Abstract: An all-pass state-variable Filter processes an input program signal into low, middle and high, frequency band signals. The middle frequency band signal has an additional inversion stage with respect to the low frequency and high frequency band signals. A first, second and third SDC (Scaled Detector Circuits) each have an input coupled to receive a respective frequency band signal and function to buffer, rectify and filter its respective frequency band signal to form a control voltage at its output. A first, second and third VCA (Voltage Control Amplifier) receives respective frequency band signals. Each VCA has a control voltage input. Each VCA reduces its gain in response to an increase in the control voltage applied to its control voltage input from an SDC output.

Abstract: An audio pre-amp and mid-band compressor circuit coupled to receive a program signal from a program signal source having a state-variable pre-amplifier responsive to a program input signal to provide a low range band-pass signal, a mid-range band-signal and a high range band-pass signal and for summing and scaling a low range band-pass signal, a mid-range band-signal and a high range band-pass signal providing a compensated signal. A voltage controlled amplifier circuit has a signal input terminal coupled to receive the compensated signal, and a control signal input coupled to receive at least a sample portion of the mid-range band-pass signal. The voltage controlled amplifier circuit responds to the amplitude of the sample portion of the mid-range band-pass signal to scale the compensated signal to provide a corrected output signal characterized to remain within a predetermined linear amplitude range at an output terminal.

Abstract: A Harmonic Generator for audio applications and a Pre-Amplifier circuit are combined to form a Harmonic Generator and Pre-Amplifier circuit. The Harmonic Generator is formed from a Buffer Circuit responsive to an input program signal for buffering the input program signal and for providing a buffered input program signal A Modulator Circuit is coupled to receive the buffered input program signal and generates harmonics in response to changes in amplitude of the program input signal to provide a modulated input program signal. A Summing Circuit adds the buffered input program signal and the modulated input program signal to provide a composite modulated input program signal. The Pre-Amplifier is coupled to receive the composite modulated input programing signal and process the signal in three audio frequency bands to provide a compensated output signal that includes harmonics generated by the modulator.