Glossary of Audio Terminology

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Index | References



IC (integrated circuit) A solid state device with miniaturized discrete active components on a single semiconductor material.

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.

IDE (Intergrated Development Environments) Software platforms for weighting code and creating new application software.

IDX (Inter-Exchange Carrier) A telecommunications service provider authorized by the FCC to provide interstate long distance communications services between LATAs; and authorized by the State to provide long distance communications services. An InterExchange Carrier provides, directly or indirectly, interLATA or intraLATA telephone toll services. May be an individual, partnership, association, joint-stock company, trust, governmental entity or corporation engaged for hire in interstate or foreign communication by wire or radio, between two or more exchanges.

 IEEE (Institute of Electrical and Electronic Engineers) The largest professional organization for electrical engineers. Membership includes engineers, scientists and students of electronics and allied fields.  Primarily concerned with education and standardization for computers and communications.

IEEE-488 also referred to as the general purpose interface bus (GPIB). Most common parallel format computer interface for simultaneous control of up to 15 multiple peripherals.

IEEE-1394 (aka Firewire) A joint Apple and TI implementation of the IEEE P1394 SerialBus 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, Firewire supports automatic configuration ("plug and play") and hot-plugging (live connection/disconnection of  peripheral devices while running without data loss or interruption). It is also isochronous, meaning that a fixed slice of bandwidth can be dedicated to a particular peripheral - video, for instance.  Fast, inexpensive and reliable it was originally developed to connect PCs to other PCs or to peripherals such as digital cameras, camcorders, scanners, etc.  Current applications include automotive, telecom, data acquisition, aerospace and a host of others.  IEEE 1394 carries all forms of digitized video and audio. A single Firewire interface can be used for all peripheral interconnections, done in a daisy-chain topology.  See: USB for a complementary searial buss system.

IETF (Internet Engineering Task Force) A large open international community of network designers, operators, vendors, and researchers concerned with the evolution of the Internet architecture and the smooth operation of the Internet. It is open to any interested individual.

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.

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. 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 RP120-1983 and DIN standard 45403 are similar. Both specify a two-sinewave test signal consisting of a large amplitude low-frequency tone linearly mixed with a high-frequency tone at 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.
  • CCIF, Twin-Tone, or Difference-Tone IMD 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.

impedance The numerical measure of the complex reaction to current flow that a general electrical network has when excited with an ac voltage. Impedance is the AC equivalent of Resistance on a DC circuit

Induction Whenever a magnetic field in the region of a conductor is moving, or changing in magnitude, such that magnetic field lines of flux are moving across the conductor, an electric current is induced in the conductor. 

infrasonic Generating or using waves or vibrations with frequencies below that of audible sound. Compare with subsonic - commonly used (erroneously) to mean infrasonic.

Interface Hardware or Software that forms a link betwene devices and allows them to communicate with each other.

Internet World wide network of computer systems.

Intranet information available on a private corporate using the Internet model and HTTP Servers.

interlayer-transfer See: print-through

inverse square law Sound Pressure Level. Sound propagates in all directions to form a spherical field.  The area of this sphere increases proportionally to the square of the distance from the center. All of the sound energy is spread equally over this increasingly large sphere.  Thus, as the distance from the source increases, the sound energy level per square area decreases.   This sound energy is therefore 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 6dB for each doubling of distance from the source.

I/O (input/output) Equipment or data used to communicate from a circuit or system to other circuits or systems, or the outside world.

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 communications between dissimilar computers across a network, IP is a standard describing software that keeps track of the inter-network addresses for different nodes, routes outgoing messages, and recognizes incoming messages. It was first standardized in 1981. See TCP/IP.

IR ( Infrared )  energy in the region of the electromagnetic spectrum at wavelengths longer ( lower frequencies ) than those of visible light, but shorter ( higher frequencies ) than those of radio waves. In most ways IR radiation behaves exactly the same as visible light except it is not visible with the human eye.

ISDN (Integrated Services Digital Network) A switched (dial-up) high-capacity digital telecommunication network service  based on an international telephone standard providing for digital connectivity for transmitting  audio, data and video simultaneously over a single line. Bandwidth can be used to provide multiple standard voice telephone calls, audio or video conferencing. Comes in two versions see BRI and PRI.

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.]

ISP (Internet Service Provider) Private company providing connections to the Internet using one of several "last mile" technologies such as 56K dial up modems and DSL.

ITU International Telecomunications Union International body that sets worldwild telecommunications standards.


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