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.

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 boost circuit having an input buffer responsive to a program input signal for providing a buffered program signal, An all pass phase inverter having an input coupled to receive the buffered program signal and an output providing an inverted buffered program signal. A band pass filter having a predetermined Q, responsive to the buffered program signal for providing an inverted band pass boosted program signal. A summing amplifier for adding the inverted buffered program signal to the inverted band pass boosted program signal and for providing a composite program signal signal. A frequency adjustment means for adjusting the frequency at which the peak gain occurs. The input buffer is a state-variable input filter that processes the program input signal into high, low and mid-range frequency signal components. The input buffer has gain control circuitry for balancing and summing the high and mid-range signal components.

Abstract: A state-variable pre-amplifier responsive to a program input signal drives a filter circuit, and an absolute value circuit. The state-variable pre-amplifier uses a state-variable filter to provide a compensated signal at an output. The compensated signal has compensated high, low and mid-range frequency signal components. The pre-amplifier has a first amplifier stage for providing a high frequency compensated signal. A second amplifier stage provides a mid-range frequency compensated signal. A third amplifier stage provides a low range frequency compensated signal. An adjusting means adjusts the balance between at least two of the three frequency compensated signals. A summing circuit adds the three compensated signals to form the compensated signal. A balance means adjusts the balance between the high frequency, the mid-range and the low frequency compensated signals to provide a compensated signal.

Abstract: An amplifier circuit having a pre-amplifier responsive to a program input signal, a filter circuit, and an absolute value circuit. The pre-amplifier provides automated balancing between the high frequency channel signals and the mid range channel signals to provide a compensated signal. The filter circuit is coupled to receive and automatically filter the compensated signal to provide an output signal and a modified compensated signal. The filter circuit has an adjustable bandwidth that is automatically adjusted in response to the control signal for automatically reducing the bandwidth of the filter circuit in response to lower values of the control signal to obtain the output signal. The filter circuit uses a voltage controlled amplifier or a photo cell in combination with an integrator. An absolute value circuit senses the modified compensated signal and provides a control signal proportional to the average peak value of the amplitude of the modified compensated signal.

Abstract: A planar wave transducer assembly comprising a rigid, unitary structure formed by a pair of foot pads attached to a planar surface, each foot pad having an upstanding leg, and a span bar extending across the tops of the legs. A piezoelectric transducer element extends between the legs of the transducer assembly in spaced, parallel alignment with the span bar to convert wave motion in the planar surface into an electrical signal. That is, the movement of one leg towards the other in response to planar wave energy causes the one leg to flex or bend so as to apply a compressive force to the piezoelectric transducer element connected between the legs. The transducer assembly herein disclosed has been found to be particularly effective as a pick up when applied to a soundboard of a musical instrument, such as a piano, and the like.