I The symbol for current.
IAAPA (International Association of Amusement Parks and Attractions) "Our mission is to serve the membership by promoting safe operations, global development, professional growth, and commercial success of the amusement parks and attractions industry." Another great resource for audio contractors, integrators, etc.
IACC (interaural cross-correlation coefficient) A measure of the difference in arrival times between the ears of a listener. It is expressed in values ranging from -1 (arriving signals equal in magnitude but exactly out of phase) to 0 (arriving signals have no similarity) to +1 (identical arriving signals, i.e. same amplitude & phase).
IAEE (International Association of Exhibitions and Events) "Organized in 1928 as the National Association of Exposition Managers to represent the interests of trade show and exposition managers, the International Association of Exhibitions and Events is today the leading association for the global exhibition industry."
IATSE - The International Alliance of Theatrical Stage Employees, Moving Picture Technicians, Artists and Allied Crafts of the United States, Its Territories and Canada.
IBOC (in-band on-channel) Original name for the digital radio technology that allows simultaneous analog and digital broadcasting using existing band allocations. See HD Radio for new name and details.
IC (integrated circuit) A solid-state device with miniaturized discrete active components on a single semiconductor material, invented by Jack Kilby.
ICIA (International Communications Industries Association) The founder of InfoComm.
idiophone Musical Instruments. Term for an instrument that produces sound from the substance of the instrument itself, being solid or elastic enough not to require stretched membranes or strings. An idiophone may be struck, plucked, blown or made to vibrate by friction; examples include cymbals, rattles (struck), jew's harps (plucked), sets of wind-chimes (blown) or the glass harmonica (friction). [Sadie]
IEC (International Electrotechnical Commission) A European organization (headquartered in Geneva, Switzerland) involved in international standardization within the electrical and electronics fields. The U.S. National Committee for the IEC operates within ANSI.
IECEE (IEC System for Conformity Testing and Certification of Electrical Equipment)
IEEE (Institute of Electrical and Electronic Engineers) The largest professional organization for electrical engineers. Primarily concerned with education and standardization.
IEEE 754-1985 Standard for binary floating-point arithmetic often referred to as IEEE 32-bit floating-point. A standard that specifies data format for floating-point arithmetic on binary computers. It divides a 32-bit data word into a 24-bit mantissa and an 8-bit exponent.
IEEE 802.3af See PoE.
IEEE-1394 (aka Firewire) A joint Apple and TI implementation of the IEEE P1394 Serial Bus Standard. It is a high-speed (100/200/400 Mbits/sec now, with 1 Gbit/s on the horizon) serial bus for peripheral devices. Supported by Apple, IBM, Intel, Microsoft and Sony, it is intended to replace Apple Desktop Bus (ADB) and SCSI (Microsoft announced Windows support for IEEE 1394). Firewire supports automatic configuration ("plug and play") and hot-plugging (changing peripheral devices while running). It is also isochronous, meaning that a fixed slice of bandwidth can be dedicated to a particular peripheral - video, for instance. IEEE 1394 aims to become the optimal digital interface for 21st-century applications. Fast, inexpensive and reliable for audio/video as well as computer peripherals, IEEE 1394 carries all forms of digitized video and audio. A single Firewire interface can be used for all entertainment-center interconnections, done in a daisy-chain fashion. New computer peripherals such as digital television, CD-ROM, DVD, digital cameras (Sony was first) and home networks are the first users. See USB for the complementary low-speed system.
IEM In-ear monitor.
IETF (Internet Engineering Task Force) "The mission of the IETF is to make the Internet work better by producing high quality, relevant technical documents that influence the way people design, use, and manage the Internet." [from website]
IEV (International Electrotechnical Vocabulary) A valuable database, made available on-line by the IEC. It contains over 18,500 electrotechnical concepts divided into 73 subject areas (IEV parts). Each concept contains equivalent terms in English, French and German.
IFB (interrupted foldback) (aka talent cueing) An audio sub-system allowing on-air personnel ("talent") to receive via headphones, or ear monitors, the normal program audio mixed with audio cues from the production director, or their assistants.
IFPI (International Federation of Phonographic Industry) The organization representing the international recording industry. It comprises a membership of 1500 record producers and distributors in 76 countries.
IGBT (insulated-gate bipolar transistor) A hybrid form of a MOSFET and bipolar transistor producing an electrically insulated gate instead of a base connection combined with a robust bipolar output. It combines MOS gate control with bipolar current control.
IHF (Institute of High Fidelity) The old organization of North American hi-fi manufacturers that created voluntary industry standards for testing and specifying consumer electronics. The IHF merged with the EIA in 1979. The IHF worked closely with the IRE. Today the AES is responsible for setting audio standards for the United States.
IIR (infinite impulse-response) filter A commonly used type of digital filter. This recursive structure accepts as inputs digitized samples of the audio signal, and then each output point is computed on the basis of a weighted sum of past output (feedback) terms, as well as past input values. An IIR filter is more efficient than its FIR counterpart, but poses more challenging design issues. Its strength is in not requiring as much DSP power as FIR, while its weakness is not having linear group delay and possible instabilities.
ILD (interaural level difference) See interaural.
IM or IMD (intermodulation distortion) An audio measurement designed to quantify the distortion products produced by nonlinearities in the unit under test that cause complex
waves to produce beat frequencies, i.e., sum and difference products not
harmonically related to the fundamentals. For example, two frequencies,
f1 and f2 produce new frequencies f3 = f1 - f2; f4 = f1 + f2; f5 = f1 -
2f1; f6 = f1 + 2f2, and so on. See the RaneNote Audio
Numerous tests exist, each designed to "stress" the unit under test differently. The most popular follow:
SMPTE/DIN IMD The most common IMD measurement. SMPTE standard RP120-1994 and DIN standard 45403 are similar. Both specify a two-sine wave test signal consisting of a large amplitude low-frequency tone linearly mixed with a high-frequency tone at ¼ the amplitude of the low frequency tone. SMPTE specifies 60 Hz and 7 kHz mixed 4:1. The DIN specification allows several choices in both frequencies, with 250 Hz and 8 kHz being the most common.
ITU-R (old CCIF), Twin-Tone, or Difference-Tone IMD, or Difference Frequency Distortion (DFD) All these terms refer to the same test and are used interchangeably. The test specifies two equal-amplitude closely spaced high frequency signals. Common test tones are 19 kHz and 20 kHz for full audio bandwidth units. While all combinations of IM distortion products are possible, this test usually measures only the low-frequency second-order product falling at f2-f1, i.e., at 1 kHz. The principal standard is IEC 60268-3.
DIM/TIM (dynamic/transient intermodulation distortion) A procedure designed to test the dynamic or transient behavior, primarily, of audio power amplifiers. The other IM tests use steady-state sine wave tones, which do not necessarily reveal problems caused by transient operation. In particular, audio power amplifiers with high amounts of negative feedback were suspect due to the inherent time delay of negative feedback loops. The speculation was that when a rapidly-changing signal was fed to such an amplifier, a finite time was required for the correction signal to travel back through the feedback loop to the input stage and that the amplifier could be distorting seriously during this time. The most popular test technique consists of a large amplitude 3 kHz square wave (band-limited to ~20 kHz). [Historical Note: This test proved that as long as the amplifier did not slew-limit for any audio signal, then the loop time delay was insignificant compared to the relatively long audio periods. Thus, properly designed negative feedback was proved not a problem. Subsequently, this test has fallen into disuse.]
image impedances The impedances that will simultaneously terminate all of a network's inputs and outputs in such a way that at each of its inputs and outputs the impedances in both directions are equal. In this manner the input and output impedances "see" their own "image." [IEEE]
imaging or stereo imaging Acoustics. Usually refers to the localization of sounds in a two-channel (normally) stereo sound system, i.e., left-to-right (or vice versa) apparent performer positions.
image parameters Fundamental network functions, namely image impedances and image transfer functions, used to design or describe a filter. [IEEE]
imaginary number A number whose square equals minus one, or, alternatively, a number that represents the square root of minus one. See Nahin's An Imaginary Tale for its incredible history.
imaginary part Mathematics. See: complex number.
impact-echo technology A process where sound waves are sent into concrete and the rebound is measured for nondestructive evaluation of concrete and masonry.
impact noise The noise which results when two masses collide. [Harris]
impedance A measure of the complex resistive and reactive attributes of a component in an alternating-current (AC) circuit. Impedance is what restricts current flow in an AC electrical circuit; impedance is not relevant to DC circuits. In DC circuits, resistors limit current flow (because of their resistance). In AC circuits, inductors and capacitors similarly limit the AC current flow, but this is now because of their inductive or capacitive reactance. Impedance is like resistance but it is more. Impedance is the sum of a circuit, or device's resistance AND reactance. Reactance is measured in ohms (like resistance and impedance) but is frequency-dependent. Think of impedance as the complete or total current limiting ohms of the circuit -- the whole banana. Since AC circuits involve phase shift -- i.e., the voltage and current are rarely in phase due to the storage effects (think time; it takes time to charge and discharge) of capacitors and inductors, the reactance is termed "complex," that is there is a "real" part (resistive) and an "imaginary" part (bad terminology, but it means the phase shifting resistance part). To summarize: resistance has no phase shift; reactance (capacitors & inductors in AC circuits) includes phase shift; and impedance, is the sum of resistance and reactance. Just that simple.
impedance matching Making the output driving impedance and the next stage input impedance equal, often requiring the insertion of a special impedance matching network. For why impedance matching is not necessary (and, in fact, hurtful) in pro audio applications, see William B. Snow, "Impedance -- Matched or Optimum" [written in 1957!], Sound Reinforcement: An Anthology, edited by David L. Klepper (Audio Engineering Society, NY, 1978, pp. G-9 - G-13), and the RaneNote Unity Gain and Impedance Matching: Strange Bedfellows.
impulse The time integral of a force over the time interval during which the force is applied. [Harris]
impulse response Acoustic measurements. A theoretical impulse has an amplitude vs. time response that is infinitely high and infinitely narrow -- a spike with zero duration and infinite amplitude, but finite energy. This means the energy is spread over a very large frequency range, making impulses an ideal source for acoustic measurements. Real world use of the mathematical impulse consists of a test impulse that has a very short time duration and whose amplitude is limited to whatever will not overload the system components. The Fourier theorem tells us that this rectangular pulse is nothing more than a sum of sine and cosine functions with known amplitudes and phases, therefore the impulse response of a linear system occurs in the time domain, but also contains all of the frequency information. By capturing the system impulse response with a digital storage scope and then performing a Fast Fourier Transform (FFT) analysis, the frequency-domain response (amplitude and phase) is obtained. [Very powerful tool.]
IMSO (Independent Music Store Owners) Organization created to "... support, encourage, educate, and inspire the independent music store owner through the sharing of knowledge and experience." [IMSO Mission Statement]
incalzando Music Terminology. A direction to increase speed. [Sadie]
inch Abbr. in or in. 1. A unit of length in the U.S. Customary and British Imperial systems, equal to 1/12 of a foot (2.54 centimeters). 2. A unit of atmospheric pressure that is equal to the pressure exerted by a one-inch column of mercury at the earth's surface at a temperature of 0°C. [AHD]
inductive loop or inductive coupling The association of two or more circuits with one another by means of inductance mutual to the circuits or the mutual inductance that associates the circuits. [IEEE] See: hearing loop.
inductive reactance See impedance.
in-ear monitor See: IEM
inert Electronics. Inactive; not requiring power.
infinite baffle Loudspeakers. A separator allowing no path or acoustical crosstalk between the front and rear of a loudspeaker, i.e., it provides complete isolation between the back and front. An infinitely large flat mounting board is an example; another is a sealed box.
InfoComm See ICIA.
infrasonic Generating or using waves or vibrations with frequencies below that of audible sound. Compare with subsonic -- commonly used (erroneously) to mean infrasonic.
infrasonic filter (aka rumble filter) A high-pass filter used with phonograph turntables to reduce the effects of low frequency noise and vibration, called rumble, caused by imperfections in turntable performance and warped records. Often mistakenly called subsonic filter. Since typical rumble frequencies occur in the 3-10 Hz area, most infrasonic filters have a corner frequency of around 15 Hz, with a steep slope, or rolloff rate, of 18 dB/octave, and a Butterworth response.
inharmonicity Music. The discrepancy between the actual overtones produced by a vibrating sting and the theoretical overtones, which are whole-number multiples of the fundamental (lowest) frequency of vibration. (from Electronic Musician, October 2006, p. 56.)
inherent noise See: self-noise.
initial time-delay gap See ITDG.
initialism An abbreviation consisting of the first letter or letters of words in a phrase (for example, IRS for Internal Revenue Service), syllables or components of a word (TNT for trinitrotoluene), or a combination of words and syllables (ESP for extrasensory perception) and pronounced by spelling out the letters one by one rather than as a solid word. Compare with acronym.
inline mixer Term referring to the normal long narrow vertical strip format common to all medium to large-scale mixing console designs (mixers). Non-inline designs typically refer to rack-mount mixers, i.e., those that are 19" wide, and designed to fit into standard rack cases. These are as small as 1U space (1.75" high). Sometimes these are designed similar to an inline design laying on its side, now having a horizontal control flow instead of a vertical one. In the middle of the pack are rack-mount mixers that still use the inline vertical format, but do rack mount, but normally take up 10 or more spaces.
input impedance Electronics. The input impedance of a device, usually high in the 2k - 100k ohm range. Input impedance can be frequency dependent and may vary with circuit feedback, therefore the value given should state the frequency range it covers.
input referred noise See EIN.
insertion loss Acoustics. Of a sound attenuator, sound barrier, or other element designed to provide sound reduction in a specified frequency band, the decrease in sound power level measured at the location of the receiver when this element is inserted in the transmission path between the sound source and the receiver. Unit: decibel. Unit symbol: dB . [Harris]
insertion loss Electronics. The loss of voltage (or power), as measured in dB, resulting from placing a pad (or other power absorbing network) between a voltage (or power) source and its load impedance. It is the ratio of the voltage (or power) absorbed in the load without the pad (or network) to that when the network is inserted. For example if the voltage across a load is 2 volts without a network and 1 volt with the network, then the insertion loss is stated as 6 dB.
insert loop The preferred term for a specialized I/O point found on mixers utilizing a single 1/4" TRS jack following the convention of tip = send, ring = return, & sleeve = signal ground. Used to patch in an outboard processor using only one cable, with unbalanced wiring. A stereo insert loop requires two jacks. Compare with effects loop.
in situ In the original position. [AHD]
instrument-level See levels.
integrated circuit See IC.
intellectual property See: IP.
intelligibility See speech intelligibility.
intensity stereo Microphones. Another name for the X-Y microphone technique.
interaural Hearing. Literally "between the ears," it is the comparison of sound heard by one ear verses the same sound heard by the other ear. Specific terms include interaural time difference (ITD) (different arrival times due to the distance between the ears) and interaural level difference (ILD) (different arrival intensities due to the diffraction or shadowing caused by the head as an obstacle). See: sound localization.
interference Acoustics. Anything that hinders, obstructs, or impedes sound travel, including another sound wave. See link.
interferometer Any of several optical, acoustic, or radio frequency instruments that use interference phenomena between a reference wave and an experimental wave or between two parts of an experimental wave to determine wavelengths and wave velocities, measure very small distances and thicknesses, and calculate indices of refraction. [AHD]
interharmonics Power Electronics. IEC-1000-2-1 defines it this way: "Between the harmonics of the power frequency voltage and current, further frequencies can be observed which are not an integer of the fundamental. They can appear as discrete frequencies or as a wide-band spectrum."
interlayer-transfer See print-through.
interleaving The process of rearranging data in time. Upon de-interleaving, errors in consecutive bits or words are distributed to a wider area to guard against consecutive errors in the storage media.
intermittor See: current intermittor
intermodulation distortion See IMD.
internal voice blindness "The near universal inability of people to articulate the tone and personality of the voice that forms their interior monologue." [A Dictionary of the Near Future by Douglas Coupland, NY Times, September 12, 2010.]
International Music Products Association See NAMM.
International System of Units See SI.
Internet of Things See: IoT.
interoperability Audio Networks. The ability to make interconnected systems work together. See AES67.
interpolate Mathematics. To estimate a value of (a function or series) between two known values. [AHD]
interpolating response Term adopted by Rane Corporation to describe the summing response of adjacent bands of variable equalizers using buffered summing stages. If two adjacent bands, when summed together, produce a smooth response without a dip in the center, they are said to interpolate between the fixed center frequencies, or combine well. [Historical note: Altec-Lansing first described their buffered equalizer designs as combining and the terminology became commonplace. Describing how well adjacent bands combine is good terminology. However, some variations of this term confuse people. The phrase "combining filter" is a misnomer, since what is meant is not a filter at all, but rather whether adjacent bands are buffered before summing. The other side of this misnomer coin finds the phrase "non-combining filter." Again, no filter is involved in what is meant. Dropping the word "filter" helps, but not enough. Referring to an equalizer as "non-combining" is imprecise. All equalizers combine their filter outputs. The issue is how much ripple results. For these reasons, Rane adopted the term "interpolating" as an alternative. Interpolating means to insert between two points, which is what buffering adjacent bands accomplishes. By separating adjacent bands when summing, the midpoints fill in smoothly without ripple.] See the RaneNote Constant-Q Graphic Equalizers and the RaneNote Exposing Equalizer Mythology.
interrupted foldback See IFB.
intimacy See ITDG.
intonation Music. The opening phrase of a plainsong composition sung as a solo part. [AHD]
inverse square law Sound Pressure Level. Sound propagates in all directions to form a spherical field, thus sound energy is inversely proportional to the square of the distance, i.e., doubling the distance quarters the sound energy (the inverse square law), so SPL is attenuated 6 dB for each doubling.
inversion Turning something upside down. See discussion of phase shift vs. inversion at polarity. Music. a. A rearrangement of tones in which the upper and lower voices of a melody are transposed, as in counterpoint. b. A rearrangement of tones in which each interval in a single melody is applied in the opposite direction. c. A rearrangement of tones in which the notes of a chord are rearranged such that the bass has a different pitch. [AHD]
inverter Power Electronics. A device that converts direct current into alternating current.
IoT (Internet of Things) Many definitions exist for this complex concept; hit the link to read all about it.
IP (intellectual property) Referring to protected proprietary information, usually in the form of a patent, maskworks (integrated circuits or printed circuit boards), a copyright, a trade secret, or a trademark. Often misused to mean many different things.
IP (internet protocol) IP is the most important of the protocols on which the Internet is based. Originally developed by the Department of Defense to support interworking of dissimilar computers across a network, IP is a standard describing software that keeps track of the Internet work addresses for different nodes, routes outgoing messages, and recognizes incoming messages. It was first standardized in 1981. This protocol works in conjunction with TCP and is identified as TCP/IP.
IPA (International Phonetic Alphabet) A phonetic alphabet and diacritic modifiers sponsored by the International Phonetic Association to provide a uniform and universally understood system for transcribing the speech sounds of all languages. [AHD]
IP address Another name for an Internet address. A 32-bit identifier for a specific TCP/IP host computer on a network, written in dotted decimal form, such as 126.96.36.199, with each of the four fields assigned 255 values, organized into hierarchical classes. Whenever you click on a name address like http://www.rane.com/, this creates a path to the domain naming system (DNS) that translates the name into the IP address, which is used to connect.
ips (inches per second) Magnetic tape recording. A measure of tape speed.
IR (infrared) Standard abbreviation found A/V remote control units, among many other things.
IRMA (International Recording Media Association) An advocacy group for the growth and development of all recording media and is the industry forum for the exchange of information regarding global trends and innovations.
iron vane Electrical meter mechanism. Rugged design and construction, used primarily in AC voltage, current and power measurements. It features an accurate true rms measurement capability when measuring distorted or non-sinusoidal waveforms.
ISBN (International Standard Book Number) In bibliography, a 13-digit number assigned to a book which identifies the work's national, geographic, language, or other convenient group, and its publisher, title, edition and volume number. Its numbers are assigned by publishers and administered by designated national standard book numbering agencies, such as R.R. Bowker Co. in the U.S., Standard Book Numbering Agency Ltd. in the U.K., Staatsbibliothek Preussischer Kulterbesitz (Prussian State Library) in Germany, and the Research Library on African Affairs in Ghana. Each ISBN is identical with the Standard Book Number, originally devised in the U.K. , with the addition of a preceding national group identifier. [Now if that isn't more than you will ever need to know about this subject then I'll eat a book.]
ISDN (Integrated Services Digital Network) A high-capacity digital telecommunication network (mainly fiber optic) based on an international telephone standard for digital transmission of audio, data and signaling -- all in addition to standard voice telephone calls. A cost-effective alternative to satellite links.
ISE (Integrated Systems Europe) European trade show for professional AV and electronic systems integration.
Isle of Wight Festival Music festival begun in 1968 on the Isle of Wight in the U.K., held three successive years, stopped, revived in 2002. Now held yearly.
iSMO See: MSO
ISO (International Standards Organization or International Organization for Standardization) Founded in 1947 and consisting of members from over 90 countries, the ISO promotes the development of international standards and related activities to facilitate the exchange of goods and services worldwide. The U.S. member body is ANSI. [Interesting tidbit: according to ISO internet info, "ISO" is not an acronym. It is a derived Greek word, from isos, equal. For example, isobar, equal pressure, or isometric, equal length. Take a small jump from "equal" to "standard" and you have the name of the organization. It offers the further advantage of being valid in all the official languages of the organization (English, French & Russian), whereas if it were to be an acronym it would not work for French and Russian.]
isobar A line on a weather map connecting points of equal atmospheric pressure. Also called isopiestic. 2. Any of two or more kinds of atoms having the same atomic mass but different atomic numbers. [AHD]
isobaric contours See: equal level contours.
isochronous (pronounced "i-sok-ronus") ("iso" equal + "chronous" time) A term meaning time sensitive; isochronous transmission is time sensitive transmission. For example, voice and video require isochronous transmission since audio/video synchronization is mandated.
isolation Acoustics. The isolation of sound is the process by which sound energy is contained or blocked as opposed to being converted into heat (see absorption). For a good discussion of the differences read the excellent short article by Kurt Graffy, "More Or Less: The Difference Between Absorption And Isolation," System Contractor News, April 2003, p. 96, who also provides this wonderful quote attributed to Ted Schultz of Bolt, Beranek and Newman: "Mistaking sound absorption for sound isolation is like mistaking a diaper for an umbrella." [... that clears up all the confusion now doesn't it!]
isotropic Physics. Identical in all directions; invariant with respect to direction. [AHD]
ISRC (International Standard Recording Code) The international identification system for sound recordings and music video recordings.
ISWC (International Standard Musical Work Code) A unique, permanent and internationally recognized reference number for the identification of musical works per International Standard ISO 15707.
IT (information technology) Defined by the Information Technology Association of America (ITAA) as "the study, design, development, implementation, support or management of computer-based information systems, particularly software applications and computer hardware."
ITD (interaural time difference) See interaural.
ITDG (initial time-delay gap) Acoustics. The difference in time between the first arrival of direct sound and the first arrival of reflected sound at the listener. The sensation of intimacy is quantitatively measured by the ITDG. First defined in 1962 by Beranek in Music, Acoustics & Architecture.
ITF (International Turntablist Federation) Founded in 1996, an organization dedicated to the spread of turntablism.
Itsy Bitsy See: Lee Pockriss.
ITU (International Telecommunications Union) Headquartered in Geneva, Switzerland, ITU is an international organization within which governments and the private sector coordinate global telecommunication networks and services. The ITU is divided into three sectors: radiocommunications (ITU-R), telecommunications development (ITU-D), and telecommunications standards (ITU-T).
ITVA (International Television Association) A global community of professionals devoted to the business and art of visual communication. Now renamed Media Communications Association - International (MCA-I).
iyailu Musical Instrument. The "mother drum" of the talking drum ensemble.
IxD ( Interaction design) "... defines the structure and content of communication between two or more interactive "beings" to understand each other." [From website]