EP3338279A1 - Feedback adaptive noise cancellation (anc) controller and method having a feedback response partially provided by a fixed-response filter - Google Patents
Feedback adaptive noise cancellation (anc) controller and method having a feedback response partially provided by a fixed-response filterInfo
- Publication number
- EP3338279A1 EP3338279A1 EP16763937.6A EP16763937A EP3338279A1 EP 3338279 A1 EP3338279 A1 EP 3338279A1 EP 16763937 A EP16763937 A EP 16763937A EP 3338279 A1 EP3338279 A1 EP 3338279A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- response
- filter
- anc
- variable
- secondary path
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
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- 230000003044 adaptive effect Effects 0.000 title claims abstract description 41
- 238000000034 method Methods 0.000 title claims description 30
- 238000012546 transfer Methods 0.000 claims abstract description 30
- 238000012545 processing Methods 0.000 claims description 23
- 230000000694 effects Effects 0.000 claims description 11
- 230000005534 acoustic noise Effects 0.000 claims description 8
- 230000005236 sound signal Effects 0.000 claims description 8
- 230000001419 dependent effect Effects 0.000 claims description 5
- 238000001914 filtration Methods 0.000 claims 2
- 238000013461 design Methods 0.000 abstract description 4
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Classifications
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
- G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
- G10K2210/10—Applications
- G10K2210/108—Communication systems, e.g. where useful sound is kept and noise is cancelled
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
- G10K2210/10—Applications
- G10K2210/108—Communication systems, e.g. where useful sound is kept and noise is cancelled
- G10K2210/1081—Earphones, e.g. for telephones, ear protectors or headsets
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
- G10K2210/30—Means
- G10K2210/301—Computational
- G10K2210/3017—Copy, i.e. whereby an estimated transfer function in one functional block is copied to another block
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
- G10K2210/30—Means
- G10K2210/301—Computational
- G10K2210/3026—Feedback
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
- G10K2210/30—Means
- G10K2210/301—Computational
- G10K2210/3027—Feedforward
Definitions
- the field of representative embodiments of this disclosure relates to methods and systems for adaptive noise cancellation (ANC), and in particular to an ANC feedback controller in which the feedback response is provided by a fixed transfer function feedback filter and a variable response filter.
- ANC adaptive noise cancellation
- Wireless telephones such as mobile/cellular telephones, cordless telephones, and other consumer audio devices, such as MP3 players, 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.
- An adaptive feedback noise cancelling system includes an adaptive filter that generates an anti-noise signal from an output of a sensor that senses the noise to be canceled and that is provided to an output transducer for reproduction to cancel the noise.
- the secondary path which is the electro-acoustic path at least extending from the output transducer that reproduces the anti- noise signal generated by the ANC system to the output signal provided by the input sensor that measures the ambient noise to be canceled, determines a portion of the necessary feedback response to provide proper noise-canceling.
- the secondary path response varies as well.
- the ANC controller includes a fixed filter having a predetermined fixed transfer function and a variable-response filter coupled together.
- the fixed transfer function relates to and maintains stability of a compensated feedback loop and contributes to an ANC gain of the ANC system.
- the response of the variable-response filter compensates for variation of a transfer function of a secondary path that includes at least a path from a transducer of the ANC system to a sensor of the ANC system, so that the ANC gain is independent of the variation of the transfer function of the secondary path.
- Figure 1A is an illustration of a wireless telephone 10, which is an example of a personal audio device in which the techniques disclosed herein can be implemented.
- Figure IB is an illustration of a wireless telephone 10 coupled to a pair of earbuds EBl and EB2, which is an example of a personal audio system in which the techniques disclosed herein can be implemented.
- Figure 2 is a block diagram of circuits within wireless telephone 10 and/or earbud EB of Figure 1A.
- Figure 3A is an illustration of electrical and acoustical signal paths in Figure 1 A and Figure IB including a feedback acoustic noise canceler.
- Figure 3B is an illustration of electrical and acoustical signal paths in Figure 1 A and Figure IB including a hybrid feed-forward/feedback acoustic noise canceler.
- Figures 4A-4D are block diagrams depicting various examples of ANC circuits that can be used to implement ANC circuit 30 of audio integrated circuits 20A-20B of Figure 2.
- Figures 5A-5F are graphs depicting acoustic and electric responses within the ANC systems disclosed herein.
- Figure 6 is a block diagram depicting a digital filter that can be used to implement fixed response filter 40 within the circuits depicted in Figures 4A-4D.
- Figure 7 is a block diagram depicting an alternative digital filter that can be used to implement fixed response filter 40 within the circuits depicted in Figures 4A-4D.
- Figure 8 is a block diagram depicting signal processing circuits and functional blocks that can be used to implement the circuits depicted in Figure 2 and Figures 4A-4D.
- the present disclosure encompasses noise canceling techniques and circuits that can be implemented in a personal audio device, such as a wireless telephone, tablet, note-book computer, noise-canceling headphones, as well as in other noise-canceling circuits.
- the personal audio device includes an ANC circuit that measures the ambient acoustic environment with a sensor and generates an anti-noise signal that is output via a speaker or other transducer to cancel ambient acoustic events.
- the example ANC circuits shown herein include a feedback filter and may include a feed-forward filter that are used to generate the anti-noise signal from the sensor output.
- a secondary path including the acoustic path from the transducer back to the sensor, closes a feedback loop around an ANC feedback path that extends through the feedback filter, and thus the stability of the feedback loop is dependent on the characteristics of the secondary path.
- the secondary path involves structures around and between the transducer and sensor, thus for devices such as a wireless telephone, the response of the secondary path varies with the user and the position of the device with respect to the user's ear(s).
- the instant disclosure uses a pair of filters, one having a fixed predetermined response and the other having a variable response that compensates for secondary path variations.
- the fixed predetermined response is selected to provide stability over the range of secondary path responses expected for the device, contributes to the acoustic noise cancellation and generally maximizes the range over which the acoustic noise cancelation operates.
- Illustrated wireless telephone 10 is shown in proximity to a human ear 5.
- Illustrated wireless telephone 10 is an example of a device in which techniques illustrated herein may be employed, but it is understood that not all of the elements or
- Wireless telephone 10 includes a transducer such as speaker SPKR that reproduces distant speech received by wireless telephone 10, along with other local audio events such as ringtones, stored audio program material, near-end speech (i.e., the speech of the user of wireless telephone 10), sources from web-pages or other network communications received by wireless telephone 10 and audio indications such as battery low and other system event notifications.
- a near-speech microphone NS is provided to capture near-end speech, which is transmitted from wireless telephone 10 to the other conversation participant(s).
- Wireless telephone 10 includes adaptive noise canceling (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 is positioned away from the typical position of a user's mouth, so that the near-end speech is minimized in the signal produced by reference microphone R.
- a third 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 wireless telephone 10 is in proximity to ear 5.
- a circuit 14 within wireless telephone 10 may include an audio CODEC integrated circuit 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 an RF integrated circuit 12 containing the wireless telephone transceiver.
- the circuits and techniques disclosed herein may be incorporated in a single integrated circuit that contains control circuits and other functionality for implementing the entirety of the personal audio device, such as an MP3 player-on-a-chip integrated circuit.
- the circuits and techniques disclosed herein may be implemented partially or fully in software and/or firmware embodied in computer-readable storage media and executable by a processor circuit or other processing device such as a microcontroller.
- the ANC techniques disclosed herein measure ambient acoustic events (as opposed to the output of speaker SPKR and/or the near-end speech) impinging on error microphone E and/or reference microphone R.
- the ANC processing circuits of illustrated wireless telephone 10 adapt an anti-noise signal generated from the output of error microphone E and/or reference microphone R to have a characteristic that minimizes the amplitude of the ambient acoustic events present at error microphone E. Since acoustic path P(z) extends from reference microphone R to error microphone E, the ANC circuits are effectively estimating acoustic path P(z) combined with removing effects of an electro-acoustic path S(z).
- Electro-acoustic path S(z) 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. Electro-acoustic path S(z) is affected by the proximity and structure of ear 5 and other physical objects and human head structures that may be in proximity to wireless telephone 10, when wireless telephone 10 is not firmly pressed to ear 5. While the illustrated wireless telephone 10 includes a two microphone ANC system with a third near-speech microphone NS, other systems that do not include separate error and reference microphones can implement the above-described techniques. Alternatively, near-speech
- microphone NS can be used to perform the function of the reference microphone R in the above- described system. 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 can be omitted without changing the scope of the disclosure. Also, the techniques disclosed herein can be applied in purely noise-canceling systems that do not reproduce a playback signal or conversation using the output transducer, i.e., those systems that only reproduce an anti-noise signal.
- FIG. IB shows wireless telephone 10 and a pair of earbuds EB1 and EB2, each attached to a corresponding ear of a listener.
- Illustrated wireless telephone 10 is an example of a device in which the techniques herein may be employed, but it is understood that not all of the elements or configurations illustrated in wireless telephone 10, or in the circuits depicted in subsequent illustrations, are required.
- Wireless telephone 10 is connected to earbuds EB1, EB2 by a wired or wireless connection, e.g., a BLUETOOTHTM connection (BLUETOOTH is a trademark of Bluetooth SIG, Inc.).
- Earbuds EB1, EB2 each have a corresponding transducer, such as speaker SPKRl, SPKR2, which reproduce source audio including distant speech received from wireless telephone 10, ringtones, stored audio program material, and injection of near-end speech (i.e., the speech of the user of wireless telephone 10).
- the source audio also includes any other audio that wireless telephone 10 is required to reproduce, such as source audio from web- pages or other network communications received by wireless telephone 10 and audio indications such as battery low and other system event notifications.
- Reference microphones Rl, R2 are provided on a surface of the housing of respective earbuds EB1, EB2 for measuring the ambient acoustic environment.
- wireless telephone 10 includes adaptive noise canceling (ANC) circuits and features that inject an anti-noise signal into speakers SPKRl, SPKR2 to improve intelligibility of the distant speech and other audio reproduced by speakers SPKRl, SPKR2.
- ANC adaptive noise canceling
- an ANC circuit within wireless telephone 10 receives the signals from reference microphones Rl, R2 and error microphones El, E2.
- all or a portion of the ANC circuits disclosed herein may be incorporated within earbuds EB1, EB2.
- each of earbuds EB1, EB2 may constitute a stand-alone acoustic noise canceler including a separate ANC circuit.
- Near-speech microphone NS may be provided on the outer surface of a housing of one of earbuds EBl, EB2, on a boom affixed to one of earbuds EBl, EB2, or on a combox pendant 7 located between wireless telephone 10 and either or both of earbuds EBl, EB2, as shown.
- the ANC techniques illustrated herein measure ambient acoustic events (as opposed to the output of speakers SPKR1, SPKR2 and/or the near-end speech) impinging on error microphones El, E2 and/or reference microphones Rl, R2.
- the ANC circuit in audio integrated circuit 20A is essentially estimating acoustic path Pi(z) combined with removing effects of an electro-acoustic path Si(z) that represents the response of the audio output circuits of audio integrated circuit 20A and the acoustic/electric transfer function of speaker SPKRl.
- the estimated response includes the coupling between speaker SPKRl and error microphone El in the particular acoustic environment which is affected by the proximity and structure of ear 5A and other physical objects and human head structures that may be in proximity to earbud EBl.
- audio integrated circuit 20B estimates acoustic path P 2 (z) combined with removing effects of an electro-acoustic path S 2 (z) that represents the response of the audio output circuits of audio integrated circuit 20B and the acoustic/electric transfer function of speaker SPKR2.
- headphone and “speaker” refer to any acoustic transducer intended to be mechanically held in place proximate to a user's ear canal and include, without limitation, earphones, earbuds, and other similar devices.
- earbuds” or “headphones” may refer to intra-concha earphones, supra-concha earphones and supra-aural earphones.
- transducer includes headphone or speaker type transducers, but also other vibration generators such as piezo-electric transducers, magnetic vibrators such as motors, and the like.
- sensor includes microphones, but also includes vibration sensors such as piezo-electric films, and the like.
- FIG. 2 shows a simplified schematic diagram of audio integrated circuits 20A, 20B that include ANC processing, as coupled to respective reference microphones Rl, R2, which provides measurements of ambient audio sounds that are filtered by the ANC processing circuits within audio integrated circuits 20A, 20B, located within corresponding earbuds EBl, EB2.
- reference microphone R may be omitted and the anti-noise signal generated entirely from error microphones El, E2.
- Audio integrated circuits 20A, 20B may be alternatively combined in a single integrated circuit, such as integrated circuit 20 within wireless telephone 10.
- the circuits disclosed in Figure 2 are applicable to wireless telephone 10 of Figure 1 A by omitting audio integrated circuit 20B, so that a single reference microphone input is provided for each of reference microphone R and error microphone E and a single output is provided for speaker SPKR.
- Audio integrated circuits 20A, 20B generate outputs for their corresponding channels that are provided to the corresponding one of speakers SPKRl, SPKR2.
- Audio integrated circuits 20A, 20B receive the signals (wired or wireless depending on the particular configuration) from reference microphones Rl, R2, near-speech microphone NS and error microphones El, E2.
- Audio integrated circuits 20A, 20B also interface with other integrated circuits such as RF integrated circuit 12 containing the wireless telephone transceiver shown in Figure 1 A. In other configurations, the circuits and techniques disclosed herein may be
- a single integrated circuit that contains control circuits and other functionality for implementing the entirety of the personal audio device, such as an MP3 player-on-a-chip integrated circuit.
- multiple integrated circuits may be used, for example, when a wireless connection is provided from each of earbuds EBl, EB2 to wireless telephone 10 and/or when some or all of the ANC processing is performed within earbuds EB1, EB2 or a module disposed along a cable connecting wireless telephone 10 to earbuds EB1, EB2.
- Audio integrated circuit 20 A includes an analog-to-digital converter (ADC) 21 A for receiving the reference microphone signal from reference microphone Rl (or reference microphone R in Figure 1 A) and generating a digital representation ref of the reference microphone signal. Audio integrated circuit 20A also includes an ADC 21B for receiving the error microphone signal from error microphone El (or error microphone E in Figure 1 A) and generating a digital representation err of the error microphone signal, and an ADC 21C for receiving the near-speech microphone signal from near-speech microphone NS and generating a digital representation of near-speech microphone signal ns.
- ADC analog-to-digital converter
- Audio integrated circuit 20B receives the digital representation of near-speech microphone signal ns from audio integrated circuit 20A via the wireless or wired connections as described above.
- Audio integrated circuit 20A generates an output for driving speaker SPKRl from amplifier Al, which amplifies the output of a digital-to-analog converter (DAC) 23 that receives the output of a combiner 26.
- DAC digital-to-analog converter
- Combiner 26 combines audio signals ia from internal audio sources 24, and the anti-noise signal anti-noise generated by an ANC circuit 30, which by convention has the same polarity as the noise in error microphone signal err and reference microphone signal ref and is therefore subtracted by combiner 26.
- Combiner 26 also combines an attenuated portion of near-speech signal ns, i.e., sidetone information st, so that the user of wireless telephone 10 hears their own voice in proper relation to downlink speech ds, which is received from a radio frequency (RF) integrated circuit 22.
- Near- speech signal ns is also provided to RF integrated circuit 22 and is transmitted as uplink speech to the service provider via an antenna ANT.
- FIG. 3A a simplified feedback ANC circuit is shown which applies in examples of the wireless telephone shown in Figure 1 A, and to each channel of the wireless telephone system shown in Figure IB.
- Ambient sounds Ambient travel along a primary path P(z) to error microphone E and are filtered by a feedback filter 38 to generate anti-noise provided through amplifier Al to speaker SPKR.
- Secondary path S(z) includes the electrical path from the output of feedback filter 38 to speaker SPKR combined with the acoustic path from the speaker SPKR through error microphone E to the input of feedback filter 38.
- the feedback gain G FB (Z) which determines the effectiveness of the acoustic noise canceling, is dependent on the response of secondary path S(z) and the transfer function H(z) of feedback filter 38.
- an ANC feedback controller must generally be designed using multiple models representing extreme values of the response of secondary path S(z) and H(z) must be conservatively designed in order to maintain a proper phase margin (i.e., the phase between the ambient sounds and the anti-noise reproduced by speaker SPKR at an upper frequency bound at which the G(z) falls to unity) and gain margin (i.e., the attenuation relative to unity of the ambient sounds and the anti-noise reproduced by speaker SPKR at one or more frequencies for which the phase between the ambient sounds and the anti-noise reaches zero, causing positive feedback).
- phase margin i.e., the phase between the ambient sounds and the anti-noise reproduced by speaker SPKR at an upper frequency bound at which the G(z) falls to unity
- gain margin i.e., the attenuation relative to unity of the ambient sounds and the anti-noise reproduced by speaker SPKR at one or more frequencies for which the phase between the ambient sounds and the anti-noise reaches zero
- phase margin/gain margin are necessary for stability of the feedback loop in an ANC system employing feedback, as the phase margin/gain margin are directly determinative of the recovery of the ANC system from a disturbance, such as high-amplitude noise, or noise that the ANC system cannot cancel.
- increasing the gain and phase margins typically requires lowering the upper limit of the frequency response of the feedback loop, reducing the ability of the ANC system to cancel ambient noise.
- a wide variation in the response of secondary path S(z) constrains any off-line design of the feedback controller such that the performance of the feedback cancelation is limited at higher frequencies.
- a wide variation in the response of secondary path S(z) is typical for wireless telephones, earbuds, and the other devices described above, which are used in or in proximity to a user's ear canal.
- FIG. 3B a simplified feed-forward/feedback ANC circuit is shown which alternatively applies to the wireless telephone shown in Figure 1 A, and to each channel of the wireless telephone system shown in Figure IB.
- the operation of the feed-forward/feedback ANC is similar to the pure feedback approach shown in Figure 3 A, except that the anti-noise signal provided to amplifier Al is generated by both the feedback filter 38 described above, and a feedforward filter 32, which generates a portion of the anti-noise signal from the output of reference microphone R.
- Combiner 36 combines the feed-forward anti-noise with the feedback anti-noise.
- FIG. 4A-4D details of various exemplary ANC circuits 20 that may be included within audio integrated circuits 20A, 20B of Figure 2, are shown in accordance with various embodiments of the disclosure.
- the above-described feedback filter 38 is implemented as a pair of filters.
- a first filter 40 has a fixed predetermined response that is related to and helps maintain stability of the compensated feedback loop and contributes to the ANC gain of the ANC system.
- the other filter is a variable-response filter 42, 42 A that compensates for the variations of at least a portion of the response of secondary path S(z).
- the result is that the feedback ANC gain G FB (Z) is rendered independent of the variations in the response of secondary path S(z).
- Figure 4A shows an ANC feedback filter 38A that receives the error microphone signal err from error microphone E, filters the error microphone signal with filter 42 having a response C(z), and filters the output of filter 42 with another filter 40 having a predetermined fixed response B(z).
- Response C(z) represents any filter response that helps stabilize the ANC system against variations in the response of secondary path S(z), and depending on other portions of the system response, may or may not be exactly equal to the inverse S (z) of the response of secondary path S(z).
- Figure 4B illustrates another ANC feedback filter 38B in which first filter 42A has a response SE " 1 z) that is an estimate of the inverse S _1 (z) of the response of secondary path S(z), and is controlled according to control signals from a secondary path estimator SE(z) control circuit.
- Figure 4C illustrates yet another ANC feedback filter 38C in which first filter 42B is an adaptive filter that estimates response S _1 (z) to generate inverse response SE (z) via off-line calibration.
- a playback signal PB (that is also reproduced by the output transducer) with delay z "D applied by delay 47 is correlated with error microphone signal err by a least-means- squared (LMS) coefficient controller 44, after the output of first filter 42B is subtracted from playback signal PB by a combiner 46.
- LMS least-means- squared
- the resulting adaptive filter obtains an estimate of the response of secondary path S(z) by directly measuring the effect of the response of secondary path S(z) on playback signal PB.
- switch SI is closed and the outputs of LMS coefficient controller 44 are held constant and converted to invert the response of adaptive filter 42A to yield response SE (z).
- Adaptive filter 42A operates as a fixed non-adaptive filter when on-line.
- Adaptive feed-forward filter 32 receives reference microphone signal ref and under ideal circumstances, adapts its transfer function W(z) to be some portion of P(z)/S(z) to generate the feed-forward anti-noise signal FF anti-noise, which is provided to output combiner 36 that combines feed-forward anti-noise signal FF anti-noise with a feedback anti-noise signal FB anti-noise generated by an ANC feedback filter 38D.
- ANC feedback filter 38D includes first filter 40 having fixed predetermined response B(z) and variable-response filter 42A that receives control inputs that cause the response of filter 42A to model inverse response SE " 1 z).
- the coefficients of feed-forward adaptive filter 32 are controlled by a W coefficient control block 31 that uses a correlation of two signals to determine the response of adaptive filter 32, which generally minimizes the error, in a least-mean squares sense, between those components of reference microphone signal ref present in error microphone signal err.
- the signals processed by W coefficient control block 31 are the reference microphone signal ref as shaped by a copy of an estimate of the response of path S(z) provided by a controllable filter 34B and another signal that includes error microphone signal err.
- adaptive filter 32 By transforming reference microphone signal ref with a copy of the estimate SE(z) of the response of secondary path S(z), response SECOPY(Z), and minimizing error microphone signal err after removing components of error microphone signal err due to playback of source audio, i.e., playback corrected error signal PBCE, adaptive filter 32 adapts to the desired portion of the response of P(z)/S(z).
- ANC circuit 30 includes controllable filter 34B having an SE coefficient control block 33 that provides control signals that set the response of adaptive filter 34A and controllable filter 34B to response SE(z).
- SE coefficient control block 33 also provides control signals to coefficient inversion block 37 that computes coefficients that set the response of variable response filter 42A to inverse response SE (z) from the coefficients that determine response SE(z).
- the other signal processed along with the output of controllable filter 34B by W coefficient control block 31 includes an inverted amount of the source audio including downlink audio signal ds and internal audio ia that has been processed by filter response SE(z), of which response SECO PY (Z) is a copy.
- adaptive filter 32 By injecting an inverted amount of source audio, adaptive filter 32 is prevented from adapting to the relatively large amount of source audio present in error microphone signal err and by transforming the inverted copy of downlink audio signal ds and internal audio ia with the estimate of the response of path S(z).
- the source audio that is removed from error microphone signal err before processing should match the expected version of downlink audio signal ds, and internal audio ia reproduced at error microphone signal err, since the electrical and acoustical path of S(z) is the path taken by downlink audio signal ds and internal audio ia to arrive at error microphone E.
- Filter 34B is not an adaptive filter, per se, but has an adjustable response that is tuned to match the response of adaptive filter 34A, so that the response of controllable filter 34B tracks the adapting of adaptive filter 34A.
- Adaptive filter 34A and SE coefficient control block 33 process the source audio (ds+ia) and error microphone signal err after removal, by combiner 36, of the above-described filtered downlink audio signal ds and internal audio ia, that has been filtered by adaptive filter 34A to represent the expected source audio delivered to error microphone E.
- the output of combiner 36 is further filtered by an alignment filter 35 having response 1+B(z) z "D to remove the effects of the feedback signal path on the source audio delivered to error microphone E.
- Alignment filter 35 is described in further detail in U.S. Patent Application Ser. No. 14/832,585 filed on August 21, 2015 entitled "HYBRID ADAPTIVE NOISE CANCELLATION SYSTEM WITH FILTERED
- Adaptive filter 34A is thereby adapted to generate a signal from downlink audio signal ds and internal audio ia, that when subtracted from error microphone signal err, contains the content of error microphone signal err that is not due to source audio (ds+ia).
- Figure 5A-5F graphs of amplitude and phase responses of portions of the ANC systems described above are shown.
- Figure 5A shows an amplitude response (top) and phase response (bottom) of secondary path S(z) for various users.
- the variation in the amplitude of the response of secondary path S(z) varies by lOdB or more in frequency regions of interest (typically 200Hz to 3KHz).
- Figure 5B shows a possible design amplitude response (top) and phase response (bottom) of filter 40 response B(z)
- Figure 5C shows the response of SE(z)SE (z) for a simulated ANC system in accordance with the above disclosure.
- Figure 5D shows a convolution of SE(z)SE (z), illustrating that the resulting response is a short delay, e.g., 3 taps of filter 42, 42A.
- Figure 5E shows the response B(z)C(z) of the adaptive controller in the simulated system, and
- Figure 5F shows the closed-loop response of the simulated system, showing that the gain variation for all users has been reduced to about 2dB across the entire illustrated frequency range.
- a filter circuit 40A that may be used to implement fixed filter 40 is shown.
- the input signal is weighted by coefficients a 1; a 2 and a by corresponding multipliers 55A, 55B and 55C and provided to respective combiners 56A, 56B, 56C at feed-forward taps of the filter stages, which comprise digital integrators 50A and 50B.
- a feedback tap is provided by a delay 53 and a multiplier 55D, providing the second-order low-pass response illustrated in Figure 5A.
- the resulting topology is a delta-sigma type filter.
- the response of fixed filter 40 may be a low-pass response, or a band-pass response.
- FIG. 7 an alternative filter circuit 40B that may be used to implement fixed filter 40 is shown.
- the input signal is weighted by coefficient ao by multiplier 65C and added to the output signal by combiner 66B to provide a feed-forward tap and the output of a first delay 62A is weighted by coefficient ao by another multiplier 65D and also combined with the output signal by combiner 66B.
- a second delay 62B provides a third input to combiner 66B.
- the input signal is combined with feedback signals provided from the output of first delay 62A and weighted by coefficient bi by a multiplier 65 A and from the output of second delay 62B and weighted by coefficient b 2 by a multiplier 65B.
- the resulting filter is a bi-quad that can be used to implement a low-pass or band-pass filter as described above.
- a processing circuit 140 includes a processor core 102 coupled to a memory 104 in which are stored program instructions comprising a computer program product that may implement some or all of the above-described ANC techniques, as well as other signal processing.
- a dedicated digital signal processing (DSP) logic 106 may be provided to implement a portion of, or alternatively all of, the ANC signal processing provided by processing circuit 140.
- Processing circuit 140 also includes ADCs 21A-21E, for receiving inputs from reference microphone Rl (or error microphone R), error microphone El (or error microphone E), near speech microphone NS, reference microphone R2, and error microphone E2, respectively.
- reference microphone Rl or error microphone R
- error microphone El or error microphone E
- near speech microphone NS reference microphone R2
- error microphone E2 have digital outputs or are communicated as digital signals from remote ADCs
- the corresponding ones of ADCs 21A-21E are omitted and the digital microphone signal(s) are interfaced directly to processing circuit 140.
- a DAC 23A and amplifier Al are also provided by processing circuit 140 for providing the speaker output signal to speaker SPKRl, including anti-noise as described above.
- a DAC 23B and amplifier A2 provide another speaker output signal to speaker SPKR2.
- the speaker output signals may be digital output signals for provision to modules that reproduce the digital output signals acoustically.
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- Soundproofing, Sound Blocking, And Sound Damping (AREA)
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PCT/IB2016/001234 WO2017029550A1 (en) | 2015-08-20 | 2016-08-19 | Feedback adaptive noise cancellation (anc) controller and method having a feedback response partially provided by a fixed-response filter |
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CN113140209A (en) * | 2021-04-23 | 2021-07-20 | 南京邮电大学 | Frequency domain active noise control method without secondary channel based on phase automatic compensation |
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CN109524021B (en) * | 2018-11-29 | 2022-01-11 | 上海交通大学 | Ultrasonic defense method and system based on active attack signal elimination strategy |
CN109545181A (en) * | 2018-12-13 | 2019-03-29 | 四川长虹电器股份有限公司 | A kind of adaptive digital active noise reduction framework |
CN111800687B (en) * | 2020-03-24 | 2022-04-12 | 深圳市豪恩声学股份有限公司 | Active noise reduction method and device, electronic equipment and storage medium |
CN112700788B (en) * | 2020-12-23 | 2024-05-03 | 普联国际有限公司 | Modeling method, device, equipment and storage medium of echo path in echo cancellation |
TWI802055B (en) * | 2021-10-22 | 2023-05-11 | 達發科技股份有限公司 | Active noise cancellation integrated circuit for stacking multiple anti-noise signals, associated method, and active noise cancellation earbud using the same |
CN116017222A (en) | 2021-10-22 | 2023-04-25 | 达发科技股份有限公司 | Active noise reduction integrated circuit, active noise reduction integrated circuit method and active noise reduction earphone using active noise reduction integrated circuit |
CN113870824A (en) * | 2021-11-03 | 2021-12-31 | 国网北京市电力公司 | Silent container |
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EP1793374A1 (en) * | 2005-12-02 | 2007-06-06 | Nederlandse Organisatie voor Toegepast-Natuuurwetenschappelijk Onderzoek TNO | A filter apparatus for actively reducing noise |
FR2913521B1 (en) * | 2007-03-09 | 2009-06-12 | Sas Rns Engineering | METHOD FOR ACTIVE REDUCTION OF SOUND NUISANCE. |
GB0725111D0 (en) * | 2007-12-21 | 2008-01-30 | Wolfson Microelectronics Plc | Lower rate emulation |
GB0725115D0 (en) * | 2007-12-21 | 2008-01-30 | Wolfson Microelectronics Plc | Split filter |
JP5241921B2 (en) * | 2008-07-29 | 2013-07-17 | ドルビー ラボラトリーズ ライセンシング コーポレイション | Methods for adaptive control and equalization of electroacoustic channels. |
RU2545384C2 (en) * | 2008-12-18 | 2015-03-27 | Конинклейке Филипс Электроникс Н.В. | Active suppression of audio noise |
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EP2584558B1 (en) * | 2011-10-21 | 2022-06-15 | Harman Becker Automotive Systems GmbH | Active noise reduction |
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EP2629289B1 (en) * | 2012-02-15 | 2022-06-15 | Harman Becker Automotive Systems GmbH | Feedback active noise control system with a long secondary path |
US9462376B2 (en) * | 2013-04-16 | 2016-10-04 | Cirrus Logic, Inc. | Systems and methods for hybrid adaptive noise cancellation |
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