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Entries found for search: noise reduction

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.

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.

dbx noise reduction : a noise reduction system that uses a companding noise reduction to reduce noise. Dbx is connected into a recording system in the same way that a Dolby system is. It provides up to 30dB of noise reduction, but unlike Dolby noise reduction, the dbx system works over the entire audio frequency range, using a 2:1/1:2 compression/expansion ratio. Dolby-encoded and dBx-encoded tapes are incompatible. Systems using dbx noise reduction are typically more expensive than systems using Dolby."

Dolby noise reduction : A type of two-ended, dynamic noise reduction for magnetic tape recording and playback. The essential difference between a compander and the Dolby system is that the Dolby system is frequency-dependent. The compander was developed to reduce distortion. Dolby applies companding to frequency variations in addition to signal amplitude variations, adjusting gain as frequency changes. The Dolby-A and Dolby-SR systems are used for professional recording in studios. Consumer tape decks use either a Dolby-B or Dolby-C system. Dolby-B operates only at high frequencies and reduces tape hiss by about 10dB. Dolby-C works over a slightly wider frequency range, providing a noise reduction of up to 20dB. All of the Dolby systems operate on quiet passages, below levels of about -10VU. Very strong signals, such as over 60dB or at frequencies below 500Hz are not affected by the Dolby system because these signals are not degraded by tape noise. When the recorded signal is played back, the Dolby circuit reduces the accentuated high-frequency signals so that the frequency response of the record/playback system is flat, hence reducing also the high-frequency tape hiss, improving the S/N ratio of the taped music. See asperity, Barkhausen effect, compander, dbxcompander,dbx, spectral recording.

Companding Noise Reduction Companding noise reduction works by first sending the source matrial through a compressor, thus compressing the source material's dynamic range (in this case by a factor of 2) before being recorded to a medium known for noise such as magnetic recording tape. The compressed audio becomes contaminated with noise, but is passed through an expander during playback, and the noise from the recording medium is masked by expansion of the dynamics. This results in a reduction of perceived noise. See also dbx noise reduction.



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