AV/IT Glossary—27 Days of #AVabc—U





UHD—Ultra-high-definition (UHD) television, also abbreviated UHDTV, is a digital television display format in which the horizontal screen resolution is on the order of 4000 pixels (4K UHD) or 8000 pixels (8K UHD).


Technically, a 4K UHD display has 3840 pixels horizontally and 2160 pixels vertically for a total of 8,294,400 pixels or 8.3 megapixels. An 8K UHD display has 7680 pixels horizontally and 4320 pixels vertically for a total of 33,177,600 pixels or 33.2 megapixels. Therefore, 4K UHDTV has roughly four times as many pixels as conventional HDTV (high-definition television), and 8K UHDTV has roughly 16 times as many pixels as conventional HDTV.


According to the Consumer Electronics Association, a display must have at least one digital input with a native (design) resolution of 3840 by 2160 pixels, along with an aspect ratio of at least 16:9, in order to qualify as UHD. Both the 4K and 8K UHD specifications described above scale precisely from the most common HDTV formats, avoiding image blurring and consequent loss of detail that can occur when differing screen resolutions fail to evenly divide horizontally or vertically.




UDP (User Datagram Protocol)—A connectionless protocol providing “best effort” delivery of packets across networks. UDP is frequently used in real-time streaming applications were best effort delivery is acceptable and the network devices and applications manage data flow control and errors.

UHF-Ultra High Frequency—A television broadcast frequency range between 300 and 3000 MHz on channels 14 through 83. Also the name for a type of connector used for video cables.

UL® - Underwriters Laboratories—When marked by the UL symbol, a product has been tested and evaluated according to nationally recognized safety standards with regard to fire, electric shock, and related safety hazards. There is also a UL for Canada, sometimes called CUL, and a UL recognized component with its own symbol, resembling a backward "UR."

Ultra Physical Contact-UPC—In fiber optics, a specific endface polish for a connector to achieve typically a -60 dB return loss in singlemode applications. UPC has become the most common polish for fiber optic connectors in digital applications. UPC polished connectors can be used with PC or SPC polished connectors but are not compatible with APC polished connectors. Intermixing APC polished connectors with UPC/SPC/PC polished connectors can damage the fiber optic cable or equipment. Multimode applications always use PC, SPC, or UPC polished connectors.

Ultraviolet (IR)—Having a wavelength shorter than that of the violet end of the visible spectrum but longer than that of X-rays.

Unbalanced Audio—An audio output where one of the two output terminals is at ground potential.

Unbalanced Circuit—Transmits the audio signal on a single conductor that is referenced to ground.

Unbalanced Connection—Connection method in which the audio signal is carried on two conductors, called signal and ground. Contrast with balanced connection, in which the audio signal is carried on three conductors.

Underfilled Launch Condition-ULC—In fiber optics, a condition where the incoming light only fills a small percentage of the fiber core.

Underscan—A decreasing of the raster size (H and V) so that all four edges of the picture are visible on the screen. Underscanning allows viewing of skew and tracking that would not be visible in normal (overscanned) mode. It is also helpful when aligning test charts to be certain they touch all four corners of the raster. Likewise, when checking the alignment of multiplexer images from a film chain, underscan allows proper framing of the projected image going into the video camera.

Unicast—The sending of messages to a single network destination host on a packet switching network. Sending a separate copy of the media stream from the server to each recipient.

Unity Gain—Derived from the number 1, unity gain refers to no change in gain.

Upconvert—Changing a video signal from one scanning rate to a signal with a higher scanning rate. HD-ready televisions upconvert 480i signals to a higher scanning rate for display.

Up Link—The transmission of a signal to a satellite, or the primary link in a microwave system.

UPS-Uninterruptible Power Supply—A power supply that continues to provide voltage for a limited time after the main power is off (fails).

Uptime—Uptime is a computer industry term for the time during which a computer is operational. Downtime is the time when it isn't operational. Uptime is sometimes measured in terms of a percentile. For example, one standard for uptime that is sometimes discussed is a goal calledfive 9s - that is, a computer that is operational 99.999 percent of the time.

URL-Uniform Resource Locator—This is the address that lets a resource on the internet be identified, located, and accessed

USB—A Universal Serial Bus (USB) is a common interface that enables communication between devices and a host controller such as a personal computer (PC). It connects peripheral devices such as digital cameras, mice, keyboards, printers, scanners, media devices, external hard drives and flash drives.

USB 1.1-Universal Serial Bus 1.1.—An external bus standard that supports data transfer rates of 12Mbps and 1.5Mpbs. A single USB port can connect up to 127 peripheral devices.

USB 2.0-Universal Serial Bus 2.0—An external bus standard that supports data transfer rates up to 480Mbps, 12Mpbs, and 1.5Mpbs. USB 2.0 is an extension of USB 1.1 and is backward compatible with USB 1.1, using the same cables and connectors.

User Interface—The “look” and “feel” of the controls and displays on a home-theater product.

UTP—Unshielded twisted pair cable typically used for data transfer, contains multiple 2-conductor pairs twisted at regular intervals, employing no external shielding.

UV-Ultraviolet—Light/heat rays that have a shorter wavelength (and higher frequency) than those in the visible spectrum. UV rays are ordinarily filtered or blocked to prevent eye damage and dye fading.

UXGA-Ultra Extended Graphic Array—1600 x 1200. A UXGA display has 1600 horizontal pixels and 1200 vertical pixels giving a total display resolution of 1,920,000 individual pixels that are used to compose the image delivered by a projector.

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