Spectral emphasis and de-emphasis

Abstract

The complementary pre-processing and post-processing circuits of this inventiona re advantageous for reducing noise introduced into a signal by a process or medium where the noise introduced rises with the signal level. The pre-processing circuit analyzes the spectral composition of an input signal and generates an emphasis control signal to so indicate. The emphasis control signal is limited by a limitation circuit to a desired bandwidth. The pre-processing circuit includes an emphasis applying circuit for amplifying or attenuating the input signal as a function of the emphasis control signal. A delay circuit delays the input signal relative to the emphasis control signal so that the input signal reaches the emphasis applying circuit when the emphasis control signal is available for controlling the amplification or attenuation applied. The post-processing circuit restores the spectral composition of the signal. The post-processing circuit comprises a circuit for deriving a de-emphasis control signal of limited bandwidth from the emphasis control signal. A de-emphasis applying circuit attenuates or amplifies the decoded signal as a function of the de-emphasis control signal to restore its spectral composition., Since the noise introduced by the process or medium is a function of the signal level, the pre-processing circuit alters the input signal in such manner that the noise introduced is reduced. The emphasis and de-emphasis applied in pre- and post-processing change slowly and the system is tolerant of component and timing errors.