WO2005091676A1 - Listening device with two or more microphones - Google Patents

Listening device with two or more microphones Download PDF

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Publication number
WO2005091676A1
WO2005091676A1 PCT/EP2005/051169 EP2005051169W WO2005091676A1 WO 2005091676 A1 WO2005091676 A1 WO 2005091676A1 EP 2005051169 W EP2005051169 W EP 2005051169W WO 2005091676 A1 WO2005091676 A1 WO 2005091676A1
Authority
WO
WIPO (PCT)
Prior art keywords
signal
signals
microphone
added
listening device
Prior art date
Application number
PCT/EP2005/051169
Other languages
French (fr)
Inventor
Christian C. BÜRGER
Original Assignee
Oticon A/S
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Oticon A/S filed Critical Oticon A/S
Priority to AU2005223798A priority Critical patent/AU2005223798B2/en
Priority to US10/593,584 priority patent/US7945056B2/en
Priority to DK05717043.3T priority patent/DK1730993T3/en
Priority to AT05717043T priority patent/ATE530028T1/en
Priority to EP05717043A priority patent/EP1730993B1/en
Publication of WO2005091676A1 publication Critical patent/WO2005091676A1/en

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R25/00—Deaf-aid sets, i.e. electro-acoustic or electro-mechanical hearing aids; Electric tinnitus maskers providing an auditory perception
    • H04R25/40—Arrangements for obtaining a desired directivity characteristic
    • H04R25/405—Arrangements for obtaining a desired directivity characteristic by combining a plurality of transducers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/32—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only
    • H04R1/40—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by combining a number of identical transducers
    • H04R1/406—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by combining a number of identical transducers microphones

Definitions

  • the invention relates to listening devices like hearing aids or headsets wherein two or more microphone units are incorporated.
  • microphone units are used generally to enhance the signal to noise ratio by introducing various kinds of directional algorithms, which will ensure, that the most clear sound source in the environment is amplified whereas other less clear sound sources are dampened.
  • the user In listening devices with directional algorithms the user usually also has the possibility of choosing an omnidirectional mode, wherein the signal from one microphone is routed to the user, and this signal will then amplify all sounds in the environment irrespective of the direction of incidence.
  • Each of the microphones will have a noise floor which means that they will produce an output even if there is no sound in the environment. This noise floor is annoying to the user when there are no sounds in the environment, and also it becomes impossible to hear sounds, which lies below the noise floor.
  • two or more microphone units are provided along with a signal processing device and means for delivering a signal to the user of the device representative of the audio signals picked up by the microphones.
  • the signal processing device comprises means for adding and scaling the signals from the at least two microphone units to provide a single added signal in a manner which allows signal parts from different directions to be equally represented in the resulting added signal.
  • the addition of the two independent microphone signals gives an overall improvement of the SNR of 3 dB in all situations where the two microphone signals are uncorrelated. This is for sure the case in silent listening situations but should also cover some noisy situations like wind noise.
  • the invention addresses the directional behaviour of the added signal in higher frequencies. The directional behaviour is in fact due to phase cancellation caused by equality between the half-period of the acoustic signal and the distance between the microphone inlets. With the device according to the invention it is attempted to cancel this directional behaviour.
  • means are provided for slightly modifying, at least in a predefined frequency range, the phase and/or the level of the signal from at least one of the added microphone signals in order to avoid the occurrence of a directional effect resulting from the addition of the signals.
  • mismatches should be selected in a way, so that the directivity index of the added microphone signals is as close to 0 dB as possible at any frequency whereby also the polar response will be close to the traditional omni directional response.
  • a FIR filter for modifying the microphone signal from at least one microphone prior to the addition of the microphone signals.
  • the invention also comprises a method for processing of the microphone signals in a listening device. The method comprises the following steps: providing two or more independent microphone signals from microphones at spaced apart locations, causing a time delay between the signals and adding and scaling the at least two different microphone signals signal in a manner which allows signal parts from different directions to be equally represented in the resulting added signal.
  • the delay in at least a frequency range is a zero delay.
  • Fig. 1 shows a schematic representation of the microphone system according to the invention.
  • Fig. 2 shows the idealized amplitude characteristic of the signal from a microphone after the filtration prior to the addition of the microphone signals.
  • the system of fig. 1 has a first microphone 1 and a second microphone 2 and in order to lower the noise floor in the signal from the microphone.
  • the signal processing schematically displayed is used.
  • the signal from the first microphone 1 is subject to a FIR filter and following this the signal from the first and the second microphones are added.
  • the system also comprises a scahng of the signals, and this can be done before, during or after the addition of the two signals and it does not affect the lowering of the noise flor of the added signals.
  • the displayed system is a digital system and the microphone signals are digitized in the usual manner prior to the processing according to the invention. A similar processing would however be possible also in the analog domain.
  • the added signal from the microphones is routed to a processing device in order to provide a signal to the user according to his or her needs.
  • a processing device in order to provide a signal to the user according to his or her needs.
  • the signal is amplified, and frequency shaped according to the users hearing loss.
  • the filter When the filter is designed it should be ensured that the directional characteristic of the added microphone signal is as close to omnidirectional as possible without any distortion in the frequency characteristics of the added microphone signals. Also the number of tabs should be kept low for simplicity and to reduce time delay.
  • a possible amplitude mis-match which is realisable with the above criteria is displayed.
  • the amplitude mis-match is close to zero at all frequencies up to about 2 kHz. From about 2 to 10 kHz the amplitude mis-match between the two microphone signals should rise to a value close to two. This corresponds to a microphone distance close to 10 mm.
  • the proposed filter characteristic will be highly dependent on the distance between the microphones and it is easily shown that the close the microphones the smaller is the needed amplitude mis-match at the higher frequencies.
  • the resulting added signals will have virtually no directionality, and thus represent signals from all directions with the same amplification in the frequency range from 0 to 10 kHz. Also the resulting signal has a frequency response which only at very high frequencies close to 10 kHz will cause some attenuation.

Landscapes

  • Health & Medical Sciences (AREA)
  • Otolaryngology (AREA)
  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • General Health & Medical Sciences (AREA)
  • Neurosurgery (AREA)
  • Circuit For Audible Band Transducer (AREA)
  • Obtaining Desirable Characteristics In Audible-Bandwidth Transducers (AREA)

Abstract

The invention regards a listening device with two or more microphone units. The listening device has a signal processing device and means for delivering a signal to the user of the device representative of the audio signals picked up by the microphones, whereby the signal processing device comprises means for adding and scaling the signals from at least two microphone units to provide a single added signal in a manner which allows signal parts from different directions to be equally represented in the resulting added signal.

Description

TITLE Listening device with two or more microphones
AREA OF THE INVENTION
The invention relates to listening devices like hearing aids or headsets wherein two or more microphone units are incorporated. Such microphone units are used generally to enhance the signal to noise ratio by introducing various kinds of directional algorithms, which will ensure, that the most clear sound source in the environment is amplified whereas other less clear sound sources are dampened.
BACKGROUND OF THE INVENTION
In listening devices with directional algorithms the user usually also has the possibility of choosing an omnidirectional mode, wherein the signal from one microphone is routed to the user, and this signal will then amplify all sounds in the environment irrespective of the direction of incidence. Each of the microphones will have a noise floor which means that they will produce an output even if there is no sound in the environment. This noise floor is annoying to the user when there are no sounds in the environment, and also it becomes impossible to hear sounds, which lies below the noise floor. In order to reduce the noise from the microphones it is known to add more microphone signals. As the noise from the microphones is un-correlated this will reduce the experienced noise floor. In doing this the omnidirectional characteristic of the signal is lost, and the user will not experience a true omnidirectional response where signals from all angles of incidence are equally attenuated. It is an object of the invention to provide a listening device wherein the noise floor is reduced below the noise floor of the single microphone units in the device while keeping an omnidirectional characteristic of the signal.
SUMMARY OF THE INVENTION
According to the invention two or more microphone units are provided along with a signal processing device and means for delivering a signal to the user of the device representative of the audio signals picked up by the microphones. The signal processing device comprises means for adding and scaling the signals from the at least two microphone units to provide a single added signal in a manner which allows signal parts from different directions to be equally represented in the resulting added signal.
Basically the addition of the two independent microphone signals gives an overall improvement of the SNR of 3 dB in all situations where the two microphone signals are uncorrelated. This is for sure the case in silent listening situations but should also cover some noisy situations like wind noise. The invention addresses the directional behaviour of the added signal in higher frequencies. The directional behaviour is in fact due to phase cancellation caused by equality between the half-period of the acoustic signal and the distance between the microphone inlets. With the device according to the invention it is attempted to cancel this directional behaviour.
In an embodiment of the invention means are provided for slightly modifying, at least in a predefined frequency range, the phase and/or the level of the signal from at least one of the added microphone signals in order to avoid the occurrence of a directional effect resulting from the addition of the signals.
Hereby it is proposed to introduce a phase mismatch and/or an amplitude mismatch to the added microphone signals. The mismatches should be selected in a way, so that the directivity index of the added microphone signals is as close to 0 dB as possible at any frequency whereby also the polar response will be close to the traditional omni directional response.
It has been discovered that the amplitude mismatch primarily is needed at the highest frequencies (closest to exact phase cancellation), but that the phase cancellation is needed for the full frequency range. This is of cause depending on the accepted deviation from the traditional omni directionality.
Preferably a FIR filter is provided for modifying the microphone signal from at least one microphone prior to the addition of the microphone signals. The invention also comprises a method for processing of the microphone signals in a listening device. The method comprises the following steps: providing two or more independent microphone signals from microphones at spaced apart locations, causing a time delay between the signals and adding and scaling the at least two different microphone signals signal in a manner which allows signal parts from different directions to be equally represented in the resulting added signal.
In a preferred embodiment of the method according to the invention the delay in at least a frequency range is a zero delay.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 shows a schematic representation of the microphone system according to the invention.
Fig. 2 shows the idealized amplitude characteristic of the signal from a microphone after the filtration prior to the addition of the microphone signals.
DESCRIPTION OF A PREFERRED EMBODIMENT
The system of fig. 1 has a first microphone 1 and a second microphone 2 and in order to lower the noise floor in the signal from the microphone. Whenever non-directional mode is wished the signal processing schematically displayed is used. Here the signal from the first microphone 1 is subject to a FIR filter and following this the signal from the first and the second microphones are added. The system also comprises a scahng of the signals, and this can be done before, during or after the addition of the two signals and it does not affect the lowering of the noise flor of the added signals. The displayed system is a digital system and the microphone signals are digitized in the usual manner prior to the processing according to the invention. A similar processing would however be possible also in the analog domain.
The added signal from the microphones is routed to a processing device in order to provide a signal to the user according to his or her needs. In the case where the invention is realized in a hearing aid the signal is amplified, and frequency shaped according to the users hearing loss.
When the filter is designed it should be ensured that the directional characteristic of the added microphone signal is as close to omnidirectional as possible without any distortion in the frequency characteristics of the added microphone signals. Also the number of tabs should be kept low for simplicity and to reduce time delay.
In fig. 2 a possible amplitude mis-match which is realisable with the above criteria is displayed. As seen the amplitude mis-match is close to zero at all frequencies up to about 2 kHz. From about 2 to 10 kHz the amplitude mis-match between the two microphone signals should rise to a value close to two. This corresponds to a microphone distance close to 10 mm. The proposed filter characteristic will be highly dependent on the distance between the microphones and it is easily shown that the close the microphones the smaller is the needed amplitude mis-match at the higher frequencies. By simulation of a system with two microphone signals wherein the one signal is subject to an amplitude modification according to fig. 2 it is easily shown that the resulting added signals will have virtually no directionality, and thus represent signals from all directions with the same amplification in the frequency range from 0 to 10 kHz. Also the resulting signal has a frequency response which only at very high frequencies close to 10 kHz will cause some attenuation.
It is possible to design a FIR filter which realizes the amplitude characteristics shown in fig. 2 and at the same time allows a zero time delay at all frequencies.

Claims

1. Listening device with two or more microphone units and a signal processing device and means for delivering a signal to the user of the device representative of the audio signals picked up by the microphones, whereby the signal processing device comprises means for adding and scaling the signals from at least two microphone units to provide a single added signal in a manner which allows signal parts from different directions to be equally represented in the resulting added signal.
2. Listening device as claimed in claim 1, wherein means are provided for slightly modifying, at least in a predefined frequency range, the phase and/or the level of the signal from at least one of the added microphone signals in order to avoid the occurrence of a directional effect resulting from the addition of the signals.
3. Listening device as claimed in claim 2, wherein two microphone signals are added, and where one of the signals prior to the addition is subject to a filter which progressively raises the amplitude of frequency elements above a limit frequency and causes a zero delay at all frequencies.
4. Listening device as claimed in claim 2, wherein two microphone signals are added, and where one of the signals prior to the addition is subject to a filter which causes a delay in the order of 5-20 μs of the signal at all frequencies.
5. Listening device as claimed in claim 2, wherein a FIR filter is provided for modifying the microphone signal from at least one microphone prior to the addition of the microphone signals.
6. Method for processing of the microphone signals in a listening device comprising the following steps: providing two or more independent microphone signals from microphones at spaced apart locations, adding and scaling the at least two different microphone signals in a manner which allows signal parts from different directions to be equally represented in the resulting added signal.
7. Metliod as claimed in claim 6, whereby the phase and/or the level of the signal from at least one of the added microphone signals in at least a predefined frequency range is modified.
8. Method as claimed in claim 7, whereby one of the signals prior to the addition is subject to a filter which progressively raises the amplitude of frequency elements above a limit frequency and causes a zero delay at all frequencies.
9. Method as claimed in claim 6, whereby the modification of the signal is caused by subjecting the signal to a FIR filter.
10. Method for processing the microphone signεds as claimed in claim 6, whereby the scaling comprises the division of the added signals by the number of added signals.
PCT/EP2005/051169 2004-03-23 2005-03-15 Listening device with two or more microphones WO2005091676A1 (en)

Priority Applications (5)

Application Number Priority Date Filing Date Title
AU2005223798A AU2005223798B2 (en) 2004-03-23 2005-03-15 Listening device with two or more microphones
US10/593,584 US7945056B2 (en) 2004-03-23 2005-03-15 Listening device with two or more microphones
DK05717043.3T DK1730993T3 (en) 2004-03-23 2005-03-15 Hearing aid with two or more microphones
AT05717043T ATE530028T1 (en) 2004-03-23 2005-03-15 LISTENING DEVICE WITH TWO OR MORE MICROPHONES
EP05717043A EP1730993B1 (en) 2004-03-23 2005-03-15 Listening device with two or more microphones

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DKPA200400471 2004-03-23
DKPA200400471 2004-03-23

Publications (1)

Publication Number Publication Date
WO2005091676A1 true WO2005091676A1 (en) 2005-09-29

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Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/EP2005/051169 WO2005091676A1 (en) 2004-03-23 2005-03-15 Listening device with two or more microphones

Country Status (7)

Country Link
US (1) US7945056B2 (en)
EP (2) EP2257081B1 (en)
CN (1) CN1957638A (en)
AT (1) ATE530028T1 (en)
AU (1) AU2005223798B2 (en)
DK (2) DK1730993T3 (en)
WO (1) WO2005091676A1 (en)

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US7856240B2 (en) * 2004-06-07 2010-12-21 Clarity Technologies, Inc. Distributed sound enhancement
EP1885156B1 (en) * 2006-08-04 2013-04-24 Siemens Audiologische Technik GmbH Hearing-aid with audio signal generator
WO2009025090A1 (en) * 2007-08-22 2009-02-26 Panasonic Corporation Directivity microphone device
EP2765787B1 (en) * 2013-02-07 2019-12-11 Sennheiser Communications A/S A method of reducing un-correlated noise in an audio processing device
DK2843971T3 (en) * 2013-09-02 2019-02-04 Oticon As Hearing aid device with microphone in the ear canal
JP6464488B2 (en) * 2016-03-11 2019-02-06 パナソニックＩｐマネジメント株式会社 Sound pressure gradient microphone
KR102466134B1 (en) * 2018-06-26 2022-11-10 엘지디스플레이 주식회사 Display apparatus
RU2751440C1 (en) * 2020-10-19 2021-07-13 Федеральное государственное бюджетное образовательное учреждение высшего образования «Московский государственный университет имени М.В.Ломоносова» (МГУ) System for holographic recording and playback of audio information

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US4536887A (en) * 1982-10-18 1985-08-20 Nippon Telegraph & Telephone Public Corporation Microphone-array apparatus and method for extracting desired signal
EP0430513A2 (en) 1989-11-27 1991-06-05 Matsushita Electric Industrial Co., Ltd. Microphone apparatus
EP0509742A2 (en) 1991-04-18 1992-10-21 Matsushita Electric Industrial Co., Ltd. Microphone apparatus
EP0869697A2 (en) * 1997-04-03 1998-10-07 Lucent Technologies Inc. A steerable and variable first-order differential microphone array
US6285771B1 (en) * 1996-12-31 2001-09-04 Etymotic Research Inc. Directional microphone assembly
US20020191805A1 (en) 1996-12-11 2002-12-19 Micro Ear Technology, Inc., D/B/A Micro-Tech In-the-ear hearing aid with directional microphone system

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Publication number Priority date Publication date Assignee Title
US4536887A (en) * 1982-10-18 1985-08-20 Nippon Telegraph & Telephone Public Corporation Microphone-array apparatus and method for extracting desired signal
EP0430513A2 (en) 1989-11-27 1991-06-05 Matsushita Electric Industrial Co., Ltd. Microphone apparatus
EP0509742A2 (en) 1991-04-18 1992-10-21 Matsushita Electric Industrial Co., Ltd. Microphone apparatus
US20020191805A1 (en) 1996-12-11 2002-12-19 Micro Ear Technology, Inc., D/B/A Micro-Tech In-the-ear hearing aid with directional microphone system
US6285771B1 (en) * 1996-12-31 2001-09-04 Etymotic Research Inc. Directional microphone assembly
EP0869697A2 (en) * 1997-04-03 1998-10-07 Lucent Technologies Inc. A steerable and variable first-order differential microphone array

Also Published As

Publication number Publication date
US7945056B2 (en) 2011-05-17
EP2257081A1 (en) 2010-12-01
ATE530028T1 (en) 2011-11-15
EP2257081A8 (en) 2011-01-05
US20070147633A1 (en) 2007-06-28
AU2005223798A1 (en) 2005-09-29
EP2257081B1 (en) 2012-08-22
DK1730993T3 (en) 2012-01-23
AU2005223798B2 (en) 2010-01-28
EP1730993B1 (en) 2011-10-19
DK2257081T3 (en) 2012-11-19
CN1957638A (en) 2007-05-02
EP1730993A1 (en) 2006-12-13

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