EP2259250A1 - Dispositif hybride de réduction active du bruit pour réduire le bruit ambiant, procédé de détermination d'un paramètre opérationnel d'un dispositif hybride de réduction active du bruit et élément de programme - Google Patents

Dispositif hybride de réduction active du bruit pour réduire le bruit ambiant, procédé de détermination d'un paramètre opérationnel d'un dispositif hybride de réduction active du bruit et élément de programme Download PDF

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Publication number
EP2259250A1
EP2259250A1 EP09161866A EP09161866A EP2259250A1 EP 2259250 A1 EP2259250 A1 EP 2259250A1 EP 09161866 A EP09161866 A EP 09161866A EP 09161866 A EP09161866 A EP 09161866A EP 2259250 A1 EP2259250 A1 EP 2259250A1
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EP
European Patent Office
Prior art keywords
signal
operational parameter
analog
digital
filter part
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.)
Withdrawn
Application number
EP09161866A
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German (de)
English (en)
Inventor
Temujin Gautama
Simon Doclo
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NXP BV
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NXP BV
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Publication date
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Priority to EP09161866A priority Critical patent/EP2259250A1/fr
Priority to PCT/IB2010/052475 priority patent/WO2010140133A2/fr
Publication of EP2259250A1 publication Critical patent/EP2259250A1/fr
Withdrawn legal-status Critical Current

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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
    • G10K11/1785—Methods, e.g. algorithms; Devices
    • G10K11/17855—Methods, e.g. algorithms; Devices for improving speed or power requirements
    • 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
    • G10K11/1781—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 characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions
    • G10K11/17821—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 characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions characterised by the analysis of the input signals only
    • G10K11/17823—Reference signals, e.g. ambient acoustic environment
    • 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
    • G10K11/1785—Methods, e.g. algorithms; Devices
    • G10K11/17857—Geometric disposition, e.g. placement of microphones
    • 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
    • G10K11/1787—General system configurations
    • G10K11/17879—General system configurations using both a reference signal and an error signal
    • G10K11/17881—General system configurations using both a reference signal and an error signal the reference signal being an acoustic signal, e.g. recorded with a microphone
    • 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
    • G10K11/1787—General system configurations
    • G10K11/17885—General system configurations additionally using a desired external signal, e.g. pass-through audio such as music or speech

Definitions

  • the invention relates to a hybrid active noise reduction device for reducing environmental noise.
  • the invention relates to a method for determining an operational parameter of a hybrid active noise reduction device.
  • the invention relates to a program element.
  • ANR Active noise reduction
  • An ANR device may comprise at least one microphone, a filter unit, and a loudspeaker.
  • the microphone receives a noise signal from the noisy environment of the person and transmits a microphone signal to the filter unit.
  • the filter unit performs a filtering operation on the microphone signal and transmits a noise reduction signal to the loudspeaker for further broadcast to the environment.
  • the noise reduction signal is in counter phase to the environmental noise such that the level of ambient noise perceived by the person is reduced, thereby enhancing the comfort of the person.
  • An ANR device may comprise a feedforward configuration or a feedback configuration, or a combination thereof, and may be implemented in a headset, in a hearing aid or in a car compartment.
  • the ANR device comprises a reference microphone which may be arranged in such a way that it mainly picks up the environmental noise from outside.
  • the noise reduction signal emitted by the loudspeaker is a filtered version of the reference microphone signal.
  • the filtering operation performed by the filter unit may be optimized by arranging an error microphone in such a way that the error microphone records ambient noise which a person perceives.
  • the filter unit may be optimized in that the sound level at the error microphone may be minimized.
  • a feedback ANR device uses only an error microphone arranged in such a way that the error microphone records ambient noise which a person may perceive.
  • the error microphone signal is filtered by the filter unit and is emitted by the loudspeaker.
  • the filter unit may also be optimized by minimizing the sound level at the error microphone.
  • the filter unit of an ANR device may comprise an analog filter and/or a digital filter.
  • An ANR device comprising an analog filter and a digital filter is known as a "hybrid" ANR device.
  • the use of an analog filter may allow for using the instantaneous analog filter response, whereas the use of a digital filter may enable a more complex signal filtering capability.
  • using a digital filter may introduce delays into the digital filter response which may result from analog-to-digital and digital-to-analog convertors being constructively indispensible in the signal processing path and being arranged upstream and downstream of the digital filter. In particular, these delays may force the digital filter response being zero in particular time intervals.
  • US 5,440,642 B1 discloses a digitally controlled hybrid ANR device in a feedback configuration which comprises a microphone, a filter unit, and a loudspeaker.
  • a microphone signal is filtered by the filter unit, and a filtered signal is transmitted to the loudspeaker.
  • the filter unit comprises an analog filter which is digitally controlled using a digital signal processor comprising a digital filter.
  • the analog filter and the digital filter are arranged in parallel to one another.
  • a hybrid active noise reduction device for reducing environmental noise for reducing environmental noise
  • a method for determining an operational parameter of a hybrid active noise reduction device for reducing environmental noise
  • a program element for determining an operational parameter of a hybrid active noise reduction device
  • a hybrid active noise reduction device for reducing environmental noise
  • the device comprising a microphone for receiving a noise signal and for transmitting a microphone signal, a filter unit for receiving the microphone signal and for transmitting a filtered microphone signal, the filter unit comprising an analog filter part and a digital filter part, the analog filter part and the digital filter part being arranged in series to one another, and a loudspeaker for transmitting a noise reduction signal based on the filtered microphone signal.
  • a headset comprising a hybrid active noise reduction device for reducing environmental noise.
  • a method for determining an operational parameter of a hybrid active noise reduction device comprising a microphone for receiving a noise signal and for transmitting a microphone signal, a filter unit for receiving the microphone signal and for transmitting a filtered microphone signal, the filter unit comprising an analog filter part and a digital filter part, and a loudspeaker for transmitting a noise reduction signal based on the filtered microphone signal, the method comprising selecting a first operational parameter of the device and determining a second operational parameter of the device based on the first operational parameter.
  • a program element which, when being executed by a processor, is adapted to control or carry out a method for determining an operational parameter of a hybrid active noise reduction device.
  • a hybrid active noise reduction device which offers the possibility for effectively reducing environmental noise such that a level of comfort of a person using the device is significantly enhanced.
  • the device is adapted to cancel or eliminate environmental noise.
  • the hybrid active noise reduction device comprises a filter unit which comprises an analog filter part and a digital filter part being arranged in series to one another such that a filtering operation of the microphone signal may be enhanced in that two filtering operations are performed in series to one another.
  • the output signal of the filter unit may combine an instantaneous filter response of the analog filter part and the complex signal modeling capability of the digital filter part.
  • the device comprises a constructively easy design, since a simple series circuit may be used for arranging the analog filter part and the digital filter part of the filter unit.
  • the noise reduction signal may be identical or be based on the filtered microphone signal.
  • the device may comprise a feedback configuration with the microphone being an error microphone and the filtered microphone signal being fed to the loudspeaker.
  • the noise reduction signal transmitted by the loudspeaker may be recorded by the microphone together with a noise signal.
  • This microphone signal may be used as an error signal for optimizing the noise reduction capability of the device.
  • the error signal may be identical or be based on a combination, particularly a sum, of an ambient noise signal received by the microphone and the noise reduction signal provided by the loudspeaker.
  • the noise reduction signal transmitted by the loudspeaker may be convolved with a transfer function describing a signal path from the loudspeaker to the microphone.
  • the error microphone and the loudspeaker may be implemented inside or form part of an inner part of an earphone of a hybrid active noise reduction headset.
  • the microphone may record ambient noise which a user perceives when wearing the headset.
  • the device may also form part of a hearing aid or a car compartment or any other device application in which the principle of active noise reduction may be usefully applied.
  • an optimization of an operation of the device may be performed such that the noise reduction capability of the device may be increased.
  • a first operational parameter of the device is selected, and a second operational parameter of the device is determined based on the first operational parameter.
  • determining the second operational parameter may comprise computational or mathematical techniques.
  • the method may be performed in an operational state or a resting state of the device.
  • the method may be applied to any hybrid active noise reduction device or device application comprising such a hybrid active noise reduction device.
  • the hybrid active noise reduction device may be of a feedback type or a feedforward type, or of a combination thereof.
  • the analog filter part and the digital filter part may be in series to one another or in parallel to one another.
  • the program element may be identical or be part of e.g. a software routine, a source code or an executable code.
  • the program element may be stored in a computer readable medium (e.g. a volatile memory, a nonvolatile memory, a CD, a DVD, a USB stick, a floppy disk or a harddisk).
  • the device may further comprise a bypass line being arranged in parallel to the digital filter part.
  • the bypass line and the signal path comprising the digital filter part may form a parallel circuit being in series to the analog filter part.
  • a first branch of the parallel circuit may be identical to or comprise the bypass line, and a second branch of the parallel circuit may be identical to or comprise the digital filter part.
  • the output signal of the filter unit and thus the noise reduction signal may comprise a combination of a signal being filtered by the analog filter part and being bypassed and a signal being filtered by the analog filter part and the digital filter part.
  • the output signal of the filter unit may comprise portions which result from the analog filtering operation and the combined analog and digital filtering operation.
  • the filter response of the analog filter part may comprise an instantaneous filter response which may compensate for delayed portions of the filter response of the digital filter part which may be equal to or almost zero over time.
  • the device may comprise a yet more enhanced noise reduction capability, since a more improved signal processing may be performed by the filter unit.
  • the noise reduction signal transmitted by the loudspeaker may be instantaneous due to a bypassing of a signal being already or subsequently to be filtered by the analog filter part.
  • the noise reduction signal may be effectively shaped by the digital filtering operation performed by the digital filter part.
  • delays resulting from the digital filter part particularly resulting from an analog-to-digital signal conversion and a digital-to-analog signal conversion may be compensated for by the instantaneous filter response of the analog filter part.
  • the device may be used for any application in which device delays due to signal conversions from the analog to the digital domain and vice versa may be present.
  • the bypass line may comprise a gain unit.
  • the bypassed signal may be amplified, in order to offer a further modification capability of the output signal of the filter unit, particularly of the noise reduction signal, before transmitting the filtered signal to the loudspeaker. Therefore the noise reduction capability of the device may be further enhanced.
  • the gain unit may comprise a controllable gain unit or a fixed gain unit.
  • the device may further comprise a signal adding unit for adding a bypassed signal and a digitally filtered signal.
  • the signal adding unit may enable a combination or mixture of the bypassed (and amplified) signal and the digitally filtered signal in that the two branches of the formed parallel circuit may be added.
  • the signal adding unit may be adapted to sum the bypassed signal and the digitally filtered signal in an analog way.
  • This embodiment of the signal adding unit may represent a very easy and effective way for performing an adding operation of two signals.
  • the analog filter part may be arranged downstream with respect to the digital filter part.
  • the device may be used in a headset offering voice communications and/or speech capabilities, since it may be desirable that the microphone signal may not be filtered by the analog filter part before inputting it to the digital filter part.
  • this arrangement of the analog filter part and the digital filter part may lead to a low degree of instrumental noise of the device which may comprise self-noise of the microphone and electrical noise of the device.
  • a further amplifier unit may be arranged downstream with respect to the digital filter part for further amplifying the digitally filtered signal.
  • the analog filter part may be arranged upstream with respect to the digital filter part. This arrangement of the analog filter part and the digital filter part may be used in device applications which may not offer voice communications or speech capabilities.
  • an amplifier unit may be arranged downstream with respect to or may be implemented in the microphone for amplifying the recorded noise signal, since the instrumental noise of the device may comprise a relatively high level.
  • the digital filter part may comprise an analog-to-digital convertor for converting an analog signal into a digital signal, a digital filter, and a digital-to-analog convertor for converting a digital signal into an analog signal.
  • This embodiment of the digital filter part offers the technical possibility for digitally filtering a recorded analog microphone signal.
  • the analog-to-digital convertor and the digital-to-analog convertor may introduce signal conversion delays into the signal transmission of the device, thereby reducing the noise reduction capability of the device.
  • the series arrangement of the analog filter part and the digital filter part in combination with the bypass line may compensate for the conversion delays in the device signal path.
  • the analog-to-digital convertor and the digital-to-analog convertor may be identical or form part of a codec (coder-encoder).
  • the codec may comprise a bypass capability, which may be with a controllable gain, thus comprising the bypass line.
  • the digital filter may be identical or form part of a digital signal processor (DSP).
  • the device may comprise a further microphone for receiving a further noise signal and for transmitting a further microphone signal, wherein the analog filter part and/or the digital filter part may operate based on the further microphone signal.
  • the device may comprise a feedforward configuration with the analog filter part and the digital filter part being arranged in series to one another.
  • the microphone may be a reference microphone recording or receiving noise.
  • the further microphone may be an error microphone which may record the further noise, which a person may perceive.
  • the filter unit may filter the reference microphone signal and transmit the filtered reference microphone signal, in particular the noise reduction signal, to the loudspeaker. An error microphone signal recorded by the error microphone may be used for optimizing the noise reduction capability of the device.
  • the error signal may be identical or be based on a combination, particularly a sum, of an ambient noise signal received by the microphone and the noise reduction signal provided by the loudspeaker.
  • the noise reduction signal transmitted by the loudspeaker may be convolved with a transfer function describing a signal path from the loudspeaker to the microphone.
  • the error microphone may be arranged in series to an analog-to-digital convertor for further converting the analog error microphone signal into the digital domain for further signal processing.
  • the error microphone and the loudspeaker may be arranged on the inside of an earphone of a headset, whereas the reference microphone may be arranged on the outside of an earphone of a headset.
  • the digital filter part may comprise a digital filter, wherein the digital filter may be a finite impulse response filter.
  • the analog filter part may comprise an analog filter, wherein the analog filter may be a first order low pass filter.
  • a cut-off frequency of the first order low pass filter may be of about 700 Hz, particularly of about 500 Hz, further particularly of about 300 Hz.
  • the analog filter may also be a higher order low pass filter, a high pass filter, a band pass filter, or a combination thereof, each of which comprising suitable cut-off frequencies.
  • the device may further comprise a bypass line in parallel to the digital filter part, wherein the bypass line may comprise a gain unit, wherein the method may comprise selecting the first operational parameter and determining a second operational parameter and a third operational parameter of the device based on the first operational parameter.
  • the analog filter part may be arranged in or be part of the bypass line.
  • the first operational parameter may be an operational parameter of the analog filter part
  • the second operational parameter may be an operational parameter of the digital filter part
  • the third operational parameter may be an operational parameter of the gain unit.
  • Determining the second operational parameter based on the first operational parameter may comprise minimizing a cost function of the device with respect to the second parameter. This measure represents a very effective and easily performable way for determining minima of the cost function for the second operational parameter, yielding the optimal second operational parameter of the device for operating the device.
  • Determining the second operational parameter and the third operational parameter based on the first operational parameter may comprise minimizing a cost function of the device with respect to the second operational parameter and the third operational parameter.
  • determining the second and third operational parameters of the device Upon simultaneously or jointly determining the second and third operational parameters of the device a very effective and easily performable optimization of the device operation may be achieved.
  • Hybrid ANR devices comprise a filter unit consisting of an analog filter part and digital filter part and thus combine the instantaneous filtering capability of an analog filter and the complex signal tuning capability of a digital filter.
  • Fig. 1 shows a prior art digital ANR device 100 in a feedback configuration.
  • the device 100 comprises a microphone 102, an analog-to-digital convertor (ADC) 104, an ANR digital filter 106, a digital-to-analog convertor (DAC) 108, and a loudspeaker 110.
  • the ADC 104, the digital filter 106, and the DAC 108 may form a digital filter part 112 of a filter unit 114.
  • the device 100 may also comprise amplifiers (not shown) which operate in their linear region.
  • This feedback device 100 may be implemented into a headset such that the microphone 102 and the loudspeaker 110 are both arranged on the inside of an earphone 116 of the headset.
  • the microphone 102 may then be called an "error microphone" and receives a noise signal which a user of the headset may perceive. This noise signal may differ from a noise signal a user may perceive without the headset.
  • analog-to-digital and digital-to-analog conversions are in the following assumed to be ideal, i.e., instantaneous and without loss of information.
  • an analog signal may be represented by a digital signal equivalent, and actual, i.e. non-ideal, conversions may then be conveniently represented by time delays ⁇ ADC and ⁇ DAC .
  • the microphone 102 picks up a signal that comprises an acoustical summation of an ambient noise signal 118 which a user perceives and a noise reduction signal 120 emitted by the loudspeaker 110.
  • An error microphone signal 122 is converted into the digital domain, thereby introducing a delay ⁇ ADC and thus yielding a digital microphone signal 124.
  • This error signal 124 is then filtered by the digital filter 106, and a digitally filtered signal 126 of the digital filter 106 is converted by the DAC 108 to the analog domain, thereby introducing a delay ⁇ ADC to the converted signal 128 and yielding the noise reduction signal 120.
  • the transfer function of the loudspeaker 110 to the microphone 102 describing the acoustical path 130 from the loudspeaker 110 to the microphone 102 is assumed to be linear.
  • the error microphone 102 hence records a sum of the ambient noise signal 118 and the noise reduction signal 120 convolved with the transfer function of the acoustical path 130.
  • the error microphone signal 122 may thus be regarded as an error signal of the device 100.
  • the device 100 shows a poor ANR performance.
  • the ANR performance of the device 100 may be expressed in terms of the "active performance" which is evaluated on the microphone 102 and may be defined as a difference in a power spectral density (PSD) with the ANR device 100 being not operational and with the ANR device 100 being operational.
  • a negative active performance indicates a noise reduction, with a lower value of the active performance indicating an increased noise reduction.
  • the digital ANR devices 100 being expected to be superior to analog ANR devices, the actual performance of the digital ANR device 100 is drastically deteriorated owing to the presence of the time delays ⁇ ADC and ⁇ DAC introduced by the ADC 104 and the DAC 108.
  • FIR digital finite impulse response
  • the first 15 filter taps comprise most of the energy (highest filter coefficients) and are the decisive filter coefficients for the digital filter operation.
  • the conversion delay ⁇ may be interpreted as a delay of the digital filter 106 or a series of zeros at the beginning of the digital filter 106. If this important part of the digital filter 106 is forced to zero, the ANR performance, particularly G ( ⁇ ) , may be substantially degraded, since the digital filter 106 cannot compensate for the acausality of the filter.
  • a hybrid feedback ANR device according to an exemplary embodiment of the invention may be used, which is shown in Fig. 5 .
  • the device 500 may be used in any ANR application. However, the device 500 is most usefully integrated in applications with conversion delays ⁇ degrading the performance of the device 500. In particular, the device 500 may be part of an ANR headset of a feedback type.
  • the hybrid device 500 comprises an error microphone 102, an analog filter part 501 comprising an analog filter 502, a subsequent digital filter part 112 being formed by an ADC 104, a digital filter 106, and a DAC 108 and being in series to the analog filter part 501, and a loudspeaker 110.
  • the ADC 104 and the DAC 108 are provided before and after the digital filter 106 seen in a signal transmitting direction.
  • a gain unit 504 is provided in parallel to the digital filter 106, thus forming a signal bypass line 505.
  • the device 500 comprises a signal adding unit 506 for electrically combining or mixing the signals of the two branches of a parallel circuit 508 of the filter unit 114 before transmitting a combined filtered microphone signal to the loudspeaker 110.
  • the parallel circuit 508 is defined by the gain unit 504 and the digital filter part 112.
  • the analog filter 502 may be designed as a first-order low pass filter.
  • the device 500 uses a combination of an analog filter 502 and digital filter 106 to span the acausal part of the desired impulse response of the filter unit 114.
  • the acausul part of the digital filter 106 can be modelled by an analog, instantaneous filter response.
  • a delay of the analog filter 502 resulting from electronic circuits is assumed to be much smaller than a single sampling period of the digital filter 106, and therefore in this context the analog filter 502 may be considered as instantaneous.
  • the two filters 502, 106 are combined in such a way that they can be conveniently implemented using a bypass of the digital filter 106 which is present in many ADC 104 and DAC 108, reducing the required circuitry of the hybrid device 500.
  • the device 500 shows an increased robustness compared to the device 100.
  • an error signal 122 corresponding to the error microphone signal 122 is filtered by the analog filter 502.
  • the filtered microphone signal 510 is then fed into the parallel circuit 508 comprising the instantaneous analog gain unit 504 and the digital filter 106 having the conversion delays ⁇ ADC and ⁇ DAC .
  • An amplified signal 512 and a digitally filtered and converted signal 128 are then summed to form the combined filtered microphone signal 514 which, in turn, is sent to the loudspeaker 110.
  • the device 500 may comprise the following modifications:
  • a microphone amplifier When performing the analog filtering operation before the signal input to the ADC 104 (shown in Fig. 5 ), a microphone amplifier may be needed for boosting the signal considerably, in order to obtain a reasonable headroom on the digital filter 106, particularly such that there is a sufficient accuracy for fixed-point representation of the signal, and, as a consequence, instrumental noise, i.e. self-noise of the microphone 102 and electrical noise, might become too large.
  • instrumental noise may be of the same order of magnitude as in a normal application such as voice communications. However, it may be possible that the noise reduction signal may need to be boosted beyond a value being possible in the DAC 108, therefore necessitating an additional amplifier stage.
  • the ANR device 500 is implemented in a system which comprises voice communications or speech capture, it may be desirable that the microphone signal remains unfiltered before inputting into the digital filter 106, yielding the configuration of the device 500 comprising the analog filter 502 after the DAC 108 when seen in a signal transmitting direction.
  • the impulse response of the device 500 is given as the superposition by a curve 404 and the impulse response of the digital filter (not shown) in a range of 15 samples to 100 samples.
  • a delay of 15 taps is assumed.
  • the acausal part of the impulse response of the digital filter 106 is given by the impulse response of the analog filter 502, here a first-order low pass filter with cut-off frequency at 700 Hz.
  • the overall impulse response of the filter unit 114 of the device 500 is given as a concatenation of the curves 404, 302.
  • analog bypass functionality of the ADC 104 and DAC 108 allows for a convenient implementation of the branches of the parallel circuit 508.
  • the analog gain unit 504 may be controlled with the digital filter 106 which may be inversely scaled in the digital domain.
  • Fig. 6 shows the active performance G ( ⁇ ) of the hybrid feedback ANR device 500 for a conversion delay ⁇ of zero, two and ten samples (curves 602 and 604, respectively).
  • the length of the digital filter 106 is set to 512 with a sampling rate of 48 kHz.
  • the analog filter 502 is designed as a first-order low pass filter with a cut-off frequency of 700 Hz.
  • a curve 606 corresponds the curve 202 and indicates the active performance of the digital feedback device 100 in the case of zero delay.
  • the noise reduction is prominent in a wide frequency area with a deep noise reduction between about 50 Hz and about 2 kHz.
  • a maximal noise reduction value is about 18 dB.
  • the active performance G ( ⁇ ) is maintained for a delay of 10 samples, since no significant changes in G ( ⁇ ) for different delays are visible.
  • the maximal delay ⁇ for which the active performance G( ⁇ ) is robust depends on a design of the device 500 and particularly on the analog filter 502 used. In this exemplary case, the active performance is maintained for delays below 10 samples using a first-order analog filter 502. When using a higher-order analog filter 502, the hybrid device 500 is made robust to longer delays ⁇ .
  • the hybrid device 500 may be optimised in terms of optimizing an operational parameter of components of the parallel circuit 508.
  • the analog gain unit 504 and the filter coefficients of the digital filter 106 may be jointly optimised without the need of a model of the analog filter 502, thereby omitting an introduction of additional errors into the optimal performance parameters of the device 500.
  • a cost function of the device may be minimized with respect to the operational parameters of the analog gain unit 504 and the digital filter 106, with the operational parameter of the analog filter 502 being fixed.
  • Fig. 7 shows a known digital ANR device 700 in a feedforward configuration.
  • the device 700 is part of a headset and comprises a reference microphone 102, an ADC 104, a digital filter 106, a DAC 108, and a loudspeaker 110. Further, the device comprises an error microphone 702, arranged together with the loudspeaker 110 on the inside of an earphone 116.
  • a further ADC 704 is provided and is arranged upstream with respect to the error microphone 702.
  • the reference microphone 102 may be arranged on the outside of the earphone 116 such that the reference microphone 102 receives the actual noise of the environment. As the error microphone 702 is arranged on the inside of the earphone 116 of the headset, the error microphone 702 receives the noise a user of the headset may perceive.
  • the reference microphone 102 records a noise signal 118 and outputs a reference microphone signal 122 which is converted by the ADC 104, yielding a delayed signal 124.
  • This signal 124 is filtered by the digital filter 106, and the digitally filtered signal 126 is converted by the DAC 108, yielding a delayed signal 128.
  • the noise reduction signal 120 is played via the loudspeaker 110.
  • the error microphone 702 receives an error signal 708 which is a combination of the ambient noise signal 706 and the noise reduction signal 120.
  • the error signal 708 is then converted by the ADC 704 and forms a digital error signal 710 to be used for operating the digital filter part 112.
  • G ( ⁇ ) The frequency dependency of the ANR active performance G ( ⁇ ) of the device 700 is shown in Fig. 8 for different delays ⁇ .
  • Curves 802-808 correspond to a delay ⁇ of zero samples, eight samples, 16 samples, and 26 samples using a sampling rate of 48 kHz.
  • a reference ANR performance for an analog, instantaneous first-order low pass filter indicated is indicated by a curve 810, the parameters of which have been optimised in a similar manner.
  • the active performance Upon increasing the delay ⁇ the active performance considerably degrades.
  • the ANR performance G ( ⁇ ) is high.
  • the gain becomes less negative meaning a lower noise reduction.
  • Fig. 9 shows the corresponding sample index dependency of the impulse response of the digital filter 106 for the delay ⁇ being zero samples, eight samples, 16 samples, and 26 samples (curves 902-908) for only the first 200 samples, in order to understand the performance degradation of the device 700. Due to the delay ⁇ the first ⁇ samples of the impulse response curves 902-908 are equal to zero. Upon increasing the delay ⁇ the acausal part of the impulse response corresponding to the zero values at low sample indices becomes longer. Thus the corresponding part of the optimal delay-free impulse response (curve 902) cannot be achieved by a causal digital filter 106, and the ANR performance of the device 700 is degraded.
  • FIR finite impulse response
  • the function g FIR ( ⁇ ) equals [1 exp(-l ⁇ ) ... exp (-t( L - 1) ⁇ ] T . Integration is performed over a frequency range ⁇ of interest. Minimization of the cost function results in optimal operational parameters of the digital filter 106, given the acoustical path 130 (without conversion delay ⁇ ) and the delay ⁇ .
  • Fig. 10 shows a hybrid ANR device 1000 according to another exemplary embodiment of the invention.
  • the device 1000 comprises a reference microphone 102, an analog filter 502, a parallel circuit 508 comprising an ADC 104, a digital filter 106, and a DAC 108 in one branch line and a gain unit 504 in a further bypass branch line 505, a signal adding unit 506, and a loudspeaker 110.
  • a sequence of arrangement of these device components is seen in a signal transmitting direction.
  • the device 1000 comprises an error microphone 702 and a further ADC 704.
  • the reference microphone 102 is arranged on the outside of an earphone 116 of the headset, and the error microphone 702 and the loudspeaker 110 are arranged on the inside of an earphone 116 of the headset.
  • a noise signal 118 is received by the reference microphone 102 and transmitted to the analog filter 502.
  • the filtered microphone signal 510 is fed into the parallel circuit 508 such that the filtered microphone signal 510 is on the one hand converted into the digital domain, filtered by the digital filter 126 and converted back to the analog domain.
  • the filtered microphone signal 510 is bypassed over the gain unit 504.
  • the amplified microphone signal 512 and the digitally filtered microphone signal 128 are summed by the signal adding unit 506 to form a filtered microphone signal 514.
  • a noise reduction signal 120 is emitted by the loudspeaker 110.
  • the error microphone 702 receives an ambient noise signal 706 and the noise reduction signal 120.
  • An error signal 708 being transmitted by the error microphone 702 is fed to a further ADC 704.
  • a converted signal 710 may be used for parameter optimization of the device 1000.
  • a method for determining a first operational parameter of the device 1000 is based on minimizing a cost function describing characteristics of the device 1000.
  • Optimizing the cost function may be performed jointly, computing the optimal operational parameters of the analog gain unit 504 (parameter K ) and of the digital filter 106 (parameter w FIR ) based on the analog filter 502 (parameter p a ).
  • Fig. 11 shows a known hybrid ANR device 1100 comprising a feedforward configuration.
  • the device 1100 is based on the device 700 with further comprising a parallel circuit 508 being part of the filter unit 114.
  • a first branch of the parallel circuit 508 corresponds to the arrangement of the ADC 104, the digital filter 106, and the DAC 108.
  • a second branch of the parallel circuit 508 comprises an analog filter 502 and a gain unit 504 being provided downstream with respect to the analog filter 502. Output signals of the two branches are summed by the signal adding unit 506.
  • the error microphone 702 may be replaced by a temporary measurement microphone.
  • the reference microphone 102 records a noise signal 118 and feeds a reference microphone signal 122 to the parallel circuit 508.
  • the signal 122 is filtered by the digital filter 106 in the digital domain and meanwhile filterd by the analog filter 502 and amplified by the gain unit 504. After signal summation a filtered microphone signal 514 is provided to the loudspeaker 110 which outputs a noise reduction signal 120.
  • the error microphone 702 records a combination of an ambient noise signal 706 and the noise reduction signal 120 and outputs an error signal 708 to the further ADC 104.
  • the device 1100 combines the instantaneous filter response of the analog filter 502 with the filter accuracy and complexity of the digital filter 106. Since the analog filter 502 is able to perform an instantaneous filtering operation, the acausal part of the impulse response of the digital filter 106 may be crudely modelled such that the ANR performance of the device 1100 is largely robust with respect to the presence of delays ⁇ ADC and ⁇ ADC of the ADC 104 and the DAC 108, respectively.
  • Fig. 12 shows a frequency dependency of the active ANR performance G ( ⁇ ) of the hybrid device 1100 for different delay values ⁇ being zero samples, eight samples, 16 samples, and 26 samples indicated by curves 1202-1208.
  • the active performance of an analog first-order low pass filter is indicated by a curve 1210. It can be observed that the ANR performance is largely maintained for increasing values of the delay ⁇ , with only a slight degradation occurring in a frequency region between about 300 Hz and about 1000 Hz.
  • Fig. 13 shows the corresponding sample index dependency of the impulse response of the filter unit 114 (sum of the filter response of the analog filter 502 with gain unit 504 and the filter response of the digital filter 106) for the delays ⁇ being zero samples, eight samples, 16 samples, and 26 samples (curves 1302-1308).
  • the acausal part of the impulse response is represented by a thick portion of the curves 1302-1308 and may be clearly modelled by exponentially decreasing functions. These functions are the impulse responses of the analog first-order low pass filter 502.
  • the method mentioned above is adapted for optimizing the operation of the device 1100.
  • ⁇ may be convenient to fix ⁇ to a predetermined value and only optimise the gain K in combination with the digital filter coefficients w FIR .
  • ⁇ the optimal gain parameters K of the analog gain unit 504 and the optimal FIR filter w FIR of the digital filter 106 of the hybrid device 1100.
  • further algorithms for computing the parameters such as an adaptive least mean square based algorithm.
  • optimisation of the parameters may then be performed offline, wherein the filter coefficients and the gain parameter may remain fixed during normal operation of the device 1100.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Health & Medical Sciences (AREA)
  • Audiology, Speech & Language Pathology (AREA)
  • General Health & Medical Sciences (AREA)
  • Soundproofing, Sound Blocking, And Sound Damping (AREA)
  • Circuit For Audible Band Transducer (AREA)
EP09161866A 2009-06-03 2009-06-03 Dispositif hybride de réduction active du bruit pour réduire le bruit ambiant, procédé de détermination d'un paramètre opérationnel d'un dispositif hybride de réduction active du bruit et élément de programme Withdrawn EP2259250A1 (fr)

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EP09161866A EP2259250A1 (fr) 2009-06-03 2009-06-03 Dispositif hybride de réduction active du bruit pour réduire le bruit ambiant, procédé de détermination d'un paramètre opérationnel d'un dispositif hybride de réduction active du bruit et élément de programme
PCT/IB2010/052475 WO2010140133A2 (fr) 2009-06-03 2010-06-03 Dispositif de réduction du bruit actif et hybride permettant de réduire le bruit ambiant, procédé de détermination d'un paramètre fonctionnel d'un dispositif de réduction du bruit actif et hybride, et élément de programme

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WO2010140133A2 (fr) * 2009-06-03 2010-12-09 Nxp B.V. Dispositif de réduction du bruit actif et hybride permettant de réduire le bruit ambiant, procédé de détermination d'un paramètre fonctionnel d'un dispositif de réduction du bruit actif et hybride, et élément de programme
WO2013108096A1 (fr) * 2012-01-16 2013-07-25 Telefonaktiebolaget L M Ericsson (Publ) Réduction de défaut de concordance de retard de groupe pour des filtres numériques radiofréquence
CN105393301A (zh) * 2013-06-11 2016-03-09 伯斯有限公司 控制anr设备中的稳定性
WO2016198481A3 (fr) * 2015-06-09 2017-01-12 Cirrus Logic International Semiconductor Limited Filtre à réponse impulsionnelle finie hybride
US9711130B2 (en) 2011-06-03 2017-07-18 Cirrus Logic, Inc. Adaptive noise canceling architecture for a personal audio device
US9721556B2 (en) 2012-05-10 2017-08-01 Cirrus Logic, Inc. Downlink tone detection and adaptation of a secondary path response model in an adaptive noise canceling system
US9773493B1 (en) 2012-09-14 2017-09-26 Cirrus Logic, Inc. Power management of adaptive noise cancellation (ANC) in a personal audio device
US9773490B2 (en) 2012-05-10 2017-09-26 Cirrus Logic, Inc. Source audio acoustic leakage detection and management in an adaptive noise canceling system
US9807503B1 (en) 2014-09-03 2017-10-31 Cirrus Logic, Inc. Systems and methods for use of adaptive secondary path estimate to control equalization in an audio device
US9824677B2 (en) 2011-06-03 2017-11-21 Cirrus Logic, Inc. Bandlimiting anti-noise in personal audio devices having adaptive noise cancellation (ANC)
US9955250B2 (en) 2013-03-14 2018-04-24 Cirrus Logic, Inc. Low-latency multi-driver adaptive noise canceling (ANC) system for a personal audio device
US10013966B2 (en) 2016-03-15 2018-07-03 Cirrus Logic, Inc. Systems and methods for adaptive active noise cancellation for multiple-driver personal audio device
US10026388B2 (en) 2015-08-20 2018-07-17 Cirrus Logic, Inc. Feedback adaptive noise cancellation (ANC) controller and method having a feedback response partially provided by a fixed-response filter
US10219071B2 (en) 2013-12-10 2019-02-26 Cirrus Logic, Inc. Systems and methods for bandlimiting anti-noise in personal audio devices having adaptive noise cancellation
US10468048B2 (en) 2011-06-03 2019-11-05 Cirrus Logic, Inc. Mic covering detection in personal audio devices

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US8873606B2 (en) * 2012-11-07 2014-10-28 Broadcom Corporation Transceiver including a high latency communication channel and a low latency communication channel
US11468874B2 (en) * 2020-11-13 2022-10-11 Google Llc Noise control system

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Cited By (19)

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Publication number Priority date Publication date Assignee Title
WO2010140133A3 (fr) * 2009-06-03 2011-06-30 Nxp B.V. Dispositif de réduction du bruit actif et hybride permettant de réduire le bruit ambiant, procédé de détermination d'un paramètre fonctionnel d'un dispositif de réduction du bruit actif et hybride, et élément de programme
WO2010140133A2 (fr) * 2009-06-03 2010-12-09 Nxp B.V. Dispositif de réduction du bruit actif et hybride permettant de réduire le bruit ambiant, procédé de détermination d'un paramètre fonctionnel d'un dispositif de réduction du bruit actif et hybride, et élément de programme
US9824677B2 (en) 2011-06-03 2017-11-21 Cirrus Logic, Inc. Bandlimiting anti-noise in personal audio devices having adaptive noise cancellation (ANC)
US10468048B2 (en) 2011-06-03 2019-11-05 Cirrus Logic, Inc. Mic covering detection in personal audio devices
US10249284B2 (en) 2011-06-03 2019-04-02 Cirrus Logic, Inc. Bandlimiting anti-noise in personal audio devices having adaptive noise cancellation (ANC)
US9711130B2 (en) 2011-06-03 2017-07-18 Cirrus Logic, Inc. Adaptive noise canceling architecture for a personal audio device
WO2013108096A1 (fr) * 2012-01-16 2013-07-25 Telefonaktiebolaget L M Ericsson (Publ) Réduction de défaut de concordance de retard de groupe pour des filtres numériques radiofréquence
US9020065B2 (en) 2012-01-16 2015-04-28 Telefonaktiebolaget L M Ericsson (Publ) Radio frequency digital filter group delay mismatch reduction
US9721556B2 (en) 2012-05-10 2017-08-01 Cirrus Logic, Inc. Downlink tone detection and adaptation of a secondary path response model in an adaptive noise canceling system
US9773490B2 (en) 2012-05-10 2017-09-26 Cirrus Logic, Inc. Source audio acoustic leakage detection and management in an adaptive noise canceling system
US9773493B1 (en) 2012-09-14 2017-09-26 Cirrus Logic, Inc. Power management of adaptive noise cancellation (ANC) in a personal audio device
US9955250B2 (en) 2013-03-14 2018-04-24 Cirrus Logic, Inc. Low-latency multi-driver adaptive noise canceling (ANC) system for a personal audio device
CN105393301B (zh) * 2013-06-11 2019-05-31 伯斯有限公司 提供anr耳机中的稳定性的方法及anr***
CN105393301A (zh) * 2013-06-11 2016-03-09 伯斯有限公司 控制anr设备中的稳定性
US10219071B2 (en) 2013-12-10 2019-02-26 Cirrus Logic, Inc. Systems and methods for bandlimiting anti-noise in personal audio devices having adaptive noise cancellation
US9807503B1 (en) 2014-09-03 2017-10-31 Cirrus Logic, Inc. Systems and methods for use of adaptive secondary path estimate to control equalization in an audio device
WO2016198481A3 (fr) * 2015-06-09 2017-01-12 Cirrus Logic International Semiconductor Limited Filtre à réponse impulsionnelle finie hybride
US10026388B2 (en) 2015-08-20 2018-07-17 Cirrus Logic, Inc. Feedback adaptive noise cancellation (ANC) controller and method having a feedback response partially provided by a fixed-response filter
US10013966B2 (en) 2016-03-15 2018-07-03 Cirrus Logic, Inc. Systems and methods for adaptive active noise cancellation for multiple-driver personal audio device

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