Automatic and Programmed Gain Control (original) (raw)

Springer eBooks, 2021

Abstract

In the electronic acquisition of geoscientific data, and their subsequent digital processing, we frequently subject the data to Gain Control which is a nonlinear transformation to maintain an approximately stationary signal of a prescribed Root Mean Square (RMS) amplitude at its output, despite time-dependent slow variations of the signal amplitude level at the input. In simple terms, Gain Control reduces the signal if it is strong and amplifies it when it is weak. There are two ways to control signal amplitude, automatically or in a preset, programmed manner. Automatic Gain Control (AGC, also called Automatic Volume Control AVC, Automatic Level Control ALC, Time-Varying Gain TGC) is realized by an algorithm where the output energy level in a sliding time-window controls the gain applied to the input to keep it within prescribed limits. Programmed Gain Control (PGC) applies a gain which is a function of record time and was determined beforehand. In some AGC or PGC systems the gain can only vary by a factor of two (Binary Gain Control BGC). Gain Control (AGC or PGC) is an important step of data processing to improve the visibility of such data where propagation effects (such as attenuation or spherical divergence) have caused amplitude decay, and to assure approximate stationarity which is a prerequisite for statistical time-series analysis.

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