
rating is based in terms of the percentage
of people who will be expected to find the
given lighting system acceptable when they
are seated in most undesirable locations.
visual display unit
a common means of
input/output to/from a computer. Consists of
a CRT and a keyboard.
visual perception
the perception of a
scene as observed by the human visual sys-
tem: it may differ considerably from the ac-
tual intensity image because of the nonlinear
response of the human visual system to light
stimuli.
visual space
the complete set of all possi-
ble images on a specific set of sampling and
quantization parameters. Any specific image
would be a member of this large space. For
a 2
× 2 bi-level image, the space contains 16
members. Allowing all 3
×3 bi-level images
increases the size of the space to 512 (num-
ber of quantized levels raised to the power
M, where M is the total number of pixels in
the image).
Viterbi algorithm
an algorithm for find-
ing the most probable sequence given that
data can be modeled by a finite-state Markov
model. For example, used in maximum like-
lihood decoding of trellis codes and in equal-
ization.
VLIW
See
very long instruction word
.
VLSI
See
very-large-scale-integration
.
voice
means for enabling a computer or
data processing system to recognize spoken
commands and input data and convert them
into electrical signals that can be used to
cause the system to carry out these com-
mands or accept the data. Various types of
algorithms and stored templates are used to
achieve this recognition.
voice activity
stimuli that can be used to
optimize channel capacity. The human voice
activity cycle is typically 35%. The rest of
the time we are either listening or pausing. In
a multiple access scenario such as CDMA,
all users are sharing the same radio chan-
nel. When users assigned to the channel are
not talking, all other users on the same chan-
nel benefit with less interference. Thus, the
voice activity cycle reduces mutual interfer-
ence by 65%, tripling the true channel capac-
ity. CDMA is not the only technology that
takes advantage of this phenomenon.
voice coil
the bobbinless coil transducer
element of a dynamic microphone.
voice
compression
See
speech
compression
.
voicing
classification of a speech segment
as being voiced (i.e., produced by glottal ex-
citation), unvoiced (i.e., produced by turbu-
lent air flow at a constriction), or some mix
of those two.
volatile
pertaining to a memory or storage
device that loses its storage capability when
power is removed.
volatile device
a memory or storage de-
vice that loses its storage capability when
power is removed.
volatile memory
memory that loses its
contents when the power supply is removed.
Examples include most types of RAM.
volt-ampere-reactive (VAR)
a unit of
power equal to the reactive power in a cir-
cuit carrying a sinusoidal current when the
product of the root-mean-square value of the
voltage (expressed in volts), the root-mean-
square value of the current (expressed in am-
peres), and the cosine of the phase angle be-
tween the voltage and the current, equals one;
the unit of reactive power in the International
System.
Also expressed as megavars and
kilovars.
c
2000 by CRC Press LLC