| 摘要 |
A noise reducing apparatus consists of a compression system and an expansion system. The compression system comprises a pre-emphasis circuit for performing a pre-emphasis operation with respect to an input signal, a first variable gain control circuit for giving a level compression characteristic to an output signal of the pre-emphasis circuit, to produce an output signal to a transmission path, a first control voltage producing circuit for dividing the output signal of the first variable gain control circuit into a plurality of bands, to produce a plurality of control voltages respectively given mutually different bands, a first weighting circuit for respectively and relatively weighting the plurality of control voltages obtained from the first control voltage producing circuit, and a first adding circuit for adding the plurality of control voltages obtained from the first weighting circuit, to obtain a first control voltage and apply this first control voltage to the first variable gain control circuit. The expansion system similar to the compression system, comprises a second variable gain control circuit for giving a level expansion characteristic to the level compressed signal obtained through the above transmission path, where the level expansion characteristic is complementary to the level compression characteristic.
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