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Dictionary of Audio Terminology - U


"U" - Abbreviation for the "modular unit" on which rack panel heights are based. Per the EIA and ANSI standard ANSI/EIA-310-D-1992 Cabinets, Racks, Panels, and Associated Equipment, the modular unit is equal to 44.45 millimeters (1.75"). Panel heights are referred to as "nU" where n is equal to the number of modular units. Examples are 1U (1.75" high), 2U (3.5" high), 3U (5.25" high), etc. Popularly called rack units and often abbreviated "RU," which is technically incorrect but not misleading.

UART - universal asynchronous receiver-transmitte - The device that performs the bidirectional parallel-to-serial data conversions necessary for the serial transmission of data into and out of a computer.

UDP - user datagram protocol - A TCP/IP protocol describing how messages reach application programs within a destination computer. This protocol is normally bundled with IP-layer software (UDP/IP). UDP is a transport layer, connectionless mode protocol, providing a datagram mode of communication for delivery of packets to a remote or local user. UDP/IP has almost no error recovery services, and is used primarily for broadcasting messages over a network.

UDP/IP - user datagram protocol/internet protocol

UHF - Ultra-High Frequency - designates the ITU Radio frequency range of electromagnetic waves between 300 MHz and 3 GHz (3,000 MHz), also known as the decimetre band or decimetre wave as the wavelengths range from one to ten decimetres (10 cm to 1 metre).


UI - user interface - As compared with GUI.

ULD - ultra low delay coder - One of Fraunhofer's (creator of MP3) proprietary forms of digital audio compression.

ULF - ultralow frequency - An electromagnetic wave whose frequency is less than 3,000 hertz.

ULSI - ultra-large-scale integration - A logic device containing a million or more gates.

ultra-directional sound systems - Pioneered by Dr. F. Joseph Pompei in the late '90s while a grad student at MIT, and patented as US Patent 6,775,388, Ultrasonic Transducers, granted 2004, this technology allows audio reproduction with extreme directionality. Using this technology sound can be literally spotlighted to whatever location is desired, producing audio at that spot only with very minimal leakage. While the ultrasonic transmission is not audible, it works by creating intermodulation frequency products at the beam's end that are audible.

ultraharmonic response - Frequencies that are not whole number multipliers but fractional multiples of the fundamental frequency of the system, e.g. 1.5 or 2.5 times the fundamental frequency. Contrast with harmonic.

ultrasonic - Of or relating to acoustic frequencies above the range audible to the human ear, or above approximately 20,000 hertz. Compare with supersonic.

ultrasonography – (1) Diagnostic imaging in which ultrasound is used to image an internal body structure or a developing fetus (also called echography). (2). An imaging technique that uses high frequency sound waves to visualize underwater surfaces, boundaries, objects, and currents.

Ultrasound - Sound at ultrasonic frequencies in any medium. The use of ultrasonic waves for diagnostic or therapeutic purposes, specifically to image an internal body structure, monitor a developing fetus, or generate localized deep heat to the tissues.

U-matic - Sony's trademarked name for their 3/4" helical-scan professional videocassette technology.

unbalanced line - an unbalanced line is a transmission line whose conductors have unequal impedances with respect to ground.

unblooped - Pertaining to motion-picture soundtrack negative wherein the discontinuities due to splices have not been minimized by making opaque the area near the splice with "bloopiing" tape or ink.

undamped - not tending toward a state of rest; not damped. Used of oscillations.

undamped frequency - Of a second-order linear system without damping, the frequency of free oscillation in radians per unit time or in hertz.

underdamped - Damped insufficiently to prevent oscillation of the output following an abrupt input stimulus.

undersampling - The use of too low a sampling frequency, resulting in aliasing.

underwater acoustics - The science of sound propagation in the sea, and of sound radiation and scattering by underwater objects.

unicasting - One-to-one communication (as opposed to broadcasting or multicasting).

unicasting Bundle - One-to-one routing of audio on the network.

Unicode - A universal system that provides a unique number for every character, regardless of platform, program, or language.

unidirectional microphone - directional microphone - One that is most sensitive to sound arriving directly at its front. Compare with omnidirectional mic and cardioid microphone.

Unidyne™ - Shure Model 55 Unidyne microphone designed by Benjamin Bauer and first sold in 1939 was the first single-element unidirectional microphone. Its performance qualities and distinctive styling ultimately make it “the most recognized microphone in the world.”

unilay - A conductor with more than one layer of helically laid wires with the direction of lay and length of lay the same for all layers.

Unimorph - A cantilever device having one active piezoelectric layer and one inactive non-piezoelectric layer. Compare with: bimorph.

units of measurement - International System of Weights and Measures, the metric system, and all English customary units.

unity gain - A gain setting of one, or a device having a gain of one, i.e., it does not amplify or attenuate the audio signal. The output equals the input.

unity power factor - In an AC circuit, a power factor equal to one, which only occurs when the voltage and current are in phase, i.e., for a purely resistive circuit, or a reactive circuit at resonance.

unmodulated track - An optical soundtrack containing no deliberate signal. For variable-area soundtracks, unmodulated track is made narrow when there is no signal present to reduce the noise caused by the optical grain of the film.

upbeat – (1) An unaccented beat or beats that occur before the first beat of a measure. Also called anacrusis and pickup. (2) The upward stroke made by a conductor to indicate the beat that leads into a new measure.

upcut - Chopping off the beginning of the audio or video of a shot or video story.

UPS - uninterruptible power supply - A back-up battery-powered supply (commonly used with computers) that automatically continues to supply power when the main AC source fails. Variations exist where the system always runs from the UPS (the AC line keeps the batteries charged when present), offering immunity from AC line fluctuations and noise.

upstage - The back of the stage farthest from the audience, as opposed to downstage.

URL - uniform resource locator - A Web address. A consistent method for specifying Internet resources in a way that all Web browsers understand.

USB - universal serial bus - A low-speed (12 Mbits/sec) serial bus that acts like a special purpose local area network. Originally proposed by a consortium of Compaq, Digital, IBM, Intel, Microsoft, NEC and Northern Telecom in March of 1995, it is now the standard PC serial connection. USB equipped machines typically have only three ports: USB, monitor, and Ethernet LAN. The USB port supports 63 devices, and eliminates the need for all specialized parallel, serial, graphics, modem, sound/game or mouse ports. USB is completely "plug and play," i.e., it detects and configures all devices automatically, and allows "hot swapping" of devices.

USITT - United States Institute for Theatre Technology - The association of design, production, and technology professionals in the performing arts and entertainment industry.

universal time - Abbr. UT The mean solar time for the meridian at Greenwich, England, used as a basis for calculating time throughout most of the world. Also called Greenwich time, Greenwich Mean Time, Zulu time.

UT - universal time .

UTP - unshielded twisted-pair.

UWB - ultrawideband radio - A type of wireless broadband radio that emits a broad spectrum of radio waves, potentially causing interference; also called impulse radio. FCC defines it as a bandwidth of at least 20% of the center frequency, or at least 500 MHz.

UV – ultraviolet - Electromagnetic radiation at frequencies higher than visible light yet lower than those of x-rays. Commonly used to erase EPROMs and in wireless and fiber optic data transmission.




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HistoryOfRecording.com acknowledges the Elsevier, Inc. publication, Audio Engineering know it all, the University of Washington Press publication, The Audio Dictionary, second edition, the Howard W. Sames & Co., Inc. publication, Audio cyclopedia, the Cambridge University Press publication, The Art of Electronics, Rane Corporation (Dennis A. Bohn, CTO), Houghton Mifflin Company publication, The American Heritage Dictionary of the English Language, Fourth Edition, the IEEE publication, IEEE 100: The Authoritative Dictionary of IEEE Standards Terms, Seventh Edition and Wikipedia in the preparation of this Dictionary of Audio Terminology.

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