Appendix B • Reference and Glossary
Extron • User’s Manual • RGB 320 Switching Interface System
Glossary of Terms
For a complete glossary, see Extron’s web site (http://www.extron.com)
AC –
Alternating current. The flow of electrons that changes direction alternately.
AC reset –
The status that changes when power is removed from a device. Many electronic
devices have live power inside, even after “power off” has been initiated from a
panel or remote control device. This is not the same as “AC reset”, when power is
removed at the AC cord.
Amp –
Ampere. The international base unit of electric current. Symbolized by “A”. 1 amp
is equal to the steady current produced by 1 volt applied across a resistance of 1
ohm.
Analog –
A continuous action or movement that takes time to make a transition from one
level to another. Standard audio and video signals are analog. An analog signal
has an infinite number of levels between its highest and lowest value. (Changes
are not made by steps, such as with digital.)
ANSI –
American National Standards Institute. The organization that sets standards for
US A/V equipment.
ASCII –
American Standard Code for Information Interchange. The standard code
consisting of 7-bit coded characters (8 bits including parity check), utilized to
exchange information between data processing systems, data communication
systems and associated equipment. The ASCII set contains control characters
and graphic characters.
Attenuation –
To reduce the amplitude (strength) of a signal or current.
Audio follow –
A term used when an audio signal is tied to the video signal and they are switched
together; the opposite of
breakaway.
Balanced audio –
Audio circuits that use three conductors for one audio signal: plus (+), minus (-)
and ground. The ground conductor is strictly for shielding, and does not carry any
signal. Also called
differential audio.
Bandwidth –
A frequency range, or “band” of frequencies, between the limits defined by the
“half power points”, where the signal loss is -3dB. In audio and video, it is this
band of frequencies that can pass through a device without significant loss or
distortion. The wider the bandwidth, the better the quality that results, such as a
sharper picture, better sound, etc. The higher the bandwidth number, the better
the performance. (300 MHz is better than 250 MHz.) When a signal passes
through a path with more than one device (including cables), the limiting factor
(bottleneck) in that path is the device with the narrowest bandwidth.
Blooming –
Most noticeable at the edges of images on a CRT, “blooming” is when the light
hitting the screen is too intense and overdrives the phosphors. The edges of an
image seem to exceed its boundaries. Thin lines and sharp edges may look thick
and fuzzy. This may be caused by the brightness being set too high, or by a high
voltage problem.
BNC –
A cylindrical bayonet connector that operates with a twist-locking motion. Two
curved grooves in the collar of the male connector are aligned with two
projections on the outside of the female collar. This allows the connector to be
locked in place without tools.
Breakaway –
The ability to separate video and audio signals for the purpose of switching them
independently. For example, an audio and video signal from the same source
may be “broken away” and switched to different destinations. This is the opposite
of
audio follow.
Buffer –
Generally referred to as a unity gain amplifier, a buffer is used to isolate the signal
source from the load. A buffer can be used for digital or analog signals. The
RGB 322, 324, 326 and 340 are input buffers to the RGB 320 switching interface.
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