j Mathematics. The symbol for the imaginary number , i.e., a number representing the square root of -1. See: complex number. [A lower case "i" is also used in mathematics but not in electronics since "i" is the symbol for current.]

J The symbol for joule, the SI unit of energy or work.

J  Electromagnetism. Symbol for current density.

jabber To talk rapidly, unintelligibly, or idly. To utter rapidly or unintelligibly. Rapid or babbling talk. [AHD]

jack Musical Instrument. The part of a harpsichord action that carries the plectrum past the string. The word is also used for the pivoted vertical lever in a piano action that forces the hammer upward when a key is depressed. [Sadie]

jacket Wire & Cable. The insulating layer of material that surrounds a wire or cable offering protection; also called sheath.

jackfield British term for patchbay.

Jack Mullin See: John Mullin.

jacks and plugs Common name for audio connectors, where jack = female and plug = male is the standard convention for 1/4" and RCA — only — not followed for other types of connectors. If a connector is on the end of a cable — XLR and others — then either sex is a plug. [Hey, don't yell at me, I don't make the rules; I just report them.]

Jackson, Bruce (1948-2011) Australian audio engineering sound pioneer who did live sound for Elvis Presley, Bruce Springsteen, Barbara Streisand and others. He started out cofounding JANDS and went on to invent and develop many digital audio innovations.

Jacob's ladder (aka high voltage traveling arc) Electricity & Magnetism. "The spark gap is formed by two wires, approximately vertical but gradually diverging away from each other towards the top in a narrow "V" shape. It was named for the "ladder to heaven" described in the Bible." [From the Wikipedia link, found about halfway down the page on spark gaps.]

JADE (Joint Audio Decoder Encoder) Siemens trademark for their device that implements voice compression algorithms.

JAES (Journal of the Audio Engineering Society) Also see: AES.

Jaguar rock See: Human Jukebox.

ja ja Spanish laugh.

jaleika (also spelled zhaleika) Musical Instrument. Russian wind instrument made from cow horn.

jam session Music. An informal gathering of musicians to play improvised or unrehearsed music. [AHD]

jam sync 1. The process of regenerating SMPTE timecode from an original source. Used for repair as well as for new copies. 2. A recording studio in Nashville specializing in multichannel and multimedia founded by KK Proffitt and Joel Silverman.

Jamaican Patois A West African influenced creole language spoken primarily in Jamaica.

James Bullough Lansing (James Martini, 1902-1949) American entrepreneur and inventor most famous for his companies: Lansing Manufacturing, Altec-Lansing and JBL.

James T. Russell American physicist who came up with a CD concept in 1965 that he licensed to Sony in 1970. See: Klass Compaan.

jamming Wire & Cable. The wedging of cables in a conduit when three cables lie side by side in a flat plane. [IEEE Std 576]

JANDS Famous pro audio, lighting and staging company, which started out as a distributor in Australia. See: Pro Audio Names Section

janggu Muscial Instrument. A Korean two-headed hand drum.

jangle To make a harsh metallic sound: The spurs jangled noisily. [AHD]

jangle pop The first and most famous jangle pop band was The Byrds.

Janissary music An ensemble of Turkish percussion instruments introduced into European military music in the 18th century an later adopted by the orchestra; it also refers to the kind of music composed for such a group. [Sadie]

Janovsky, W. German engineer responsible for one of the earliest papers on non-linear distortion thresholds as published in his 1929 paper: "The Audibility of Distortion (in German language), Elek. Nachr.-Tech., vol. 6, pp. 421-439 (Nov., 1929).

jansky Abbr. Jy A unit of spectral power flux density: 10^-26 times one watt per square meter per Hertz (IEEE Std 211). Also called the flux unit.

jarana jarocha Musical Instrument. Stringed guitar-like fretted instrument with eight strings.

JASA (Journal of the Acoustical Society of America) Also see: ASA

jass Jazz music, written both ways from 1913 up until around 1920, when the word "jazz" became the accepted spelling. [Decharne]

Jawaiian Music. A reggae genre combining traditional Hawaiian and Jamaican styles. Compare with reggaeton.

Java^TM The trademarked name for a powerful object-oriented programming language developed by Sun Microsystems. Java allows high-speed fully interactive Web pages to be developed for the Internet or any type of platform.

jazz A style of music, native to America, characterized by a strong but flexible rhythmic understructure with solo and ensemble improvisations on basic tunes and chord patterns and, more recently, a highly sophisticated harmonic idiom. [AHD] See jass.

jazz birthplace Recognized as Armstrong Park, in the Tremé section of New Orleans.

Jazz Fest Music festival held annually in New Orleans featuring mostly jazz musicians.

Jazz Festivals Worldwide Incredible online database of over 1,200 jazz festivals held in 45+ countries worldwide.

Jecklin disk Microphones. Official name, after inventor Jürg Jecklin, the former Swiss Radio chief sound engineer, for placing a baffle between two microphones in an AB setup.

JEDEC (Joint Electron Device Engineering Council) Standards creating body for the microelectronics industry.

jeep Probably pronunciation of the letters "GP", the designation for this vehicle in the manufacturer's parts numbering system : G(overnment) + P, designator for 80-inch wheelbase reconnaissance car. [AHD]

JEITA (Japan Electronics and Information Technology Industries Association) A trade organization for the electronics and IT industries.

jellyfish display Multichannel Sound. A type of metering used to display multichannel surround sound characteristics, i.e., usually the relative amplitude between channels; so-called for its roundish changing jellyfish-like pattern.

jerk Mathematics. The (first) derivative of acceleration, i.e., it is a measure of the rate of change of acceleration — just as velocity is the derivative of speed, and acceleration is the derivative of velocity. Elevator makers are among those interested in measuring it. For example Otis Elevator Company has a transducer that measures jerk by differentiating acceleration. (Thanks to Glenn White for the Otis information.)

jerking or jerkin' Hip-Hop Dance Style. Originated in Los Angeles, it is a dance movement consisting of rapidly moving your legs in and out, as well as other complicated moves.

jeté Music Terminology. In string playing, a bowstroke that bounces or ricochets off the string. [Sadie]

Jewish telegram "Start worrying. Details to follow." [Newton]

jew's harp Musical Instrument. A small musical instrument consisting of a lyre-shaped metal frame that is held between the teeth and a projecting steel tongue that is plucked to produce a soft twanging sound. [AHD] [For those controlled by political correctness, the revised name is "jaws harp." ]

JFET (junction field-effect transistor) See FET

jiaohu Musical Instrument. A Chinese bowed string instrument.

jiffy An actual unit of time, representing 1/100th of a second. [See Rowlett's "How Many? A Dictionary of Units of Measurement" for the complete details.]

jig Music. Any of various lively dances in triple time. The music for such a dance. Also called gigue. [AHD]

jiggumbob A trinket; a knick-knack; a slight contrivance in machinery. [Lynch]

Jim Williams (1948-2011) American engineer, analog IC guru, and cofounder of Linear Technology. Wonderful tribute video here.

Jimmy Savile (1926-2011) Scandalous British radio disc jockey credited as the first person to launch a DJ dance party in 1943 in Otley, England, and later resulted in the first known simultaneous use of two turntables to keep the music going continuously.

jinghu Musical Instrument. Chinese bowed 2-stringe fiddle.

jingle Noun 1. The sound produced by or as if by bits of metal striking together. 2. A piece of light singsong verse or rhyme. 3. A catchy, often musical advertising slogan. Verb 1. To make a tinkling or ringing metallic sound. 2. To have the catchy sound of a simple, repetitious rhyme or doggerel. To cause to make a tinkling or ringing metallic sound. [AHD]

JIRA Software. Popular software development tool that eases bug tracking, issue tracking and project management. The name is not an acronym; it is a truncation of the word "Gojira," which is the Japanese name for Godzilla, that wonderful fictional Japanese monster.

jit Dance Music. Fast guitar and drum rhythm popular in Zimbabwe. Hit the link for all the details. See also: Detroit Jit.

JITC (Joint Interoperability Test Command) A military compatibility testing organization.

jitter A tendency towards lack of synchronization caused by electrical changes. Technically the unexpected (and unwanted) phase shift of digital pulses over a transmission medium. Time skew; a discrepancy between when a digital edge transition is supposed to occur and when it actually does occur — think of it as nervous digital, or maybe a digital analogy to wow and flutter.

Here is the official definition from AES-12id, AES Information Document for Digital audio measurements — Jitter performance specifications:

"Jitter is the dynamic deviation of event instants in a stream or signal from their positions in time, excluding modulation components below 10 Hz."

jitter timing error Short-term deviations of the transitions of a digital signal from their ideal positions in time.

J. J. Cale (1938-2013) American musician who was a major songwriter and influence on Neil Young, Eric Clapton, Lynyrd Skynyrd and John Mayer, among many others. He wrote some of the '60s and '70s top songs, including "Cocaine," "After Midnight," and "Call Me The Breeze."

jnd (just noticeable difference) Physiology. The smallest difference in a sensory input detectable by a human being.

Joe, cup of Coffee. There is no clear origin but according to World Wide Words the most probable suggestion is that it is a modification of java or jamoke for coffee and that "It is significant that an early example appears in 1931 in the Reserve Officer’s Manual by a man named Erdman: 'Jamoke, Java, Joe. Coffee. Derived from the words Java and Mocha, where originally the best coffee came from'."

Joel, Irving ("Irv") Louis (1931-2015) American recording engineer and a very early member of the AES joining in 1957. His participation earned him multiple awards, including the AES Distinguished Service award in 2009.

John T. "Jack" Mullin (1913–1999) American who pioneered modern tape recording based on his discovery of the first German tape recorders during WWII.

Johnston factor The ratio of fh/fl, where fh and fl are the highest and the lowest signal frequency limits, respectively. When the signal or waveform' Johnston factor is larger than the fraction 9/7 or decimal 1.3, corresponding to a fractional bandwidth of 0.25, the signal or waveform is UWB.

Johnson noise or thermal noise A form of white noise resulting from thermal agitation in electronic components. For example, a simple resistor hooked up to nothing generates noise, and the larger the resistor value the greater the noise. It is called thermal noise or Johnson noise and results from the motion of electron charge of the atoms making up the resistor (called thermal agitation, which is caused by heat - the hotter the resistor, the noisier. [After John Bertrand Johnson (1887-1970), Swedish-born American physicist who first observed thermal noise while at Bell Labs in 1927, publishing his findings as "Thermal agitation of electricity in conductors," Phys. Rev., vol. 32, pp. 97-109, 1928.]

John William Strutt See: Lord Rayleigh

joint probability Mathematics. The likelihood that two or more things will occur together.

Jones, R.G. Founded in 1926, near London by Reginald Geoffrey Jones, the RG Jones company, along with Swanson Sound Service (Oakland, CA) are considered the first sound companies, and both are still going strong.

jookin Street dance born in Memphis.

Joplin, Scott(1867-1917) American musician and composer of ragtime music.

Jordan, Vilhelm L. (1909-1982) Danish acoustics engineer, who, among many other designs, consulted on the Sydney Opera House, and authored Acoustical Design of Concert Halls and Theatres: A Personal Account.

jouhikko Finnish bowed lyre.

joule Abbr. J or j. 1. The International System unit of electrical, mechanical, and thermal energy. 2. a. A unit of electrical energy equal to the work done when a current of one ampere is passed through a resistance of one ohm for one second. b. A unit of energy equal to the work done when a force of one newton acts through a distance of one meter. [AHD]

Joule, James Prescott (1818-1889) British physicist who established the mechanical theory of heat and discovered the first law of thermodynamics: a form of the law of conservation of energy whose discovery he shared with Hermann von Helmholtz, Julius von Mayer and Lord Kelvin. [AHD]

Joule's Law It was James Prescott Joule (see above) who came up with (and published in 1841) the basic power equations P = I²R; P = IE; & P = E²/R, NOT Georg Simon Ohm as is commonly believed. Contrast with Ohm's Law.

joystick Potentiometer/Encoders. A type of potentiometer or digital encoder with movement over two axes (sometimes three with the third being in-out, z-axis). [This is also called two or three degrees of freedom]. Usually the axis are left-right, x-axis, and up-down (or away-toward), y-axis, with each controlling a separate potentiometer or encoder. The term is borrowed from aviation technology meaning an aircraft control stick.

JPEG (Joint Photographic Experts Group) A standard for lossy compression of graphic-image files.

JSA (Japanese Standards Association) The National Standards organization responsible for coordinating standards preparation in Japan.

jùjú Music. A style of Nigerian popular music featuring electric guitars and traditional drums. [AHD]

juke A roadside drinking establishment that offers inexpensive drinks, food, and music for dancing, especially to the music of a jukebox. [Derivative Note: probably from Gullah juke, joog disorderly, wicked of West African origin; Wolof dzug to live wickedly Mandingo (Bambara) dzugu wicked. Gullah, the English-based Creole language spoken by Black people off the coast of Georgia and South Carolina, retains a number of words from the West African languages brought over by slaves. One such word is juke, — bad, wicked, disorderly, -- the probable source of the English word juke.] Used chiefly in the Southeastern states, juke (also appearing in the compound juke joint) means a roadside drinking establishment that offers cheap drinks, food, and music for dancing and often doubles as a brothel. "To juke" is to dance, particularly at a juke joint or to the music of a jukebox whose name, no longer regional and having lost the connotation of sleaziness, contains the same word. [AHD] ... and you thought you were smart.

Jukebox Multimedia Portable Media Player. Developed by Archos and released in 2002, it is recognized as the first handheld MP3/MP4 media player, combining an audio player, image viewer and video player.

julian date A chronological year date system where the days are sequentially numbered beginning with January 1, 4713 BC, Greenwich noon. Here is a handy converter.

jump cut Broadcast. An edit between two video shots or audio sound bites that creates a "jump" or break in continuity.

jumper Electronics. A conductor placed across the clear space between the ends of two conductors, or to connect conductors on different layers, on a printed circuit board.

junction Semiconductors. The transition boundary between semiconductor regions of different electrical properties (e.g., n-n+, p-n, p-p+ semiconductors, or between a metal and a semiconductor). [IEEE]

junction, rectifying Semiconductors. A region between two materials, typically n-type or p-type semiconductors, or between a metal and a semiconductor, arranged to provide a very low resistance to current flow in one direction and a very high resistance to current flow in the opposite direction. [IEEE]

JUST Abbreviation for Department of Justice, also known as DOJ. [IEEE Std 1512.2™-2004, IEEE Standard for Public Safety Traffic Incident Management Message Sets for Use by Emergency Management Centers]

just intonation or just temperament Music. A musical scale employing frequency intervals represented by the ratios of the smaller integers of the harmonic series. [Olson] Compare with equal temperament.

just noticeable difference See: jnd.

justify To shift a numeral so that the most significant digit, or the least significant digit, is placed at a specific position in a row.