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视音频专业术语表

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视音频专业术语表(4)

2017-02-13 09:15 admin 人关注

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D
D connector - A connector with rounded corners and angled ends, taking on the shape of the letter D. Commonly used in computers and video, most D connectors have two rows of pins. If they have more than two rows, they are usually called HD (High Density) connectors.
D/A - Digital to analog.
D1 - A component digital recording format that conforms to the ITU-R BT.601 standard, using 19mm tape, uncompressed. Though largely obsolete as a digital recording format, “D1” is commonly used to describe component digital video utilizing a 4:2:2 (Y Cb Cr) signal structure.
D5 - A component digital videotape recording format that conforms to ITU-R BT.601 standard, using 1/2” tape, 10 bits video coding, uncompressed. The primary manufacturer is Panasonic.
D9 - A component digital videotape recording format that conforms to ITU-R BT.601 standard, using 1/2” tape, eight bits, 3:1 compressed. Previously called Digital-S. The primary manufacturer is JVC.
DA - Distribution amplifier. A device that allows connection of one input source to multiple, isolated (buffered) output destinations such as monitors or projectors.
DAC - Digital to analog converter.
Damping factor - The measurement of a power amplifier’s ability to control the motion of a speaker’s cone after a signal disappears. The higher the number, the better the damping factor.
Dark Fiber - A term in fiber optics to denote fiber that is installed at a facility but reserved for future use.
DAT - Digital Audio Tape. A method developed by Sony and Hewlett-Packard for recording large amounts of information in digital form on a small cassette tape.
Data - (1) A representation of facts, concepts, or instructions in a format suitable for communication, interpretation, or processing by human or automated means. (2) Any representations, such as characters or analog quantities, that have meaning.
Data Compression - A mathematical algorithm for compressing or encoding data to fit within given bandwidth requirements for transmission or storage.
Data Compression Ratio - The ratio representing the data output from a compression system relative to the original data. A computer-science term used to quantify the reduction in data-representation size produced by a data compression algorithm.
Data Link - A fiber optic system comprising the cable, transmitter, and receiver for transmission of data between two locations.
Data Services - A telecommunications service that transmits high-speed data rather than voice. Internet access is the most common data service, which may be provided by the telephone and cable companies as well as cellular carriers.
dB (Decibel) - The standard unit used to express gain or loss of power between two values. A decibel is 10 times the logarithm of a ratio of two power values. When comparing voltage or pressure, the values in the ratio are squared or the log is multiplied by 20 instead of 10. An extension is placed behind the ‘dB’ when one of those values is a fixed reference (i.e. dBV, dBu, dBSPL).
dB per octave - How quickly a crossover or filter attenuates signals (decreases their power) outside its passband (those frequencies intended to pass through without attenuation); expressed in decibels per octave. Crossover and filter slopes are designed as first order (attenuates signals slowly, cutting output by 6 dB per octave); second order (12 dB per octave); third order (18 dB per octave); and fourth order (24 dB per octave). The steeper the slope the quicker the attenuation.
dBm - dB referenced to 1 milliwatt. To convert into an equivalent voltage level, the impedance must be specified. For example, 0 dBm into 600 ohms gives an equivalent voltage level of 0.775V, or 0 dBu; however, 0 dBm into 50 ohms, for instance yields an equivalent voltage of 0.24 V. Since modern audio engineering is concerned with voltage levels, as opposed to power levels in the early years of telephone, the convention of using a reference level of 0 dBm is academic. But in the A/V industry, many people still refer to 0.775Vrms (600 r) as 0 dBm, which should be more accurately called 0dBu.
dBSPL - dB referenced 20 micro pascals (0.00002 PA). 0dBSPL is a scale used to express acoustic energy, that is as loud as sound is. For example, when a sound is described as being “110 dB,” the measurement is expressing the sound pressure level of the source. Benchmarks include: 30-40 dBSPL - ambient room noise; 50-70 dBSPL - normal conversation; 110-120 dBSPL - rock concert; 130-140 dBSPL - painful sound.
dBu - dB unterminated. 0 dBu is a voltage reference point equal to 0.775Vrms. [This reference originally was labeled dBv (lower case) but was too often confused with dBV (upper case), so it was changed to dBu (for unterminated).] +4 dBu is a standard pro audio voltage reference level equal to 1.23Vrms. XLR and captive screw audio connectors are commonly used in this equipment.
dBV - dB referenced to 1.0 Vrms. -10dBV is a standard audio line level for consumer and some professional audio use, equal to 0.316 Vrms. RCA audio connectors are a good indicator of units operating at -10 dBV levels.
DC - Direct Current. The flow of electrons in one direction.
DC coupled - A circuit that passes both AC and DC components of a signal, and therefore is sensitive to DC offsets. Also see "AC coupled."
DC offset - Refers to the degree to which a DC voltage is skewed away from a zero or baseline value.
DC restoration - The correct blanking level for a video signal is zero volts. When a video signal is AC-coupled between stages, it loses its DC reference. A DC restoration circuit clamps the blanking at a fixed level. If set properly, this level is zero volts.
DCF - Dispersion Compensating Fiber
DDC - Display Data Channel. A bi-directional communications standard developed by VESA (Video Electronics Standards Association) that defines a universal data transmission standard for the connectivity between display devices and computers.
DDSP™ - Digital Display Sync Processing™. A signal handling method, trademarked by Extron, that allows the sync signal to pass through without altering sync pulse timing or width. DDSP disables other sync processing features such as horizontal and vertical centering.
DDWG - Digital Display Working Group. The DDWG develops standards for digital displays. Developer of the DVI standard.
Dead Zone - A region within a fiber optic system where an OTDR – Optical Time Domain Reflectometer cannot effectively make measurements.
Decoder - 1) In analog video, a device used to separate the RGBS (red, green, blue and sync) signals from a composite video signal. Also known as an NTSC decoder. 2) In digital systems, a device which does the reverse of an encoder, undoing the encoding so that the original information can be retrieved. The same method used to encode is usually just reversed in order to decode. Video over IP decoders accept IP data streams and output an analog or digital video signal. 3) In control systems, the device in a synchronizer or programmer which reads the encoded signal and turns it into a form of control.
Deep Color - A very wide color gamut with a bit depth of 30 bits or more, capable of displaying billions of colors.
Default gateway - The routing device used to forward all traffic that is not addressed to a station within the local subnet.
Definition - The fidelity with which a video picture is reproduced. The clearer the picture, the higher the definition. Definition is influenced by resolution.
Degausser - A device that produces a strong alternating electromagnetic field which quickly erases an entire reel, cassette, or cartridge of tape. Also used for eliminating ghosting in television monitors by demagnetizing the CRT.
De-interlacing - The process of combining pairs of interlaced fields of video into one progressive frame of video.
Delay - A basic DSP process in which the output of the input signal is delayed by a specified time (called the delay time).
Dense Wavelength Division Multiplexing – DWDM - The multiplexing, or combining of several wavelengths into a single optical signal. DWDM is distinguished from Coarse Wavelength Division Multiplexing–CWDM in that the separation between wavelengths – 0.8 to 1.6 nm – is much smaller.
Detail enhancement -
Detector - A device within fiber optic receivers that converts optical energy to electrical energy.
DHCP - Dynamic Host Configuration Protocol. A standardized client-server IP networking protocol that enables network administrators to centrally and automatically manage the assignment of IP addresses in an organization’s network.
Dichroic - A type of mirror, reflector, or filter that selectively reflects different wavelengths of light, permitting a projector to transmit more visible light with less heating of the film. Dichroic mirrors are also used for internal convergence of three-tube single lens video or computer projectors.
Dielectric - Insulating material in coaxial cables between center conductor and outer conductor.
Differential audio - See "Balanced audio."
Differential gain - Unwanted variations in a chrominance subcarrier’s amplitude that result from changes in the signal’s DC level, usually specified between 10% and 90% of full scale .
Differential Mode Delay – DMD - A limiting factor in the performance of transmissions over multimode fiber, in which there is a differential in the arrival times at the receiver of various wavelengths, or modes along the fiber. This differential is caused by model dispersion which is inherent in multimode fiber.
Differential phase - Unwanted variations in a subcarrier’s phase as a result of changes in the chrominance signal’s DC level, usually specified in degrees over a frequency range.
Digital - A system of data or image values in the form of discrete, non-continuous codes, such as binary. When data is in a digital format, it can be processed, stored (recorded), and reproduced easily while maintaining its original integrity.
Digital Betacam® - A component digital videotape recording format that conforms to CCIR 601 standard, using 1/2" tape, 10 bits, 2:1 compressed. The primary manufacturer is Sony.
Digital component video - See "Component digital."
Digital composite video - “See Composite Digital.” Also see "Composite digital."
Digital control - A method using discrete digital impulses to control individual functions within a system.
Digital signal - An electrical signal which possesses two distinct states (on/off, positive/negative); typically represented by “0” or “1”.
Digitization - The transformation of an analog signal into digital information.
Digitizers - Video digitizers utilize video cameras to take pictures of photographs or live and still action. The information is decoded into RGB (digital form) and stored in the frame buffer.
D-ILA™ - Direct Drive Image Light Amplifier. The D-ILA is a device based on the Image Light Amplifier or ILA developed by Hughes-JVC Technology Corporation. The D-ILA technology is a reflective liquid crystal modulator whereby electronic signals are addressed directly to the device. The D-ILA device has an X-Y matrix of pixels configured on a C-MOS single crystal silicon substrate mounted behind the liquid crystal layer using a planar process that is standard in Integrated Circuit technology.
DIN connector - An acronym for Deutsche Industrie Norm. A round connector with notches, or keys, for alignment. They exist in several sizes: 4 pins, 5 pins, 8 pins, etc. A convenient way of combining all of the signal lines in one connector, 4-pin DIN connectors are often used for S-video.
Diode - An electronic device that allows current to flow in one direction only.
DIP - Dual In-line Package. A universal method of manufacturing integrated circuits (ICs) with the pins arranged in two parallel rows. Some DIP components are soldered in and some use DIP sockets.
DIP switches - Small switches that are used to change settings on printers, computers, interfaces, switchers, modems, etc. They are designed to fit in a DIP (Dual Inline Package) space on a circuit board.
Discrete Cosine Transform (DCT) - A Fourier-related transform which is used to convert an image from a spatial domain to a frequency domain. Video systems then process the information in the frequency domain. Typically, more signal energy is located in the lower frequencies than the higher frequencies. The DCT is used in many video compression codecs including JPEG, MPEG, MPEG-2, MPEG-4 and H.264.
Discrete Wavelet Transform (DWT) - A transform used to convert an image from a spatial domain a wavelet domain. Two filters are involved, the first a “wavelet filter” is a high pass filter, and the second a “scaling filter” a low pass filter. The DWT provides more efficient image compression than the DCT as it due to advantages analyzing signals with sharp discontinuities or spikes.
Dispersion - A limiting factor in optical fiber transmission performance, where a light pulse is broadened, or separated into modes or individual wavelengths. Dispersion limits transmission bandwidth and distance capability. The two major types of dispersion are modal dispersion and chromatic dispersion.
Dispersion Compensating Fiber – DCF - A special type of fiber designed to exhibit a large negative dispersion. DCF is typically used in long-haul telecommunication systems to compensate for dispersion in optical fiber.
Dispersion Shifted Fiber – DSF - A singlemode optical fiber with its optimal dispersion wavelength shifted, through the addition of dopants, to a wavelength that delivers optimal attenuation.
Display device - Any output device for presenting information visually. Examples include: CRT (Cathode Ray Tube), LED (Light Emitting Diode), or LCD panel (Liquid Crystal Display). A general term for a projector or monitor.
DisplayID - Released in December 2007, this second-generation version of VESA EDID – Extended Display Identification Data is intended to replace all previous versions. DisplayID represents a 256-byte data structure that conveys display-related information to attached source devices. It is meant to encompass PC display devices, consumer televisions, and embedded displays such a LCD screens within a laptop without need for multiple extension blocks. Display ID is not directly backward compatible with previous EDID/E-EDID versions.
DisplayPort - The newest digital audio/video interconnect standard, designed primarily for use between a computer and display device. DisplayPort supports data rates up to 10.8 Gbps at a distance of 2 meters for full bandwidth transmissions, and up to 15 meters for reduced bandwidth signals such as 1080p/60, over copper cable. DisplayPort is not directly compatible with DVI or HDMI, but a DisplayPort connector can pass these signals, and the standard does provide an emulation mode for ease of integration with DVI or HDMI equipped products.
Dissolve - (1) An effect in which one scene or picture fades out as another fades in. In projection, the dissolve effect is achieved by varying the intensity of the lamps in the two projectors involved. Sometimes called lap dissolve or cross fade. (2) The hardware controlling the dissolve effect, which is properly called dissolve control or dissolve unit. A visual effect wherein one scene gradually fades away while slowly being replaced by another. Also see "Fade, Fade-to-black."
Distribution amplifier - A device that distributes multiple outputs from a single source input. Distribution Amplifiers (DAs) split signals, but also provide amplification and enhancement features to maintain the integrity of the signals.
Distribution Cable - Fiber optic cable comprising a bundle of jacketed fibers encased within an outside jacket.
Distribution Panel - For fiber optic applications, this is both a patch panel and splice panel, usually installed at a hub or entrance facility
Dither - (1) The process of filling a gap between two pixels with another pixel having an average value of the two to minimize the difference or add detail to smooth the result. (2) In audio, a process that deliberately adds a tiny amount of noise to a signal in order to mask unwanted sounds introduced when the signal’s original bit depth is reduced. Dithering is recommended when transferring audio to a device that uses a lower bit depth.
DLP™ - Digital Light Processing. An imaging technology for video projection developed by Texas Instruments, based on the modulation of light reflected from mirror elements known as Micromirrors(tm). Each pixel is represented by its own Micromirror, which mechanically tilts in accordance to the extent of light reflected toward or away from the screen. A matrix of Micromirrors comprising the video image is situated on a microchip, or DMD(tm) (Digital Micromirror Device). DLP is implemented as a three-chip configuration (one DMD for each of the RGB colors), or as a one-chip configuration (R, G, and B are sequentially processed by a single DMD via a color wheel).
DMI™ - Dynamic Motion Interpolation™. This Extron video processing technique is an advanced motion prediction and compensation method that treats motion content and still content with different algorithms to yield high fidelity images.
DMM - Digital Multimeter. A test and measurement device, typically handheld, that combines measurement tools for voltage, amperage, resistance, and other common electrical and electronic measurement needs.
DNS - Domain Name System. DNS is the way that an Internet domain name is located and translated into Internet Protocol (IP) addresses. A domain name is a meaningful and easy-to-remember “handle” for an Internet address.
DOC - Declaration of Conformity. A document that states the European Union directives and standards to which particular equipment should comply.
Dolby noise reduction - A patented noise reduction technique from Dolby Labs that raises the volume of sound track elements most likely to be affected by inherent noise during recording and then lowers them again during playback so that the noise seems lower in relation to the wanted elements of the audio recording.
Dolby® Digital - A digital audio encoding and decoding technology utilized for DVDs, Blu-ray Discs, video games, and many cable and satellite television services. Also referred to as “AC-3.” Dolby Digital can transmit mono or standard two-channel stereo audio, as well as 5.1 channel surround sound (left front, center front, right front, left rear, right rear, and sub-woofer).
Dolby® Digital Plus - A digital audio compression technology designed as an optional codec for use with Blu-ray Disc. Dolby Digital Plus is an extension of the earlier Dolby Digital format and supports up to 13 audio channels, although Blu-ray Disc is limited to 8 discrete channels. The extra audio channels are often used to support multiple languages.
Dolby® TrueHD - An advanced, lossless multi-channel audio encoder and decoder technology intended primarily for high-definition content and is optional for Blu-ray Disc; support for TrueHD is also optional in the HDMI 1.3 specification. TrueHD supports up to 8 discrete audio channels at 96 kHz sampling, or up to 6 channels at 192 kHz sampling. Since TrueHD is optional for Blu-ray Disc, discs encoded with a TrueHD audio track must also include a separate 2-channel digital audio track.
Domain - When referring to the Internet, a name that identifies a network. (i.e. yahoo.com)
Dot clock - Also referred to as pixel clock. The timing device in a graphics card that determines the pixel resolution. The dot clock runs at a rate that produces the highest possible pixel resolution for that device. In a digital projector, the dot clock samples the analog video at a rate that produces the resultant pixel resolution. Also see "Pixel clock."
Dot crawl - Sometimes called “zipper effect,” dot crawl refers to a specific image artifact that is a result of the composite video system. Dot crawl may be seen on TV news, for example, when a picture appears over the anchorperson’s shoulder, or when some text appears on top of the video clip. If you look closely, along the edges of the picture, or the text that has been overlaid, you’ll notice some jaggies rolling up or down.
Dot pitch - The vertical distance (measured in millimeters) between the centers of like-colored phosphors that are in adjacent pixels on the monitor screen. The closer the spacing, the better the resolution. Dot pitch is specified in pixels/mm.
DPCP – DisplayPort Content Protection - DPCP is a content-protection scheme for DisplayPort developed by Advanced Micro Devices. Like HDCP 2.0, DPCP uses AES 128 encryption. To date, DPCP has not been implemented by any manufacturer of source or display devices equipped with DisplayPort. All devices currently on the market use HDCP for digital rights management.
Drain wire - Non-insulated wire used in cable termination as a ground connection.
DRM – Digital Rights Management - A generic term for technologies such as content scrambling in cable or satellite television transmission, HDCP, and DPCP that can be used to control the access to, or reproduction of, copyrighted, commercially-available content. DRM is used primarily to prevent piracy, the unized duplication and distribution of copyrighted material. However, DRM often also governs how content can be used. Commercially-available DVDs and Blu-ray Discs, for example, are typically licensed for personal use in a residential environment. Use of such content in a public venue, such as a school or business setting, without express consent or licensing by the copyright holder, is typically in violation of the media’s license.
Dry contact closure - A pair of electrical contacts that carry no live voltage.
DSL - Digital Subscriber Line. A generic name for a family of digital lines (also called xDSL) provided by telephone carriers to business and consumers.
DSP - Digital Signal Processor. A specialized CPU or circuit designed to process signals such as audio and video which have been converted to digital form. DSP is used to process sound, video, and images in a variety of ways.
DSS - Digital Satellite System.
DSVP™ - Digital Sync Validation Processing™. In critical environments or unmanned, remote locations, it is vital to know that sources are active and switching. Extron's exclusive DSVP technology confirms that input sources are active by scanning all sync inputs for active signals. DSVP provides instantaneous frequency feedback for composite sync or separate horizontal and vertical sync signals via the switcher's RS-232/422 port.
DTS® Digital Surround - A digital audio encoding and decoding technology from DTS, Inc. that delivers 5.1 channels of surround sound. It is an optional surround sound format for DVDs but is mandatory for Blu-ray Disc. DTS Digital Surround has also been used in some LaserDisc releases as well as CDs, and is also featured in some video games.
DTS-HD High Resolution Audio - An extension to the DTS Digital Surround format that offers up to 7.1 channels at 24-bit resolution and 96 kHz sampling. DTS-HD High Resolution Audio is an optional surround sound format for Blu-ray Disc.
DTS-HD Master Audio - A lossless audio encoder/decoder technology from DTS, Inc. DTS-HD Master Audio allows a bit-for-bit representation of a movie’s original studio master soundtrack and supports up to 8 audio channels. Support for DTS-HD Master Audio is optional in the HDMI 1.3 specification released in 2006, and is also optional for Blu-ray Disc.
DTV - Digital Television. Often used to describe one of the many new forms of digital terrestrial transmission of video program material.
Dual-Link DVI - A dual-link DVI output has two TMDS links and twice the bandwidth of single-link DVI, and can therefore support much higher resolutions. With two TMDS links, the number of data channels is doubled, although there is still only one clock signal, so both links are clocked identically. Apples 30 Cinema Display with a native resolution of 2560x1600, is an example of a display requiring dual-link DVI. See also Single-Link DVI. Also see "Single-Link DVI."
Dual-Link HD-SDI - Is a method applying two HDSDI signals 1920x1080 video at 50 or 60Hz as progressive frames, at 12 bit depth or with 4:4:4 color quantization.
Duplex - Data transmission in both directions. Half duplex denotes transmission in one direction at a time, while full duplex refers to simultaneous transmission in both directions. In fiber optics, duplex also refers to a type of cable comprising two fibers for duplex transmission.
Dust Cap - A plastic cap that covers the connector ferrule, plug, or sleeve, and protects the connector endface.
DV - Digital Video. A serial digital video format. DV has the advantage over standard analog video of maintaining clear, crisp video without degradation from generation to generation.
DVB/ASI – Digital Video Broadcasting/Asynchronous Serial Interface - A standard for the broadcast of digital television signals. Terrestrial broadcast, primarily seen in Europe, is often stated as DVB-T. In the US, DVB-S is often used for compression and encoding of digital satellite transmission; for terrestrial applications, North America utilizes the ATSC standard.
DVD - Digital Versatile Disc. An optical disc similar in physical size to a CD-ROM, but capable of storing an entire movie. The technology uses MPEG-2 compression. Typical capacity for these discs is 4.5 GB, or about 133 minutes of digital video.
DVD-Audio - A digital format for delivering high-fidelity audio content on DVD – Digital Video Discs. DVD-Audio is a standalone format intended for audio only and is not used for the audio portion of DVD video content. DVD-Audio is similar in application to SACD, although to maintain compatibility with DVD players, the format is not capable of the very high sampling rates found in SACD. Support for DVD-Audio was added to the HDMI 1.1 specification in 2004.
D-VHS - Digital-VHS. A new technology based on VHS, offering the features of conventional VHS with bit stream recording capability which allows the recording and playback of compressed digital data including digital television broadcasts and prerecorded high definition software.
DVI - Digital Visual Interface. The digital video connectivity standard that was developed by the DDWG – Digital Display Working Group. This connection standard offers two different connectors: one with 24 pins that handles digital video signals only and one with 29 pins that handles both digital and analog video. This standard uses TMDS – Transition Minimized Differential Signal from Silicon Image and DDC – display Data Channel from VESA – Video Electronics Standards Association.
DVI-D - DVI connector that supports digital signals only.
DVI-I - DVI connector that supports both digital and analog signals.
Dynamic IP address - An IP address that is automatically assigned to a client host in a TCP/IP network, typically by a DHCP server. Network devices that serve multiple users, such as servers and printers, are usually assigned static (unchanging) IP addresses.
Dynamic range - The highest and lowest potential signal levels on a given device. Also applies to fiber optic applications in terms of the ratio between the most – or strongest – and least – or weakest – observable optical signals.
Dynamic transducer - Technical description of a loudspeaker or dynamic microphone. A dynamic transducer uses a paper, plastic, fabric, or metal cone which is driven by a voice coil that moves back and forth through a magnetic field produced by the audio signal.

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