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A/D An acronym for “Analog to Digital,” which refers to the conversion of analog signals to digital data.


Acronym A word formed from the first letters of other words (e.g., GUI, ADAT, TRS, etc.).


ADAT An acronym for “Alesis Digital Audio Tape.” ADAT was the name given to the Alesis-branded products of the 1990s which recorded eight tracks of digital audio on a standard S-VHS video cassette. The term now generally refers to the 8-channel optical “Lightpipe” connection that is used in a wide range of digital products from many manufacturers.


AES (sometimes written as “AES/EBU“) The name of a digital audio transfer standard jointly developed by the American-based Audio Engineering Society and the European Broadcast Union. Designed to carry two channels of 16-, 20- or, 24-bit digital audio at sampling rates of up to 192kHz, the most common AES physical interconnect utilizes a 3-conductor 110 ohm twisted pair cable, terminating at standard XLR connectors. (See “Dual Wire” and “Single Wire”)


Analog Literally, an analog is a replica or representation of something. In audio signals, changes in voltage are used to represent changes in acoustic sound pressure. Note that analog audio is a continuous representation, as opposed to the quantized, or discrete “stepped” representation created by digital devices. (See “Digital”)


API Acronym for Application Programming Interface. A software layer between an operating system and third-party hardware (such as an audio interface) and/or software (such as a DAW). For example, a computer OS’s audio API enables audio hardware and audio software from different vendors to communicate with the OS and each other.


ASIO Acronym for Audio Stream Input/Output. ASIO is an audio interface driver protocol for Windows operating systems developed by Steinberg GmbH.


Authorize / Authorization Authorizing the UAD/Apollo system updates the list of plug-ins owned by the user. UAD plug-ins must be authorized before they can be used.           

Balanced Audio cabling that uses two twisted conductors enclosed in a single shield, thus allowing relatively long cable runs with minimal signal loss and reduced induced noise such as hum.


Bit A contraction of the words “binary” and “digit,” a bit is a number used in a digital system, and it can have only one of two values: 0 or 1. The number of bits in each sample determines the theoretical maximum dynamic range of the audio data, regardless of sample rate being used. Each additional bit adds approximately 6 dB to the dynamic range of the audio. In addition, the use of more bits helps capture quieter signal more accurately. (See “Sample” and “Dynamic range”)


Bit Depth (See “Bit Resolution”)               


Bit Resolution Often used interchangeably with “bit depth,” this is a term used to describe the number of bits used in a digital recording. Apollo converts analog audio and transmits digital audio with a resolution of 24 bits (thus yielding a theoretical dynamic range of approximately 145 dB), the highest audio interface resolution in common use today. (See “Dynamic Range”)


BNC A bayonet-type coaxial connector often found on video and digital audio equipment, as well as on test devices like oscilloscopes. In digital audio equipment, BNC connectors are normally used to carry word clock signals between devices. BNC connectors are named for their type (Bayonet), and their inventors, Paul Neil and Carl Concelman. (See “Word Clock”)


Buffer, buffers, buffering The transference of data in small batches instead of continuously. Buffering induces latency (delay) and is inherent in most digital audio systems.


Bus A signal path that carries more than one signal, e.g., a mix bus, auxiliary bus, headphone cue bus, etc.


Channel Input Strip A group of controls that pertain only to the functions contained within a particular mixer input channel. In most mixing consoles, the “strips” are duplicated for each input.


Class A One design technique used in electronic devices such that their active components are drawing current and working throughout the full signal cycle, thus yielding a more linear response. This increased linearity results in fewer harmonics generated, hence lower distortion in the output signal.


Condenser Microphone A microphone design that utilizes an electrically charged thin conductive diaphragm stretched close to a metal disk called a backplate. Incoming sound pressure causes the diaphragm to vibrate, in turn causing the capacitance to vary in a like manner, which causes a variance in its output voltage. Condenser microphones tend to have excellent transient response but require an external voltage source, most often in the form of 48 volts of “phantom power.”


Clock In digital audio or video, a clock serves as a timing reference for a system. Every digital device must carry out specified numbers of operations per period of time and at a consistent speed in order for the device to work properly. Digital audio devices such as Apollo normally have an internal clock, and are also capable of locking to external clock routed from other digital devices. In order to avoid signal degradation or undesirable audible artifacts, it is absolutely critical that all digital devices that are interconnected in a system be locked to the same clock.


Clock Distribution Refers to the process of routing a master clock signal (either from an internal clock or an external source) to multiple devices by means of multiple outputs, thus removing the need to cascade the clock through external devices, which can degrade the signal.


Core Audio The audio API for Mac OS X.


D/A Acronym for “Digital to Analog,” which refers to the conversion of a digital data to an

analog signal.


DAW Acronym for “Digital Audio Workstation” – that is, any device that can record, play back, edit, and process digital audio.


dB Abbreviation for “decibel,” a logarithmic unit of measure used to determine, among other things, power ratios, voltage gain, and sound pressure levels.


dBm Abbreviation for “decibels as referenced to milliwatt,” dissipated in a standard load of 600 ohms. 1 dBm into 600 ohms results in 0.775 volts RMS.


dBV Abbreviation for “decibels as referenced to voltage,” without regard for impedance; thus, one volt equals one dBV.


DI Acronym for “Direct Inject” or “Direct Input,” a recording technique whereby the signal from a high-impedance instrument such as electric guitar or bass is routed to an input. DI into mixer or tape recorder inputs often employ use of a “DI box,” which raises the signal to the correct voltage level at the right impedance.


Digital Information or data that is stored or communicated as a series of bits (binary digits, with values of 0 or 1). Digital audio refers to the representation of varying sound pressure levels by means of a series of numbers. (See “Analog” and “Bit”)


Dither Minute amounts of shaped noise added intentionally to a digital recording in order to reduce a form of distortion known as “quantization noise” and aid in low level sound resolution.


Dry Refers to a signal that is unprocessed, e.g., recording a dry signal. The antonym of a “wet” signal.


DSP Acronym for “Digital Signal Processing” (or “Digital Signal Processor.”)


DSP Accelerator A device dedicated to digital signal processing. UAD-2 devices are DSP accelerators.


Dynamic Microphone A type of microphone that generates signal with the use of a very thin, light diaphragm which moves in response to sound pressure. That motion in turn causes a voice coil which is suspended in a magnetic field to move, generating a small electric current. Dynamic mics are generally less expensive than condenser or ribbon mics and do not require external power to operate.


Dynamic Range The difference between the loudest sections of a piece of music and the softest ones. The dynamic range of human hearing (that is, the difference between the very softest passages we can discern and the very loudest ones we can tolerate) is considered to be approximately 120 dB. (See “Bit resolution”)


EQ Abbreviation for “Equalization,” a circuit that allows selected frequency areas in an audio signal to be attenuated or boosted.


External Clock A clock signal derived from an external source. (See “Clock”)


FET Acronym for “Field Effect Transistor.” A type of transistor that relies on an electric field to control the shape, and hence the conductivity, of a “channel” in a semiconductor material.


Firewire (Interface) FireWire is a high-speed real-time interface for serial bus and isochronous/synchronous data transfer between enabled devices.                    

Firmware Software that is embedded in hardware.       


Flex Driver Apollo technology that enables customized I/O mapping at the Core Audio driver level.


Flex Routing Apollo technology that enables its physical inputs to be routed to various physical outputs. Compare to Virtual I/O.


FPGA Acronym for “Field Programmable Gate Array.” A type of integrated circuit that can be programmed after manufacturing (“in the field”) to perform specialized functions.


Front End Refers to a device that provides analog and digital input/output (I/O) to a digittal audio workstation (DAW). Apollo is a front end.


Graphical User Interface A software window, panel, or screen containing controls where parameters are adjusted by the user. (See “GUI”)


GUI Acronym for Graphical User Interface.

Hi-Z Abbreviation for “High Impedance.” Apollo’s Hi-Z input allows direct connection of an instrument such as electric guitar or bass via a standard unbalanced 1⁄4” jack.


High Resolution In digital audio, refers to 24-bit signals at sampling rates of 88.2 kHz or higher.


Hz Abbreviation for “Hertz,” a unit of measurement describing a single analog audio cycle (or digital sample) per second.


Impedance A description of a circuit’s resistance to a signal, as measured in ohms, thousands of ohms (Kilohms), or millions of ohms (megohms).


Internal Clock A clock signal derived from onboard circuitry. (See “Clock”)


I/O Acronym for “input/output.”


kHz Abbreviation for “kiloHertz” (a thousand Hertz), a unit of measurement describing a thousand analog audio cycles (or digital samples) per second. (See “Hz”)


JFET Acronym for Junction Field Effect Transistor, a specific type of FET which has some similarities to traditional bipolar transistor designs that can make it more appropriate for use in some audio circuit designs. (See “FET”)


Jitter Refers to short-term variations in the edges of a clock signal, caused by a bad source clock, inferior cabling or improper cable termination, and/or signal-induced noise. A jittery signal will contain spurious tones at random, inharmonic frequencies. Usually, the jitter will be worse with higher signal frequencies. The internal digital clock of Apollo was designed for extreme stability and jitter-free operation, and its onboard phase aligned clock conditioner circuitry removes jitter from external sources, so conversion quality is unaffected by clock source.


Lightpipe A digital connection made with optical cable. This was a phrase coined by Alesis to make a distinction between the proprietary 8-channel optical network used in their ADAT products and standard stereo optical connectors used on CD players and other consumer products.


Line Level Refers to the voltages used by audio devices such as mixers, signal processors, tape recorders, and DAWs. Professional audio systems typically utilize line level signals of +4 dBm (which translates to 1.23 volts), while consumer and semiprofessional audio equipment typically utilize line level signals of -10 dBV (which translates to 0.316 volts).


Low Cut Filter An equalizer circuit that cuts signal below a particular frequency. Same as “high pass filter.”


Mic Level Refers to the very low level signal output from microphones, typically around 2 millivolts (2 thousandths of a volt).


Mic Preamp The output level of microphones is very low and therefore requires specially designed mic preamplifiers to raise (amplify) their level to that needed by a mixing console, tape recorder, or digital audio workstation (DAW).


Mute “Turn off the signal.” Mute stops the signal from being routed. Native Refers to computer-based digital audio recording software controlled by the computer’s onboard processor, as opposed to software that requires external hardware to run.


OS Acronym for Operating System. The OS is the software used to control the computer hardware, such as OS X (Mac) and Windows (PC).


Pan Abbreviation for “Panorama” or “Panoramic.” A pan control determines a monophonic signal’s positioning in the stereo field.


Patch Bay A passive, central routing station for audio signals. In most recording studios, the line-level inputs and outputs of all devices are connected to a patch bay, making it an easy matter to re-route signal with the use of patch cords.


Patch Cord A short audio cable with connectors on each end, typically used to interconnect components wired to a patch bay.


PDF Acronym for “Portable Document Format.” PDF is the standardized file format used for distribution of documentation in electronic form. Various applications can open PDF files; one such “reader” application is available for free at


Plug-In Software components that are added to host software applications to enhance their functionality and/or performance.


Powered Plug-Ins High-quality audio processing plug-ins, developed and sold by Universal Audio, that run exclusively on UAD DSP accelerator products.


Quantization Noise A form of digital distortion caused by mathematical rounding-off errors in the analog to digital conversion process. Quantization noise can be reduced dramatically by dithering the digital signal. (See “Dither“)


Realtime UAD Processing Universal Audio’s DSP + FPGA technology that enables UAD Powered Plug-Ins to run with latencies in the sub-2ms range. Realtime UAD processing provides the ultimate sonic experience while monitoring and/or tracking. Realtime UAD processing is a special function that is available only within the Console application.


Register / Registration All UAD / Apollo devices must be registered into the user’s UA account before they can be used.


Ribbon Microphone A type of microphone that works by loosely suspending a small element (usually a corrugated strip of metal) in a strong magnetic field. This “ribbon” is moved by the motion of air molecules and in doing so it cuts across the magnetic lines of flux, causing an electrical signal to be generated. Ribbon microphones tend to be delicate and somewhat expensive, but often have very flat frequency response.


Sample A digital “snapshot” of the amplitude of a sound at a single instant in time. The number of samples taken per second is determined by the device’s sample rate. (See “Sample rate”)


Sample Rate The number of samples per second. In digital audio, there are six commonly used sample rates: 44.1 kHz (used by audio CDs), 48 kHz, 88.2 kHz (2 x 44.1 kHz), 96 kHz (2 x 48 kHz, used by DVDs), 176.4 kHz (4 x 44.1 kHz), and 192 kHz (4 x 48 kHz). The higher the sample rate, the greater the frequency response of the resulting signal; however, higher sample rates require more storage space. (See “kHz”)


Sample Rate Conversion The process of altering a digital signal’s sample rate to a different sample rate.


S/MUX (sometimes written as “S-MUX”) Abbreviation for Sample Multiplexing. S/MUX is a method for transmitting two channels of high sample rate (88.2, 96, 176.4, or 192 kHz) 24-bit digital audio over a legacy optical “lightpipe” ADAT connection, which was originally designed to carry eight channels of 16-, 20- or 24-bit audio at 44.1 kHz or 48 kHz sampling rate. (See “ADAT” and “Lightpipe”)


SPDIF (sometimes written as “S/PDIF”) An acronym for “Sony/Philips Digital Interface Format,” a digital audio transfer standard largely based on the AES/EBU standard. De- signed to carry two channels of 16-, 20- or, 24-bit digital audio at sampling rates of up to 192 kHz, the most common SPDIF physical interconnect utilizes unbalanced, 75 ohm video-type coaxial cables terminating at phono (RCA-type) connectors. (See “AES”)


Superclock A proprietary format used by some early Pro Tools systems to distribute clock signal running at 256x the system’s sample rate, thus matching the internal timing resolution of the software. (See “Clock” and “Pro Tools”)


Thunderbolt (Interface) Thunderbolt is a hardware interface that allows the connection of external peripherals to a computer.                   

Transcoding Converting one type of digital signal to another (i.e, from AES to SPDIF, or from ADAT to AES).


Transformer An electronic component consisting of two or more coils of wire wound on a common core of magnetically permeable material. Audio transformers operate on audible signal and are designed to step voltages up and down and to send signal between microphones and line-level devices such as mixing consoles, recorders, and DAWs.


Transient A relatively high volume pitchless sound impulse of extremely brief duration, such as a pop. Consonants in singing and speech, and the attacks of musical instruments (particularly percussive instruments), are examples of transients.                       


Transimpedance Preamplifier A transformerless solid-state preamplifier utilizing a transistor configuration that employs current feedback for ultra-low distortion and the highest possible quality of signal from input to output. The transimpedance design allows audio from 4 Hz to 150 kHz to pass through without altering the phase relationships between fundamental frequencies and overtones. Noise and distortion are kept to near-theoretical minimums so critical signals may be generously amplified without degrading the quality or character of the sound source.


TRS Acronym for Tip-Ring-Sleeve. A 1⁄4” phone connector with three conductors, typically used for balanced signal connections (e.g., I/O) or carrying two unbalanced signals (e.g., headphones).


TS Acronym for Tip-Sleeve. A 1⁄4” phone connector with two conductors, typically used for unbalanced signal connections. Note that TS, like TRS and XLR, denotes the connector only and does not necessarily indicate the signal level of the connection. TS/TRS/ XLR cables are used for both low-level (e.g., microphones and instruments) and line-level connections.


UAD Acronym for “Universal Audio Digital.” Used in reference to digital products created by Universal Audio.


UAD-2 A line of DSP accelerator products developed and manufactured by Universal Audio.


Unison Universal Audio’s exclusive preamp hardware/software integration technology that enables UAD preamp plug-ins reconfigure the physical input impedance, gain staging response, and other parameters of Apollo’s mic preamp hardware to match the emulated preamp’s hardware design characteristics with bi-direction control.


Virtual I/O Apollo audio inputs and outputs that exist in software but not in hardware. Virtual I/O is used to route digital audio channels between Console and other audio applications. Compare to Flex Routing.


Wet Refers to a signal that is processed, e.g., recording a wet signal. The opposite of a “dry” signal.


Word Clock A dedicated clock signal based on the transmitting device’s sample rate or the speed with which sample words are sent over a digital connection. (See “Clock”)


XLR A standard three-pin connector used by many audio devices, with pin 1 typically connected to the shield of the cabling, thus providing ground. Pins 2 and 3 are used to carry audio signal, normally in a balanced (out of phase) configuration.