Automatic dynamic equalizing

Automatic dynamic equalization apparatus for use with a sound reproducing system having a nominal low frequency cutoff frequency in the low bass frequency range comprising,

• an input terminal,
• an output terminal,
• output combining means having first and second inputs and an output coupled to said output terminal for cummulatively combining signals on said first and second inputs,
• means for coupling said input terminal to said first input to establish a forward signal path for carrying an unmodified representation of the signal on said input terminal,
• means defining a side path for intercoupling said input terminal with said second input to provide a processed input signal to said second input,
• said means defining a side path comprising compressor means having an input coupled to said input terminal and an output having a gain inversely proportional to the level of the signal on said input terminal and dynamic equalization bandpass filter means having an input coupled to the output of said compressing means and an output coupled to said second input for transmitting spectral components within a predetermined low bass frequency range centered at said nominal low cutoff frequency,
• said apparatus coacting to impart between said input and said output terminals negligible boost to voice format spectral components at frequencies at a middle range of frequencies beginning at 200 Hz for different signal levels at said input terminal while significantly changing bass boost in the bass frequency region therebelow as a function of said levels so that at low listening reproduced sound levels of an audio signal on said input terminal, reproduced bass spectral components at said output terminal are perceived by listeners without degrading reproduced voices when carried by said audio signal.