EP2816818B1 - Sound field spatial stabilizer with echo spectral coherence compensation - Google Patents
Sound field spatial stabilizer with echo spectral coherence compensation Download PDFInfo
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- EP2816818B1 EP2816818B1 EP13173053.3A EP13173053A EP2816818B1 EP 2816818 B1 EP2816818 B1 EP 2816818B1 EP 13173053 A EP13173053 A EP 13173053A EP 2816818 B1 EP2816818 B1 EP 2816818B1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R3/00—Circuits for transducers, loudspeakers or microphones
- H04R3/005—Circuits for transducers, loudspeakers or microphones for combining the signals of two or more microphones
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R2410/00—Microphones
- H04R2410/05—Noise reduction with a separate noise microphone
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R2410/00—Microphones
- H04R2410/07—Mechanical or electrical reduction of wind noise generated by wind passing a microphone
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R2499/00—Aspects covered by H04R or H04S not otherwise provided for in their subgroups
- H04R2499/10—General applications
- H04R2499/11—Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R2499/00—Aspects covered by H04R or H04S not otherwise provided for in their subgroups
- H04R2499/10—General applications
- H04R2499/13—Acoustic transducers and sound field adaptation in vehicles
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R3/00—Circuits for transducers, loudspeakers or microphones
- H04R3/02—Circuits for transducers, loudspeakers or microphones for preventing acoustic reaction, i.e. acoustic oscillatory feedback
Description
- This disclosure refers to:
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U.S. Patent Application Serial No. 13/753,198 -
U.S. Patent Application Serial No. 13/753,198 - The present disclosure relates to the field of processing sound fields. In particular, to a system and method for maintaining the spatial stability of a sound field.
- Stereo and multichannel microphone configurations may be used for processing a sound field that is a spatial representation of an audible environment associated with the microphones. The audio received from the microphones may be used to reproduce the sound field using audio transducers.
- Many computing devices may have multiple integrated microphones used for recording an audible environment associated with the computing device and communicating with other users. Some computing devices use multiple microphones to improve noise performance with noise suppression processes. The noise suppression processes may result in the reduction or loss of spatial information. In many cases the noise suppression processing may result in a single, or mono, output signal that has no spatial information.
- The system may be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the disclosure. Moreover, in the figures, like referenced numerals designate corresponding parts throughout the different views.
- Other systems, methods, features and advantages will be, or will become, apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included with this description, be within the scope of the invention, and be protected by the following claims.
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Fig. 1 is a schematic representation of a system for maintaining the spatial stability of a sound field. -
Fig. 2 is a further schematic representation of a system for maintaining the spatial stability of the sound field. -
Fig. 3 is a schematic representation of another system for maintaining the spatial stability of a sound field when reproduced in an output sound field. -
Fig. 4 is a further schematic representation of a system for maintaining the spatial stability of the sound field. -
Fig. 5 is a further schematic representation of a system for maintaining the spatial stability of the sound field. -
Fig. 6 is a representation of a method for maintaining the spatial stability of the sound field. -
Fig. 7 is a further schematic representation of a system for maintaining the spatial stability of the sound field. -
Fig. 8 is a representation of a method for maintaining the spatial stability of the sound field. -
Fig. 9 is a further schematic representation of a system for maintaining the spatial stability of the sound field. -
Fig. 10 is a representation of a method for maintaining the spatial stability of the sound field. -
Fig. 11 is a further schematic representation of a system for maintaining the spatial stability of the sound field. -
EP 2426950 A2 discloses noise suppression for sending voice with binaural microphones. -
US 2007/0258579 A1 discloses a multi-channel echo cancel method, a multi-channel sound transfer method, a stereo echo canceller, a stereo sound transfer apparatus and a transfer function calculation apparatus. - In a system and method for maintaining the spatial stability of a sound field balance gains may be calculated for each of two or more microphone signals. The balance gain may be associated with a spatial image in the sound field. One or more signal values may be calculated for each of the two or more microphone signals. The signal values may be the background noise estimate or signal gains associated with echo cancellation and noise reduction processes. Structured noise content may be detected for each of the two or more microphone signals. The structured noise content may be for example, impulse noise or tonal noise. A first microphone signal of the two or more microphone signals may be mixed with a second microphone signal of the two or more microphone signals responsive to the detected structured noise. Increasing amounts of detected structured noise may increase the amount of mixing, or blending, of the first microphone signal with the second microphone signal. The gain may be adjusted for the two or more microphone signals, including the mixed first microphone signal and second microphone signal, responsive to the calculated balance gains and the one or more signal values for each of the two or more microphone signals.
- In a system and method for maintaining the spatial stability of a sound field balance gains may be calculated for each of two or more microphone signals. The balance gain may be associated with a spatial image in the sound field. One or more signal values may be calculated for each of the two or more microphone signals. The signal values may be the background noise estimate or signal gains associated with echo cancellation and noise reduction processes. A pair-wise spectral coherence may be calculated between each of the two or more microphone signals. The pair-wise spectral coherence may indicate that two or more microphone signals are correlated and may have captured a signal of interest. The two or more microphone signals may be gain adjusted responsive to the calculated balance gains, the one or more signal values, and the pair-wise spectral coherence for each of the two or more microphone signals. The spectral coherence value may be used to prevent high amplitude high frequencies signals from being unnecessarily attenuated and may also be used to increase the gain of low amplitude high frequency signals.
- In a system and method for maintaining the spatial stability of a sound field balance gains may be calculated for each of two or more microphone signals. The balance gain may be associated with a spatial image in the sound field. One or more signal values may be calculated for each of the two or more microphone signals. The signal values may be the background noise estimate or signal gains associated with echo cancellation and noise reduction processes. A predicted echo may be calculated for a received audio signal. The predicted echo may be used to reduce an echo signal. A pair-wise echo spectral coherence may be calculated between the predicted echo and the two or more microphone signals. The pair-wise echo spectral coherence may indicate that the predicted echo is correlated to one or more of the captured two or more microphone signals. A pair-wise spectral coherence between each of the two or more microphone signals. The pair-wise spectral coherence may indicate that two or more microphone signals are correlated and may have captured a signal of interest. The two or more microphone signals may be gain adjusted responsive to the calculated balance gains, the one or more signal values, the echo spectral coherence and the pair-wise spectral coherence for each of the two or more microphone signals. Using both of the echo spectral coherence and the spectral coherence values in order to adjust the signal gains may reduce the noise artifacts, preserve and enhance the signal of interest, and reduce the echo.
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Figure 1 is a schematic representation of a system for maintaining the spatial stability of asound field 100. Two ormore microphones 102 receive the sound field. Stereo and multichannel microphone configurations may be utilized for processing the sound field that is a spatial representation of an audible environment associated with themicrophones 102. Many audible environments associated with themicrophones 102 may include undesirable content that may be mitigated by processing the received sound field.Microphones 102 that are arranged in a far field configuration may receive more undesirable content, noise, thanmicrophones 102 in a near field configuration. Far field configurations may include, for example, a hands free phone, a conference phone and microphones embedded into an automobile. Far field configurations are capable of receiving a sound field that represents the spatial environment associated with themicrophones 102. Near field configurations may place themicrophone 102 in close proximity to a user. Undesirable content may be mitigated in both near and far field configurations by processing the received sound field. - Processing that may mitigate undesirable content received in the sound field may include echo cancellation and noise reduction processes. Echo cancellation, noise reduction and other audio processing processes may calculate one or more suppression, or signal, gains utilizing a
suppression gain calculator 106. An echo cancellation process and a noise reduction process may each calculate one or more signal gains. Each respective signal gains may be applied individually or a composite signal gain may be applied to process the sound field using again filter 114. Echo cancellation processing mitigates echoes caused by signal feedback between two or more communication devices. Signal feedback occurs when an audio transducer on a first communication device reproduces the signal received from a second communication device and subsequently the microphones on the first communication device recapture the reproduced signal. The recaptured signal may be transmitted to the second communication device where the recaptured signal may be perceived as an echo of the previously transmitted signal. Echo cancellation processes may detect when the signal has been recaptured and attempt to suppress the recaptured signal. Many different echo cancellation processes may mitigate echoes by calculating one or more signal gains that, when applied to the signals received by themicrophones 102, suppress the echoes. In one example implementation, the echo suppression gain may be calculated using coherence calculation between the predicted echo and the microphone disclosed inU.S. Patent No. 8,036, 879 . - When the
microphone 102 and an audio transducer are close in proximity, the echo cancellation process may determine that a large amount of suppression, or calculate large signal gains, as a result of the signal produced by the audio transducer dominating, or coupling with, themicrophone 102. - When one of the
microphones 102 and an audio transducer are in close proximity, the echo cancellation process may determine that a large amount of suppression may mitigate the signal produced by the audio transducer from dominating or coupling with, themicrophone 102. The echo cancellation process may calculate large signal gains to mitigate the coupling. The large signal gains may result in a gating effect where the communication device effectively supports only half duplex communication. Half duplex communication may occur when the communication channel allows for reliable communication from alternatively either the far side or near side but not both simultaneously. The large signal gains may suppress the coupling but may also suppress all content, including desired voice content resulting in half duplex communication. - Background noise is another type of undesirable signal content that may be mitigated by processing the received sound field. Many different types of noise reduction processing techniques may mitigate background noise. An exemplary noise reduction method is a recursive Wiener filter. The Wiener suppression gain Gi,k , or signal gain, is defined as
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- Here |N̂ i,k | is a background noise estimate. In one example implementation, the background noise estimate, or signal values, may be calculated using the background noise estimation techniques disclosed in
U.S. Patent No. 7,844,453 . In other implementations, alternative background noise estimation techniques may be used, such as, for example, a noise power estimation technique based on minimum statistics. - Additional noise reduction processing may mitigate specific types of undesirable noise characteristics including, for example, wind noise, transient noise, rain noise and engine noise. Mitigation of some specific types of undesirable noise may be referred to as signature noise reduction processes. Signature noise reduction processes detect signature noise and generate signal gains that may be used to suppress a detected signature noise. In one implementation, wind noise suppression gains (a.k.a. signal gains) may be calculated using the system for suppressing wind noise disclosed in
U.S. Patent No. 7,885 ,420 . - The sound field received by the two or
more microphones 102 may contain a spatial representation, or a spatial image, of an audible environment. Balance gains may be calculated responsive to the spatial image in the sound field. The balance gains may be calculated with abalance calculator 108. Thebalance calculator 108 may calculate the balance gains by measuring an energy level in a signal from eachmicrophone 102. The energy level differences may represent the approximate balance of the spatial image. One or more energy levels may be calculated for eachmicrophone 102 generating one or more balance gains. A single balance gain may be utilized in a two microphone configuration where the single balance gain may be the ratio of energy levels between the two microphone signals 118. - A subband filter may process the received
microphone signal 118 to extract frequency information. The subband filter may be accomplished by various methods, such as a Fast Fourier Transform (FFT), critical filter bank, octave filter band, or one-third octave filter bank. Alternatively, the subband analysis may include a time-based filter bank. The time-based filter bank may be composed of a bank of overlapping bandpass filters, where the center frequencies have non-linear spacing such as octave, 3rd octave, bark, mel, or other spacing techniques. The one or more energy levels may be calculated for each frequency bin or band of the subband filter. The resulting balance gains may be filtered, or smoothed, over time and/or frequency. Thebalance calculator 108 may update the balance gains responsive to desired signal content. For example, the balance gains may be updated when, for example, the energy level exceeds a threshold, the signal to noise ratio (SNR) exceeds a threshold, a voice activity detector detects voice content or any combination thereof. - The
background noise estimator 104 may calculate a background noise estimate, or signal value, for eachmicrophone signal 118. When themicrophones 102 are spaced apart, thebackground noise estimator 104 may calculate different signal values responsive to the received sound value. Some difference in the calculated background noise estimate may be acceptable but relatively large differences may indicate a potential corruption or misrepresentation of one or more of the signals. For example, a user may be blocking onemicrophone 102 with a finger resulting in a relatively large difference in the background noise estimate. The background noise estimate may be utilized for many subsequent calculations including signal-to-noise ratios, echo cancellers and noise reduction calculators. When the subsequent calculations utilize background noise estimates that contain relatively large differences the subsequent calculations may yield corrupted or misrepresentative results. For example, large differences in suppression gains betweenmicrophones 102 may result in audible distortions in the spatial image of the sound field. - A
difference limiter 110 may limit the difference in the background noise estimates, or signal values, and/or the adaption rates utilized in thebackground noise estimator 104. Thedifferent limiter 110 may mitigate audio distortions in the spatial image when reproduced in the output sound field. For example, a difference between corresponding signal values in the calculated background noise estimates may be acceptable when the difference is about 2 dB (decibels) to about 4 dB but noticeable when the difference exceeds about 6 dB. Thedifference limiter 110 may, for example, limit the difference between signal values to about 6 dB or may allow a difference proportional to the signal value when the difference is greater than about 6 dB. Thedifference limiter 110 may utilize a coherence and/or correlation calculation between microphones to limit a difference between the signal values. Two signals that are correlated may indicate that the difference between signal values should be limited. Thedifference limiter 110 may smooth, or filter, the amount of limiting over time and frequency. - The
difference limiter 110 may be applied to other signal values including suppression gains, or signal gains, calculated using thesuppression gain calculator 106. Thesuppression gain calculator 106 may calculate signal gains for the echo cancellation and noise reduction processes described above. Signature noise reduction processes may calculate signal gains that have large differences between microphone signals 118. For example, in the case of wind noise reduction, afirst microphone 102 may receive significant wind noise and thesecond microphone 102 may receive negligible wind noise. An example portable computing device may have twomicrophones 102 placed several inches apart where thefirst microphone 102 may be located on the bottom surface and thesecond microphone 102 may be located on the top surface. Thefirst microphone 102 and thesecond microphone 102 may be relatively close in position although they may not be close enough to process phase differences to utilize, for example, a beam forming combining process. Even though themicrophones 102 are relatively close in position on the example portable computing device, onemicrophone 102 may receive significant wind noise. Thesuppression gain calculator 106 may calculate signal gains that may contain relatively large differences. Thedifference limiter 110 may allow some of the wind noise to be suppressed while mitigating audio distortions in the spatial image of the sound field. For example, a difference between corresponding signal gains generated by thesuppression gain calculators 106 may be acceptable when the difference is about 2 dB to 4 dB but noticeable when the difference exceeds about 6 dB. Thedifference limiter 110 may limit the difference between signal values to about 6 dB or may allow a difference proportional to the signal value when the difference is greater than 6 dB. Thedifference limiter 110 may smooth, or filter, the amount of limiting over time and frequency. - The
difference limiter 110 may mitigate some distortion in the spatial image when reproduced in the output sound field although it may be possible that the combination of one or more of the signal values calculated utilizing thebackground noise estimator 104 andsuppression gain calculator 106 may still distort the spatial image. Additionally, in some cases thesuppression gain calculator 106 may not utilize thedifference limiter 110. For example, when themicrophone 102 and audio transducer are coupled as described above resulting in a gating effect, thedifference limiter 110 may not be utilized because the audible artifacts associated with the coupling are perceptibly more distracting than distorting the spatial image. In this case, the echo cancellation process may be allowed to gate themicrophone signal 118 without applying thedifference limiter 110. - A
balance adjuster 112 may maintain the spatial stability when reproduced in the output sound field. Thebalance adjuster 112 may mitigate distortions in the spatial image that may not be mitigated with thedifference limiter 110. Additionally, thebalance adjuster 112 may mitigate audio distortions in the spatial image where thedifference limiter 110 may not be applied. Thebalance adjuster 112 may adjust the signal gains using the balance gains calculated with thebalance calculator 108 and the signal gains. The balance gains may represent the approximate balance of the spatial image. Thebalance adjuster 112 may adjust the signal gains responsive to the balance gains. Additionally, thebalance adjuster 112 may mix, or borrow, between two or more microphone signals 118 to maintain the spatial stability and to more closely track the balance gains. In one example, the echo-gating triggered half-duplex use case described above may have afirst microphone signal 118 that may be gated. Thebalance adjuster 112 may mitigate audio distortions in the spatial image by borrowing audio from asecond microphone signal 118 responsive to the balance gain. Thesecond microphone signal 118 may have associated signal gains that may be adjusted responsive to the balance gain. Thesecond microphone signal 118 that is borrowed may be mixed into thefirst microphone signal 118. Thebalance adjuster 112 may adjust the signal gains and the borrowing of microphone signals 118 may be filtered, or smoothed, over time and frequency. The adjustments may be performed on a frequency bin and/or band using the subband filter described above. - A
gain filter 114 applies the signal gains to the two or more microphone signals 118. The signal gains may be a combination of signal gains associated with one or moresuppression gain calculators 106. Thegain filter 114 may utilize the subband filter described above. -
Figure 2 is a schematic representation of a further system for maintaining the spatial stability of a sound field when reproduced in an output sound field. The system ofFigure 2 may provide the same or similar functionality as the system described with reference toFigure 1 .Figure 2 does not show themicrophones 102 and thebackground noise estimator 104 but they may be included in thesystem 200. Thesystem 100 inFigure 1 may be able to reduce common audio noise artifacts such as wind noise when two ormore microphones 102 capture a similar voice of interest. One of themicrophones 102 may capture more of the example wind noise thanother microphones 102. The gain of a higheramplitude microphone signal 118 may be brought down, or reduced, to a loweramplitude microphone signal 118, on a frequency bin-by-frequency bin basis, and to the extent to which the microphone signals 118 are "unbalanced". Small differences between microphone signals 118 may be normal so no adjustment is made. A large difference may not be normal and may result in a maximum amount of gain reduction on the higheramplitude microphone signal 118. - The
system 200 adds processing components relative to thesystem 100 where gain reduction alone may not be able to remove the noise artifacts. Some noise artifacts, including impulses and tonal noises, may still be audible even after the gain has been reduced on the higheramplitude microphone signal 118. These types of noise artifacts, or structured noise, may have all the information stored in their phase. For example, an impulse has energy at all frequencies, and the phase at all frequencies is aligned so that the energy is delivered at one point in a time-series train. Reducing the gain of amicrophone signal 118 containing an impulse may only result in making the impulse quieter. Thesystem 200 includes achannel mixer 204 to blend the higheramplitude microphone signal 118 with the loweramplitude microphone signal 118, responsive to the amount of structured noise in the higheramplitude microphone signal 118. A maximum reduction of the highamplitude microphone signal 118 may take the form of a full copy of the lowamplitude microphone signal 118. The blending, or mixing, may be performed on a frequency bin-by-frequency bin basis so that when the higheramplitude microphone signal 118 contains tonal noise, and therefore may be confined to one or two frequency bins, only those frequency bins are affected. Blending the higheramplitude microphone signal 118 with the loweramplitude microphone signal 118 may reduce structured noises that occur during voice content with minimal impact to the voice content. - A structured
noise detector 202 detects structured noise artifacts, including impulse noise and tonal noise, in two or more microphone signals 118. In one implementation, transient noise may be detected using the system for repetitive transient noise removal disclosed inU.S. Patent No. 8,073,689 , which is incorporated herein by reference, except that in the event of any inconsistent disclosure or definition from the present specification, the disclosure or definition herein shall be deemed to prevail. In one implementation, tonal noise may be detected using the system for noise reduction with integrated tonal noise reduction disclosed inU.S. Publication No. 2008/0167870 . Alternatively, the structurednoise detector 202 may indicate noise content when the amplitude of afirst microphone signal 118 exceeds a threshold when compared to the amplitude of asecond microphone signal 118. Thechannel mixer 204 may be responsive to the outputs of the structurednoise detectors 202 to blend the higheramplitude microphone signal 118 with the loweramplitude microphone signal 118, responsive to the amount of structured noise in the higher amplitude microphone signal 118.An increasing amount of structured noise detected in the structurednoise detector 202 may blend more of the loweramplitude microphone signal 118 with the higheramplitude microphone signal 118. Athird microphone signal 118 with higher amplitude may blend more of the loweramplitude microphone signal 118 or a combination of lower amplitude microphone signals 118. A maximum reduction of the highamplitude microphone signal 118 may take the form of a full copy of the lowamplitude microphone signal 118. For example, when the highamplitude microphone signal 118 contains a strong impulse detected by the structurednoise detector 202, the channel mixer may copy the contents of the loweramplitude microphone signal 118 to the highamplitude microphone signal 118. Thechannel mixer 204 may adjust the gain of the blendedmicrophone signal 118 responsive to, for example, matching a filtered, or smoothed, energy level over time. - A
gain adjuster 206 may adjust the signal gains 208 using the balance gains 210 calculated with thebalance calculator 108 and the signal gains 208. Thegain adjuster 206 may perform similarly to thebalance adjuster 112 described above inFigure 1 . The adjustedsignal gains 208 are applied to each of the blended two or more microphone signal 118 using thegain filter 114. The signal gains 208 may be a combination ofsignal gains 208 associated with one or moresuppression gain calculators 106. Thegain filter 114 may utilize the subband filter described above. -
Figure 3 is a schematic representation of another system for maintaining the spatial stability of a sound field when reproduced in an output sound field. The system ofFigure 3 may provide the same or similar functionality as the systems described with reference toFigure 1 andFigure 2 .Figure 3 does not show themicrophones 102, thebackground noise estimator 104, the structurednoise detector 202, thechannel mixer 204 and thegain adjuster 206 but they may be included in thesystem 300. Thesystem 300 may include acoherence calculator 302 that calculates a pair-wise spectral coherence between two or more microphone signals 118. In the case of twomicrophone signals 118 including a left and aright microphone signal 118 the spectral coherence may be referred to as CohLR. In one implementation, the spectral coherence CohLR may be calculated in a similar fashion to that of CohDY using the system for noise estimation control disclosed inU.S. Patent Application Serial No. 13/753, 162 . The result of the spectral coherence calculation may be used to prevent high frequencies signals from being unnecessarily attenuated. When twomicrophones 102 are asymmetrically located (e.g., top edge and front face of a computing device) there may be audio content that while perpendicular to the computing device may be perceived as off-axis. The off-axis perception may be due to the acoustic shadowing from the body of the computing device. For example, when a user is speaking straight into a mobile phone, the front-facing microphone may capture the audio well, but the microphone on the top edge may not capture the high frequencies as well because they are more likely to be blocked by the body of the mobile phone. The resulting signals captured by the asymmetrically located microphones may comprise lower frequencies that are nearly equal and higher frequencies that may be attenuated in thetop edge microphone 102 signal relative to thefront facing microphone 102 signal.Other microphone 102 arrangements and angles of incidence may further exaggerate the effect of attenuated high frequencies. - The structured
noise detector 202 andchannel mixer 204 described with reference toFigure 2 may detect amplitude differences in the high frequency components of the respective microphone signals 118 as artifacts and reduce the gain of high frequency components resulting in a slightly muffled sound. Reducing the gain, or suppressing, of the high frequency components may result in good noise rejection at the expense of lower fidelity. When bothmicrophones 102 capture the voice, or signal of interest, the CohLR measurement may indicate that the microphone signals 118 may be correlated and that the amplitude differences may not be artifacts to be suppressed. In fact, the correlation may indicate that the high frequencies should be preserved. - The
coherence calculator 302 may calculate a CohLR number, or value, that ranges from about 0 to about 1. A calculated CohLR value of one may indicate that even if the amplitude is 20 dB higher on onemicrophone signal 118 than on asecond microphone signal 118, that themicrophones 102 have captured a common signal of interest and the amplitude difference is not an artifact to be reduced or suppressed. When thecoherence calculator 302 calculates a CohLR value less than one, some gain reduction may occur above a threshold. Below a threshold, the CohLR may have no effect on the calculated signal gains 208. Acoherence gain adjuster 304 may adjust the signal gains 208 using the balance gains 210 calculated with thebalance calculator 108, the signal gains 208 and the CohLR calculated by thecoherence calculator 302. Thecoherence gain adjuster 304 may perform similarly to thebalance adjuster 112 described above inFigure 1 . The adjustedsignal gains 208 are applied to each of the two or more microphone signal 118 using the gain filters 114. The signal gains 208 may be a combination ofsignal gains 208 associated with one or moresuppression gain calculators 106. The gain filters 114 may utilize the subband filter described above. Adjusting the signal gains 208 may prevent the high frequency components from being unnecessarily reduced thereby preserving the fidelity of the output sound field. - Further processing of the CohLR value may improve the fidelity. For example, the CohLR may be calculated for a given frequency bin as the coherence between the left signal and the right signal across three frequency bins surrounding, and including, the given frequency bin (i.e. bin +/- 1). The calculated CohLR value, for example, may be almost 1 for a
microphone signal 118 that contains a harmonics. The CohLR may be variable between about 0 and about 0.85 for noisy signals that may not be useful to determine if two signals are correlated. The limited range may be rescaled from 0.85 and 1 to between 0 and 1. Raising the rescaled range to the power of 4 may emphasize the desired content of highly correlated signals at a particular frequency. Applying additional psychoacoustic-based frequency and temporal smoothing may improve the fidelity further. The psychoacoustic-based smoothing may ignore frequency and temporal components that the human ear may not perceive. -
Figure 4 is a schematic representation of yet another system for maintaining the spatial stability of a sound field when reproduced in an output sound field.Figure 4 shows asystem 400 that adds asignal mixer 402 to thesystem 300. Thesignal mixer 402 may combine two ormore output signals 116 into a singlemixed output signal 404. Thesignal mixer 402 may average the output signals 116 together or thesignal mixer 402 may applied a weighted average to combine the output signals 116. Thesystem 400 may output any combination ofoutput signals 116 and mixed output signals 404. For example, thesystem 400 may produce oneoutput signal 116 and onemixed output signal 404 resulting in a two-signal output that comprises the output sound field. Thesystem 300 utilizes thecoherence calculator 302 to preserve the fidelity, or high frequency content, of the higheramplitude microphone signal 118. The CohLR value calculated by thecoherence calculator 302 may also be used to increase the gain of the loweramplitude microphone signal 118 when the spectral coherence is relatively high. Normalizing the amplitude of the two or more microphone signals 118 may allow beam forming of two or more microphone signals 118 to be based on time differences and not amplitude differences. Any signal content that is highly correlated across the twomicrophones signals 118 may be enhanced, and any signal content that is not well correlated is either not enhanced or may be significantly reduced. Thesignal mixer 402 may perform beam forming in addition to combining two ormore output signals 116 together. -
Figure 5 is a schematic representation of a still further system for maintaining the spatial stability of a sound field when reproduced in the output sound field. The system ofFigure 5 may provide the same or similar functionality as the systems described with reference toFigure 1 ,Figure 2 andFigure 3 .Figure 5 does not show thebackground noise estimator 104, the structurednoise detector 202, thechannel mixer 204, thegain adjuster 206 and thecoherence gain adjuster 304 but they may be included in thesystem 500. Thesystems more microphones 102. Thesystem 500 includes areceiver 502 that may receive an audio signal representing, for example, a far side conversation. The received audio signal content, for example the far side conversation, may be reproduced using anaudio transducer 504 that may be within range to be captured by two ormore microphones 102. A system such as, for example,system 300 may enhance the captured far side conversation instead of suppressing the recaptured audio, or echo. The correlated recaptured audio, or echo, using two ormore microphones 102 may not be suppressed because thecoherence calculator 302 may indicate that the recaptured audio may be a signal of interest resulting in enhancement of the undesirable echo. - The
receiver 502 may receive a far side audio signal from another computing device or other similar audio source. Thereceiver 502 may be connected to a wireless or wired network. The far side audio signal may be reproduced using theaudio transducer 504. Themicrophones 102 may recapture the far side audio signal reproduced using theaudio transducer 504. The recaptured far side audio signal may be perceived as an echo. When the echo is correlated on any two or more of the microphones thecoherence calculator 302 may indicate that the echo is a signal of interest that may result in the echo being enhanced. The echo may be considered an undesirable signal component to be removed. Anecho filter 506 may calculate a predicted echo (D) 508 that when applied to the microphone signals 118 may reduce the echo. In one implementation, echo noise may be reduced using the system for fast echo cancellation disclosed inU.S. Patent No. 8,036,879 , which is incorporated herein by reference, except that in the event of any inconsistent disclosure or definition from the present specification, the disclosure or definition herein shall be deemed to prevail. Theecho filter 506 and thecoherence calculator 302 may indicate opposite gain values to be applied to the microphone signal 118 (Y) where theecho filter 506 may indicate that the gain should be reduced and thecoherence calculator 302 may indicate that the gain should be increased. In some cases, the echo may be enhanced. Acoherence echo calculator 510 may calculate a pair-wise spectral coherence, or a pair-wise echo spectral coherence, CohDY that may be used as an indicator of a correlation between the predicted echo (D) and the observed microphone signal (Y). Thecoherence echo calculator 510 may receive both the predicted echo (D) 508 and themicrophone signal 118. A strong correlation between the predicted echo (D) 506 and the microphone signal 118 (Y) may indicate that the higheramplitude microphone signal 118 should not be preserved and the loweramplitude microphone signal 118 should not be increased. - A coherence
echo gain adjuster 512 may adjust the signal gains 208 using the balance gains 210, the signal gains 208, the CohLR and the CohDY calculated by thecoherence echo calculator 510. The coherenceecho gain adjuster 512 may perform similarly to thebalance adjuster 112 described above with reference toFigure 1 . The CohLR value may be multiplied by 1-CohDY and the product applied to the signal gains 208 in a similar fashion described above in reference to thecoherence gain adjuster 304. Using both of the CohLR and the CohDY values in order to adjust the signal gains 208 may reduce the noise artifacts, preserve and enhance the signal of interest, and reduce the echo. The adjustedsignal gains 208 are applied to each of the two or more microphone signal 118 using the gain filters 114. The signal gains 208 may be a combination ofsignal gains 208 associated with one or moresuppression gain calculators 106. The gain filters 114 may utilize the subband filter described above. -
Figure 6 is a representation of a method for maintaining the spatial stability of the sound field. Themethod 600 may be, for example, implemented using thesystems 200 described herein with reference toFigures 2 . Themethod 600 includes the act of calculating balance gains for each of two or more microphone signals 602. The balance gain may be associated with a spatial image in the sound field. One or more signal values may be calculated for each of the two or more microphone signals 604. The signal values may be the background noise estimate or signal gains associated with echo cancellation and noise reduction processes. Structured noise content may be detected for each of the two or more microphone signals 606. The structured noise content may be for example, impulse noise or tonal noise. A first microphone signal of the two or more microphone signals may be mixed with a second microphone signal of the two or more microphone signals responsive to the detectedstructured noise 608. Increasing amounts of detected structured noise may increase the amount of mixing, or blending, of the first microphone signal with the second microphone signal. The gain may be adjusted for the two or more microphone signals, including the mixed first microphone signal and second microphone signal, responsive to the calculated balance gains and the one or more signal values for each of the two or more microphone signals 610. -
Figure 7 is a schematic representation of a system for maintaining the spatial stability of the sound field. Thesystem 700 comprises aprocessor 702, memory 704 (the contents of which are accessible by the processor 702) and an I/O interface 706. Thememory 704 may store instructions which when executed using theprocess 702 may cause thesystem 700 to render the functionality associated with maintaining the spatial stability of the sound field as described herein. For example, thememory 704 may store instructions which when executed using theprocessor 702 may cause thesystem 700 to render the functionality associated with thebackground noise estimator 104, thesuppression gain calculator 106, thebalance calculator 108, thedifference limiter 110, thegain filter 114, the structurednoise detector 202, thechannel mixer 204 and thegain adjuster 206 as described herein. In addition, data structures, temporary variables and other information may store data indata storage 708. - The
processor 702 may comprise a single processor or multiple processors that may be disposed on a single chip, on multiple devices or distributed over more that one system. Theprocessor 702 may be hardware that executes computer executable instructions or computer code embodied in thememory 704 or in other memory to perform one or more features of the system. Theprocessor 702 may include a general purpose processor, a central processing unit (CPU), a graphics processing unit (GPU), an application specific integrated circuit (ASIC), a digital signal processor (DSP), a field programmable gate array (FPGA), a digital circuit, an analog circuit, a microcontroller, any other type of processor, or any combination thereof. - The
memory 704 may comprise a device for storing and retrieving data, processor executable instructions, or any combination thereof. Thememory 704 may include non-volatile and/or volatile memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or a flash memory. Thememory 704 may comprise a single device or multiple devices that may be disposed on one or more dedicated memory devices or on a processor or other similar device. Alternatively or in addition, thememory 704 may include an optical, magnetic (hard-drive) or any other form of data storage device. - The
memory 704 may store computer code, such as thebackground noise estimator 104, thesuppression gain calculator 106, thebalance calculator 108, thedifference limiter 110, thegain filter 114, the structurednoise detector 202, thechannel mixer 204 and thegain adjuster 206 as described herein. The computer code may include instructions executable with theprocessor 702. The computer code may be written in any computer language, such as C, C++, assembly language, channel program code, and/or any combination of computer languages. Thememory 704 may store information in data structures including, for example, suppression gains. - The I/
O interface 706 may be used to connect devices such as, for example, themicrophones 102, to other components of thesystem 700. - All of the disclosure, regardless of the particular implementation described, is exemplary in nature, rather than limiting. The
system 700 may include more, fewer, or different components than illustrated inFigure 7 . Furthermore, each one of the components ofsystem 700 may include more, fewer, or different elements than is illustrated inFigure 7 . Flags, data, databases, tables, entities, and other data structures may be separately stored and managed, may be incorporated into a single memory or database, may be distributed, or may be logically and physically organized in many different ways. The components may operate independently or be part of a same program or hardware. The components may be resident on separate hardware, such as separate removable circuit boards, or share common hardware, such as a same memory and processor for implementing instructions from the memory. Programs may be parts of a single program, separate programs, or distributed across several memories and processors. -
Figure 8 is a representation of a method for maintaining the spatial stability of the sound field. Themethod 800 may be, for example, implemented using thesystems 300 described herein with reference toFigures 3 . Themethod 800 includes the act of calculating balance gains for each of two or more microphone signals 802. The balance gain may be associated with a spatial image in the sound field. One or more signal values may be calculated for each of the two or more microphone signals 804. The signal values may be the background noise estimate or signal gains associated with echo cancellation and noise reduction processes. A pair-wise spectral coherence may be calculated between each of the two or more microphone signals 806. The pair-wise spectral coherence may indicate that two or more microphone signals are correlated and may have captured a signal of interest. The two or more microphone signals may be gain adjusted responsive to the calculated balance gains, the one or more signal values, and the pair-wise spectral coherence for each of the two or more microphone signals 808. The spectral coherence value may be used to prevent high amplitude high frequencies signals from being unnecessarily attenuated and may also be used to increase the gain of low amplitude high frequency signals. -
Figure 9 is a schematic representation of a system for maintaining the spatial stability of the sound field. Thesystem 900 comprises aprocessor 902, memory 904 (the contents of which are accessible by the processor 902) and an I/O interface 906. Thememory 904 may store instructions which when executed using theprocess 902 may cause thesystem 900 to render the functionality associated with maintaining the spatial stability of the sound field as described herein. For example, thememory 904 may store instructions which when executed using theprocessor 902 may cause thesystem 900 to render the functionality associated with thebackground noise estimator 104, thesuppression gain calculator 106, thebalance calculator 108, thedifference limiter 110, thegain filter 114, thecoherence calculator 302, thecoherence gain adjuster 304 and thesignal mixer 402 as described herein. In addition, data structures, temporary variables and other information may store data indata storage 908. - The
processor 902 may comprise a single processor or multiple processors that may be disposed on a single chip, on multiple devices or distributed over more than one system. Theprocessor 902 may be hardware that executes computer executable instructions or computer code embodied in thememory 904 or in other memory to perform one or more features of the system. Theprocessor 902 may include a general purpose processor, a central processing unit (CPU), a graphics processing unit (GPU), an application specific integrated circuit (ASIC), a digital signal processor (DSP), a field programmable gate array (FPGA), a digital circuit, an analog circuit, a microcontroller, any other type of processor, or any combination thereof. - The
memory 904 may comprise a device for storing and retrieving data, processor executable instructions, or any combination thereof. Thememory 904 may include non-volatile and/or volatile memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or a flash memory. Thememory 904 may comprise a single device or multiple devices that may be disposed on one or more dedicated memory devices or on a processor or other similar device. Alternatively or in addition, thememory 904 may include an optical, magnetic (hard-drive) or any other form of data storage device. - The
memory 904 may store computer code, such as thebackground noise estimator 104, thesuppression gain calculator 106, thebalance calculator 108, thedifference limiter 110, thegain filter 114, thecoherence calculator 302, thecoherence gain adjuster 304 and thesignal mixer 402 as described herein. The computer code may include instructions executable with theprocessor 902. The computer code may be written in any computer language, such as C, C++, assembly language, channel program code, and/or any combination of computer languages. Thememory 904 may store information in data structures including, for example, suppression gains. - The I/
O interface 906 may be used to connect devices such as, for example, themicrophones 902, to other components of thesystem 900. Thesystem 900 may include more, fewer, or different components than illustrated inFigure 9 . Furthermore, each one of the components ofsystem 900 may include more, fewer, or different elements than is illustrated inFigure 9 . Flags, data, databases, tables, entities, and other data structures may be separately stored and managed, may be incorporated into a single memory or database, may be distributed, or may be logically and physically organized in many different ways. The components may operate independently or be part of a same program or hardware. The components may be resident on separate hardware, such as separate removable circuit boards, or share common hardware, such as a same memory and processor for implementing instructions from the memory. Programs may be parts of a single program, separate programs, or distributed across several memories and processors. -
Figure 10 is a representation of a method for maintaining the spatial stability of the sound field. Themethod 1000 may be, for example, implemented using thesystems 500 described herein with reference toFigures 5 . Themethod 1000 includes the act of calculating balance gains for each of two or more microphone signals 1002. The balance gain may be associated with a spatial image in the sound field. One or more signal values may be calculated for each of the two or more microphone signals 1004. The signal values may be the background noise estimate or signal gains associated with echo cancellation and noise reduction processes. A predicted echo may be calculated for a receivedaudio signal 1006. The predicted echo may be used to reduce an echo signal. A pair-wise echo spectral coherence may be calculated between the predicted echo and the two or more microphone signals 1008. The pair-wise echo spectral coherence may indicate that the predicted echo is correlated to one or more of the captured two or more microphone signals. A pair-wise spectral coherence between each of the two or more microphone signals 1010. The pair-wise spectral coherence may indicate that two or more microphone signals are correlated and may have captured a signal of interest. The two or more microphone signals may be gain adjusted responsive to the calculated balance gains, the one or more signal values, the echo spectral coherence and the pair-wise spectral coherence for each of the two or more microphone signals 1012. Using both of the echo spectral coherence and the spectral coherence values in order to adjust the signal gains may reduce the noise artifacts, preserve and enhance the signal of interest, and reduce the echo. -
Figure 11 is a schematic representation of a system for maintaining the spatial stability of the sound field. Thesystem 1100 comprises aprocessor 1102, memory 1104 (the contents of which are accessible by the processor 1102) and an I/O interface 1106. Thememory 1104 may store instructions which when executed using theprocess 1102 may cause thesystem 1100 to render the functionality associated with maintaining the spatial stability of the sound field as described herein. For example, thememory 1104 may store instructions which when executed using theprocessor 1102 may cause thesystem 1100 to render the functionality associated with thebackground noise estimator 104, thesuppression gain calculator 106, thebalance calculator 108, thedifference limiter 110, thegain filter 114, thecoherence calculator 302, theecho filter 506, thecoherence echo calculator 510 and the coherenceecho gain adjuster 512 as described herein. In addition, data structures, temporary variables and other information may store data in data storage 1108. - The
processor 1102 may comprise a single processor or multiple processors that may be disposed on a single chip, on multiple devices or distributed over more that one system. Theprocessor 1102 may be hardware that executes computer executable instructions or computer code embodied in thememory 1104 or in other memory to perform one or more features of the system. Theprocessor 1102 may include a general purpose processor, a central processing unit (CPU), a graphics processing unit (GPU), an application specific integrated circuit (ASIC), a digital signal processor (DSP), a field programmable gate array (FPGA), a digital circuit, an analog circuit, a microcontroller, any other type of processor, or any combination thereof. - The
memory 1104 may comprise a device for storing and retrieving data, processor executable instructions, or any combination thereof. Thememory 1104 may include non-volatile and/or volatile memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or a flash memory. Thememory 1104 may comprise a single device or multiple devices that may be disposed on one or more dedicated memory devices or on a processor or other similar device. Alternatively or in addition, thememory 1104 may include an optical, magnetic (hard-drive) or any other form of data storage device. - The
memory 1104 may store computer code, such as thebackground noise estimator 104, thesuppression gain calculator 106, thebalance calculator 108, thedifference limiter 110, thegain filter 114, thecoherence calculator 302, theecho filter 506, thecoherence echo calculator 510 and the coherenceecho gain adjuster 512 as described herein. The computer code may include instructions executable with theprocessor 1102. The computer code may be written in any computer language, such as C, C++, assembly language, channel program code, and/or any combination of computer languages. Thememory 1104 may store information in data structures including, for example, suppression gains. - The I/
O interface 1106 may be used to connect devices such as, for example, themicrophones 102, thereceiver 502 and theaudio transducer 504 to other components of thesystem 900. Thesystem 1100 may include more, fewer, or different components than illustrated inFigure 11 . Furthermore, each one of the components ofsystem 1100 may include more, fewer, or different elements than is illustrated inFigure 11 . Flags, data, databases, tables, entities, and other data structures may be separately stored and managed, may be incorporated into a single memory or database, may be distributed, or may be logically and physically organized in many different ways. The components may operate independently or be part of a same program or hardware. The components may be resident on separate hardware, such as separate removable circuit boards, or share common hardware, such as a same memory and processor for implementing instructions from the memory. Programs may be parts of a single program, separate programs, or distributed across several memories and processors. - The functions, acts or tasks illustrated in the figures or described may be executed in response to one or more sets of logic or instructions stored in or on computer readable media. The functions, acts or tasks are independent of the particular type of instructions set, storage media, processor or processing strategy and may be performed by software, hardware, integrated circuits, firmware, micro code and the like, operating alone or in combination. Similarly, the microphones may comprise devices that convert sound into signals (e.g., electrical signals) and may include hardware that converts the signal output into digital data. Likewise, processing strategies may include multiprocessing, multitasking, parallel processing, distributed processing, and/or any other type of processing. In one embodiment, the instructions are stored on a removable media device for reading by local or remote systems. In other embodiments, the logic or instructions are stored in a remote location for transfer through a computer network or over telephone lines. In yet other embodiments, the logic or instructions may be stored within a given computer such as, for example, a CPU.
Claims (15)
- A computer implemented method for maintaining spatial stability of a sound field comprising:calculating (1002) balance gains (210) for each of two or more microphone signals (118);calculating (1004) one or more signal values (208) for each of the two or more microphone signals (118);calculating (1006) a predicted echo (508) for a received audio signal;calculating (1008) a pair-wise echo spectral coherence between the predicted echo and each of the two or more microphone signals (118);calculating (1010) a pair-wise spectral coherence between each of the two or more microphone signals (118); andgain (1012) adjusting the two or more microphone signals (118) responsive to the calculated balance gains (210), the one or more signal values (208), the echo spectral coherence and the pair-wise spectral coherence for each of the two or more microphone signals (118); andwhere the one or more signal values (208) is characterized as a background noise estimate or signal gains associated with an echo cancellation or noise reduction processes..
- The computer implemented method of claim 1, where the one or more signal values (208) comprise the background noise estimate.
- The computer implemented method of claim 1 where the one or more signal values (208) comprise signal gains associated with the noise reduction processes and the noise r echo cancellation.
- The computer implemented method of claim 3, where the noise reduction processes comprises any one or more of a wind noise reduction calculation, transients noise reduction calculation, a road noise reduction calculation, a repetitive noise reduction calculation and an engine noise reduction calculation.
- The computer implemented method of any of claims 1 to 4, where the received audio signal is a far side audio signal.
- The computer implemented method of any of claims 1 to 5, where gain adjusting the two or more microphone signals (118) responsive to an increased pair-wise spectral coherence includes reducing the balance gains for a higher amplitude microphone signal (118) of the two or more microphone signals (118).
- The computer implemented method of claim 6, where the increased pair-wise spectral coherence is greater than about 0.85.
- The computer implemented method of claim 7, where a pair-wise spectral coherence range between about 0.85 and about 1.0 is rescaled to between 0 and about 1.
- The computer implemented method of any of claims 1 to 8, where gain adjusting the two or more microphone signals (118) responsive to an increased pair-wise echo spectral coherence includes increasing the balance gains for the two or more microphone signals (118).
- The computer implemented method of claim 9, where the increased pair-wise echo spectral coherence is greater than about 0.85.
- The computer implemented method of claim 10, where a pair-wise echo spectral coherence range between about 0.85 and about 1.0 is rescaled to between 0 and about 1.
- The computer implemented method of any of claims 1 to 11, where gain adjusting the two or more microphone signals (118) responsive to an increased produce of the pair-wise spectral coherence and one minus the pair-wise spectral coherence includes increasing the balance gains for a higher amplitude microphone signal (118) of the two or more microphone signals (118).
- The computer implemented method of any of claims 1 to 12, further comprising generating a set of sub-bands for each of the two or more microphone signals using a subband filter or a Fast Fourier Transform.
- The computer implemented method of any of claims 1 to 13, further comprising generating a set of sub-bands for each of the two or more microphone signals according to a critical, octave, mel, or bark band spacing technique.
- A system for maintaining spatial stability of a sound field, the system comprising:a processor (1102);a memory (1104) coupled to the processor (1102) containing instructions, executable by the processor (1102), for performing the instructions executing the steps of any of claims 1 to 14.
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