Now looking at definitions starting with letter "n"
noise (1) a sound which contains all of the frequencies in the audible range. (2) An unwanted sound which is not related to the wanted sound; if it is, it is called distortion. Noise is comprised of all audio frequencies at constantly varying amplitudes, therefore, it has no definable pitch or timbre. See white noise, pink noise, residual noise, ambient noise, quantization noise, modulation noise, NC-Curve, noise floor.
noise figure Most simply, the noise figure of an electronic device is the measurement of how much worse the S/N ratio is at the output of the device than it was at the input, expressed in dBindB. The noise figure is usually important only for low signal-level devices, such as a mic preamp, where there is a very low input signal level, which approaches the intrinsic noise floor of the environment. Also called the noise factor, but only if the measurement is expressed as a linear quantity.
noise filter Either a narrowband or notch filter used to eliminate pitched noise, or a broadband filter used to attenuate the entire high or low frequency range.
noise floor The noise floor is the intrinsic noise of any audio device or other electronic system, generally measured in dBm. Sometimes the noise floor is measured in terms of RMS voltage rather than power, and this makes sense in the case of devices such as voltage amplifiers or tape recorders. Includes Johnson noise and flicker noise. See quiescent noise.
To calculate the intrinsic noise level of a device, expressed in watts: if one took one 600Ω resistor on the input of a (noiseless) microphone preamp with a 60dB gain, the output would be about -100dBm. This is the lowest possible noise floor:"
noise gate A noise reduction device through which an audio signal is passed. When the signal level is very small, the noise gate will close, eliminating any residual noise that may be riding on the signal. In the presence of a signal, the noise gate will open, allowing both signal and noise to pass through, as under these conditions, the noise is masked by the signal. A noise gate is a special type of expander with an infinite expansion ratio below a preset threshold. The effectiveness is determined by the time constants associated with the gain reduction, and often the background noise can be heard switching on and off with the signal. See breathing, gate, floor.
noise generator A device to generate
white noise or
pink noise, a random signal that contains all frequencies at the same time.
noise level (1) The
noise floor of an electronic device. (2) The steady-state decibel level of
ambient noise in an acoustical environment. See
NC Curve. (3) The
residual noise of a magnetic tape.
noise modulation See dither.
noise pumping See breathing, noise gate.
noise reduction Two technologies for noise reduction have become standard in the consumer and professional recording industry: dbx and Dolby. All two-ended noise reduction systems are a type of compander, i.e., they operate by encoding the signal at the record end, and decoding the signal, restoring the dynamic range and frequency spectrum, upon playback.
Single-ended noise reduction systems need no encoding or decoding. The NR is applied to noisy instruments or microphones and works either by dynamic filtering or downward expan-sion. Dynamic filtering works will with noisy synthesizer sounds, but can cause pumping and breathing. A downward expander attenuates any signal below the threshold. It works when applied to cut the buzz on a noisy guitar amplifier, but it can also cut off quiet signals like reverb tails if the threshold is set too high. See dynamic filter, spectral recording.
noise shaping :Signal processing used in DAC to shift the frequency of noise in a digital signal so that, on conversion, the noise will be outside (usually above) the audio range. This is done by reducing the number of parallel bits used to carry the data, increasing the number of serial bits and so the frequency of the digital signal. In oversampling digital systems, digital filtering is used to reduce quantization error. By changing the shape of the spectrum of the quantization noise, increasing its high-frequency content by lowering its low-frequency content, an anti-imaging filter can then be used to reduce the increased high-frequency noise. See dither.
nominal level : The optimum level at which a signal is processed in a particular piece of audio equipment. For instance, if the unit has a VU meter, this level would be represented by the 0VU "0" mark, past which the meter goes into the red. Normally expressed in dBVindBV for professional recording equipment, the two output levels are commonly called mic-level and line-level. Also called output level.
non-real-time (1) The situation where events can occur at any time, independently of other events and without the need for human input or synchronization. See real-time. (2) See Universal System Exclusive.
nonlinear distortion Linearity would predict an invariant ratio of gain to input voltage in an audio device such as an amplifier. Manifested as harmonic distortion and intermodulation distortion, there is a point at which the amplifier gain is reduced as the input gain is increased. This is the nonlinear region of the amplifier. All audio devices have local peculiarities or deviations from linearity at specific signal levels. See also distortion, linear distortion.
nonlinear recording Use of a recording medium which is random access, i.e., not recorded to conventional tape. Digital recording systems allow for playback in any order, while linear systems require that playback occur in the order in which the material was recorded.
NoNoise Sonic Solutions’ digital signal processing system that analyzes the digitized signal and senses transient noises, such as clicks and pops, and continuous noises, such as tape hiss and AC hum. It removes the transients and makes a substitute signal by interpolation. Used to restore old recordings. A competitive program is called CEDAR, developed at Cambridge.
normal stereo See coincident pair.
normalize To boost the highest level of a waveform or sample in a digital system to its maximum amplitude the sampler is capable of encoding, short of clipping, to 0dB and then raising all other samples by the same proportion. This maximizes resolution and minimizes certain types of noise.
normalled connection A connection, typically on a mixer or patch panel, where the signal path is continuous in the absence of a plug inserted into the signal chain. Usually normalled connections are made via TRS jacks. In a solidly grounded system, inserting a stereo plug half-way into the jack, where the tip makes a connection, but not the ring, would yield an additional channel output, as opposed to a channel insert. In a poorly grounded system, this yields hum. See also breakjack. Called normalized connections in the UK. (verb) Normalling.
norvalizing Film slang for playing a sound effect at a low level in an attempt to hide the fact that it is not in sync with the picture.
NOS See ORTF.
notch filter See band-reject filter.
note number The value which appears in the first data byte of a MIDI Note On or Note Off message. It determines which note will be turned on or off. 128 notes (more than 10 octaves) can be described, with note number 60 being middle- C.
Note Off A Channel Voice message which causes a device to stop playing the note defined in the message. True Note Offs are seldom used, except on those devices that implement release velocity sensing, the preferred method being to send a Note On with zero velocity. This allows the use of Running Status, reducing the amount of data transmitted.
Note On A Channel Voice message which causes a device to sound the note defined in the message. See Note Off.
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