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Audio recording
Published in John Watkinson, Audio for Television, 1997
Both of these are processes in which frequency dependent filtering is applied. They differ in principle and achieve different purposes. Pre-emphasis is part of the interchange standard for the tape format and is designed to reduce high frequency noise by boosting HF in the record process and applying an equal and opposite response on playback. Equalization (eq) is necessary to compensate for losses and deficiencies in the record and playback processes. In the absence of pre-emphasis the actual magnetization of the tape should be constant with respect to frequency. Consequently any departure from a flat frequency response in the record process is compensated by record eq, and any departure in the replay process is similarly corrected by replay eq. These compensations are highly machine dependent and vary with head wear. Thus, eq is adjustable, whereas pre-emphasis is fixed. Different tape formats use different pre-emphasis, and a switch may be provided to select the correct pre-emphasis so that one machine may be used with several formats.
Video recording
Published in John Watkinson, Television Fundamentals, 1996
Fortunately it was discovered that if the gain of the lower side band is increased whilst the gain of the upper sideband is reduced by the same amount, no distortion occurs. Thus if the replay signal, after equalization, is subject to a filter with a frequency response falling at 6 dB per octave, the demodulated signal is undistorted and a useful improvement in signal-to-noise ratio is obtained because the higher noise level in the upper sideband has less effect on the demodulated signal. A further improvement may be obtained if the video signal is subject to pre-emphasis on recording and a matching de-emphasis on replay. Pre-emphasis causes high frequencies to be boosted with respect to low frequencies.
D
Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
de-assert to return an enabling signal to its inactive state. de-emphasis refers to the receiving process of correcting the amplitude of certain signal components that have been "pre-emphasized" prior to transmission in order to improve signal-tonoise (S/N) ratio. In commercial FM broadcast receivers, de-emphasis is accomplished with a simple resistor capacitor lowpass filter that represents the inverse transfer function characteristic of the pre-emphasis network situated at the transmitter. See the figure for a de-emphasis network. See preemphasis.
Vibration monitoring for the West-East Gas Pipeline Project of China by phase optical time domain reflectometry (phase-OTDR)
Published in Instrumentation Science & Technology, 2021
Gang Li, Kehong Zeng, Bin Zhou, Wenming Yang, Xiaohui Lin, Fei Wang, Yun Chen, Xutao Ji, Dahai Zheng, Barerem-Melgueba Mao
The pre-emphasis process is important in order to improve the signal-to-noise ratio (SNR) by reducing interferences from individual characteristics. It has been reported that the pre-emphasis makes the recognition remains valid even when the human voice is altered by illness.[17] In the distributed vibration sensing system, the mission of the pre-emphasis is more complicated for three reasons.