Hifi audio


ADC- Analogue to Digital converter. A device that converts analog signals into digital signals.

AGC(automatic gain control)- A circuit for automatically controlling amplifier gain in order to maintain a constant output voltage with a varying input voltage within a predetermined range of input-to-output variation.

Analog- Any form of signal that carries information in the form of variable physical values, such as amplitude or frequency modulation. A signal which moves through a continuous range of settings or levels. An adjective describing any signal that varies continuously as opposed to a digital signal that contains discrete levels representing the binary digits 0 and 1.

Aperture-The effective diameter of the lens that controls the amount of light reaching the photo conductive or photo emitting image pickup sensor.

Aperture Correction- Compensation for the loss in sharpness of detail because of the finite dimensions of the image elements or the dot-pitch of the monitor.

Artifact- A defect or distortion of the video image, introduced along the sequence from origination and image capture to final display. Artifacts may arise from the overload of channel capacity by excess signal bandwidth. Artifacts may also result from: sampling effects in temporal, spatial, or frequency domains; processing by the transfer functions; compromises and inadequacies in the system employed; cascading of minor defects; basically any other departure of the total system from “complete transparency” resulting in visual errors.

Aspect Ratio- The ratio of width to height for the frame of the televised picture. 4:3 for standard systems, 5:4 for 1K x 1K, and 16:9 for HDTV.

ATSC- An acronym for "Advanced Televisions System Committee", the organization that defines the standard for high-definition TV in the United States.

Attenuation-In general terms, a reduction in signal strength.

Auto Balance- A system for detecting errors in color balance in white and black areas of the picture and automatically adjusting the white and black levels of both the red and blue signals as needed for correction.

Auto Light Range-The range of light, e.g., sunlight to moonlight, over which a TV camera is capable of automatically operating at specified output.

Automatic Brightness Control- In display devices, the self-acting mechanism which controls brightness of the device as a function of ambient light.

Automatic Frequency-An arrangement whereby the frequency of an oscillator is automatically maintained within specified limits.

Automatic Iris Lens-A lens that automatically adjusts the amount of light reaching the imager.

Automatic Light Control-The process by which the illumination incident upon the face of a pickup device is automatically adjusted as a function of scene brightness.

AC (Alternating Current) - Electrical current that alternates direction (positive to negative). AC is often contrasted with direct current (DC), commonly produced by batteries.

Absorption- The tendency of sound waves to be soaked up by soft surfaces. Opposite: reflection.

Acoustic Feedback­- The dreaded "sound man's (and sound woman's)curse," is caused by a regeneration of sound leaving a speaker and entering a microphone. This tone - a sustained shriek - is a self-perpetuating cycle which can be stopped by decreasing the volume. Sometimes referred to as a standing wave.

Acoustics – 1.The science or scientific study of sound. 2. The properties of a room or environment that affect the qualities of sound.

Acoustic Power Output- The output, as measured in watts, of anything that generates sound.

Acoustic Suspension-A type of speaker cabinet which is sealed to control the action of its woofer and prevent the leakage of air.

Ambient Noise Level -"Background" noise from any source - that affects the listener's ability to hear what is produced by a sound system. Machinery, hum from florescent lights, traffic, etc.

Amplifier (Amp) – An electronic device that increases the amplitude of a signal. 2. A combination speaker/amplifier designed for use with an instrument, as with a guitar amp or keyboard amp. See preamp; power amplifier

Amplitude – The strength of sound waves or an electrical signal, as measured against a mean. 2. That which determines loudness.

Anechoic – The complete absence of reflected sound (echo). 2. An environment that prevents (through dissipation and absorption of sound waves) all reflected sound, as in an anechoic chamber.




Back Porch - That portion of the composite picture signal which lies between the trailing edge of the horizontal sync pulse and the trailing edge of the corresponding blanking pulse.

Bandwidth - The range of signal frequencies that a piece of audio or video equipment can encode or decode; the difference between the limiting frequencies of a continuous frequency band. Video uses higher frequency than audio, thus requires a wider bandwidth.

Bar Test Pattern (SMPTE) - Special test pattern for adjusting color TV receivers or color encoders. The upper portion consists of vertical bars of saturated colors and white. The power horizontal bars have black and white areas and I and Q signals.

Bit - Short for "Binary Digit". The smallest piece of binary digital data and is represented by either 0 or 1.

Bit Depth - The number of levels that a pixel might have, such as 256 with an 8-bit depth or 1024 with a 10-bit depth.

Bit Rate - a) The rate at which the compressed bit stream is delivered from the storage medium to the input of a decoder. The digital equivalent of analog bandwidth. b) The speed at which bits are transmitted, usually expressed in bit/s (sometimes abbreviated "bps").video information, in a digitized image for example, is transferred, recorded, and reproduced through the production process at some bit rate appropriate to the nature and capabilities of the origination, the channel, and the receptor. c) The amount of data transported in a given amount of time, usually defined in Mbit/s. Bit rate is one means used to define the amount of compression used on a video signal. The uncompressed D1 format has a bit rate of 270 Mbit/s. MPEG-1 has a bit rate of 1.2 Mbit/s.

Blooming - This effect is sometimes called whiter-than-white. Blooming occurs when the white voltage level is exceeded and screen objects become fuzzy and large. The defocusing of regions of a picture where brightness is excessive.

Bounce - Sudden variations in picture presentation (brightness, size, etc.,) independent of scene illumination.

Brightness - The attribute of visual perception in accordance with which an area appear to emit more of less light. (Luminance is the recommended name for the photo-electric quantity which has also been called brightness.)

Broadband - In TV system use, a device having a bandpass greater than the band of a single VHF TV channel.

Burned-In-Image - Also called burn. An image which persists in a fixed position in the output signal of a camera tube after the camera has been turned to a different scene or, on a monitor screen.

Balanced Line - A pair of ungrounded conductors whose voltages are opposite in polarity but equal in magnitude. Balanced lines reduce interference from external sources like radio frequencies and light dimmers since they are typically shielded by a third conductor surrounding them.

Basket - The frame to which a driver's cone is mounted.

Bass - The lower end of the frequency range, from about 20 Hz to about 300 Hz.

Bass Reflex - A speaker that, as a means of enhancing the efficiency of the reproduction of bass frequencies, channels some of the sound pressure generated by its woofer(s) through an opening (port) in its cabinet.

Biamplification - The use of separate amplifiers to power woofers and tweeters.


Candela - A unit for measuring luminous intensity. One candela is approximately equal to the amount of light energy generated by an ordinary candle. Since 1948 a more precise definition of a candela has become: “the luminous intensity of a black body of 1 square centimeter heated up to a temperature at which platinum converges from a liquid state to a solid.”

Charged Couple Device - a) A semiconductor device that converts optical images to electronic signals. CCDs are the most commonly found type of image sensor in consumer camcorders and video cameras. b) Serial storage technology that uses MOS capacitors. c) A solid-state image sensor that converts light energy to electricity.

Chroma - The quality of color that embraces both hue and saturation. White, black, and grays have no chroma.

Chroma Control - A color TV receiver control that regulates the saturation (vividness) of colors in a picture.

Chroma Detector - Detects the absence of chrominance information in a color encoder input. The chroma detector automatically deletes the color burst from the color encoder output when the absence of chrominance is detected.

Chromatic Aberration - An optical defect of a lens that causes different colors or wavelengths of light to be focused at different distances from the lens. It is seen as color fringes or halos along edges and around every point in the image.

Clamp - A device which functions during the horizontal blanking or synchronizing interval to fix the level of the picture signal at some predetermined reference level at the beginning of each scanning line.

Clamping - The process that established a fixed level for the picture level at the beginning of each scanning line.

Clipping - An electronic limit usually imposed in cameras to avoid overly bright or dark signals. When improperly applied can result in loss of picture information in very bright or very dark areas; Also used in switchers to set the cutoff point for mixing video signals. The electronic process of shearing off the peaks of either the white or black excursions of a video signal for limiting purposes. Sometimes, clipping is performed prior to modulation, and sometimes to limit the signal, so it will not exceed a predetermined level.

Closed-Circuit Television - Video primarily used for surveillance and security that is not broadcast to the general public.

CMOS (complementary metal-oxide-semiconductor) - A type of digital camera sensor.

C-Mount - The first standard for CCTV lens screw mounting. This mounting is defined by a 1-inch (2.54 cm) diameter hole with 32 TPI (turns/threads per inch), female on the camera side, male on the lens side, and a back flange-to-CCD distance of 17.526 mm (0.69 inches). The C-mount description applies to both lenses and cameras. C-mount lenses can be put on both, C-mount and CS-mount cameras; only in the latter case a 5 mm (.19 inches) adaptor is required.

Coaxial Cable - A particular type of cable capable of passing a wide range of frequencies with very low signal loss. Such a cable in its simplest form consists of a hollow metallic shield with a single wire accurately placed along the center of the shield and isolated from the shield.

CODEC (Coding/Decoding) - a) The algorithm used to capture analog video or audio in digital form. b) Used to implement the physical combination of the coding and decoding circuits. c) A device for converting signals from analog to coded digital and then back again for use in digital transmission schemes. Most codecs employ proprietary coding algorithms for data compression.

Color - A visual perception that humans correspond to the categories called red, green, blue and others.

Color Burst - That portion of the composite color signal, comprising a few cycles of a sine wave of chrominance subcarrier frequency, which is used to establish a reference for demodulating the chrominance signal; Normally approximately 9 cycles of 3.579545 MHz.

Color Edging - Extraneous colors appearing at the edges of colored objects, and differing from the true colors in the object.

Color Encoder - A device which produces an NTSC color signal from separate R, G, and B video inputs.

Color Fringing - Spurious colors introduced into the picture by the change in position of the televised object from field to field.

Color Purity - The degree to which a color is free of white or any other color. In reference to the operation of a tri-color picture tube it refers to the production of pure red, green or blue illumination of the phosphor dot faceplate.

Color Saturation - The degree to which a color is free of white light.

Color Sync Signal - A signal used to establish and to maintain the same color relationships that are transmitted.

Color Transmission - The transmission of a signal which represents both the brightness values and the color values in a picture.

Communications Network - The path over which all signals are transmitted.

Composite Video Signal - The combined picture signal, including vertical and horizontal blanking and synchronizing signals.

Compression - a) The process of electronically processing a digital video picture to make it use less storage or to allow more video to be sent down a transmission channel. b) The process of removing picture data to decrease the size of a video image. c) The reduction in the volume of data from any given process so that more data can be stored in a smaller space. There are a variety of compression schemes that can be applied to data of which MPEG-1 and MPEG-2 are called lossy since the data produced by compression is not totally recoverable. There are other compression schemes that are totally recoverable, but the degree of compression is much more limited.

Contrast - The range of light to dark values in a picture or the ratio between the maximum and minimum brightness values.

Contrast Range (Ratio) - The ratio between the whitest and blackest portions of a TV image.

Convergence - The crossover of the three electron beams of a three-gun tri-color picture tube. This normally occurs at the plane of the aperture mask.

Core Components - Equipment in the video system that can change the video signal, thereby affecting the quality of the delivered video.

Cropping - A rectangular cutting off of image edges.

Crosstalk - An undesired signal from a different channel interfering with the desired signal.

CS-Mount - A standard for CCTV lens screw mounting. This mounting is defined by a 1-inch (2.54 mm) diameter hole with 32 TPI (turns/threads per inch), female on the camera side, male on the lens side, and a back flange-to-CCD distance of 12.5 mm (0.49 inches). The CS-mount description applies to both lenses and cameras. CS-mount lens cannot be put on C-mount cameras. C-mount lenses can be put on CS-mount cameras but a 5 mm (1.9 inches) adaptor is required.

CPS (Cycles Per Second) - The number of plus/minus voltage swings or compressions/rarefactions of air molecules occurring each second in an electrical or audio signal; usually expressed as hertz (Hz).

Cardioid - "Heart" shaped pattern exhibited by some microphones which reduces pick-up from the sides and back.

Clipping - Audible distortion that occurs when a signal's level exceeds the limits of a particular circuit. When an amp is "turned up too loud," and begins to distort, it is said to be clipping. On an oscilloscope clipping appears to flatten the tops and/or bottoms of the wave forms as if someone took a scissors and "clipped or cut" the top and bottom of the wave.

Compression Driver - A transducer, designed for use with a horn, which utilizes a diaphragm (rather than a cone) to reproduce mid and high frequencies. See: Horn

Compressor - A device that reduces - compresses - a signal's dynamic range.

Condenser Microphone -A mic that depends on an external power supply or battery to electrostatically charge its condenser plates.

Conductor - A substance - in electronics, usually a metal - that allows the free flow of electrons.

Cone - The vibrating diaphragm, employed in some speakers designs, that generates sound waves.

Console - A large or elaborate mixer required to massage the ego of the band's sound man.

Critical Distance - The distance from a sound source at which sound pressure levels emitted by the source equal those being reflected off of other surfaces.

Crossover (Crossover Network) - Electronic An electronic device or circuit that, when inserted between a mixer and amplifier, divides the audio spectrum into individual frequency ranges (low, high, and/or mid) before sending them to specialized amplifier/speaker combinations. An advantage of this type of crossover is that it increases efficiency.

Crossover (Crossover Network) - Passive An electronic device that, when inserted after the amplifier, divides the audio spectrum into individual frequency ranges (low, high, and/or medium) before sending them to specialized speakers (see: tweeter, woofer, and mid-range).

Current - The movement or flow- of electrons.



DAT - An acronym for Digital Audio Tape. Developed by Sony in 1987, it looks similar to an analogue audio cassette but contains professional quality digital information. It is capable of high fidelity music reproduction.

dB (Decibel) - A measure of the power ratio of two signals. In system use, a measure of the voltage ratio of two signals, provided they are measured across a common impedance.

Decoder - Device used to recover the component signals from a composite (encoded) source. Decoders are used in displays and in various processing hardware where components signals are required from a composite source such as composite chroma keying or color correction equipment. Device that changes digital signals to analog, or reconstructs information (data) by performing the inverse (reverse) functions of an encode process.

Definition - The aggregate of fine details available on-screen. The higher the definition of an image, the greater the number of details [that can be discerned by the human eye or displayed]. During video recording and subsequent playback, several factors can conspire to cause a loss of definition. Among these are the limited frequency response of magnetic tapes and signal losses associated with electronic circuitry employed in the recording process. These losses occur because fine details appear in the highest frequency region of a video signal and this portion is usually the first casualty of signal degradation. Each additional generation of a videotape results in fewer and fewer fine details as losses are accumulated.

Depth of Field - The in-focus range of a lens or optical system around an item of interest. It is measured from the distance behind an object of interest, to the distance in front of the object of interest, when the viewing lens is specifically focused on the object of interest. Depth of field depends on subject-to-camera distance, focal length of the lens, and f-stop.

Depth of Focus - The range of sensor-to-lens distance for which the image formed by the lens is clearly focused.

Digital Imager - A fundamental component in every digital camera. The imager records the view received from the camera lens.

Digital Signal - a) An electronic signal where every different value from the real-life excitation (sound, light) has a different value of binary combinations (words) that represent the analog signal. b) An analog signal that has been converted to a digital form.

Digital Signal Processing (DSP) - When applied to video cameras, DSP means that the analog signal from the CCD sensors is converted to a digital signal. It is then processed for signal separation, bandwidth settings and signal adjustments. After processing, the video signal either remains in the digital domain for recording by a DVR or is converted back into an analog signal for recording or transmission. DSP is also used in other parts of the video chain, including DVRs, and switching and routing devices.

Digital Television - The transmission of a broadcast audio/video signal that consists of digital data.

Digitizing - Converting analog audio and/or video into digital form.

Discrimination Level (also known as Level of Discrimination) - a) Qualitatively: Capacity for seeing distinctly fine details that have a very small angular separation.

  1. b) Quantitatively: Any of a number of measures of spatial visual resolution such as the reciprocal of the value of the angular separation in minutes of arc of two neighboring objects (points or lines or other specified stimuli) which the observer can just perceive to be separate.

A generalized use class aspect that specifies what discrimination level you need to recognize a target of interest. See the Discrimination Level topic for video quality requirements considerations.

Display - a) The ultimate image presented to a viewer; the process of presenting that image. b) CRT, LCD, LED or other photo luminescent panel upon which numbers, characters, graphics or other data is presented.

Distortion - The deviation of the received signal waveform from that of the original transmitted waveform.

Distribution Amplifier - A device that provides several isolated outputs from one looping or bridging input, and has a sufficiently high input impedance and input-to-output isolation to prevent loading of the input source.

Dynamic Range - The difference between the maximum acceptable signal level and the minimum acceptable signal level.

DVD - An acronym for "Digital Versatile Disk". It is the same size as a compact disc (CD). A single layer DVD has a storage capacity of 4.7gb and a dual layer disc has a capacity of 8.5gb.

dB (Decibel) – 1.A relative unit of measure between two sound or audio signal levels. A difference 1 dB is considered to be the smallest that can be detected by the human ear. An increase of 6 dB equals twice the sound pressure. 2. As a measure of sound pressure levels, used to indicate loudness.

DC (Direct Current) - Electrical current that flows in only one direction.

Delay – The postponement of an audio signal for a specific amount of time, usually measured in milliseconds. 2. A device designed to delay an audio signal.

Diaphragm – The radiating surface of a compression driver; its vibrations emit sound waves. 2. The moving element of a microphone.

Dimmer Noise (hash) - The noise that originates in the switches used to dim lights and can be heard in a sound system.

Directivity - The ability of a speaker or horn to direct sound to a given area which can be described by its directivity factor (Q).

Dispersion - The area throughout which the sound produced by a speaker is distributed.

Distortion - Any discrepancy between the source material and the sonic output of a sound system.

Ducking - The use of an electronic device to automatically reduce the volume of music or other background fill when an announcer begins speaking.

Dynamic Microphone - A microphone that converts sound into electrical pulses by means of a moving electromagnetic coil.

Dynamic Range - The difference between the softest and loudest extremes within an audio signal.

Dynamics Processing - The use of electronic devices to control the levels of audio signals and compress or expand their dynamic range.



Equalizer - An electronic circuit that introduces compensation for frequency discriminative effects of elements within the television system, particularly long coaxial transmission systems.

Effects - Loop inputs and outputs that allow the sending of an audio signal to and from a signal processor such as a reverb unit, delay, gate or limiter.

Efficiency - The ratio of a device's energy output to its energy intake.

Electret Microphone - A condenser microphone which, instead of employing an external high voltage power source, relies on permanently polarized plates, a low voltage power supply, and internal preamp.

Equalization (EQ) - The electronic manipulation of specific frequencies.

Equalizer (EQ) - A device that permits the precise control of specific frequency ranges. Examples are: Graphic, Parametric, Notch Filter, Cut only.

Expander - an electronic device that increases dynamic range by reducing a signal's level any time it falls below a specific threshold.



Fiber Optics (use of light transmitted through fibers) - The technology of transferring information, e.g., in communications or computer technology, through thin flexible glass or plastic tubes of optical fibers using modulated light waves.

Fidelity (precision of reproduction field) - The extent to which an electronic device such as a stereo system or television accurately reproduces sound or images. a) In interlaced scan systems, the information for one picture is divided up into two fields. Each field contains one-half of the lines required to produce the entire picture. Adjacent lines in the picture are in alternate fields. b) Half of the horizontal lines (262.5 in NTSC and 312.5 in PAL) needed to create a complete picture. c) One complete vertical scan of an image. In a progressive scanning system, all of the scanning lines comprising a frame also comprise a field. d) An area in a window in which you can type text. e) A television picture is produced by scanning the TV screen with an electron beam. One complete scan of the screen is called a field. Two fields are required to make a complete picture, which is called a frame. The duration of a field is approximately 1/60 of a second in NTSC and 1/50 or 1/60 of a second in PAL. f) One half of a complete interlaced video picture (frame), containing all the odd or even scanning lines of the picture.

Field of View - The maximum angle of view that can be seen through a lens.

Flutter - A rapid variation in the pitch or of a recorded audio signal usually on a turntable or tape recording, caused by variations in the speed of the turntable or tape drive.

Focal Length (of a lens) - The distance from the focal point to the principal point of the lens. The focal length is usually measured in millimeters of the lens. Focal length is an indication of the lens capability to capture a wide angle of view or a narrow view of objects that are far away (telephoto).

Focal Plane - A plane (through the focal point) at right angles to the principal point of the lens.

Focal Point - The point at which a lens or mirror will focus parallel incident radiation.

Frame - The total area, occupied by the television picture, which is scanned while the picture signal is not blanked. a) A frame consists of all the information required for a complete picture. For interlaced scan systems, there are two fields in a frame. For progressive video, these lines contain samples starting from one time instant and continuing through successive lines to the bottom of the frame. b) A complete picture composed of two fields. In the NTSC system, 525 interlaced horizontal lines of picture information in 29.97 frames per second. In the PAL system, 625 interlaced horizontal lines of picture information in 25 frames per second.

Frame Rate (also known as frame frequency) - a) The rate at which frames of video data are scanned on the screen. In an NTSC system, the frame rate is 29.97 frames per second. For PAL, the frame rate is 25 frames per second. b) The number of frames per second at which a video clip is displayed. c) The rate at which frames are output from a video decoding device or stored in memory.

Frame Transfer - A CCD imager where an entire matrix of pixels is read into storage before being output from the camera. This differs from interline transfer where lines of pixels are output.

Frequency Interlace - The method by which color and black-and-white sideband signals are interwoven within the same channel bandwidth.

Frequency Response - The range of frequencies that a piece of equipment can process and is directly related to the system’s ability to uniformly transfer signal components of different frequencies over the entire video spectrum without affecting their amplitudes. This parameter is also known as gain/frequency distortion or amplitude versus frequency response. The amplitude variation maybe expressed in dB, percent or IRE.

Front Porch - The portion of a composite picture signal that lies between the leading edge of the horizontal blanking pulse and the leading edge of the corresponding sync pulse.

F-Stop (also known as f-number or f-system) - The speed or ability of a lens to pass light. It is calculated by dividing the focal length of the lens by its diameter. The f-stop also is a factor in more areas of focus in the image known as Depth of Field.

Fader - The signal output control found on the channel, submaster, and master sections of a mixer.  

FerroFluid - An emulsion containing metal particles, used to conduct heat away from a speaker's voice coil.

Filter - A device that removes unwanted frequencies or noise from a signal.

Flat - The state of an audio signal or tone whose frequency is unaltered by equalization. On most mixers and equalizers flat is indicated by the tone controls being at dead center.

Fletcher Munson Curve - A graphic representation of average hearing responses of carbon based units at particular sound pressure levels.

Foldback - an output, that by splitting an input signal (independently of the mixer controls), allows that signal to be sent a separate device. Foldback makes it possible for a performer to create his/her own monitor mix without affecting the front of house mix.

Frequency – The number of sound waves that pass a given point in one second. 2. The determiner of pitch. (Ask Kenneth).

Frequency Response - The range of frequencies that are reproducible by a speaker or electronic component.

Front of House (FOH) - the components of a PA that are directed toward the audience, as opposed to the back of the house or monitor system.



Gain - An increase in voltage or power, usually expressed in dB.

Gamma - A numerical value, or the degree of contrast in a video picture, which is the exponent of that power law which is used to approximate the curve of output magnitude versus input magnitude over the region of interest. Since picture monitors have a nonlinear relationship between the input voltage and brightness, the signal must be correspondingly pre distorted. Gamma correction is always done at the source (camera).

Gamma Correction - To provide for a linear transfer characteristic from input to output device.

Genlock - A device used to lock the frequency of an internal sync generator to an external source.

Ghost - A spurious image resulting from an echo.

Gray Scale - Variations in value from white, through shades of gray, to black on a display.

Gain – The amplification characteristic of an electrical or mechanical device. 2. The amount of volume that may be achieved before acoustical feedback occurs.

Gate - An electronic device that increases dynamic range by cutting off a signal when its level falls below a specific threshold. Used to control leakage of sound source into adjacent mics (ie drums).


Hz (Hertz) - A unit of measure that equals one cycle per second.

High Pass Filter - A circuit that discriminates between high and low frequencies and allows only the high frequencies to pass.

Horn - An acoustical transformer which, when coupled to a driver, provides directivity and increases the driver's loudness. See: Compression Driver

Hpercardioid - A narrower heart-shaped pick-up pattern than that of cardioid microphones.

264 - Also known as MPEG-4 AVC (Advanced Video Coding) it is now one of the most commonly used recording formats for high definition video. It offers significantly greater compression than previous formats.

HDTV (high-definition television) - a) General term for standards pertaining to consumer high-resolution TV. b) A TV format capable of displaying on a wider screen (16:9) as opposed to the conventional 4:3) and at higher resolution. Rather than a single HDTV standard the FCC has approved several different standards, allowing broadcasters to choose which to use. This means new TV sets will have to support all of them. All of the systems will be broadcast as component digital. c) By HDTV, we normally understand transmission, rendering and display systems that feature about double the number of scanning lines, improved color quality, and less artifacts than that of composite systems.

Hertz - The standard unit for measuring frequency. One hertz (abbreviated Hz) equals one cycle per second. It is commonly used to measure sound waves, light waves and radio waves.

High Pass Filter - An electronic filter that attenuates audio frequencies below a certain level and allows them above that level.

Hue - Corresponds to colors such as red, blue, etc. A color wheel contains basic pigments. All the hues of the rainbow encircle the cone’s perimeter. The wavelength of the color that allows color to be distinguished such as red, blue and green. Often used synonymously with the term tint. It is the dominant wavelength that distinguishes a color such as red, yellow, etc. Most commonly, video hue is influenced by a camera’s white balance or scene lighting. Video color processors, such as the video equalizer, are the main tools used to adjust and correct hue problems.

Hue, Saturation, and Intensity (HSI) - Color space system based on the values of Hue, Saturation, and Intensity. Intensity, analogous to luma, is the vertical axis of the polar system. The hue is the angle and the saturation is the distance out from the axis.

Hue, Saturation, and Lightness (HSL) - Nearly identical to HSI except Intensity is called Lightness. Both serve the same function.

Hue, Saturation, and Value (HSV) - Nearly identical to HSI and HSL except Intensity and Lightness are called Value. All three serve the same function.

Hum - Electrical disturbance at the power supply frequency or harmonics thereof.


Image - a) A bit stream duplicate of the original data. b) An imitation or representation of a person or thing, drawn, painted, photographed, axis etc.

Image Intensifier - A device that intensifies low light-level images to light levels that can be seen with the human eye or can be detected by a video camera. (Lambert Instruments)

Image Plane - The plane in which an image produced by an optical system is formed; if the object plane is perpendicular to the optical axis, the image plane will ordinarily also be perpendicular to the axis.

Impedance (input or output) - The total of the resistance, measured in ohms, that a circuit presents to the flow of alternating current at a given frequency (Columbia University). The characteristics of a system component that determines the type of transmission cable to be used. The cable used must have the same characteristic impedance as the component. Video distribution has standardized on 75-ohm coaxial and 124-ohm balanced cable.

Incident Light - The direct light that falls on an object.

Insertion Loss - The signal strength loss when a piece of equipment is inserted into a line.

Interference - Disturbance to the normal or expected operation electronic devices, equipment and systems. The inhibition or prevention of clear reception of broadcast signals.

Interline Transfer - A technology of CCD design, where rows of pixels are output from the camera. The sensor’s active pixel area and storage register are both contained within the active image area. This differs from frame transfer cameras that move all active pixels to a storage register outside of the active area.

Interlaced Scanning - A technique of combining two television fields in order to produce a full frame. The two fields are composed of only odd and only even lines, which are displayed one after the other but with the physical position of all the lines interleaving each other, hence interlace.

Iris - An adjustable aperture built into a camera lens to permit control of light transmission through the lens.

Isolation Amplifier - An amplifier with input circuitry and output circuitry designed to eliminate the effects of changes made at either upon the other. They provide electrical isolation and a safety barrier.

Impedance - The measure of total resistance to the current flow in an alternating current circuit; expressed in ohms, as a characteristic of electrical devices (particularly speakers and microphones). Most speakers are rated at 8 ohms. Microphones are usually classified as being either high impedance (10,000 ohms or greater) or low impedance (50 to 250 ohms).

Inductance - A circuit's opposition to a change in current flow.

Input Overload Distortion - Distortion caused by too great an input signal being directed to an amplifier or preamplifier. Input overload distortion is not affected by volume control settings and most frequently occurs when mics are positioned too close to the sound source. Input overload distortion is controllable through the use of an attenuator.

Inverse Square Law - The law that states that in the absence of reflective surfaces, sound pressure 9or light) falls off at a rate inverse to the square of the distance from its source. In other words, every time you double your distance from the sound source, the sound pressure level is reduced by 6 dB.



Jitter - Small, rapid variations in a waveform due to mechanical disturbances or to changes in the characteristic of components. Supply voltages, imperfect synchronizing signals, circuits, frequency pulses, etc.

Jack - A female input or output connector, usually for a mic or an instrument



KHz - Symbol for kilohertz. It is a unit of frequency. One kilohertz is equal to 1,000 hertz or 1,000 cycles per second.


Lens - One or more pieces of curved optical glass or similar material designed to form an image of an object by converging or diverging rays of light from the object.

Lens Preset Positioning - Follower Pots are installed on lens that allows feedback to the controller information relevant to zoom and focus positioning allowing the controller to quickly adjust to a preselected scene and arrive in focus at the proper focal length automatically.

Lens Speed - The ability of a lens to transmit light, represented as the ratio of the focal length to the diameter of the lens. The largest lens opening (smallest f-number) at which the lens can be set. A fast lens transmits more light and has a larger opening than a slow lens.

Letterbox - A method of displaying widescreen video on a screen with a different aspect ratio by leaving a space, usually black bars, above and below the image.

Light - Electromagnetic radiation that has a wavelength in the range from about 400 to 750 nm and may be perceived by the normal unaided human eye.

Lighting Level - A generalized use class aspect that specifies the level of lighting do you anticipate in a scene of interest. See also, the Lighting Level topic for video quality requirements considerations.

Line Amplifier - An amplifier for audio or video signals that in installed in the transmission line to boost the signal as it travels over certain distances; also called program amplifier.

Loop - Either a repeating section of audio or video material, or of cartoon cells or a synonym for "post-sync": dialog replacement (i.e. dubbing) during post-processing to improve audio quality.

Loop Through - The method of feeding a series of high impedance circuits (such as multiple monitor/displays in parallel) from a pulse or video source with a coax transmission line in such a manner that the line is bridged (with minimum length stubs) and that the last unit properly terminates the line in its characteristic impedance. This minimizes discontinuities or reflections on the transmission line.

Loss - The ratio of the power at one point in a transmission system to the power at a point farther along the line; usually expressed in decibels. The actual power that is lost in transmitting signal from one point to another through a medium or along a line.

Low-Frequency Distortion - An undesired change in a waveform or signals which occur at low frequencies. In television, generally considered as any frequency below the 15.75-kHz line frequency.

Lowpass Filter - A filter that attenuates frequencies above a specified frequency and allows those below that value to pass.

Lumen (LM) - A unit of measurement of the amount of brightness that comes from a light source. Lumens define “luminous flux,” which is energy within the range of frequencies we perceive as light.

Lumen/FT2 - A unit of incident light. It is the illumination on a surface one square foot in area on which a flux of one lumen is uniformly distributed, or the illumination at a surface all points of which are at a distance of one foot from a uniform source of one candela.

Luminance (Photometric Brightness) - Luminous intensity of any surface in a given direction per unit of projected area of the surface viewed from that direction. The amount of brightness, measured in lumens that is given off by a pixel or area on a screen.

Luminance Signal (See also, Y Signal.) - That portion of the NTSC color television signal which contains the luminance or brightness information.

Lux - SI unit of illumination, equal to one lumen per square meter. Lux is a measurement in light intensity.

Limiter - A device that electronically controls or "limits" the peak levels of program material.

Line Level - A signal whose voltage is between approximately 0.310 volts and 10 volts across a load of 600 ohms or greater.

Load - Any device to which power is delivered

Low Pass Filter - A circuit that discriminates between high and low frequencies and allows only the low frequencies to pass.



Matrix Switcher - A combination or array of electromechanical or electronic switches which route a number of signal sources to one or more destinations.

Mbps - Abbreviation of megabits per second. One megabit is equal to one million bits or 1,000 kilobits. It is used to measure high data transfer speeds of connections such as Ethernet and cable modems.

Megabyte - A measure of computer memory or storage. It is one million bytes (in the context of computer memory, sometimes used to mean 1,048,576 (2 to the power 20) bytes).

Megahertz - A unit of frequency equal to one million hertz or cycles per second. Usually abbreviated to MHz.

Megapixel - The term pixel comes from the phrase picture element. One megapixel is equal to 1,000,000 (one million) pixels. For the most part, the larger number of pixels, the better the quality of the picture.

Modulation - The process, or results of the process, whereby some characteristic of one signal is varied in accordance with another signal. The modulated signal is called the carrier. The carrier may be modulated in three fundamental ways: by varying the amplitude, called amplitude modulation; by varying the frequency, called frequency modulation; by varying the phase, called phase modulation.

Monitor - A device that accepts video signals from a computer or video camera and displays information on a screen; a video display.

Monochrome - Black and white with all shades of gray.

Monochrome Signal - In monochrome television, a signal wave for controlling the brightness values in the picture. In color television, that part of the signal wave which has major control of the brightness values of the picture, whether displayed in color or in monochrome.

Monochrome Transmission - The transmission of a signal wave which represents the brightness values in the picture, but not the color (chrominance) values.

Motion - A generalized use class aspect that specifies the level of motion you anticipate in a scene of interest. See also, the Motion topic for video quality requirements considerations.

Motion Picture Expert Group (MPEG) - A group of standards for encoding and compressing audiovisual information such as movies, video, and music. MPEG compression is as high as 200:1 for low-motion video of VHS quality, and broadcast quality can be achieved at 6 Mbit/s. Audio is supported at rates from 32 kbit/s to 384 kbit/s for up to two stereo channels.

Multi-factor Authentication (MFA) - A security system that requires more than one method of authentication from independent categories of credentials to verify the user's identity for a login or other transaction.

Microphone Processor - A device that, when installed between a mic and an amp or preamp, allows the manipulation of the signal originating at the mic.

Mixer - An electronic device that permits the combining of a number of inputs into one or more outputs. Mixers commonly provide a variety of controls - tone, volume, balance and effects - for each "channel." See: Board, Console.

Monitor - A speaker or earphone dedicated to making it possible for a performer to hear - or monitor - his/her own performance. Examples are: floor wedges, sidefills, or mini-monitor.



National Television Systems Committee (NTSC) - A committee that worked with the FCC in formulating standards for the present day United States color television system.

Neutral Density Filter (ND filter) - A filter that attenuates light evenly over the visible light spectrum. It reduces the light entering a lens, thus forcing the iris to open to its maximum.

Noise - The word noise originated in audio practice and refers to random spurts of electrical energy or interference. In some cases, it will produce a “salt-and-pepper” pattern over the televised picture. Heavy noise is sometimes referred to as snow.

Non-Composite Video - A video signal containing all information except sync.

Noise Gate - A device that attenuates a signal when the program level falls below a preset threshold.



Output - The signal level at the output of an amplifier or other device.

Ohm - The basic unit of measurement of resistance.

OHM'S Law - The law that states the relationship between current, resistance and voltage in an electrical circuit: Amperage times resistance equals applied voltage.

Omnidirectional - Capable of picking-up sound or radiating sound equally from all directions; as with an unidirectional microphone or subwoofer.

Oscilloscope - An electronic device that displays, on a video screen, a representation of an electrical signal.



Packet - One unit of binary data capable of being routed through a computer network. To improve communication performance and reliability, each message sent between two network devices is often subdivided into packets by the underlying hardware and software.

PAL - Short for Phase Alternate Line. The TV broadcasting system used in Europe and other countries.

Pan and Tilt - A device upon which a camera can be mounted that allows movement in both the azimuth (pan) and in the vertical plane (tilt).

Pan/Tilt Preset Positioning - Follower pots are installed on pan/tilt unit to allow feedback to the controller and provides information relevant to horizontal and vertical positioning, allowing the controller to quickly adjust to a pre-selected scene automatically.

Patch Panel - A panel where circuits are terminated and facilities provided for interconnecting between circuits by means of jacks and plugs.

Peak Pulse Amplitude - The maximum absolute peak value of a pulse, excluding those portions considered to be unwanted, such as spikes.

Peak-to-Peak - The amplitude (voltage) difference between the most positive and the most negative excursions (peaks) of an electrical signal. A full video signal measures one volt peak to peak.

Pixel - Short for Picture Element. The most basic unit of an image displayed on a computer or video display screen. Pixels are generally arranged in rows and columns; a given combination among the pixels of various brightness and color values forms an image.

Phono plug - Also called RCA connector, it is a widely used cable connector for home audio and video equipment.

Primary Colors - Three colors wherein no mixture of any two can produce the third. In color television these are the additive primary colors red, blue and green.

Processed Image - Any image that has undergone enhancement, restoration or other operation.

Progressive Scan - Display scan pattern where each line of the frame is scanned sequentially.

PA - Abbreviation of public address system: one or more speakers connected to an amplifier; may include a mixer and any combination of sound reinforcement devices.

Pad - An attenuator.

Patch Cord - A short electrical cable used to connect individual components of a sound system

Personal Monitor - A monitor that is small enough to be directed at a specific performer. Before these devices, monitors were usually arrayed along the front of the stage and shared by the entire ensemble.

Piezo Tweeter - A driver which is dedicated to the reproduction of high frequencies and operated by means of a crystal rather than an electromagnet.

Phantom Power - Operating voltage supplied to a condenser mic by a mixer or external power source.

Phase - The relationship of an audio signal or sound wave to a specific time reference.

Phase shift - The phase relationship of two signals at a given time, or the phase change of a signal over an interval of time.

Pin 2 Hot - Considered the standard polarity for pro audio.

Pitch Tone - A function of frequency.

Polarity - A condition which has two states (in or out) and is usually described in one of three ways: 1. Acoustical to electrical (microphone): Positive pressure at diaphragm produces positive voltage at pin 2 of XLR or at the tip of a ¼-inch phone plug. 2. Electrical to acoustic: Positive voltage into the "plus" terminal of a speaker causes the speaker's diaphragm to move forward (produces positive pressure). 3. Electrical to electrical: Positive voltage into pin 2 of an XLR plug or at the tip of a ¼-inch phone plug produces positive voltage at the output (pin 2 of XLR jack, the tip of a ¼-inch phone plug, or the red (plus) connector of a binding post (banana terminal)).

Potentiometer (Pot) - A variable resistor (rotary or linear) used to control volume, tone, or other functions of an electronic device.

Power Amplifier - An electronic device that increases the volume of a signal. A basic unit of all sound systems. Power amps are typically connected to a preamp which provides controls for individual functions: level, tone, etc.

Preamplifier - See: power amplifier

Proximity Effect - An increase in the bass response of some mics as the distance between the mic and its sound source is decreased


Q - A ratio obtained by complex mathematical calculations involving the relationship of a speaker's direct radiated energy to its total radiated energy (directivity index). When measured on-axis, Q (which is dependent on frequency) is used to determine a speaker's suitability for a particular application.


Radio Frequency Interference (RFI) - Radio signals from external sources that invade and can be heard through, sound systems.

Reflection - A term that describes the amount of sound "bouncing" off of hard surfaces.

Rejection - A microphone's ability to selectively exclude sounds coming from outside it's pickup pattern.

Resistance - Opposition measured in ohms to the flow of electrical current.

Reverberation - sound waves that continue to bounce around a space after the sound source has ended.

Room - Any enclosed space in which a performance is staged. It can be as small as a closet or as large as the Superdome.


SPL (Sound Pressure Level) - A measurement of the volume of sound, expressed in decibels (dB): a function of amplitude.

Sensitivity - The sound pressure level directly in front of the speaker (on axis) at a given distance and produced by a given amount of power.

Shield - A metal enclosure that prevents electronic components from being affected by unwanted interference. Shielded speakers may be placed near a TV, for instance, because their magnets cannot affect the picture tube.

Shelving - The setting of the on-axis output of complementary drivers (woofers, mid-range, tweeters) to provide the desired frequency response.

Sibilance - A hissing sound produced when pronouncing S and Z. Sibilance is undesirable in professional sound reinforcement and can be controlled through the use of a "de-esser" like Valley Audio's 401 Microphone Processor, 815 Dynamic Sibilance Processor, or 730 DynaMap Digital Dynamics Processor.

Signal - An electrical impulse. First popularized by Paul Revere.

Signal-To-Noise-Ratio - The ratio, expressed in dB, of an electronic device's nominal output to its noise floor.

Snake - A cable often running between the stage and control board - that combines multiple lines; used to connect mics, instruments and monitors to a mixer.

Sound Level Meter - A device that measures, in dB, the amplitude of sound waves.

Sound Pressure Level (SPL) - The measurement of loudness, or amplitude, of sound, expressed in dB.

Sound Reinforcement - The use of electronic devices to reinforce, alter or increase the level of sound.

Spider - An internal speaker component whose function is to precisely position the voice coil in relation to a gap in the motor.


Toe-in - The degree to which the inside front edges of a pair of speakers are angled toward each other.

Transducer - A device which converts sound into electrical energy (a microphone), or electrical energy into sound (a speaker).

Transformer - A device that alters electrical current.

Tweeter - A speaker (driver) that reproduces only frequencies above a certain range, usually about 3 kHz.


Unbalanced Line - Cable that consists of one conductor and a shield. Here the shield is also carrying the other half of the signal.

Unidirectional - A mic that picks up sound primarily from one direction.


VCA (Voltage Controlled Amplifier) - An amplifier whose output is controlled by varying its voltage rather than by direct resistance (as with a potentiometer).

Voice Coil - Wire, usually copper, wrapped around a former (tubular core). When attached to a cone or diaphragm, surrounded by a magnetic field, and set into vibration by an alternating current, a voice coil causes a speaker to emit sound waves.

Voltage - The electrical pressure (electromotive force) of a current within a circuit.


Watt – A unit of measurement that equals about 1/746 horsepower or enough electrical energy to perform 1 joule per second. A joule describes the energy of 1 newton displace 1 meter in the direction of the applied force. A newton is the amount needed to accelerate 1 kilogram 1 meter per second. 2. One volt multiplied by one amp.

Wedge - A monitor speaker, in the shape of a wedge, designed to sit on the floor and be directed toward the performer(s).

Woofer - A speaker (driver) that reproduces only frequencies below a certain range, usually about 800 Hz.


XLR Connector - A three pin connector widely used in the audio industry.



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