U

UART
An acronym standing for Universal asynchronous receiver/transmitter. A UART is an integrated circuit (chip) found in most modern computers that interfaces a microprocessor to a serial I/O port.
UL
Short for Underwriters' Laboratories, which is a standards and testing agency financed by the insurance industry. The purpose of UL testing is to ensure fire safety of electrical equipment. A device which has been tested and passed by UL will have the familiar round label of certification. UL approval has nothing to do with the audio quality or the functionality of a device. In some states UL approval is a requirement in order to sell equipment that uses electricity.
Ultra SCSI
Ultra SCSI, or FAST-20, is an emerging high-performance SCSI standard which began as an offshoot of the SCSI-2 command set, and is also incorporated in the SCSI-3 parallel command set. Ultra SCSI effectively doubles the maximum transfer rates provided under Fast SCSI-2 to up to 20MB per second on an 8-bit bus and up to 40MB per second on a 16-bit bus (called Ultra Wide). Its terrific performance specifications make Ultra SCSI an attractive data storage and retrieval system for high-end servers and workstations.
Ultra2 SCSI
Ultra2 SCSI, also known as FAST-40 is the latest generation of SCSI delivering faster bus speed and longer cable lengths for today's systems and peripherals. Utilizing Low Voltage Differential (LVD) technology, Ultra2 SCSI enables faster data rates and longer cable lengths on the SCSI bus. It doubles the data burst rate of Ultra Wide SCSI (see WFTD archive Ultra SCSI) to 80 MByte/sec, providing greater system throughput. And it quadruples the maximum cable length of Ultra Wide SCSI to 12 meters, allowing increased flexibility. The benefit of the 80 MB/sec throughput is that data intensive applications, such as CAD/CAM, database access, and 3-D imaging, process more rapidly with Ultra2 SCSI I/O. The greater SCSI bus length translates into greater flexibility in adding external storage and in configuring clustered servers.
Ultra2 Wide SCSI
A wide version of Ultra2 SCSI. Having a 16-bit bus, Ultra2 Wide is one of the fastest SCSI formats currently available and is used in the most demanding audio or video applications.
Ultra Wide SCSI
Basically Ultra Wide SCSI is a cross between Ultra SCSI and Wide SCSI (which we have not yet defined). Ultra Wide SCSI doubles the bit width of Ultra SCSI from an 8-bit bus to a 16-bit bus, providing much more data throughput (up to 40 MB per second). Ultra Wide SCSI has become the SCSI format of choice for many demanding audio and video hard disk applications.
Ultrasonic
Having frequencies above the range of human hearing, commonly considered to be 20 kHz. Not to be confused with "supersonic," which means faster than the speed of sound. Ultrasonic frequencies in the signal path can sometimes cause distortion in audio components that are in the human hearing range and quite audible.
Unbalanced
  1. Uneven (as in many musician's salary histories)
  2. Prone to tipping over (like many musicians after Saturday night's bar gig)
  3. An unstable mental condition (like some inSync editors we could mention...)
  4. In electronics, a condition where the two legs of the circuit are unbalanced with respect to ground, usually because one leg is kept at ground potential. In other words: An audio signal requires two wires or conductors to function. In an unbalanced situation, one of those conductors is used to carry both signal and ground (shield). Unbalanced circuits tend to be less expensive to construct, but they are much more susceptible to induced noise problems than their balanced counterparts. This is because any induced noise in one conductor is not canceled by similar noise in the other conductor (as in a balanced line) and may be carried with signal into connected equipment. In general, unbalanced lines should be kept as short as possible (certainly under 25-30' maximum) to minimize potential noise problems.
Unformated Capacity
The opposite of formatted capacity (see WFTD archive Formatted Capacity). It is the capacity of a disk drive (in number of bytes of data that can be stored on the disk) before it is formatted for a particular kind of computer. Unformatted capacity is a physical property of the drive, relating to the number of platters and the density of data on the platters.
Unidirectional
With reference to microphones, the opposite of omnidirectional (see WFTD archive, "omnidirectional"). A unidirectional microphone is one which is more sensitive to sound from one direction than from others. The level of "unidirectionality" will vary with the mic's particular polar pattern (i.e. cardioid, hypercardioid, etc.). There is no such thing as a perfectly unidirectional microphone, but the more unidirectional a mic is, the better it is able to reject off-axis sound, producing more isolated signals.
Unison
In music the word unison is used to describe an identity of pitch. When two or more tones are sounding at the same frequency or pitch they are said to be in unison with one another.
Unity Gain
A device or setting which does not change signal level (amplify or attenuate the signal) is said to be at "unity gain." Many processors are set up for unity gain; that is, they can be plugged into a system without changing its overall levels. In practice, unity gain is often a desired setting for maintaining gain staging, and for optimizing operating levels and signal to noise ratios.
UPS
Abbreviation for Uninteruptable Power Supply. A device that is designed to provide electrical power to critical equipment in the event of brown outs or black outs of the normal electrical service. They exist in a wide variety of sizes, shapes, and capabilities, but are all based on the same principles. They employ a battery that stays charged while the electrical service is in operation. In the event of a power event such as a brown out or black out the battery takes over and supplies the required power to keep equipment online. In the modern day era of critical computer (and other) systems it is common to find these devices in most businesses and a growing number of homes. Because of their cost, however, their use is usually limited to critical systems that need to run constantly. Obviously a battery has a limited time it will operate, but the idea is to cover short-term power events and/or at least provide some time to properly shut down volatile systems.
USB
An abbreviation for Universal Serial Bus. USB is an emerging standard for interconnecting PCs with peripheral devices. The USB standard was developed by Compaq, DEC, IBM, Intel, Microsoft, NEC, and Northern Telecom to provide an intelligent serial bus for low to mid-speed peripherals. The USB standard allows new peripherals to be configured automatically upon attachment without the need to reboot or run setups. USB will also allow up to 127 devices to run simultaneously on a computer with the capability to perform isochronous data transfers, which can be assigned to meet specific bandwidth targets to support audio and/or phone and data conversations. There is not enough bandwidth, however, to do video as FireWire does. USB is a real boon to the Windows based PC community because it all but eliminates frustrating set up issues historically encountered when new peripherals must be connected. Further, as a standard it reduces the overall cost and confusion of getting devices connected to any computer.

Not only is USB a new standard for interfacing computer hardware, but it also stands for Upper Side Band. This is the name given to the by-product of the new signal created when modulating a signal with another signal, as happens in broadcast and FM synthesis. The Upper Side Band is the result of summing the two signals together.

UV-22
A process developed and patented by Apogee Electronics for maximizing the dynamic range of digital audio. UV-22 is sometimes referred to as a dithering or bit-mapping scheme. While it is very similar to these conceptually, it is a unique process. UV-22 encoding adds an inaudible, high-frequency 'bias' to the digital bit stream, placing an algorithmically-generated 'clump' of energy around 22kHz. Much as the bias on an analog tape recorder smoothes out magnetic tape recording non-linearity, UV-22 silently captures resolution up to and even beyond 20 bits on standard, 16-bit digital audio. Many pros use UV-22 upon final mixing to a 16-bit format for CD release.