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A Design of Noise Reduction Circuit for A radio Telephonic System  

Moon, Jong-Kyu (Dept. of Eletronics, Information and Communication, Daewon Science College)
Kim, Duk-Gyoo (School of Electrical Engineering and Computer Science, Kyungpook National University)
Publication Information
Journal of the Institute of Electronics Engineers of Korea TE / v.39, no.2, 2002 , pp. 84-89 More about this Journal
Abstract
In this paper, we present the design method of noise reduction circuit in telephonic system. The circuit consists of compressor, expander and a filter. The basic idea of a proposed method compresses the audible signal in order to mask the channel noise during transmission and then expand at the reverse rate the transmitted signal to naturally recover the original signal. Of course, there should be no distortion or other degradation of the audio itself in passing through companding(compress/expand) cycle. In the compressing process, the gain of compressor is automatically controlled by the envelope level of input signal in order to increase the effective dynamic range of input signal and to improve the signal to noise ratio. The compressed rate is the root time of a audible signal. The compressed signal should be expanded at the square time of the signal to recover a original signal. Simulation shows the proposed method improves the performance of the noise reduction of a channel noise as well as stability. 
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