Audio-Visual Glossary



JACK:     A plug in type terminal widely used in electronic apparatus for temporary connections.



1) The condition of a stuck machine unable to work due to a stuck tape or bent mechanism. 

2) A computer or computerised device that will no longer perform its function or duty is said to be  “jammed”. 

3) An informal, unrehearsed musical performance or practice session. 

4) To really be rocking - “to jam” to be “jamming”. 

5) Short for “jam synch”.


JAM SYNCH: “Jam synch” is a slang term that refers to the use of an electronic timing signal called “time code”. In order to ensure that two pieces of equipment will operate at exactly the same rate of time, their internal “clocks” have to be synchronised with each other.  As an example, in recording sound on the set, the internal clock of the camera must match exactly that of the sound recording system.  To do this, the camera’s timing signal is fed (“jammed”) into the unit that generates the time code for the sound recorder.  There is a little switch on the sound recorder’s time code generator that accepts this jammed-in signal and sends it to the generator’s internal clock.  The instant the signal hits the internal clock, that clock starts running at the exact same rate as the jammed-in signal from the camera.  At that point the camera’s signal wire can be disconnected and the time code generator will run in perfect synch with the camera for a few hours - at which point the action of “jamming” is repeated.  It can be said that the camera and sound recorder are running on “jam synch”.  Sometimes this is shortened to just “jam”.  “It’s been nearly four hours since jammed, so we have to jam again.”  Many types of audio, video and computer equipment are capable of receiving a jam synch signal.


JAVA:     A computer programming language developed by Sun Microsystems (one of the largest computer makers of computer servers and networks).  “Java” is not an acronym, but is simply named after the slang for a cup of coffee. The Java programming language is often used in programming Internet sites.  In this language, symbols are used to represent commands as a shortcut to programming and using a computer to do work.  Java is quite versatile and can be used with any computer platform, including both Apple and Microsoft operating systems.  There is a more recent version of Java called “J2ME”, Java version 2 Micro Extension.  J2ME is an extension of the original Java computer language that has been made more compact (“micro”) especially for use with cell phones and wireless personal digital assistants. 


JAZ, JAZ DRIVE: The model name of a cartridge-based magnetic storage format popular with personal computers.  “Jaz” is not an acronym, it is just a model name.


JBL:        A brand name of loudspeaker.  JBL is an abbreviation for JB Lansing, who started the JBL Corporation.   JBL loudspeakers are often used in mixing control rooms as monitor speakers.   There are also types of JBL speakers used for live PA systems.  Several guitar and other instrument amplifiers have JBL speakers in them. 


J CARD: This is the small printed insert that goes inside the plastic case of a tape cassette together with the tape itself.  It is called a J card because it is literally shaped like a “J” to fit properly - it has a fold that creates the “J” shape.


JCI FIRELINE:     The name of a fibre optic signal transmission provider employed chiefly for transmitting video and audio signals.  This company’s service and lines are capable of very high quality picture and sound transmission and are often used by professional studios, broadcasters, etc. Its system is geared towards servicing the film and television news industries.  A major use of the JCI Fireline service is for the film and video industries to send videos of daily film rushes or video news footage to various locations within the Los Angeles area or across the country to New York.  JCI Fireline has their own fibre optic cables in Los Angeles and New York City, with interconnection between these two cities.  They also provide links from live venues to studios and broadcast stations.


JEWEL CASE:       This is the plastic shipping and storage case for CDs.


JINGLE: A short catchy song or memorable bit of music, usually associated to a TV or radio commercial.


JITTER: 1) Jitter is a rapid fluctuation in a video picture or in an audio tape machine caused by such things as faulty connections and-or electrical, magnetic or radio interference. 2) Jitter is a technical term regarding the transfer of digital signal information between two digital audiovisual devices.  Jitter is a type of distortion that occurs when the digital bits arriving at the digital to analogue converter are not perfectly evenly spaced.  3) In CD and DVD players, “jitter” is a rapid variation up and down in the player’s speed that causes the laser beam used to read the disc’s information to lose its stability and may cause sound and picture glitches. Digital to analogue converters translate the digital bits into an analogue waveform as they arrive and if there is a variation in the timing of their arrival, distortion will be introduced into the analogue signal.  This is why digital copies (“clones”) can sound different from each other.  The data may be the same but if there is any variation in the timing of the data stream the resulting (analogue) sound will be subtly different.  Jitter is time distortion of a digital signal.  The slight movement of a transmission signal in time or phase that can induce errors and loss of synchronisation in high-speed synchronous communications.  The timing error or inconsistency between audio samples, when digital audio is being recorded or played back through a converter.


JOG:       To jump from one portion of an audio or video programme to another.  To scan forward or backward on such a programme’s tape.


JOG KNOB:   A control on a video or audio tape machine that allows one to quickly scan forward or backwards while still hearing or seeing just enough to help you know where you are at and find the portion you are looking for.   In “jog” mode, the programme moves forward or reverse at the speed that one manually turns the knob and the picture and sound don’t move unless the knob is being manually rotated.   (Compare SHUTTLE.)


JOY STICK:  A control which will move specific sounds in a film’s soundtrack to various locations within the surround sound field (to different loudspeakers) according to the rotation of a knob or small stick on a mixboard. 


JPEG:     Stands for Joint Photography Experts Group.  This is a method of storing, sending and manipulating still photography and video images with a computer such as over the Internet or to process still images within a computer itself.  It is a method of compressing the digital information for such images so they can be handled by the computer system.  It was developed by a committee of technical people who “jointly” got together and worked out how still images would be processed and manipulated digitally by computers. 

For more technical information, read on… JPEG is a still image (photo) compression standard developed by the International Standards Organisation. It is a versatile and commonly used colour graphics compression specification adopted by the Joint Photography Experts Group. It is also used in some video applications, such as in AVID computers. Hardware and software JPEG implementations allow setting the desired compression, from 24-bit lossless (usually 2:1) to smaller bit size lossy compression rates (up to 60:1 in some cases).  (LOSSLESS COMPRESSION and LOSSY COMPRESSION are defined as separate entries.) The various levels of compression allow users to choose how much retention of detail and precision of the original can be done when trying to fit picture information into a limited amount of digital storage capacity.   For everyday graphics work, recommended JPEG compression ratios range between 25 and 35:1.


JUDDER:       To shake violently.  This term is usually used in regards to video images.


J2ME:     See JAVA.



1) A machine that holds many CDs or DVD’s which can be selected or the machine programmed to play such in a certain order. 

2) Such a machine used for professional purposes to store vast amounts of information on CD or DVD type discs.  Some companies make jukeboxes that will hold 200, 400, 500, up to over 1000 CDs.  There are also professional “optical jukeboxes” which store incredible amounts of video information on large computer storage discs or with other large-scale computer storage methods.

3) A jukebox record player or CD player found in commercial establishments.


JUMPER WIRE:   A short wire used to allow an electrical signal to flow or to bypass certain parts (to jump around them).  


JUNCTION BOX: A box or connection point equipped with a number of signal connectors or jacks for the receipt and routing of signals.   


JVC:       Abbreviation for Japanese Victor Corporation.  JVC makes professional and home audiovisual equipment.