Circuit for selectively obtaining automatic dynamic compression or expansion

A circuit, having an input terminal and first and second output terminals, for selectively compressing or expanding a signal having frequency components within a given frequency spectrum, comprising:

• amplifier means having first and second inputs and an output, said first input being coupled to said input terminal and said output to said first output terminal;
• a summing circuit having an input and an output, the output of said summing circuit being coupled to the second input of said amplifier means when said signal is being compressed and to said second output terminal when said signal is being expanded, the compressed signal being obtained at said first output terminal;
• and
• a plurality of frequency selective channels each capable of transmitting signals having frequencies within a predetermined portion of said frequency spectrum, coupled in parallel between the output of said amplifier means and the input of said summing circuit, one of said frequency selective channels being adapted for transmitting signals in the high frequency range of said frequency spectrum and consisting of only a passive filter and an associated variable impedance, the remaining frequency selective channels each including a passive filter, variable impedance and an impedance converter.