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Entries found for search: noise

ambient noise : Ambient sound which is environmental in nature, such as traffic noise coming through walls, heating or air conditioning, or other extraneous sounds which cannot be turned off or removed.

biased noise : A tape loop of audio silence, processed by a recorder with some kind of noise-reduction enabled, such as Dolby-SR (where it is called SR noise) or dbx or dB. Used to check equipment for ground loops or other problems in recordings and/or masters. Sometimes called an alignment recording. See Dolby noise.

clock noise : An artifact of digital-to-analog conversion that creates staircase-like changes in voltage produced by the converter. Most clock noise is caused by shifts in the zero-crossing times. See quantization noise, reconstruction filter.

correlated noise : See distortion.

electrostatic noise : A field of random electrical charges that can affect an audio line. Electrostatic noise can be generated by neon or fluorescent lighting, electrical motors, and other broad-spectrum emissions sources. Electrostatic noise is the electrical field which is generated by EMI.

equivalent input noise (EIN) : EIN is becomming a common method for specifying noise in audio equipment. This is a computed figure equal to the noise measued at some gain setting, minus the gain. For example, if a microphone preamplifier puts out -85dBV noise when set for 40dB of gain, the EIN is -125dBV. Note that, while -125dBV seems better than -85dBV, both figures represent the same amount of noise."

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 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:


flicker noise : At high frequencies, intrinsic noise is dominated by Johnson noise. At lower frequencies, there exists a critical frequency, ƒ, at which noise rises proportional to 1/ƒ. Below this critical frequency, the noise is called flicker noise. Sometimes referred to as flicker effect.

high-output low-noise (HOLN) : A type of magnetic recording tape with very high sensitivity to applied magnetic fields, and with a very high S/N ratio, commonly used in professional audio applications.

intrinsic noise : The intrinsic noise of any (electronic) system is the noise which is a function of the real part of the input impedance (Z) impedance and the temperature, i.e., noise which is inherent in the system itself, as opposed to being induced by any source external to the system or device. See Johnson noise.

Johnson noise : See noise floor. Johnson noise is the broadband white noise power associated with electrical resistance at temperatures above absolute zero. The Johnson noise level is the limiting minimum noise any circuit can attain. Also called thermal noise.

microphonic noise : Noise generated within an audio cable, caused by changes in capacitance between the inner conductors in the cable and/or its shield. Microphonic noise can result from unstable dielectric (insulating) material that allows the conductors and/or shield to move in relation to one another.

modulation noise : Noise which is present only in conjunction with a signal is called modulation noise. In analog tape recorders, the recording process has a certain granularity due to the fact that the magnetic characteristics of the tape are not completely uniform as the magnetic domains are of finite size. A recorded signal has an irregularity which sounds like the addition of noise. In digital audio systems, there is also an uncertainty in the level of the signal because of quantization error in the A/D converter. This uncertainty also sounds like added noise and is not present if the signal is not present. Compare with distortion. See Barkhausen effect, granularity.

SR noise : See biased noise.

single-ended noise reduction : Single-ended NR systems work on playback only. Analog systems work by combining dynamic filters with low-level expanders so that the signal level decays, high frequencies are progressively filtered out. At very low levels, the expander acts as a soft gate to clean up pauses. Digital systems are more complicated and use a split-band expander. See noise reduction.

self-noise : The intrinsic electrical noise or hiss produced by a microphone, measured in the absence of any input signal. Usually the self-noise specification is A-weighted: a self-noise figurespec of 18dB SPL or less is excellent, 28dB SPL is good, and over 35dB SPL is not good enough for quality recording. Dynamic mics have very low self-noise. The S/N ratio of a microphone is the difference in dB between the microphone’s sensitivity and its self-noise. See also reach.

residual noise : The noise that remains on magnetic recording tape after full erasure.

random noise : Sound where there is no predictable relationship between the frequency or amplitude of the waveform over time. See white noise, pink noise.

quiescent noise : (1) See noise floor. (2) The combined intrinsic noise produced by all sound reinforcement devices, plus all extrinsic noise present in the listening space, such as HVAC equipment, traffic noise, measured when the listening/recording space is empty. Sometimes used as a synonym for noise floor, confusing everyone.

quantization noise : One of the types of error introduced into an analog audio signal by encoding it in digital form. The digital equivalent of tape hiss, quantization noise is caused by the small differences between the actual amplitudes of the points being sampled and the bit depth of the analog to digital converter. In the quantization of a sine wave whose frequency is a submultiple of the sampling frequency, the error will have a definite pattern which repeats at the frequency of the signal, having a frequency content consisting of multiples of this frequency, where it can be considered as harmonic distortion rather than noise. In music, however, the signal is constantly changing and no such regularity exists, resulting in quantization error, producing wideband noise, called quantization noise. See granulation.

popcorn noise : Film expression for ambient noise in a theater environment that influence the low end of the dynamic range, and how soft a sound will be heard (or "read") in an actual theater. See Little Old Ladies with Umbrellas.

pink noise : A type of random noise which has a constant amount of energy in each octave band, as opposed to white noise, which has equal energy at all frequencies. Pink noise can be made from white noise by passing it through a filter with a 3dB per octave rolloff. Pink noise is used to align the frequency response of tape recorders and loudspeaker systems.

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.

noise modulation See dither.

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