Bandlimiting anti-noise in personal audio devices having adaptive noise cancellation (ANC)
First Claim
1. A personal audio device, comprising:
- a personal audio device housing;
a transducer mounted on the personal audio device housing for reproducing an audio signal including both source audio for playback to a listener and an anti-noise signal for countering effects of ambient audio sounds in an acoustic output of the transducer;
a reference microphone mounted on the personal audio device housing for providing a reference microphone signal indicative of the ambient audio sounds;
an error microphone mounted on the personal audio device housing in proximity to the transducer for providing an error microphone signal indicative of the acoustic output of the transducer and the ambient audio sounds at the transducer; and
a processing circuit that implements an adaptive filter having a response that generates the anti-noise signal from the reference microphone signal to reduce a presence of the ambient audio sounds heard by the listener, wherein the processing circuit implements a first fixed filter having a predetermined response acting in functional series with the adaptive filter, wherein the first fixed filter alters an anti-noise signal component of the audio signal, wherein the processing circuit further implements a secondary path adaptive filter having a secondary path response that shapes the source audio to generate shaped source audio and a combiner that removes the shaped source audio from the error microphone signal to provide an error signal indicative of the combined anti-noise and ambient audio sounds delivered to the listener, wherein the processing circuit further subtracts the output of the first fixed filter from the source audio provided to the secondary path adaptive filter and adds a signal generated from the output of the adaptive filter to the source audio provided to the secondary path adaptive filter to prevent a frequency response of the first fixed filter from appearing in the error signal, wherein the processing circuit shapes the response of the adaptive filter in conformity with the error microphone signal and the reference microphone signal by adapting the response of the adaptive filter to minimize the ambient audio sounds at the error microphone.
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Abstract
A personal audio device, such as a wireless telephone, includes noise canceling circuit that adaptively generates an anti-noise signal from a reference microphone signal and injects the anti-noise signal into the speaker or other transducer output to cause cancellation of ambient audio sounds. An error microphone may also be provided proximate the speaker to measure the output of the transducer in order to control the adaptation of the anti-noise signal and to estimate an electro-acoustical path from the noise canceling circuit through the transducer. A processing circuit that performs the adaptive noise canceling (ANC) function also either adjusts the frequency response of the anti-noise signal with respect to the reference microphone signal, and/or by adjusting the response of the adaptive filter independent of the adaptation provided by the reference microphone signal.
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Citations
16 Claims
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1. A personal audio device, comprising:
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a personal audio device housing; a transducer mounted on the personal audio device housing for reproducing an audio signal including both source audio for playback to a listener and an anti-noise signal for countering effects of ambient audio sounds in an acoustic output of the transducer; a reference microphone mounted on the personal audio device housing for providing a reference microphone signal indicative of the ambient audio sounds; an error microphone mounted on the personal audio device housing in proximity to the transducer for providing an error microphone signal indicative of the acoustic output of the transducer and the ambient audio sounds at the transducer; and a processing circuit that implements an adaptive filter having a response that generates the anti-noise signal from the reference microphone signal to reduce a presence of the ambient audio sounds heard by the listener, wherein the processing circuit implements a first fixed filter having a predetermined response acting in functional series with the adaptive filter, wherein the first fixed filter alters an anti-noise signal component of the audio signal, wherein the processing circuit further implements a secondary path adaptive filter having a secondary path response that shapes the source audio to generate shaped source audio and a combiner that removes the shaped source audio from the error microphone signal to provide an error signal indicative of the combined anti-noise and ambient audio sounds delivered to the listener, wherein the processing circuit further subtracts the output of the first fixed filter from the source audio provided to the secondary path adaptive filter and adds a signal generated from the output of the adaptive filter to the source audio provided to the secondary path adaptive filter to prevent a frequency response of the first fixed filter from appearing in the error signal, wherein the processing circuit shapes the response of the adaptive filter in conformity with the error microphone signal and the reference microphone signal by adapting the response of the adaptive filter to minimize the ambient audio sounds at the error microphone. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method of canceling ambient audio sounds in the proximity of a transducer of a personal audio device, the method comprising:
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first measuring ambient audio sounds with a reference microphone to produce a reference microphone signal; second measuring an acoustic output of the transducer and the ambient audio sounds at the transducer with an error microphone; adaptively generating an anti-noise signal from a result of the first measuring and the second measuring for countering effects of ambient audio sounds at the transducer by adapting a response of an adaptive filter that filters the reference microphone signal; filtering a result of the adaptively generating with a first fixed filter having a predetermined response; shaping a copy of source audio with a secondary path response to generate shaped source audio; removing the shaped source audio from the error microphone signal to produce an error signal indicative of the combined anti-noise and ambient audio sounds delivered to a listener; second filtering the reference microphone signal with a response according to a copy of the secondary path adaptive filter to provide an input to the adaptive filter; and subtracting the output of the first fixed filter from the source audio provided to the secondary path adaptive filter and adding a signal generated from the output of the adaptive filter to the source audio provided to the secondary path adaptive filter to prevent a response of the first fixed filter from appearing in the error signal; and combining the anti-noise signal with a source audio signal to generate an audio signal provided to the transducer. - View Dependent Claims (8, 9, 10, 11, 12)
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13. An integrated circuit for implementing at least a portion of a personal audio device, comprising:
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an output for providing a signal to a transducer including both source audio for playback to a listener and an anti-noise signal for countering effects of ambient audio sounds in an acoustic output of the transducer; a reference microphone input for receiving a reference microphone signal indicative of the ambient audio sounds; an error microphone input for receiving an error microphone signal indicative of the output of the transducer and the ambient audio sounds at the transducer; and a processing circuit that implements an adaptive filter having a response that generates the anti-noise signal from the reference microphone signal to reduce a presence of the ambient audio sounds heard by the listener, wherein the processing circuit implements a first fixed filter having a predetermined response acting in functional series with the adaptive filter, wherein the first fixed filter alters an anti-noise signal component of the audio signal, wherein the processing circuit further implements a secondary path adaptive filter having a secondary path response that shapes the source audio to generate shaped source audio and a combiner that removes the shaped source audio from the error microphone signal to provide an error signal indicative of the combined anti-noise and ambient audio sounds delivered to the listener, wherein the processing circuit further subtracts the output of the first fixed filter from the source audio provided to the secondary path adaptive filter and adds a signal generated from the output of the adaptive filter to the source audio provided to the secondary path adaptive filter to prevent a frequency response of the first fixed filter from appearing in the error signal, wherein the processing circuit shapes the response of the adaptive filter in conformity with the error microphone signal and the reference microphone signal by adapting the response of the adaptive filter to minimize the ambient audio sounds at the error microphone. - View Dependent Claims (14, 15, 16)
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Specification