Abstract: A microphone output limiter which detects the amplitude of a microphone and produces a control signal which lowers the microphone's impedance when the amplitude of the audio signal exceeds a preselected threshold level. The output signal is detected at the output of the microphone or it may be detected at the output of a later pre-amplifier stage. Once a control signal is generated it is coupled to a variable impedance device which produces a shunt load impedance across the output of the microphone thereby lowering its impedance. The microphone, as well as the variable impedance device, may be coupled through impedance converters in order to facilitate component matching.

Abstract: The present invention phase coherent crossover incorporates a method and apparatus for providing phase coherent crossover (PCC) signals. The PCC method and apparatus involve the utilizing of an all-pass filter for receiving an input signal and producing an all-pass signal, and a partial-pass filter also receiving the input signal and producing a partial-pass signal at a partial-pass output. The PCC method and apparatus further involve the combining of the partial-pass signal produced by the partial-pass filter with the all-pass signal produced by the all-pass filter to produce an opposite partial-pass signal at an opposite partial-pass output.

Abstract: A drift canceling method and apparatus is used in conjunction with an analog to digital converter. The drift canceling method and apparatus analyzes the duty cycle of the target analog to digital converter's most significant output data bit to determine if the average numeric value of the analog to digital converter's output data stream is data centered upon the analog to digital converter's numeric data range or if it is ranging above or below the data range center. If the average data value is above or below center, a servo error signal is generated which is added to the analog to digital converter's input signal to cause the analog to digital converter's average output data magnitude to slew towards the data range center. In this way, the average analog to digital converter output data offset is continuously canceled without interfering with the normal and continuous operation of the target analog to digital converter.

Abstract: A sticky leveler utilizing a window detection technique to preserve the relatively small level changes of an audio signal. The sticky leveler includes a voltage controlled amplifier (VCA) and a sticky detector, where an input signal is received by the VCA for creating a variable gain path to the VCA output. The control output of the sticky detector is coupled to the VCA control input for controlling the VCA gain. The detection input of the sticky detector may be coupled to the input signal for generating a feedforward automatic gain control leveler. Alternatively the sticky detector may be coupled to the output signal of the VCA for generating a feedback automatic gain control leveler.

Abstract: A distributed pre-emphasis equalizer comprises a partial pre-emphasizer and a (50) microsecond pre-emphasizer. The partial pre-emphasizer receives an input signal and produces a partially pre-emphasized output signal. The (50) microsecond pre-emphasizer receives the partially pre-emphasized output signal from the partial pre-emphasizer and adds a (50) microsecond equalization to produce a pre-emphasized output signal equal to a standard (75) microsecond pre-emphasis curve. The distributed pre-emphasis equalizer allows an FM audio processor to produce only the "dulling" effect of a (50) microsecond pre-emphasis even when generating a (75) microsecond pre-emphasis curve. The distributed pre-emphasis equalizer also creates a pre-emphasizing method which is inherently compatible with both the (75) microsecond and (50) microsecond standards. Furthermore, the distributed pre-emphasis equalizer creates a pre-emphasizing method which is easily switchable between the (75) and (50) microsecond standards.

Abstract: A split-band clipper which generates less distortion, minimizes or reduces the occurrence of all IMD, or at least will minimize and reduce the occurrence of widely space IMD, and reduce the quantity of harmonic distortion caused by clipping of bass frequencies.

Abstract: A functional control block (FCB) device for use in conjunction with a signal regulating apparatus which has a signal regulator for producing an output signal and delivers an actual signal on a load through an external conductor, and which further has an inner servo loop and an outer servo loop. The FCB device includes a first input connected to the signal regulator, and a second input connected to the outer servo loop. The FCB device has an internal functional signal processing circuity for processing an output signal from the signal regulator, and the signal from the outer servo loop, and producing a functional sense signal and a functional reference signal. The FCB device further has a first output connected to a sense input of the inner servo loop for delivering the functional sense signal, and a second output connected to a reference input of the inner servo loop for delivering the functional reference signal.

Abstract: The present invention is a concentric servo method and apparatus using two servo loops to control and stabilize the output of an electronic voltage regulator. An inner and outer servo loop are employed. The inner servo loop resembles the control loop of a conventional voltage regulator while the outer servo loop controls the sense threshold of the inner servo loop. The outer servo loop senses the voltage delivered to an external load resistance and controls the sense threshold of the inner servo loop to compensate for the voltage loss which may occur between the regulator output and the actual load resistance. The inner loop retains its high speed to regulate out any input voltage irregularities such as ripple and noise. The present invention gives better stability than conventional remote sensing voltage regulator circuits.

Abstract: An audio compressor using interactive layered time constants to create an easy to use compressor which self adapts to the program characteristics and provides a desirable and pleasing effect over a wide range of audio program material. The audio compressor includes an adaptable filter connected between an output signal path and a control feedback signal path of a voltage control amplifier. The adaptable filter comprises a first resistor-capacitor circuit connected to the output signal path and producing a charging/discharging voltage which is more dependent on a transient peak value of the audio signals and a second resistor-capacitor circuit working under the charging/discharging voltage of the first resistor/capacitor circuit for producing a charging/discharging voltage which is more dependent on an average value of the audio signals.

Abstract: A peak accelerated compressor comprising a voltage controlled amplifier, a level detector and a peak accelerated filter circuit. The voltage controlled amplifier circuit is utilized for processing an input audio signal and producing an output audio signal. The level detector circuit is utilized for processing a sample audio signal which contains transient peaks and average waveforms. The peak accelerated filter circuit is coupled between the level detector circuit and the voltage controlled amplifier circuit for producing a control output signal to change the gain of the voltage controlled amplifier circuit in response to the transient peaks in the sample audio signal. The peak accelerated compressor effectively enhances the compression for transient peaks without adversely affecting the normal compression of average waveforms.

Abstract: A reflected plate amplifier (RPA) for use with electronic audio equipment. The RPA comprises an input circuit for receiving an input signal, a vacuum tube, a plate current reflector, and an output circuit for delivering an output signal. The vacuum tube has a control grid coupled to the input circuit for receiving the input signal, and a plate for delivering a plate current responsive to the input signal. The plate current reflector is a transistor having an input terminal coupled to the plate of the vacuum tube for receiving the plate current, and an output terminal for delivering a reflected current which is responsive to the plate current of the vacuum tube and therefore responsive to the input signal, while the plate current reflector holds the plate voltage of the vacuum tube substantially constant for a wide range of the plate current of the vacuum tube.

Abstract: A transient discriminate harmonics generator which receives an audio input signal and produces an output signal containing harmonics of the input signal. The output signal is amplitude shaped as a function of the input signal's time and amplitude envelope.

Abstract: A frequency discriminate leveler ("FDL") which controls its attack rate depending on the audio frequency to more perfectly preserve the natural sound of the audio program while very effectively controlling the long term average program level. The FDL has a function to attack more slowly for low frequency signals than for high frequency signals. The FDL includes a gain controller, an FDL control generator and a leveling detector. The gain controller coupled to an input signal and an output signal. The input signal is the unleveled audio program which can vary widely in average level. The output signal is the leveled signal which contains a more constant average level. The FDL control generator generates a suitable control output to cause the gain controller to increase or decrease gain. The FDL control generator is coupled to the leveling detector for the purpose of receiving the output of the leveling detector, and generating a control output to control the gain of the gain controller.

Abstract: A device for enhancing the bass frequency components in an audio signal while avoiding overload problems associated with fixed levels of bass frequency enhancement. The device divides the input signal into two parts, the first of which passes through to the output of the device. The second part of the input signal is input into a low pass filter which passes only the bass components of the input signal and imparts a frequency dependent phase shift to the bass components. The bass components then pass through a variable gain amplifier which may or may not invert the polarity of the bass components and then are recombined with the first part of the audio signal. The gain of the variable gain amplifier is varied in accord with the level of the bass components.

Abstract: An apparatus and a method using logical functions to improve the performance of a noise gate. When the input or triggering signal exceeds the gate threshold, a first bistable logic element is set. Simultaneously, a second monostable logic element is triggered for a set time-out. A third logic element determines if the second monostable logic element is reset after the time-out and the triggering signal is below the gate threshold, at which time the first bistable logic element is forced to the reset condition. Under no other condition can the first bistable logic element be reset. The logic output of the first bistable logic element controls the noise gate, causing it to open when set and close when reset. The advantage of this method over prior art is a more decisive gate operation whereby a short transient triggering signal can fully and definitely trigger the gate open.

Abstract: A discrete parallel path modulation multiplexer for use in generating a composite baseband signal from separate left and right input signals. The composite baseband signal includes the sum of the left and right input signals and the product of the difference between the left and right input signals and a subcarrier. The composite baseband signal may also include a pilot subcarrier at one-half the frequency of the subcarrier. In one signal path, the multiplexer multiplies the right input signal by the function (1+sin (wt)) and in a second signal path the multiplexer multiplies the left input signal by the function (1-sin (wt)). The products are then combined to obtain the composite baseband signal. A pilot subcarrier may also be generated and included as part of the composite baseband signal.

Abstract: An audio signal compression device which utilizes both a broad band compressor and a high frequency expander. The level of the compression provided by the compressor and the level of expansion provided by the high frequency expander are both controlled by a voltage or other signal that is output by signal level detection circuitry within the device. The broadband compressor provides a variable level of amplification (or attenuation) that is relatively uniform as a function of frequency. The high frequency expander provides a variable level of expansion wherein the high frequency components are expanded more than the mid and low frequency components.

Abstract: An impulse detection circuit for use in triggering circuits such as those used for detecting drum beats within background noise and then triggering music synthesizers in response to the drum beat. Differentiators and peak-rectifiers and filters are used to detect impulse like inputs over a wide dynamic range in a noisy background. The input signal is rectified and differentiated and then inputted into a peak-rectifier and filter having a fast charging and a slow discharging time constant. The output of this peak-rectifier and filter is differentiated and inputted into a pair-rectifier and filters operating in parallel, which filters have rapid charging and slow discharging time constants. The time constants of one of the two filters are approximately twice those of the other. The outputs of the two peak-rectifier and filters are compared in a comparator.