Transient control aspects of circuit arrangements for altering the dynamic range of audio signals
First Claim
1. A circuit for modifying the dynamic range of an input signal comprisingmeans for modifying the dynamic range of said input signal in response to a control signal to provide an output signal, andmeans for generating said control signal, said control signal generating means includingcapacitance means for smoothing the control signal,means for deriving a first signal from a signal point substantially the same dynamically as said output signal,the rate of change of amplitude with time of said first signal being less than the rate of change of amplitude with time of said output signal,means for charging said capacitance means with said first signal in response to steady-state conditions,means for deriving a second signal from a point substantially the same dynamically as said output signal,the rate of change of amplitude with time of said second signal being substantially similar to that of said output signal,means for charging said capacitance means very rapidly with said second signal in response to transient input signal conditions, andmeans for deriving said control signal from the charge on said capacitance means.
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Accused Products
Abstract
In circuits for generating rapidly changing, yet smooth and controlled, control signals in response to transient signals for use in audio compressors and expanders, a steady-state portion of the control circuit includes first and second smoothing stages (alternatively, a single stage may be employed) and an overshoot suppression portion of the control circuit rapidly charges the capacitor in the steady-state smoothing stage from which the control voltage is derived. A first additional overshoot suppression circuit provides further charging of the capacitor in response to low frequency signal components. Modulation control signals, which make the compressor or expander less susceptible to control by stop-band signal components, are combined in opposition to the signals in the steady-state and overshoot suppression portions of the control circuit. A further overshoot suppression circuit provides additional charging of the capacitor in order to compensate in certain cases for the use of modulation control signals.
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Citations
72 Claims
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1. A circuit for modifying the dynamic range of an input signal comprising
means for modifying the dynamic range of said input signal in response to a control signal to provide an output signal, and means for generating said control signal, said control signal generating means including capacitance means for smoothing the control signal, means for deriving a first signal from a signal point substantially the same dynamically as said output signal, the rate of change of amplitude with time of said first signal being less than the rate of change of amplitude with time of said output signal, means for charging said capacitance means with said first signal in response to steady-state conditions, means for deriving a second signal from a point substantially the same dynamically as said output signal, the rate of change of amplitude with time of said second signal being substantially similar to that of said output signal, means for charging said capacitance means very rapidly with said second signal in response to transient input signal conditions, and means for deriving said control signal from the charge on said capacitance means.
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21. A circuit for modifying the dynamic range of an input signal, comprising
means for modifying the dynamic range of said input signal in response to a control signal to provide an output signal, and means for generating said control signal, said control signal generating means including means for deriving a first signal from a signal point substantially the same dynamically as said output signal, means for rectifying said first signal, means, including capacitance means, for smoothing said rectified first signal, said capacitance means being charged by said rectified first signal, means for deriving a second signal from a signal point substantially the same dynamically as said output signal, means for rectifying said second signal, means, having a variable low impedance, for applying a charging current to said capacitance means, the amplitude of said charging current being determined by the amplitude of said rectified second signal, and increasing as the amplitude of said rectified second signal increases, whereby overshoot suppression effects are controllably phased in, and means for deriving said control signal from the charge on said capacitance means.
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36. A circuit for modifying the dynamic range of an input signal, comprising
frequency selective circuit means for dividing the frequency spectrum in which the input signal lies into pass-band and stop-band regions, means for modifying the dynamic range of signal components in the pass-band region in response to a control signal to provide an output signal, said control signal acting in response to signal components lying in the pass-band and stop-band regions, means for deriving at least one modulation control signal from a signal point substantially the same dynamically as said output signal, said modulation control signal having the characteristic that when combined in opposition with said control signal, the control signal is altered, in a level dependent way, so as to make the control signal less responsive to stop-band signal components as the level of the input signal rises, and means for generating said control signal, said control signal generating means including capacitance means, means for deriving a first signal by combining said modulation control signal in opposition with a signal derived from a signal point substantially the same dynamically as said output signal, means for charging said capacitance means with said first signal in response to steady-state input signal conditions, means for deriving a second signal by combining said modulation control signal in opposition with a signal derived from a signal point substantially the same dynamically as said output signal, means for charging said capacitance means very rapidly with said second signal in response to transient input signal conditions, and means for deriving said control signal from the charge on said capacitance means.
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57. A circuit for modifying the dynamic range of an input signal, comprising
first dynamic action means having a fixed band characteristic action acting in response to a first control signal to provide a first output signal, said first dynamic action means including means for generating a first control signal, said means for generating a first control signal including capacitance means, means for deriving a first signal from a signal point substantially the same dynamically as said first output signal, means for charging said capacitance means with said first signal in response to steady-state input signal conditions, means for deriving a second signal from a signal point substantially the same dynamically as said first output signal, means for charging said capacitance means very rapidly with said second signal in response to transient input signal conditions, and means for deriving said first control signal from the charge on said capacitance means, second dynamic action means having a sliding band characteristic action in response to a second control signal to provide a second output signal, said second dynamic action means including means for generating a second control signal, said means for generating a second control signal including further capacitance means, means for deriving a third signal from a signal point substantially the same dynamically as said second output signal, means for charging said further capacitance means with said third signal in response to steady-state input signal conditions, means for deriving a fourth signal from a signal point substantially the same dynamically as said second output signal, means for charging said further capacitance means very rapidly with said fourth signal in response to transient input signal conditions, and means for deriving said second control signal from the charge on said further capacitance means, and means for coupling said first dynamic action means to said second dynamic action means.
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68. A circuit for modifying the dynamic range of an input signal, comprising
means for modifying the dynamic range of said input signal in response to a control signal to provide an output signal, and means for generating said control signal, said control signal generating means including capacitance means from which said control signal is derived, and said means for generating said control signal further comprising means for deriving a charging signal from a signal point substantially the same dynamically as said output signal, and means for charging said capacitance means with said charging signal, said means for charging said capacitance means charging said capacitance means slowly in response to low frequency increases in the amplitude of said output signal.
Specification