5.1 surround sound The digital audio multichannel format
developed by the Moving Picture Experts Group (see: MPEG) for digital soundtrack encoding for film, laser discs,
video tapes, DVD, and HDTV
broadcast. The designation "5.1" refers to the five
discrete, full bandwidth channels  left, right, & center,
plus left & right surrounds  and the ".1"
usually refers to the limited bandwidth subwoofer channel,
but can also refer to a special effects/feature channel. Terminology
used by both Dolby Digital and
DTS Zeta Digital (the home
version of their theater Coherent Acoustics system).
FAQ (frequently asked question) Acronym commonly
seen on bulletin boards, Internet Web sites, and corporate information
centers. By compiling FAQ lists (FAQs), organizations significantly
reduce time spent repeatedly answering the same questions.
fax on demand One of the terms for the process of ordering
fax documents from remote machines via telephone, using a combination
of voice processing and fax technologies.
FFT (fast Fourier transform)
1. Similar to a discrete
Fourier transform except the algorithm requires the number
of sampled points be a power of two. 2. A DSP
algorithm that is the computational equivalent to performing a
specific number of discrete Fourier transforms, but by taking
advantage of computational symmetries and redundancies, significantly
reduces the computational burden. [It is believed the FFT was
first described by Cornelius Lanczos of the Boeing Co. in the
1940's.]
fiber optics The technology
of using glass fibers to convey light and modulated information.
filter Any of
various electric, electronic, acoustic, or optical devices used
to reject signals, vibrations, or radiations of certain frequencies
while passing others. For audio use the most common electronic
filter is a bandpass filter, characterized by three parameters:
center frequency, amplitude (or magnitude), and bandwidth.
Bandpass filters form the heart of audio graphic equalizers and parametric
equalizers.
Firewall A network component set up to prevent
unauthorized network traffic form one side of the device
from crossing to the other side while passing authorized traffic.
Firewire See: IEEE 1394
flanging Originally, "flanging"
was achieved using two reeltoreel tape recorders playing the
same program, in synchronization, with their outputs summed together.
By alternately slowing down one machine, then the other, different
phase cancellations occurred in the summation process. The "slowing
down" was done simply by pressing against the flanges
of the tape reels, hence the original term "reel flanging,"
soon shortened to just "flanging." Since the two identical
signals would alternately add and subtract due to the introduced
phase (timing) difference, the audible effect was one of a sweeping
comb filter. It was described as a "swishing" or "tunneling"
sound. Soon electronic means were devised to mimic true "reel
flanging" by using delay lines and mixing techniques. Adding
a lowfrequency oscillator to modulate the audio delay line's
clock signal created a sweeping effect, much like a jet airplane
taking off. The best flangers used two delay lines. Compare with:
phaser
Flash Memory Electronic memory chips which are compact
in size an do not require continuous power to retain the stored
contents.
FletcherMunson Curves Fletcher
and Munson were researchers in the '30s who first accurately measured
and published a set of curves showing the human's ear's sensitivity
to loudness verses frequency. They conclusively demonstrated that
human hearing is extremely dependent upon loudness. The curves
show the ear to be most sensitive to sounds in the 3 kHz to 4
kHz area. This means sounds above and below 34 kHz must be louder
in order to be heard just as loud. For this reason, the
FletcherMunson curves are referred to as "equal loudness
contours." They represent a family of curves from "just
heard," (0 dB SPL) all the way to "harmfully loud"
(130 dB SPL), usually plotted in 10 dB loudness increments.
floating unbalanced line
A quasibalanced output stage consisting of an unbalanced output
connected to the tip of a ¼" TRS (tipringsleeve)
jack through an output resistor (typically in the 50300 ohms
range). An equal valued resistor is used to tie the ring
terminal to signal ground. The sleeve connection is left
open or "floating." Thus, from the receiver's viewpoint,
what is "seen" are two lines of equal impedance, used
to transfer the signal. In this sense, the line is 'balanced,"
even though only one line is actually being driven. Leaving the
sleeve open, guarantees that only one end of the shield (the receiving
end) will be grounded. A practice that unbalanced systems often
require. For troublefree interconnections, balanced lines are always the preferred choice.
FM (Frequency Modulation) the
frequency of the modulating signal is changed in proportion to the
input audio signal.
FOH Abbreviation for front of house,
used to describe the main mixer usually located in the audience
for sound reinforcement systems. Meant to differentiate the main
house mixer from the monitor mixer normally located to the side
of the stage.
foldback The original term for monitors,
or monitor loudspeakers, used by stage musicians to hear themselves
and/or the rest of the band. The term "monitors" has replaced "foldback"
in common practice
foreground music Officially
music with (or without) lyrics used where it is believed people
will pay attention to it. Foregroun music is often performed by
the original recording artist. Contrast with background
music.
Fourier analysis Mathematics. Most often the approximation
of a function through the application of a Fourier series to periodic
data, however it is not restriced to periodic data.
The Fourier series applies to periodic data only,
but the Fourier integral transform converts an infinite
continuous time function into an infinite continuous frequency
function, with perfect reversibility in most cases. The DFT
and FFT are examples of the Fourier analysis.
Fourier, Baron Jean Baptiste Joseph (17681830)
French mathematician and physicist who formulated a method for
analyzing periodic functions and studied the conduction of heat.
Fourier series Application
of the Fourier theorem to a periodic function, resulting
in sine and cosine terms which are harmonics of the periodic frequency.
[After Baron Jean Baptiste Joseph Fourier.]
Fourier theorem A mathematical
theorem stating that any function may be resolved into sine and
cosine terms with known amplitudes and phases.
FPGA (fieldprogrammable gate array)
A programmable logic device.
FPS (Frames Per Second) The Frequency at which
video frames are transmitted and displayed on a video display.
Broadcast vidio (NTSC standard) containes 60 1/2 frames per second
alternating between the even and odd line sets.
Videoconferencing links may support as few as 10 FPS.
Frame Relay A highspeed packet switched protocol used
for wide area networks (WANs). It is faster that older x.25
networks, because it was designed for today's faster and more
reliable circuits and therefore performs less rigorous error
correction. It provides for scaled transfer rates up to DS1
rates of 1.544 Mbps.
frequency 1. The property or condition of reoccurring
at constant measurable intervals. The number of times a specified
phenomenon occurs within a specified interval, such as the number
of repetitions per unit time for a complete waveform. Usually
measured in hertz.
Frequency Response A measure
of a component's ability to reproduce all frequencies equally.
Sometimes called magnitude response, it is the measurement of the
amplitude linearity of a component over a given frequency range.
It is usually presented as a plot of the output of a device versus
frequency. The term is sometimes used to characterizes the range
of frequencies over which a device is designed to operate without
stating dB range of
variations. The perfect frequency response should
theoretically be flat ( a straight line graph ), however, most
components exhibit some dips and peaks in the signal; varying to
some degree from a perfect response Most amplifiers and
other electronic audio components can easily reproduce the entire
audible spectrum. However, speakers that can reproduce the entire
audile spectrum are more difficult to create. Excessive
fluctuations in a curve indicate colorations, which can result in
muddy, tinny, boomy or dull sound
full duplex Redundant term. See: duplex
Full Motion Video Compressed video that provides a frame
rate that is generally acceptable to users although not of
broadcast quality. Typical full motion compressed video provides
from 10 to 30 FPS depending on the bandwidth available.

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