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Glossary
Advanced Audio Coding (AAC) — A standardized compression and encoding scheme for
lossy (low quality) digital audio. Higher bit rates provide higher quality. Part of the
MPEG-2 and MPEG-4 specifications. The SME 211 supports AAC-LC (MPEG-2 part 7,
MPEG-4 part 3, sub-part 4 and part 14, MP4 audio).
Advanced Video Coding (AVC) — Video compression format, H.264/MPEG-4 part 10
(see the
H.264 (MPEG-4 AVC)
definition on page 111).
Address Resolution Protocol (ARP) — A protocol for assigning an
IP address
(see
page 112) to a device based on the device
MAC (Media Access Control)
(see
page 112) address or physical machine address, that maintains a table showing the
correlation between the two.
Aspect ratio control — The aspect ratio of the video output can be controlled by selecting
a fill mode, which provides a full screen output, or a follow mode, which preserves the
original aspect ratio of the input signal.
Auto-Image — An Extron technology for scan converters and signal processors that
simplifies setup by executing image sizing, centering, and filtering adjustments with a single
button push.
Auto Memory — Auto memory recalls input and image settings for signals that have
previously been applied. If this feature is disabled, the device treats every newly applied
input as a new source.
B-frames — Bidirectionally predictive coded picture. Contains predictive, difference
information from the preceding and following I- or P-frame within a
GOP
(see page 111).
Data preceding or following the B-frame are required to recreate video information in a
B-frame. They offer significantly better compression than I or P frames, but are not available
in Baseline profile.
Bandwidth — The total range of frequencies required to pass a specific signal without
significant distortion or loss of data. In analog terms, the lower and upper frequency limits
are defined as the half power, or -3 dB signal strength drop, compared to the signal strength
of the middle frequency, or the maximum signal strength of any frequency, expressed as
xx Hz to xx kHz (or MHz) @ -3 dB. In digital terms, it is the maximum bit rate at a specified
error rate, expressed in bits per second (bps). The device bandwidth should be wider than
the highest possible bandwidth of the signals it may handle. (In general, the wider the
bandwidth, the better the performance. However, bandwidth that is too wide can pass
excessive noise with the signal.)
Baud — The speed of data transmission, often in bits per second or megabits per second.
Bit rate — The number of bits that are conveyed or processed per unit of time. Bit rate is
quantified using the bits per second (bit / s) unit, often in conjunction with an SI prefix such
as kilo- (kbit / s or kbps), mega- (Mbit / s or Mbps), or giga- (Gbit / s or Gbps).
Codec — (1) Coder/decoder: A device that converts analog video and audio signals into a
digital format for transmission over telecommunications facilities and also converts received
digital signals back into analog format. It may also dial up the connection, like a modem for
teleconferencing. (2) Compressor/decompressor. Codecs can be implemented in software,
hardware, or a combination of both.
Compression — The art and science of reducing the amount of data required to represent
a picture or a stream of pictures and sound before sending or storing it. Compression
systems are designed to eliminate redundant or repeated information to the desired data
level while allowing the original information to be reproduced to the desired quality.
SME 211 • Reference Information
109
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