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视音频专业术语表

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视音频专业术语表(14)

2017-02-13 09:15 admin 人关注

A B C D E F G H I  J K L M N O P Q R S T U V W X Y Z

N
NAB - National Association of Broadcasters, the body that sets standards for US broadcast stations. www.nab.org
Nanometer – nm - A nanometer, or one billionth (10-9) of a meter.
NAS - Network Attached Storage. One or more storage devices associated with a single server which exists as a node on a LAN (Local Area Network).
NAT - Network Address Translation. Method of concealing a set of host addresses on a private network behind a pool of public addresses. It allows conservation of registered IP addresses within private networks and simplifies IP address management tasks through a form of transparent routing, and increases network privacy by hiding internal IP addresses from external networks.
Native Resolution - Refers to the single fixed resolution of an LCD, plasma, or other fixed matrix display. An image said to match the native resolution of a display is one where pixels between the image source and display are perfectly aligned and require no additional scaling or other signal processing.
Near end - In videoconferencing, the party or group at the local end of the connection.
NEC - National Electrical Code. The National Electrical Code is the product and responsibility of the National Fire Protection Association (NFPA). The NEC covers the installation of electric conductors and equipment in public and private buildings and other premises, such as yards, parking lots, carnivals, etc. In general, the NEC is used in every state in the nation and provides safeguards of persons and property from hazards arising from the use of electricity.
Networking - Two or more devices (or people) communicating with each other and sharing resources.
NEXT - Near-End Crosstalk. A measure of interference between the conductors of a cable. A measure of the unwanted signal coupling from a transmitter at the near end (source end) into neighboring pairs measured at the near end. NEXT loss is expressed in decibels relative to the received signal level.
NIC - Network Interface Card. A piece of hardware, usually a peripheral card, that interfaces a computer to a network.
Nit - A unit of measurement of luminance, or the intensity of visible light, where one nit is equal to one candela per square meter. Nits are used to describe the brightness of computer displays, such as LCD and CRT monitors.
Node - One specific point or connected location on a network (i.e., a client or print server).
Noise - Any unwanted signal that adversely affects the quality of the picture or sound.
Noise criteria - Abbreviated “NC”. An NC level is a standard that describes the relative loudness of a room or space, across a range of frequencies. The NC level illustrates the extent to which ambient noise interferes with speech intelligibility. NC should be considered for any project where excessive noise would be irritating to the users, especially where speech intelligibility is important.
Noise gate - An audio processing device that reduces background noise by muting a sound signal when it falls below a pre-determined level, and restores it when the level increases again. For example, in a board room where multiple microphones are installed, a noise gate may be used to mute the microphones of those not currently speaking, in order to eliminate disturbing background noise in the sound support system.
Noise reduction - Any technique for reducing the amount of undesired noise in an audio signal. A common technique is called “companding”, a circuit that combines a COMPressor and an exPANDer. The signal is compressed before recording (which maximizes the signal to noise ratio), then expanded during played back. As the signal is expanded, noise tends to be “pushed down,” resulting in a quieter signal.
Noise-canceling - A microphone designed to cancel ambient noise so that it will not be broadcast or recorded. The housing of the microphone allows noise to reach both sides of the diaphragm simultaneously, one side canceling the other out. A close speaking voice strikes the diaphragm on only one side, generating a stronger signal with less background noise.
Nominal level - The signal strength level at which a product is designed to operate for optimized performance. Most of the specifications are tested at the nominal level and all of the built-in signal meter reference levels (e.g. 0dB) are set at the nominal level. A device’s input nominal level should match the nominal level of the source device it is connected to, while the output nominal level of a device should match the nominal level of the destination device it is connected to. The most commonly used nominal levels for video and audio are: video, 1Vp-p (video with sync), 0.7Vp-p (video without sync), 0.3Vp-p (chroma); audio, +4dBu (1.23V, pro audio line level), -10dBV (316mV, consumer audio line level), -60dBV (1mV, mic level).
Non-blocking matrix switchers - These are true matrix switchers allowing any input to switch to any or all outputs. They have no switching limitations contingent on hardware or software. Extron builds only true matrix switchers with all switching paths available at all times; there is no blocking.
Non-composite video signal - A video signal that contains picture and blanking information only with no sync information.
Non-interlaced - Also called progressive scan. A method by which all the video scan lines are presented on the screen in one pass instead of two. Also see "Interlacing" and "Progressive scan."
Non-plenum - A cable that does not meet CMP or CL2P flame test requirements.
Non-segmented - A system of video recording that uses one head to scan one field of video onto the tape.
Normally closed contact - Relay or switch contacts that are closed when the relay is not activated.
Normally open contact - Relay or switch contacts that are open when the relay is not activated.
Notch filter - A circuit that effectively separates the NTSC black and white information from the color 3.58 MHz carrier signal. The name is based on the fact that the circuit takes a notch out of the frequency band.
NSCA - National Systems Contractors Association. The NSCA is an international trade association of companies specializing in audio, video, security/life safety, presentation, lighting, or other low-voltage systems. This association offers an annual expo. www.nsca.org
NTSC - The color video standard used in North America and some other parts of the world created by the National Television Standards Committee in the 1950s. A color signal must be compatible with black-and-white TV sets. NTSC utilizes an interlaced video signals, 525 lines of resolution with a refresh rate of 60 fields per second (60 Hz). Each frame is comprised of two fields of 262.5 lines each, running at an effective rate of 30 frames per second.
Numerical Aperture – NA - In fiber optics, the sine of the acceptance angle, a critically defined angle measurement from the center axis of the fiber. Incoming light must be directed below this angle in order to enter the core of the fiber and propagate along its length through total internal reflection.
Nyquist frequency - The highest frequency that can be reproduced accurately when a signal is digitally encoded at a given sample rate. Theoretically, the Nyquist frequency is half of the sampling rate. For example, when a digital recording uses a sampling rate of 44.1kHz, the Nyquist frequency is 22.050kHz. If a signal being sampled contains frequency components that are above the Nyquist limit, aliasing (stair-stepping) will be introduced in the digital representation of the signal unless those frequencies are filtered out prior to digital encoding.
NZDS - Non-Zero Dispersion Shifted fiber. A singlemode fiber with the zero-dispersion wavelength slightly beyond the spectral region for transmission in order to improve performance.
 

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