Audio peripheral mixer circuit and method for noise reduction
First Claim
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1. A circuit for mixing a first audio signal with a second audio signal, comprising:
- a control signal generator coupled to receive the first audio signal and having an output, the control signal generator generating at its output a control signal having a first state corresponding to the first audio signal not lower than a threshold value and a second state corresponding to the first audio signal lower than the threshold value;
a selective attenuator coupled to receive the first audio signal and the control signal, the selective attenuator producing at its output an attenuated first audio signal to reduce noise in response to the control signal in the first state and a substantially unattenuated first audio signal in response to the control signal in the second state; and
a mixing circuit coupled to receive the output signal from the selective attenuator and the second audio signal, the mixing circuit combining the selective attenuator output with the second audio signal, wherein the second audio signal is substantially unattenuated.
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Abstract
A circuit and method for mixing signals from audio sources provide noise reduction by employing a noise gate to selectively attenuate one of the source signals. The noise gate has a low gain state and a unity gain state. The noise gate switches to its unity gain state when a control signal reaches a predefined threshold voltage. The control signal is generated by rectifying and integrating the noisy source audio signal, so that the noise gate enters the unity gain state only when a useful sound occurs. Thus, the noise in the combined audio signal is reduced, without attenuating useful components of the source signals.
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Citations
8 Claims
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1. A circuit for mixing a first audio signal with a second audio signal, comprising:
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a control signal generator coupled to receive the first audio signal and having an output, the control signal generator generating at its output a control signal having a first state corresponding to the first audio signal not lower than a threshold value and a second state corresponding to the first audio signal lower than the threshold value; a selective attenuator coupled to receive the first audio signal and the control signal, the selective attenuator producing at its output an attenuated first audio signal to reduce noise in response to the control signal in the first state and a substantially unattenuated first audio signal in response to the control signal in the second state; and a mixing circuit coupled to receive the output signal from the selective attenuator and the second audio signal, the mixing circuit combining the selective attenuator output with the second audio signal, wherein the second audio signal is substantially unattenuated. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A circuit for providing selective attenuation of a first set of audio signals to reduce noise, the first set including a plurality of audio signals, and for mixing the selectively attenuated first set of audio signals with a second set of audio signals, the circuit comprising:
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a summer for generating a sum signal representing an algebraic sum of the plurality of audio signals; a rectifier coupled to receive the sum signal, for rectifying the sum signal; a voltage divider coupled to the rectifier, for biasing the rectifier; an integrator coupled to the rectifier, for integrating the rectified sum signal to produce a control signal; a noise gate coupled to receive the first set of audio signals, for selectively attenuating the first set of audio signals responsive to the control signal; and a mixing amplifier coupled to the noise gate and coupled to receive the second set of audio signals, for combining the selectively attenuated first set of audio signals with the second set of audio signals, wherein the second set of audio signals is substantially unattenuated.
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8. A method of selectively attenuating a plurality of audio signals to reduce noise, and mixing the selectively attenuated plurality of audio signals with at least one substantially unattenuated audio signals, the method comprising the steps of:
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generating a sum signal representing an algebraic sum of the plurality of audio signals; and rectifying the sum signal; integrating the rectified sum signal to produce a control signal indicating one of two states; responsive to the control signal indicating a first of the two states, attenuating the plurality of audio signals; and combining the selectively attenuated plurality of audio signals with at least one substantially unattenuated audio signal.
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Specification