Noise reduction system having series connected variable frequency filters

A noise reduction system having a compressor circuit and an expander circuit, said compressor circuit comprising:

• first input and output terminals, means connected to the first output terminal for generating a first control signal representing a high frequency component of a signal at said first output terminal, means connected to said first output terminal for generating a second control signal representing a low frequency component of said signal at said first output terminal, a first high frequency band variable filter, the cut-off frequency of which is variable as a function of said first control signal, and a first low frequency band variable filter, the cut-off frequency of which is variable inversely as a function of said second control signal, said high and low frequency band variable filters being connected in series between said first input and output terminals, said expander circuit comprising:
• a second input terminal adapted for connection to said first output terminal, a second output terminal, means connected to said second input terminal for generating a third control signal representing a high frequency component of the signal at said second input terminal, means connected to said second input terminal for generating a fourth control signal representing a low frequency component of said signal at said second input terminal, a second low frequency band variable filter characterized with a complementary frequency response to the frequency response characteristic of said first high frequency band variable filter, and a second high frequency band variable filter characterized with a complementary frequency response to the frequency response characteristic of said first low frequency band variable filter, said second variable filters being connected in series between said second input and output terminals, the cut-off frequency of said second low frequency band variable filter being variable as a function of said third control signal and the cut-off frequency of said second high frequency variable filter being variable inversely as a function of said fourth control signal.