Noise reduction system having series connected low and high frequency emphasis and de-emphasis filters

A noise reduction system having a compressor and an expander having a complementary frequency response characteristic to the frequency response characteristic of the compressor, said compressor 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 applied to 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 high frequency emphasis variable frequency filter circuit of which the cutoff frequency is variable as a function of said first control signal, and a low frequency emphasis variable gain filter circuit of which the amount of emphasis is variable inversely as a function of said second control signal, said filter circuits being connected in a series circuit between said first input and output terminals, and
• said expander 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 low frequency de-emphasis variable gain filter circuit of which the amount of de-emphasis is variable inversely as a function of said fourth control signal, and a high frequency de-emphasis variable frequency filter circuit of which the cutoff frequency is variable as a function of said third control signal, said filter circuits being connected in a series circuit between said second input and output terminals.