Term	Definition	Demo
A/D Converter	A device that accepts an analog signal at its input, and outputs a digital version of the signal.
AC	see Alternating Current
Active Crossover	An analog or digital device performing high-pass, low-pass and bandpass functions ahead of power amplifiers driving the transducers in a loudspeaker.
Active Loudspeaker	A loudspeaker which has a built-in power amplifier for at least one driver, usually the woofer or subwoofer. It may also have amplifiers for mid and high frequency drivers. See: Powered Tower
Alternate Channel Selectivity	A measure of the ability of a radio tuner to reject information from a radio station close to the frequency of the one being listened to.
AM Rejection	A specification describing to how well a radio tuner can ignore changes in the amplitude of an FM signal, such as those caused by propagation effects and interference.
Amperage	The magnitude of an electrical current as expressed in amperes.
Amplification	An increase in signal level.
Amplifier	A device that increases the magnitude of the voltage, current or power in an electronic system. In audio systems, preamplifiers and surround processors amplify voltages. Power amplifiers amplify both voltage and current, therefore providing more power output in order to drive loudspeakers.
Amplitude Modulation	A method of radio broadcasting in which the radio carrier frequency is amplitude modulated by the audio signal. Typically limited in bandwidth, and susceptible to interference and static. However, it propagates well over long distances and around hills and buildings. Abbreviated AM.
Analog	An electrical signal in which the voltage (or current) waveform has the same form as the original acoustical sound waves. See also Digital
Aspect Ratio	The width-to-height ratio of a visual image. Standard NTSC television sets have an aspect ratio of 4:3 (4 units wide by 3 units high). Widescreen television sets have an aspect ratio of 16:9. Many films are produced with even wider ratios. Pictures with aspect ratios different from the display will show dark bars at the top and bottom, or at the sides. See: Widescreen, NTSC.
Audio Frequency Range	The range of human hearing commonly accepted as 20 to 20,000 Hertz (cycles per second).
Audio Signal	An audio frequency signal in electronic form or after conversion to sound.
Balance Control	In stereo systems, a control to adjust relative sound levels in the left and right loudspeakers. In multichannel systems there is a front-back balance adjustment. In car audio, the front-back adjustment is called a 'fader'.
Bandwidth	The difference between the upper and lower usable frequency limits of a circuit, a device, or a communications (radio, TV or digital data transmission) channel.
Bass	Low-frequency audio signals. Frequencies below approximately 300Hz (below 100Hz in cars).
Bass Control	A tone control allowing the user to boost or cut the low frequency portion of the audio signal.
Bass Management	A function in a multichannel surround processor that combines the low bass frequencies from all of the channels (including the LFE channel) in a recording, and directs it to the appropriate loudspeakers. To do this, the customer must tell it the number, kind (small or large), and placement of loudspeakers, and whether there is a subwoofer in the system. See: LFE
Bridging	Combining the outputs of two amplification channels to provide one more powerful channel. Note that bridging may raise the minimum load impedance that the amplifier can safely drive.
Broadband	A term implying very wide bandwidth. In the context of data communications it implies a connection with higher data rates (wider bandwidth) than telephone modems.
CD	CD = Compact Disc. An optical disc format for storing digital signals, developed jointly by Sony and Philips.
CD-DA	CD-DA = Compact Disc Digital Audio, the original PCM digital music storage format, defined by the Red Book standard.
CD-R	A disc in the CD format that can be recorded once. Defined by the Orange Book standard.
CD-ROM	A Read-Only Memory (ROM) in the CD format, used for storing computer data. Defined by the Yellow Book standard.
CD-RW	A disc in the CD format that can be recorded many times. It is rewritable.
Channel	A signal path. Stereo consists of two channels, starting from the signal source, and ending at the loudspeakers. Multichannel audio can have 5, 6 or 7 channels, plus a so-called .1 channel for low bass sound effects.
Channel Separation	See: Separation.
Chrominance	The color (hue and saturation) of light, independent of luminance (brightness), or that portion of a video signal that carries this information. Designated by the symbol 'C'. See: Luminance.
Codec	A combination encoder and decoder for any kind of digital signals, audio or video. See: Perceptual Coding, Compression.
Component Video	A video signal consisting of three components: red/green/blue (RGB) or a Color Difference method going by one of several names: Y,U,V or Y, Pb, Pr or Y, B-Y, R-Y. The latter is the method of video storage on DVD's and the component connection is the preferred way to communicate video infomation to displays. The green, blue and red cables may be terminated in either RCA or BNC plugs. See: Chrominance, Luminance, RCA, S-Video, BNC.
Composite Video	A video signal in which the chrominance and luminance signals are combined, along with synchronizing signals. These tend to use cables, looking like yellow audio cables, with RCA connectors. This is the most basic form of video found on virtually all TV's, VCR's, etc. See: Chrominance, Luminance, RCA, S-Video, Component Video.
Cone	A cone-shaped diaphragm of a loudspeaker that vibrates and radiates sound. Loosely used to describe all diaphragms, some of which have other profiles, such as domes.
Crossover	Electrical filters that direct the appropriate frequencies to the woofer, midrange, tweeter, etc. in a loudspeaker system. The crossover frequency is the frequency at which the loudspeaker driver being turned off (e.g. a woofer) is at the same sound level as the one being turned on (e.g. a tweeter).
Crossover Frequency	See crossover.
Crosstalk	Unwanted sound from one channel that leaks into another.
D/A Converter	A device that accepts a digital signal as an input and converts it to analog form at its output.
DAC	See D/A Converter.
dB	see Decibel.
DC	Direct Current. A condition in which the polarity of the voltage is constant, and current flows only in one direction. Batteries and rectified AC power supplies are examples of DC power sources.
Decibel	A logarithmic measure of relative voltage, current or power. A decibel is one-tenth of a bel, abbreviated dB. In terms of power, 3 dB = 2x, 10 dB = 10x. In terms of current or voltage: 6 dB = 2x. In terms of perceived loudness: 1 dB is just audible, a 10 dB sound level change represents double or half loudness.
Digital	The representation of a quantity in numeric form, normally in binary. In audio, this means that waveforms of sounds are sampled at very high frequencies, and each sample is stored in numeric form, so that the waveform can subsequently be reconstructed. See A/D converter, D/A converter, Analog.
Discrete Circuitry	The use of separate components such as transistors, resistors, capacitors, and diodes in an electronic circuit instead of IC's (Integrated Circuits) in which these components are fabricated in microscopic size on a silicon chip. Performance and economic factors usually determine which alternative is chosen.
Distortion	When an audio signal has been changed by the nonlinear behavior of the microphones, electronics, and loudspeakers. The nonlinearities, whether acoustical, mechanical or electrical, change the audio signals which are passed through them. See: Linear Distortion, Non-Linear Distortion.
DSP	Digital Signal Processing. Any form of manipulation performed on an audio or video signal while it is in digital form. The term DSP acquired an unfortunate reputation when, in the early days, it came to be associated with artificial reverberation (hall, stadium, etc.) effects that could be added in during playback. Many of these effects were not good. Now, the quality of DSP processing is undisputed, and limited only by the competence of the programmers.
DSS	See: Digital Satellite System
DVD	Initially interpreted as meaning Digital Video Disc, but now that there are several uses for the medium, it is more popularly known as the Digital Versatile Disc.
DVD-A (DVD-Audio)	An audio version of DVD, in which multiple digital audio channels can be stored in uncompressed PCM form, or using a lossless compression algorithm (the digital audio signals are reconstructed without alteration). The massive storage capacity of DVD allows for many options.
Dynamic Range	The difference between the loudest and softest sounds that can be reproduced by a device or format. Usually expressed in dB.
EQ	See: Equalizer
Equalizer	A device consisting of adjustable filters that can change the frequency response of an audio system. Equalizers can compensate for frequency response aberrations in loudspeakers, loudspeaker/room combinations, and also for adjusting the tonal balance of recordings. See also: Graphic Equalizer, Parametric Equalizer, Tone Controls.
Feedback	In Amplifiers: the practice of connecting (feeding back) a portion of the output signal to the input so that it can be compared to the input signal and errors corrected. The signal must be inverted (negative feedback) to prevent oscillation, or uncontrolled, very loud, howling (positive feedback). Positive feedback is sometimes experienced in public address systems as a ringing or howling when too much of the amplified sound is picked up by the microphones.
Fidelity	See: High Fidelity
FM	see Frequency Modulation
Frequency	The number of vibrations or cycles completed by a signal in one second. Frequency is expressed in cycles, or more commonly, Hertz (Hz).
Frequency Modulation	A method of radio broadcasting in which the radio carrier frequency is frequency modulated by the audio signal. Capable of high sound quality, and relatively immune to interference and static. However, it propagates poorly over long distances and suffers from multipath interference and shadow zone problems in cities and hilly areas.
Frequency Response	A measure of the amplitude vs. frequency performance of an audio component, measured from its input to its output. A perfect electronic device should have a flat, or linear, frequency response over its useful frequency range, indicating that it reproduces all frequencies at the correct level. Loudspeakers are more complicated since the output is sound which is radiated in all directions. It is necessary to measure the frequency response at many locations all around the loudspeaker in order to be able to predict how it may sound in a room. For loudspeakers, there is no single frequency response measurement that is completely descriptive of its performance. See: Transfer Function, Spectrum.
Harmonic	A tone that is a whole-number multiple of the original, or fundamental, tone. Numerically, the first harmonic is the fundamental. Harmonics are abundant in musical sounds, helping to give instruments and voices their distinctive qualities. When harmonics occur as a result of nonlinear distortion, they change the timbre of musical sounds and voices. See: Missing Fundamental, Overtones.
Harmonic Distortion	The form of distortion that occurs when a nonlinear device is driven with a pure tone. See Harmonic, Non-Linear Distortion, Distortion.
HDCD	High Definition Compatible Digital. An encode/decode process aimed at enhancing the performance of conventional 16-bit audio signals on compact discs.
HDTV	See: High Definition Television
Hertz	The basic unit of frequency also called cycles per second. The number of full cycles completed by an alternating signal in one second.
High Definition Television	A video system with approximately twice the horizontal and vertical resolution of conventional NTSC television, and presented in a 16:9 aspect ratio. See: NTSC, Aspect Ratio, Resolution
High Fidelity	Many years ago, the term suggested an audio component designed to meet the highest performance standards. Now it applies to anything that can make sound. Still, the words retain their original dictionary meanings, and they describe the underlying, if unstated, objective of all serious practitioners of the audio arts and science.
Hz	Abbreviation for Hertz. See Hertz.
Imaging	In sound reproduction: the perceived illusions of direction and space relating to the locations of musical instruments and voices, and to the acoustical environment in which they are performing.
Impedance	In electronics: the opposition to alternating current flow in a circuit or device. Properly expressed as a complex quantity, it is also simplified as a magnitude only. The latter is commonly used in describing the impedance of loudspeaker drivers and systems. There are also acoustical and mechanical impedances.
Infrared	Invisible light that is just below red in the visible spectrum of colors. In large quantities, it is manifested as heat. In small quantities it is used as a signalling medium for remote controls.
Interlace	A video display made up of two alternating fields, one that scans the even-numbered lines followed by one that scans the odd-numbered lines. The field repetition rate is normally tied to the local AC power line frequency e.g. 60 fields/second in North America, thus presenting a complete picture, or frame, 30 times per second. See: NTSC, PAL, SECAM, Scan Line.
Intermodulation Distortion	Distortion created when a nonlinear device is driven by multiple tones. Intermodulation distortion products are complex multiples and submultiples of the test signals, making them more easily audible than the harmonic distortion products which are simultaneously created in such a test. Music, being a complex signal, generates abundant intermodulation distortion when processed by a nonlinear device. See: Harmonic Distortion, Non-Linear Distortion.
IR Remote	A remote control that communicates by means of Infrared (IR) light. Such controls need line of sight to the devices being controlled, or good optical reflecting surfaces to help the light signal to get there. See: RF remote.
LCD	Liquid Crystal Display is one in which the reflectivity and/or transparency can be changed by the application of a voltage. It is divided into many tiny independently conrolled pixels. They are very common: digital watches, calculators, dashboards, computer screens, rear and front projection video displays, etc. Since they are used as light transmission devices in most applications, there are losses, and getting the control voltages to each of the pixels presents challenges in maximizing the aperture ratio. See: Aperture Ratio, Projector.
LED	Light Emitting Diode. An electronic component that emits light when energized. Commonly used as indicator lights on electronic equipment, and nowadays in arrays as tail lights on cars and traffic lights.
Letterbox	The method of displaying a widescreen image on a standard 4:3 aspect ratio display. The width of the image is the width of the display, but the height is less, meaning that there are black bars above and below - like a letterbox.
LFE	See: Low-Frequency Effects
Loudness	The perceptual correlate of sound level. Subjective perception of loudness is highly non-linear. Doubling or halving loudness requires about 10 dB change in sound level at middle and high frequencies. At low frequencies, it can be as little as 4 dB. The smallest audible change in overall loudness level is about 1 dB. 3 dB is just nicely audible. Loudness also depends on the frequency, bandwidth and duration of the sound. See: Loudness Contours' class='link'>Equal Loudness Contours.
Low Frequency	Generally refers to sounds below about 300 Hz.
Low Frequency Effects	The 0.1 channel in 5.1-channel Dolby Digital signals. All 5 main channels are full range, so this additional channel, covering the frequency range 3 Hz to 120 Hz is there to accommodate very loud low frequency special effects sounds, such as explosions. It is included in the bass managed subwoofer outputs of surround processors and receivers, but is discarded in the two-channel downmixes of Dolby Digital that occur in many DVD players. See: Downmix, Dolby Digital, Bass Management
Magnetic Shielding	A design of loudspeaker motor in which the stray magnetic field is suppressed to avoid distortions to CRT, or other magnetically sensitive, video displays.
MPEG Audio	MPEG-1 is a perceptual coding algorithm for two audio channels. MPEG-2 does multichannel audio. See: Perceptual Coding
MPEG Video	MPEG-1 is a data compression algorithm for low-quality video, such as that on Video CD. MPEG-2 is used for DVD and HDTV. See:
Multichannel	A sound recording/reproduction system with more than two channels and loudspeakers. Current systems have 5, 6 or 7 channels plus a low-frequency effects (LFE) channel. Multichannel sound can also be simulated from two-channel sources. See Logic 7, Dolby ProLogic Plus.
Multiroom	A feature of custom whole-house systems, and of some AV Receivers, allowing sound to be delivered to loudspeakers in other rooms, without interfering with what is happening in the main entertainment room.
Nominal Impedance	The stated impedance rating of a speaker, used by manufacturers to represent the load the speaker will present to an amplifier. In fact, the impedance of most loudspeakers varies considerably with frequency, so the nominal impedance is only a very rough guide. In practice, the minimum impedance also needs to be known.
Ohm	Basic unit for measuring resistance and impedance.
Pan and Scan	A method of converting widescreen programs and movies for viewing on a standard 4:3 aspect ratio television. It involves rerecording the program while panning and scanning (sweeping left and right) with a camera, selecting the portion of the picture to be shown in the reduced size. Obviously, the result is not the same movie that the director created, but it fills the entire TV screen. Letterboxing is the alternative. See: Letterbox, widescreen, aspect ratio.
PCM	A straightforward, uncompressed coding method in which analog signals are sampled at regular intervals, and each sample is represented by a digital number representing the amplitude at that instant in time. Sampling is done at a frequency at least two times the highest frequency of interest, and the digital number must have a sufficient number of bits to capture and reconstruct the essential qualities of the audio signal (dynamic range, low distortion and noise, etc.). For example, typical CDs are recorded using a sampling frequency of 44.1kHz, using a 16-bit digital number. See Bit, Compression.
Pixel	The smallest element in a picture. An individual dot in a picture composed of dots, as in all digital video systems.
Power	The amount of energy delivered or used by a device or system, expressed in Watts. In audio, power ratings of amplifiers and loudspeakers are subject to a lot of variation and uncertainty because of the very large difference in the long-term, steady-state, power rating, and the transient, or momentary, power rating, which can be several times larger. Further confusion is added when ratings at a single frequency (say, 1 kHz) are compared with the more realistic 20 - 20 kHz rating. In multichannel amplifiers, there is the further variable of ratings done with a single channel operating vs. ratings with all channels operating. The result, for consumers, is that advertised power ratings are often almost meaningless.
Power Rating	See: Power.
Preamplifier	An audio component that selects signal sources, and provides volume and tone compensation functions. There may be special gain stages for phono cartridge inputs. It has line-level outputs to drive a power amplifier. Normally a stereo device, its multichannel equivalent is a surround processor.
Progressive Scan	A video display that scans all lines sequentially in each pass. A Line Doubler can create a progressively scanned image from an interlaced scan signal. See: Line Doubler.
Pulse-Code Modulation	A straightforward, uncompressed, coding method in which analog signals are sampled at regular intervals and each sample is represented by a digital number representing the amplitude at that instant in time. Sampling is done at a frequency at least 2 times the highest frequency of interest, and the digital number must have a sufficient number of bits to capture and reconstruct the essential qualities of the audio signal (dynamic range, low distortion and noise, etc.). E.G. normal CD's are recorded using a sampling frequency of 44.1 kHz using a 16 bit digital number. See: Bit, Compression.
Resolution	VIDEO: in digital displays, it is the number of pixels along the width and height of the picture. In any display, it is an assessment of the clarity of details in the picture. This can be different for stationary and moving objects, and the perceived resolution can be different from that which is technically defined. AUDIO: a loosely defined term used to describe perceptions of small details in music. See: Pixel
Sensitivity	A standardized measure of the sound output of a loudspeaker for a known input signal. Originally, the input power was 1 watt. Nowadays, the input is standardized to 2.83 volts (1 watt into 8 ohms). Measurements are made on axis in an anechoic space, at a distance that places the microphone in the far-field of the loudspeaker system, and then the sound pressure level is calculated for a microphone distance of 1 meter. A measurement distance of 1 meter is too close for all but single drivers and very small loudspeaker systems. See also: Far Field, Input Sensitivity.
Tone Control	A simple filter that can boost or cut portions of the audio frequency range, used to change the tonal balance of reproduced sound. See Bass Control, Treble Control, Equalizer.
Treble Control	A tone control allowing the user to boost or cut the high frequency portion of the audio signal.
Tuner	A device that tunes, or selects, radio or television stations from broadcast signals received on a terrestrial antenna, by cable or satellite.
Video Shielded	See Shielded Loudspeaker
Volt	See Voltage
Voltage	Electrical potential difference measured in volts.
Volume	Audio: loosely, the loudness of sound, and the control that allows us to vary it. Loudspeakers: The cubic measure of space in a speaker enclosure.
Watt	The basic unit for electrical or acoustical power. See: Power
Wattage	Amount of electrical power expressed in watts. See: Power.
Widescreen	A video display that is wider than the standard 4:3 aspect ratio although, in the context of DVD and HDTV, widescreen refers specifically to a 16:9 aspect ratio. See: Aspect Ratio.