Audio peak limiter using Hilbert transforms
First Claim
Patent Images
1. An audio-frequency peak limiter comprising:
- filter means for filtering an audio frequency signal into a first band which includes low-frequency signals and a second band which includes high frequency signals;
first clipping means for providing clipping with substantially no harmonic distortion of a signal, coupled to said filter means for receiving said first band;
second clipping means for providing audio frequency clipping of a signal coupled to said filter means for receiving said second band;
combining means coupled to said first and second clipping means for combining the outputs of these means to provide a peak limited audio signal;
whereby a peak limiter is realized which provides low harmonic distortion for low-frequency signals and which permits harmonic distortion only when excited by high frequencies.
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Abstract
A peak limiter is described which employs the Hilbert transform. Effectively distinct processing occurs for low frequency and high frequency signals and harmonic distortion results only when the limiter is excited by high frequencies.
71 Citations
21 Claims
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1. An audio-frequency peak limiter comprising:
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filter means for filtering an audio frequency signal into a first band which includes low-frequency signals and a second band which includes high frequency signals; first clipping means for providing clipping with substantially no harmonic distortion of a signal, coupled to said filter means for receiving said first band; second clipping means for providing audio frequency clipping of a signal coupled to said filter means for receiving said second band; combining means coupled to said first and second clipping means for combining the outputs of these means to provide a peak limited audio signal; whereby a peak limiter is realized which provides low harmonic distortion for low-frequency signals and which permits harmonic distortion only when excited by high frequencies. - View Dependent Claims (2, 3, 4)
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5. An audio frequency limiter for peak limiting an audio signal comprising:
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input means for receiving said audio signal and for processing said audio frequency signal into a first signal containing all frequency components of said audio signal and a second signal containing only the low frequency components of said audio signal, and for providing an approximately 90 degree phase shift between said first and second signals; a vector sum generator for providing an output signal representing the vector sum of two input signals, said generator coupled to receive as inputs said first and second signals from said input means; threshold means for defining a voltage threshold for a signal, said threshold means coupled to receive said output signal from said generator; and
,controllable amplifier means for providing a gain controllable by a control signal, said amplifier means coupled to said threshold means for receiving said control signal and coupled to receive said first signal from said input means, whereby peak limiting is obtained at the output of said amplifier means with harmonic distortion only for said high frequency components of said audio signal. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. An audio frequency limiter comprising:
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input means for receiving an audio signal and for providing a first signal containing all frequency components of said audio signal and a second signal containing only the law frequency components of said audio signal, and for providing an approximately 90 degrees difference in phase between said first and second signals; a first processing path comprising; a first voltage controlled amplifier (VCA) coupled to said input means for receiving said first signal; a first lowpass filter coupled to said input means for receiving a signal containing all frequency components of said audio signal; a second VCA coupled to receive the output of said first lowpass filter; a second filter coupled to receive the output of said first VCA; summing means for summing two signals coupled to the output of said second filter and the output of said second VCA;
a control path comprising;a vector sum generator for providing a vector sum of two signals coupled to receive said first and second signals from said input means; threshold means for defining a threshold voltage coupled to the output of said generator, the output of said threshold means being coupled to said first VCA for providing a control signal for said first VCA; a third lowpass filter coupled to receive the output of said threshold means, the output of said third lowpass filter providing a control signal for said second VCA; whereby a peak limiter is realized which avoids causing harmonic distortion for low frequency audio signals and permits introduction of harmonic distortion for high frequency audio signals. - View Dependent Claims (16, 17, 18, 19, 20, 21)
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Specification