The present disclosure relates in general to adaptive noise cancellation in connection with an acoustic transducer, and more particularly, to bandlimiting anti-noise in personal audio devices having adaptive noise cancellation.
Personal audio devices, such as mobile/cellular telephones, cordless telephones, and other consumer audio devices, such as MP3 players and headphones or earbuds, are in widespread use. Performance of such devices with respect to intelligibility can be improved by providing noise canceling using a microphone to measure ambient acoustic events and then using signal processing to insert an anti-noise signal into the output of the device to cancel the ambient acoustic events. Because the acoustic environment around personal audio devices such as wireless telephones can change dramatically, depending on the sources of noise that are present and the position of the device itself, it is desirable to adapt the noise canceling to take into account such environmental changes. However, adaptive noise canceling circuits can be complex, consume additional power and can generate undesirable results under certain circumstances.
Therefore, it would be desirable to provide a personal audio device, including a wireless telephone, that provides noise cancellation in a variable acoustic environment.
In accordance with the teachings of the present disclosure, the disadvantages and problems associated with improving audio performance of a personal audio device may be reduced or eliminated.
In accordance with embodiments of the present disclosure, an integrated circuit for implementing at least a portion of a personal audio device may include an output, a reference microphone input, an error microphone input, and a processing circuit. The output may provide a signal to a transducer including both source audio for playback to a listener and an anti-noise signal for countering the effects of ambient audio sounds in an acoustic output of the transducer. The reference microphone input may receive a reference microphone signal indicative of the ambient audio sounds. The error microphone input may receive an error microphone signal indicative of the output of the transducer and the ambient audio sounds at the transducer. The processing circuit may implement an adaptive filter having a response that generates the anti-noise signal from the reference microphone signal to reduce the presence of the ambient audio sounds heard by the listener. The processing circuit may shape 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. The response of the adaptive filter may be further adjusted independent of the adapting by combining injected noise with the reference microphone signal and the processing circuit further implements a copy of the adaptive filter to receive the injected noise so that the response of the copy of the adaptive filter is controlled by the adaptive filter adapting to cancel a combination of the ambient audio sounds and the injected noise. The processing circuit may further control the response of the adaptive filter with the coefficients adapted in the copy of the adaptive filter, whereby the injected noise is not present in the anti-noise signal. Each of a sample rate of the copy of the adaptive filter and a rate of adapting of the adaptive filter may be significantly less than a sample rate of the adaptive filter.
In accordance with these and other embodiments of the present disclosure, an integrated circuit for implementing at least a portion of a personal audio device may include an output, a reference microphone input, an error microphone input, and a processing circuit. The output may provide a signal to a transducer including both source audio for playback to a listener and an anti-noise signal for countering the effects of ambient audio sounds in an acoustic output of the transducer. The reference microphone input may receive a reference microphone signal indicative of the ambient audio sounds. The error microphone input may receive an error microphone signal indicative of the output of the transducer and the ambient audio sounds at the transducer. The processing circuit may implement an adaptive filter having a response that generates the anti-noise signal from the reference microphone signal to reduce the presence of the ambient audio sounds heard by the listener. The processing circuit may shape 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. The response of the adaptive filter may be further adjusted independent of the adapting by combining injected noise with the reference microphone signal, and the processing circuit may further implement a copy of the adaptive filter to receive the injected noise so that the response of the copy of the adaptive filter is controlled by the adaptive filter adapting to cancel a combination of the ambient audio sounds and the injected noise. The processing circuit may further control the response of the adaptive filter with the coefficients adapted in the copy of the adaptive filter, whereby the injected noise is not present in the anti-noise signal. The injected noise may be provided by a periodic shaped noise signal stored in a buffer, such that the copy of the adaptive filter generates a periodic error noise signal from the periodic shaped noise signal, further such that the processing circuit shapes the response of the adaptive filter in conformity with a combination of the error microphone signal and the periodic error noise signal, and a combination of the periodic shaped noise signal and the reference microphone signal.
In accordance with these and other embodiments of the present disclosure, a method may include receiving a reference microphone signal indicative of ambient audio sounds at the acoustic output of a transducer and receiving an error microphone signal indicative of an acoustic output of a transducer and the ambient audio sounds at the acoustic output of the transducer. The method may also include generating an anti-noise signal from filtering the reference microphone signal with an adaptive filter to reduce the presence of the ambient audio sounds heard by the listener and shaping 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. The method may also include further adjusting the response of the adaptive filter by combining injected noise with the reference microphone signal and receiving the injected noise by a copy of the adaptive filter so that the response of the copy of the adaptive filter is controlled by the adaptive filter adapting to cancel a combination of the ambient audio sounds and the injected noise. The method may also include controlling the response of the adaptive filter with the coefficients adapted in the copy of the adaptive filter, whereby the injected noise is not present in the anti-noise signal and wherein each of a sample rate of the copy of the adaptive filter and a rate of adapting of the adaptive filter is significantly less than a sample rate of the adaptive filter.
In accordance with these and other embodiments of the present disclosure, a method may include receiving a reference microphone signal indicative of ambient audio sounds at the acoustic output of a transducer and receiving an error microphone signal indicative of an acoustic output of a transducer and the ambient audio sounds at the acoustic output of the transducer. The method may also include generating an anti-noise signal from filtering the reference microphone signal with an adaptive filter to reduce the presence of the ambient audio sounds heard by the listener and further adjusting the response of the adaptive filter by combining injected noise with the reference microphone signal. The method may also include receiving the injected noise by a copy of the adaptive filter so that the response of the copy of the adaptive filter is controlled by the adaptive filter adapting to cancel a combination of the ambient audio sounds and the injected noise and controlling the response of the adaptive filter with the coefficients adapted in the copy of the adaptive filter, whereby the injected noise is not present in the anti-noise signal and is provided by a periodic shaped noise signal stored in a buffer, such that the copy of the adaptive filter generates a periodic error noise signal from the periodic shaped noise signal. The method may additionally include shaping of the response of the adaptive filter in conformity with a combination of the error microphone signal and the periodic error noise signal, and a combination of the periodic shaped noise signal and the reference microphone signal.
Technical advantages of the present disclosure may be readily apparent to one of ordinary skill in the art from the figures, description and claims included herein. The objects and advantages of the embodiments will be realized and achieved at least by the elements, features, and combinations particularly pointed out in the claims.
It is to be understood that both the foregoing general description and the following detailed description are examples and explanatory and are not restrictive of the claims set forth in this disclosure.
A more complete understanding of the present embodiments and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, in which like reference numbers indicate like features, and wherein:
Referring now to
Personal audio device 10 may include adaptive noise cancellation (ANC) circuits and features that inject an anti-noise signal into speaker SPKR to improve intelligibility of the distant speech and other audio reproduced by speaker SPKR. A reference microphone R may be provided for measuring the ambient acoustic environment, and may be positioned away from the typical position of a user's mouth, so that the near-end speech may be minimized in the signal produced by reference microphone R. Another microphone, error microphone E, may be provided in order to further improve the ANC operation by providing a measure of the ambient audio combined with the audio reproduced by speaker SPKR close to ear 5, when personal audio device 10 is in close proximity to ear 5. Circuit 14 within personal audio device 10 may include an audio CODEC integrated circuit (IC) 20 that receives the signals from reference microphone R, near-speech microphone NS, and error microphone E, and interfaces with other integrated circuits such as a radio-frequency (RF) integrated circuit 12 having a wireless telephone transceiver. In some embodiments of the disclosure, the circuits and techniques disclosed herein may be incorporated in a single integrated circuit that includes control circuits and other functionality for implementing the entirety of the personal audio device, such as an MP3 player-on-a-chip integrated circuit. In these and other embodiments, the circuits and techniques disclosed herein may be implemented partially or fully in software and/or firmware embodied in computer-readable media and executable by a controller or other processing device.
In general, ANC techniques of the present disclosure measure ambient acoustic events (as opposed to the output of speaker SPKR and/or the near-end speech) impinging on reference microphone R, and by also measuring the same ambient acoustic events impinging on error microphone E, ANC processing circuits of personal audio device 10 adapt an anti-noise signal generated at the output of speaker SPKR from the output of reference microphone R to have a characteristic that minimizes the amplitude of the ambient acoustic events at error microphone E. Because acoustic path P(z) extends from reference microphone R to error microphone E, ANC circuits are effectively estimating acoustic path P(z) while removing effects of an electro-acoustic path S(z) that represents the response of the audio output circuits of CODEC IC 20 and the acoustic/electric transfer function of speaker SPKR including the coupling between speaker SPKR and error microphone E in the particular acoustic environment, which may be affected by the proximity and structure of ear 5 and other physical objects and human head structures that may be in proximity to personal audio device 10, when personal audio device 10 is not firmly pressed to ear 5. While the illustrated personal audio device 10 includes a two-microphone ANC system with a third near-speech microphone NS, some aspects of the present invention may be practiced in a system that does not include separate error and reference microphones, or a wireless telephone that uses near-speech microphone NS to perform the function of the reference microphone R. Also, in personal audio devices designed only for audio playback, near-speech microphone NS will generally not be included, and the near-speech signal paths in the circuits described in further detail below may be omitted, without changing the scope of the disclosure, other than to limit the options provided for input to the microphone covering detection schemes. In addition, although only one reference microphone R is depicted in
Referring now to
Combox 16 or another portion of headphone assembly 13 may have a near-speech microphone NS to capture near-end speech in addition to or in lieu of near-speech microphone NS of personal audio device 10. In addition, each headphone 18A, 18B may include a transducer such as speaker SPKR that reproduces distant speech received by personal audio device 10, along with other local audio events such as ringtones, stored audio program material, injection of near-end speech (i.e., the speech of the user of personal audio device 10) to provide a balanced conversational perception, and other audio that requires reproduction by personal audio device 10, such as sources from webpages or other network communications received by personal audio device 10 and audio indications such as a low battery indication and other system event notifications. Each headphone 18A, 18B may include a reference microphone R for measuring the ambient acoustic environment and an error microphone E for measuring of the ambient audio combined with the audio reproduced by speaker SPKR close to a listener's ear when such headphone 18A, 18B is engaged with the listener's ear. In some embodiments, CODEC IC 20 may receive the signals from reference microphone R, near-speech microphone NS, and error microphone E of each headphone and perform adaptive noise cancellation for each headphone as described herein. In other embodiments, a CODEC IC or another circuit may be present within headphone assembly 13, communicatively coupled to reference microphone R, near-speech microphone NS, and error microphone E, and configured to perform adaptive noise cancellation as described herein.
The various microphones referenced in this disclosure, including reference microphones, error microphones, and near-speech microphones, may comprise any system, device, or apparatus configured to convert sound incident at such microphone to an electrical signal that may be processed by a controller, and may include without limitation an electrostatic microphone, a condenser microphone, an electret microphone, an analog microelectromechanical systems (MEMS) microphone, a digital MEMS microphone, a piezoelectric microphone, a piezo-ceramic microphone, or dynamic microphone.
Referring now to
Referring now to
By transforming reference microphone signal ref with a copy of the estimate of the response of path S(z), response SECOPY(z) of filter 34B, and minimizing the difference between the resultant noise-modified reference microphone signal and the noise-modified playback corrected error based on error microphone signal err, adaptive filter 32 may adapt to the desired response of P(z)/S(z). The noise-modified playback corrected error signal compared to noise-modified reference microphone signal by W coefficient control block 31 may be derived from a playback corrected error (labeled as “PBCE” in
To implement the above, adaptive filter 34A may have coefficients controlled by SE coefficient control block 33, which may compare the source audio signal and the playback corrected error. SE coefficient control block 33 may correlate the actual source audio signal with the components of the source audio signal that are present in error microphone signal err. Adaptive filter 34A may thereby be adapted to generate a secondary estimate signal from the source audio signal, that when subtracted from error microphone signal err to generate the playback corrected error, includes the content of error microphone signal err that is not due to the source audio signal.
As mentioned above, ANC circuit 30A may inject a noise signal n(z) using a noise generator 37 that may be supplied to a copy WCOPY(z) of the response W(z) of adaptive filter 32 provided by an adaptive filter 32C. A combiner 36B may add noise signal n(z) to the output of adaptive filter 34B provided to W coefficient control 31. Noise signal n(z), as shaped by filter 32C, may be subtracted from the output of combiner 36 by a combiner 36C so that noise signal n(z) is asymmetrically added to the correlation inputs to W coefficient control 31, with the result that the response W(z) of adaptive filter 32 may be biased by the completely correlated injection of noise signal n(z) to each correlation input to W coefficient control 31. Because the injected noise appears directly at the reference input to W coefficient control 31, does not appear in error microphone signal err, and only appears at the other input to W coefficient control 31 via the combining of the filtered noise at the output of filter 32C by combiner 36C, W coefficient control 31 may adapt W(z) to attenuate the frequencies present in noise signal n(z). The content of noise signal n(z) may not appear in the anti-noise signal, only in the response W(z) of adaptive filter 32 which may have amplitude decreases at the frequencies/bands in which noise signal n(z) has energy. For example, if it is desirable to decrease the response of W(z) in the vicinity of 1 kHz, noise signal n(z) can be generated to have a spectrum that has energy at 1 kHz, which will cause W coefficient control 31 to decrease the gain of adaptive filter 32 at 1 kHz in an attempt to cancel an apparent source of ambient acoustic sound due to injected noise signal n(z).
Implementation of noise signal n(z), filter 32C, and W coefficient control 31 may require significant processing resources, especially if such elements are operated at the same bandwidth as response W(z) of filter 32, and thus, addition and processing of such injected noise may contribute significantly to expense of producing a personal audio device including such an ANC circuit 30A. Such processing complexity and related expense may be reduced by implementation of a decimator 38A which may decimate reference microphone signal ref prior to its combination with noise signal n(z) by combiner 36B. Similarly, decimator 38B may decimate the playback corrected error prior to its combination with the noise signal n(z) as filtered by filter 32C. Because of the presence of decimators 38A and 38B, each of a sample rate of filter 32C and a rate of adapting of adaptive filter 32 (as controlled by W coefficient control block 31) may be significantly less (e.g., at least one order of magnitude less) than a sample rate of the adaptive filter. For example, in some embodiments filter 32 may sample at a rate of 1.5 MHz while noise generator 37, W coefficient control block 31, and filter 32C may operate at 48 kHz.
Referring now to
Referring now to
This disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that a person having ordinary skill in the art would comprehend. Similarly, where appropriate, the appended claims encompass all changes, substitutions, variations, alterations, and modifications to the example embodiments herein that a person having ordinary skill in the art would comprehend. Moreover, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, or component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative.
All examples and conditional language recited herein are intended for pedagogical objects to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are construed as being without limitation to such specifically recited examples and conditions. Although embodiments of the present inventions have been described in detail, it should be understood that various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the disclosure.
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