J
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.]
jabber To talk rapidly, unintelligibly, or idly. To utter rapidly or unintelligibly. Rapid or babbling talk. [AHD]
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.]
JADE (Joint Audio Decoder Encoder) Siemens trademark for their device that implements voice compression algorithms.
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.
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.
JANDS Famous pro audio, lighting and staging company, which started out as a distributor in Australia. See: Pro Audio Names Section
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.
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).
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.
JavaTM 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.
Jecklyn-disk Microphones. Official name for placing a baffle between two microphones in an AB setup.
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.)
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]
JFET (junction field-effect transistor) See FET
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]
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.
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'."
John T. "Jack" Mullin (1913–1999) American who pioneered modern tape recording based on his discovery of the first German tape recorders during WWII.
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.]
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.
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.
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.
julian date A chronological year date system where the days are sequentially numbered, i.e., the first day is 001, the second is 002, and the last is 365 (or 366 in a leap year). 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. [KU Input-Output Glossary]
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.
JSA (Japanese Standards Association) The National Standards organization responsible for coordinating standards preparation in Japan.
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.
