Glossary of Audio, Video and Home Theater Terms
There is a very large vocabulary of technical and descriptive terms that go with home theater. We've included the terms that you are most likely to encounter. If you are very technically involved you may find some of the more technical terms omitted from our list.
Click on a letter to jump to that section of our glossary
AAC - Advanced Audio Coding. An audio codec
used increasingly for downloaded music files, streaming-media,
and satellite-radio applications.
AAD - Analog Analog Digital. A designation that indicates the recorded material was first recorded with analog equipment, then remixed on analog equipment and finally placed onto a digital recording medium.
AC - Alternating Current. The standard
electrical current delivered to homes and businesses in the
U.S. As opposed to DC - Direct Current.
AC-3 - The original named used for Dolby
Digital. The name was later changed to feature the Dolby name.
Accuracy - When audio or video signals
pass through a component, the signal may be changed slightly.
The closer the output is to the original input, the greater
the accuracy of the component.
Acoustic Suspension Speaker - A sealed-box
speaker that uses the air behind the woofer to control cone
movement.
Active Speaker - A speaker which includes
an integral power amplifier to power or drive the speaker.
Active Scan Lines - The scan lines in a
video frame that carry picture information rather than data
for closed captioning or synchronization.
A/D - Analog to Digital. Refers to the
conversion of analog sound or video to digital during storage,
manipulation, or recording.
ADD - Analog Digital Digital. A designation
that indicates the recorded material was first recorded with
analog equipment, then remixed on digital equipment and finally
placed onto a digital recording medium.
Adjacent Channel Selectivity - When tuning
an FM station, the next station up or down the dial may interfere
with the signal. A tuner's ability to reject those neighboring
signals is measured by its selectivity.
ALiS - Alternate Lighting of Surfaces. An HD plasma panel technology designed to optimize performance when displaying 1080i material. Alternate rows of pixels are lit, similar to interlaced scanning. The resulting picture is bright, clear and improves the smoothness of movement as well extending the life of the plasma panel.
AM - Amplitude Modulation. The encoding
of a signal into a radio wave by modulating its amplitude (the
height of the wave). As opposed to FM, frequency modulation,
wherein the frequency of the wave is modulated.
Amplifier - An audio component that takes line level audio inputs and increases the gain or level and outputs the signal to speakers. Amplifiers are used with other separate components or can be integrated together to make an Integrated Amplifier. Amplifiers are also available for other signals besides audio.
Analog - When a signal is continuously variable,
it is analog. When a signal is broken into units that are rounded
to discrete values, it is digital. Analog signals contain "all of the data" but
it is prone to interference and degradation. It is not possible
to catch and remove all of the interference from an analog signal
and so the quality declines as it travels to your TV. With a
digital signal, certain values are expected. When a value is
received that is not within the expected range, it can be filtered
or adjusted. This ability to detect and filter or repair a digital
signal makes it possible to deliver a signal to your TV that
is as good as when it left the studio.
Anamorphic - It
is the preferred DVD format for widescreen (16:9) TVs because
the image is restored to its widescreen format without any reduction
in image quality. Anamorphic DVDs contain the highest level
of resolution (460 to 480 lines) and thus yield the best picture
quality. DVDs are often not labeled as anamorphic, so look also
for the words "enhanced", " widescreen", "16:9". DVDs labeled "letterboxed" and in most cases "fullscreen" will
have reduced image quality or even have some of the image edited
to force it to fit a 4:3 screen. Anamorphic DVDs can be played
on regular 4:3 TVs, but unless your TV or DVD player has a setting
to vertically adjust the image, it will appear tall and thin.
ANSI Lumens - A standard
for measuring the brightness of a projection TV. ANSI is the
organization that set the standards for measurement. The IEC
is now the organization setting the standard, but manufacturers
are reluctant to switch, fearing consumer confusion.
Antenna - A device for transmitting or receiving signals. The size and shape of antennas are determined primarily by the frequency of the signal they are designed to receive. A high gain antenna is highly focused, whereas a low gain antenna receives or transmits over a wide angle.
Artifact - Any imperfection in a video
image resulting from digital processing such as interlacing,
up or down-conversion of the signal or conversion from a native
to non-native format and vice-versa.
Aspect Ratio - Essentially the shape of
the screen or image. It is the ratio of the width to the height.
The standard square television screen is 4:3 or 1.33:1, while
widescreen TV is 16:9 or 1.78:1. Most modern films are released
in 1.85:1 or 2.35:1 aspects, which means that even on a widescreen
TV the image will result in black bars at the top and bottom
of the screen.
ATSC - Advanced Television Systems Committee. The organization that set the U.S. HDTV standards. It also refers to the TV channel tuner used to tune in HD signals. Compare to the NTSC which set the standard for pre HDTV signal and the tuner that tunes analog programming.
Attenuate - To decrease or otherwise reduce,
as in to attenuate signal noise.
ATV - Advanced Television. The system
and the standards defined by the ATSC.
Auto-Reverse - A feature that automatically
reverses a tape when it reaches the end.
Auto-Rewind - A feature that automatically
rewinds a tape to its beginning when it reaches the end.
A/V Receiver - Also called a Home Theater
receiver, sometimes the term "integrated" is also
used. Receivers take audio signals from components such
as a CD player, tape deck and phonograph, amplify it and
output it to the speakers. An A/V receiver is designed to
also accept video inputs, such as from a DVD player, cable
box and VCR, and output the signal to a television. In most
cases the video signal is not processed but simply passed
through to the TV. A/V receivers, in most cases, also have
Dolby and DTS decoders to play multi-channel audio.
A/V Inputs - The connections on any
component, such as a TV, receiver or VCR that enable connection
to other output devices. The inputs often take the form
of RCA jacks.
Audio outputs - An audio output is a connection (most often
an RCA jack) on a device, such as a TV, that can be connected
to a stereo or home theater system. A fixed output means the
stereo is used to control the volume. A variable output means
that the TV and the stereo can each control the volume.
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