WO2014198307A1 - Method for operating a hearing device capable of active occlusion control and a hearing device with active occlusion control - Google Patents

Method for operating a hearing device capable of active occlusion control and a hearing device with active occlusion control Download PDF

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Publication number
WO2014198307A1
WO2014198307A1 PCT/EP2013/062078 EP2013062078W WO2014198307A1 WO 2014198307 A1 WO2014198307 A1 WO 2014198307A1 EP 2013062078 W EP2013062078 W EP 2013062078W WO 2014198307 A1 WO2014198307 A1 WO 2014198307A1
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WO
WIPO (PCT)
Prior art keywords
signal
audio signal
filtered
hearing device
range
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Application number
PCT/EP2013/062078
Other languages
French (fr)
Inventor
André Niederberger
Original Assignee
Phonak Ag
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 Phonak Ag filed Critical Phonak Ag
Priority to PCT/EP2013/062078 priority Critical patent/WO2014198307A1/en
Publication of WO2014198307A1 publication Critical patent/WO2014198307A1/en

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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
    • H04R25/30—Monitoring or testing of hearing aids, e.g. functioning, settings, battery power
    • H04R25/305—Self-monitoring or self-testing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2460/00—Details of hearing devices, i.e. of ear- or headphones covered by H04R1/10 or H04R5/033 but not provided for in any of their subgroups, or of hearing aids covered by H04R25/00 but not provided for in any of its subgroups
    • H04R2460/03—Aspects of the reduction of energy consumption in hearing devices
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2460/00—Details of hearing devices, i.e. of ear- or headphones covered by H04R1/10 or H04R5/033 but not provided for in any of their subgroups, or of hearing aids covered by H04R25/00 but not provided for in any of its subgroups
    • H04R2460/05—Electronic compensation of the occlusion effect

Definitions

  • the present invention is related to a method of operating a hearing device capable of active occlusion control (AOC) as well as to a hearing device adapted to perform the method.
  • AOC active occlusion control
  • the present invention is directed to
  • hearing devices for instance comprise hearing aids, such as in-the-ear (ITE), completely-in-canal (CIC) or behind-the-ear (BTE) hearing aids, earphones, hearing protection devices, as well as ear-level communication, noise reduction and sound enhancement devices.
  • Hearing aids also commonly referred to as hearing instruments or hearing prostheses
  • ITE in-the-ear
  • CIC completely-in-canal
  • BTE behind-the-ear
  • occlusion effect occurs when an object fills the outer portion of a person's ear canal (commonly also referred to as the auditory canal) and is especially pronounced when the ear canal is sealed, e.g. by an otoplastic. It is caused by bone-conducted sound vibrations reverberating off the object filling the ear canal.
  • the occlusion effect can be reduced by employing large vents. However, large vents give rise to increased acoustic feedback, so the amount of amplification that is applied by a hearing device must be limited in order to avoid it generating unpleasant
  • transducer transmission function which is defined for the transmission path from the input of the receiver via the auditory canal to the output of the microphone, is measured and the filter can for instance be adjusted as a function thereof.
  • an optimal filter is selected during the process of hearing device fitting, i.e. adjusting the hearing device settings to the needs of the user, by a hearing device professional such as a hearing device acoustician based on a variety of criteria, such as for example the user's impression/perception of his/her own voice .
  • the combining of the filtered version of the audio signal picked up by the ear canal microphone with a processed, e.g. amplified, version of an audio signal picked up by an ambient microphone can also result in undesirable artefacts which degrade the user' s hearing experience.
  • a further disadvantage of using such an occlusion reduction scheme is that the computations that need to be performed require a considerable amount of processing power, which leads to an increase in the power consumption of the hearing device and consequently reduces the amount of time the hearing device can operate until the battery is empty and has to be exchanged.
  • AOC active occlusion control
  • the present invention is first directed to a method for operating a hearing device adapted for being worn at least partially within an ear canal of a user, the hearing device comprising an ambient microphone, a signal processing unit, a receiver, and an ear canal microphone, the method
  • step h) comprises the steps:
  • step i) applying the gain to the filtered second audio signal is dependent on the comparing the first and the second extracted signal, in particular applying a gain of zero if a difference between the first and the second extracted signal, or a difference between processed versions of the first and second extracted signals, is outside of a predefined interval or greater than a
  • step hi) comprises bandpass filtering the combined audio signal with a first bandpass filter having a passband for a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60 Hz
  • step h2) comprises bandpass filtering the second audio signal with a second bandpass filter having a passband for a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60 Hz.
  • the method further comprises detecting whether a body sound of the user is present or not with an own voice (own body sound) detection unit, and wherein at least one of steps d) to i) is not carried out if no body sound of the user is detected.
  • the filtering unit has a frequency response with a notch, a centre frequency of the notch being in a range from 100 Hz to 300 Hz and an attenuation of the notch at the centre frequency being at least 10 dB.
  • the filtering unit comprises up to 5 bi-quad sections which can be
  • the low frequency signal is one of a sinusoidal tone, a multisine signal or a narrowband noise.
  • the magnitude and/or the frequency of the low frequency signal is selected dependent on the user's hearing loss or hearing ability.
  • the magnitude and/or the frequency of the low frequency signal is adjusted dependent on at least one of:
  • a transfer function from an output of the receiver to the input of the ear canal microphone measured during fitting of the hearing device in particular a magnitude of the transfer function within a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60 Hz;
  • step h3 At least one of the following operations is applied to the first and/or second extracted signal:
  • step h3) comprises performing a range check on a difference between the first and the second extracted signal or a processed version of first and the second extracted signal, and step i) is dependent on the outcome of the range check.
  • the method further comprises monitoring over time of the first and/or second extracted signals and/or of processed versions of the first and second extracted signals.
  • the method further comprises the step of changing the frequency response of the filtering unit dependent on the monitoring over time, in particular if a difference between the first and the second extracted signal or between processed versions of the first and the second extracted signal is outside of a predefined interval or greater than a predefined value during most (e.g. during more than 50%, preferably during more than 80%) of a period of time, in particular during a period of time of at least 10 seconds.
  • a rate of repeating at least one of steps e) , h) and j) is dependent on the step hi) . It is a further object of the present invention, as a second aspect, to provide a method for operation a hearing device with active occlusion control (AOC) where unpleasant sounding artefacts resulting from combining a processed version of an audio signal picked up by an ambient micro and a filtered version of an audio signal picked up by an ear canal microphone are prevented.
  • AOC active occlusion control
  • This object of the invention is especially achieved by the method according to claim 15 and by the hearing device according to claim 36.
  • the method further comprises as part of step f) calculating a first sum of the processed first audio signal and the filtered second audio signal with a first adder having a first range of representable output values, and determining if the first sum is within the first range of representable output values for
  • the method further comprises as part of step f) calculating a second sum of the processed first audio signal and the filtered second audio signal with a second adder having a second range of representable output values which is a sub-range of the first range of representable output values, and determining if the second sum is within the second range of representable output values for detecting clipping/saturation of the second adder output.
  • the method further comprises monitoring a rate of change of the spectrum, in particular for helping to detect clipping/saturation of the combined audio signal.
  • the method further comprises estimating a level of the combined audio signal, in particular for detecting clipping/saturation of the
  • the method further comprises reducing the gain applied to the filtered second audio signal dependent on if clipping/saturation (or a nearness to clipping/saturation) of at least one of the first adder output, the second adder output, and the combined audio signal is detected.
  • AOC active occlusion control
  • This object of the invention is especially achieved by the method according to claims 4 and 21 and by the hearing device according to claims 25 and 42.
  • the method further comprises determining at least one of the following signal
  • characteristics of the first and the second audio signal - broadband level
  • the present invention is directed to a hearing device adapted for being worn at least partially within an ear canal of a user, the hearing device comprising:
  • an ambient microphone for picking up an ambient sound at an input of the ambient microphone and providing a first audio signal representing the ambient sound at an output of the ambient microphone
  • a signal processing unit adapted to process the first audio signal provided at an input of the signal
  • a filtering unit for filtering the second audio signal provided at an input to the filtering unit configured to reduce a perceived level of body sounds produced by the user, and providing a filtered second audio signal at an output of the filtering unit;
  • a signal generator adapted to generate a low frequency signal, which is preferably not audible for the user, in particular within a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60
  • a signal combiner adapted to combine the processed first audio signal provided at a first input of the signal combiner, the filtered second audio signal provided at a second input of the signal combiner, and the low
  • a signal analysis unit adapted to analyse the combined audio signal and the second audio signal
  • a gain element adapted to apply .
  • a gain to the filtered second audio signal provided at an input to the gain element dependent on the outcome of analysing the combined audio signal and the second audio signal.
  • the signal analysis unit comprises: - a first signal extraction unit adapted to perform low frequency signal extraction on the combined audio signal provided at an input to the first signal extraction unit and providing a first extracted signal at an output of the first signal extraction unit; - a second signal extraction unit adapted to perform low frequency signal extraction on the second audio signal provided at an input to the second signal extraction unit and providing a second extracted signal at an output of the second signal extraction unit; and
  • a signal comparator adapted to compare the first and the second extracted signal, respectively, provided at a first and second input, respectively, of the signal comparator and to provide a comparison result at an output of the signal comparator
  • the gain element is adapted to apply a gain to the filtered second audio signal provided at an input to the gain element dependent on the comparison result provided at a further input of gain element, in particular adapted to apply a gain of zero if the comparison result indicates that a difference between the first and the second
  • the first signal extraction unit comprises a first bandpass filter having a passband for a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60 Hz
  • the second signal extraction unit comprises a second bandpass filter having a passband for a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60 Hz.
  • the hearing device further comprises a first bandpass filter having a passband for a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60 Hz.
  • an own voice (own body sound) detection unit adapted to detect whether a body sound of the user is present or not and to deactivate, in particular to switch to a lower-power state, more particularly power off, at least one of the filtering unit, the signal generator, the first bandpass filter, and the second bandpass filter, if no body sound of the user is detected.
  • the filtering unit has a frequency response with a notch, a centre frequency of the notch being in a range from 100 Hz to 300 Hz and an attenuation of the notch at the centre frequency being at least 10 dB.
  • the filtering unit comprises up to 5 bi-quad sections which are
  • the low frequency signal is one of a sinusoidal tone, a multisine signal or a narrowband noise.
  • the magnitude and/or the frequency of the low frequency signal is selectable dependent on the user' s hearing loss or hearing ability .
  • the magnitude and/or the frequency of the low frequency signal is adapted to be adjusted dependent on at least one of: - a transfer function from an output of the receiver to the input of the ear canal microphone measured during fitting of the hearing device, in particular a magnitude of the transfer function within a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60 Hz;
  • the hearing device further comprises
  • a range checking unit adapted to perform a range check on a difference between the first and the second extracted signal, respectively, or a processed version of first and the second extracted signal, respectively, provided to a first and to a second input of the range checking unit, and to provide an outcome of the of the range check at an output of the range checking unit, and wherein the gain element is adapted to apply the gain to the filtered second audio signal provided at the input to the gain element dependent on the outcome of the range check provided at the further input of gain element.
  • a monitoring unit adapted to monitor over time the first and/or second extracted signals and/or processed versions of the first and second extracted signals.
  • monitoring unit is adapted to change the frequency response of the filtering unit dependent on the monitoring over time, in particular if a difference between the first and the second extracted signal or between processed versions of the first and the second extracted signal is greater than a predefined value during most of a period of time, in particular during a period of time of at least 10 seconds.
  • at least one of the signal generator, the first bandpass filter, the second bandpass filter, the signal comparator (14), and the gain element is adaptable such that an operating frequency thereof is dependent on the comparison result.
  • the signal combiner comprises a first adder having a first range of representable output values, and adapted to calculate a first sum of the processed first audio signal and the filtered second audio signal and to determine if the first sum is within the first range of representable output values for detecting clipping/saturation of the first adder output .
  • the signal combiner comprises a second adder having a second range of representable output values which is a sub-range of the first range of representable output values, and adapted to calculate a second sum of the processed first audio signal and the filtered second audio signal and to determine if the second sum is within the second range of representable output values for detecting clipping/saturation of the second adder output.
  • a spectrum monitoring unit adapted to monitor a spectrum of at least one of the following signals: - processed first audio signal or a filtered/time-averaged version of the processed first audio signal;
  • the spectrum monitoring unit is further adapted to monitor a rate of change of the spectrum, in particular for helping to detect clipping/saturation of the combined audio signal.
  • the hearing device comprises a level estimator adapted to estimate a level of the combined audio signal, in particular for detecting clipping/saturation of the combined audio signal, and in particular by performing at least one of monitoring a level of the first audio signal, estimating a (frequency- dependent) gain to be applied when processing the first audio signal in the signal processing unit, and monitoring the second audio signal.
  • the gain element is adapted to reduce the gain applied to the filtered second audio signal dependent on if
  • the filtering unit to compare the determined signal characteristics of the first and the second audio signal, and deactivate, in particular switch to a lower-power state, more particularly power off, at least one of the filtering unit, the signal generator, the first bandpass filter, the second bandpass filter, and the own voice detection unit, if the result of comparing indicates that the determined signal characteristics of the first and the second audio signal differ by less than a predetermined threshold value.
  • Fig. 1 depicts a schematic high-level block diagram of an exemplary hearing device 1 according to the present
  • the ear canal microphone 5 picks up the sound present within the ear canal an applies the output signal of the ear canal microphone 5 to the filtering unit 6, which is configured to modify the input signal
  • the filtered signal will reduce the level of the own voice sound within the ear canal, by superposition of sound produced by the receiver 4 based on the filtered signal and own voice sound produced by the user.
  • This is achieved by combining the filtered signal from the filtering unit 6 with the processed signal from the signal processing unit 1 by means of the signal combiner 13 and outputting the combined signal via the receiver 4 into the ear canal.
  • the present invention adapts the gain of the signal output by the filtering unit 6 by means of the gain element 15.
  • the gain depends on the low-frequency transfer function of the sound path from the receiver output to the ear canal microphone input. If this transfer function exhibits a high level of low-frequency gain, the gain at the output of the filtering unit is reduced accordingly.
  • a low- frequency "watermark" signal is generated within the hearing device 1 by the signal generator 7 and combined with the processed signal and the filtered signal and then output via the receiver 4 into the ear canal.
  • the frequency of the "watermark” signal is chosen to be lower than the lowest frequency components of human speech. This frequency can be chosen dependent on the lowest frequency components of the specific user's speech.
  • the watermark signal is amplified within the ear canal. The level of amplification experienced by the "watermark” signal can then be determined by comparing the level of the
  • the signal applied to the receiver 4 is also bandpass filtered by means of a second bandpass filter 9 which is preferably identical to the first bandpass filter 8 (see for instance the exemplary magnitude response depicted in Fig. 2) .
  • the low-frequency gain of the sound path from the receiver 4 through the ear canal to the ear canal microphone 5 can then be determined by comparing the level of the output signals of the first and second bandpass filters 8, 9 by means of the signal comparator 14. If the low-frequency gain determined out the output of the signal comparator 14 is outside of a certain range, e.g. larger than a
  • the gain provided by the gain element 15 is set to zero, so that the output signal of the
  • filtering unit 6 has no effect of the sound generated by the receiver 4, and therefore the feedback loop is
  • Fig. 3 illustrates a schematic signal flow diagram of a further exemplary embodiment of a hearing device especially according to the second aspect of the present invention, which aims to prevent saturation when combining the output of the signal processing unit 3 and the output of the filtering unit 6 in the signal combiner 13.
  • the sum of environmental sound and own voice conducted through the air is picked up by an ambient microphone r M i CExt and applied to hearing device amplification and pre-equalised, yielding the signal u H i .
  • Ear canal sound is picked up by the ear canal microphone located in the ear canal, yielding the signal y ic- This ear canal signal is then filtered by AOC filter C, yielding the signal u AO c- The two signals u H i and UAOC are then added to give u Rec , and applied to the
  • the behaviour of the adder is directly monitored, for example by detecting if a
  • saturation flag has been set.
  • the output of said adder is passed to a saturation block with upper and lower limits closer to zero than the signal range allowed. If there is a tendency towards clipping, this adder would clip first without causing artefacts on the actual adder. This could be detected by monitoring an additional saturation flag.
  • the spectrum or bandpass-filtered (or otherwise filtered) versions of one or several of the following signals are investigated:
  • aforementioned signals, or bandpass-filtered (or otherwise filtered) versions thereof, or of their spectrum are monitored.
  • the level of the external sound is monitored and together with an estimate of the amplification applied in the signal processing unit an estimate of the level of the receiver signal is determined. If any of these methods indicates a nearness to clipping, the gain applied to the AOC filter and the associated blocks will be adjusted, for example reduced.
  • Fig. 4 illustrates a further schematic signal flow diagram of another exemplary embodiment of a hearing device especially according to the third aspect of the present invention, which aims to turn off automatic occlusion control if the hearing device is for instance not inserted into the ear canal or when level of own voice sound is too low.
  • the ear canal and ambient microphone signals are applied to the signal processing unit. Their signal characteristics are compared, for example:
  • the hearing device is probably not inserted, or no signal such as own voice is present to be cancelled.
  • the activity of the AOC system is changed, for example reduced to a lower value or zero, i.e. disabled.

Abstract

The present invention is related to a method of operating a hearing device (1) capable of active occlusion control (AOC) as well as to a hearing device (1) adapted to perform the method. In particular, the present invention is directed to preventing instabilities, avoiding saturation of the output transducer (e.g. receiver) as well as saving power in a hearing device employing AOC. As part of the proposed method a low frequency signal, which is preferably not audible for the user, is generated within the hearing device (1) and combined with a processed version of an audio signal picked, up by an ambient microphone (2) as well as a filtered version of an audio signal picked up by an ear canal microphone (5), and outputting the combined audio signal via a receiver (4) into an ear canal of the user. Furthermore, a gain is applied to the filtered version of the audio signal picked up by an ear canal microphone (5), whereby the gain is dependent on the outcome of analysing at least the audio signal picked up by the ear canal microphone (5) and for instance also the combined audio signal applied to the receiver (4).

Description

METHOD FOR OPERATING A HEARING DEVICE CAPABLE OF ACTIVE OCCLUSION CONTROL AND A HEARING DEVICE WITH ACTIVE OCCLUSION CONTROL
TECHNICAL FIELD
The present invention is related to a method of operating a hearing device capable of active occlusion control (AOC) as well as to a hearing device adapted to perform the method. In particular, the present invention is directed to
preventing instabilities, avoiding saturation of the output transducer (e.g. receiver) as well as saving power in a hearing device employing AOC.
BACKGROUND OF THE INVENTION
Within the context of the present invention hearing devices for instance comprise hearing aids, such as in-the-ear (ITE), completely-in-canal (CIC) or behind-the-ear (BTE) hearing aids, earphones, hearing protection devices, as well as ear-level communication, noise reduction and sound enhancement devices. Hearing aids (also commonly referred to as hearing instruments or hearing prostheses) are specifically utilised by persons having a hearing
impairment, in order to compensate their hearing loss and improve their hearing ability as much as possible to the level of a person with normal hearing.
Users' most frequent complaint about hearing devices, especially when they start wearing them for the first time, is that the sound of their own voice is too loud or that it sounds like they are talking into a barrel. This so-called "occlusion effect" occurs when an object fills the outer portion of a person's ear canal (commonly also referred to as the auditory canal) and is especially pronounced when the ear canal is sealed, e.g. by an otoplastic. It is caused by bone-conducted sound vibrations reverberating off the object filling the ear canal. The occlusion effect can be reduced by employing large vents. However, large vents give rise to increased acoustic feedback, so the amount of amplification that is applied by a hearing device must be limited in order to avoid it generating unpleasant
whistling and squealing sounds. Alternatively, methods exist for actively reducing occlusion such as described in EP 2 104 376 A2. Hereby, sound in the auditory canal is picked up by a microphone and the microphone signal is applied to a filter. The filtered microphone signal is fed back to an input of a receiver which is used to emit the sound into the auditory canal. At least part of a
transducer transmission function, which is defined for the transmission path from the input of the receiver via the auditory canal to the output of the microphone, is measured and the filter can for instance be adjusted as a function thereof. Typically, an optimal filter is selected during the process of hearing device fitting, i.e. adjusting the hearing device settings to the needs of the user, by a hearing device professional such as a hearing device acoustician based on a variety of criteria, such as for example the user's impression/perception of his/her own voice .
A major problem encountered when using such an occlusion reduction scheme based on filtering the audio signal picked up by the ear canal microphone and outputting the filtered audio signal via the receiver into the ear canal is that instabilities can occur, which are manifested as loud
"whistling" sounds that are very unpleasant for the user. This can for instance occur when the seat of the hearing device within the ear is much better (i.e. increased sealing of the ear canal) than it was during the fitting process, which leads to an increased amplification of low frequency signals within the ear canal. If the filter designed/adjusted to operate in the situation where the hearing device is being worn with a comfortable, loose fit is used in a situation where the hearing device is being worn with a tight fit, i.e. with increased sealing, thus preventing sound from exiting the rear end of the ear canal to the exterior of the ear canal, resulting in a higher low frequency gain (at frequencies below 200 Hz) , instability will occur, which gives rise to unpleasant sounding artefacts. Moreover, the combining of the filtered version of the audio signal picked up by the ear canal microphone with a processed, e.g. amplified, version of an audio signal picked up by an ambient microphone can also result in undesirable artefacts which degrade the user' s hearing experience. A further disadvantage of using such an occlusion reduction scheme is that the computations that need to be performed require a considerable amount of processing power, which leads to an increase in the power consumption of the hearing device and consequently reduces the amount of time the hearing device can operate until the battery is empty and has to be exchanged.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method for operation a hearing device with active occlusion control (AOC) where instabilities are prevented.
This object of the invention is achieved by the method according to claim 1 and by the hearing device according to claim 22. Specific embodiments are provided in the
dependent claims.
The present invention is first directed to a method for operating a hearing device adapted for being worn at least partially within an ear canal of a user, the hearing device comprising an ambient microphone, a signal processing unit, a receiver, and an ear canal microphone, the method
comprising the steps of: a) picking up an ambient sound at an input of the ambient microphone which provides a first audio signal
representing the ambient sound;
b) processing the first audio signal in the signal
processing unit which provides a processed first audio signal;
c) picking up an ear canal internal sound at an input of the ear canal microphone which provides a second audio signal representing the ear canal internal sound;
d) filtering the second audio signal with a filtering unit configured to reduce a perceived level of body sounds produced by the user, the filtering unit providing a filtered second audio signal;
e) generating with a signal generator a low frequency
signal, which is preferably not audible for the user, in particular within a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60 Hz, and having a low magnitude within a magnitude range from 30 dB to 60 dB, in particular within a magnitude range from 40 dB to 50 dB;
f) combining the processed first audio signal, the filtered second audio signal and the low frequency signal
yielding a combined audio signal;
g) applying the combined audio signal to an input of a
receiver which outputs sound into an ear canal of the user;
h) analysing at least the second audio signal and for
instance also the combined audio signal; and i) applying a gain to the filtered second audio signal dependent on the outcome of analysing at least the second audio signal and for instance also the combined audio signal.
In an embodiment of the proposed method step h) comprises the steps:
hi) performing low frequency signal extraction on the
combined audio signal providing a first extracted signal ;
h2) performing low frequency signal extraction on the
second audio signal providing a second extracted signal; and
h3) comparing the first and the second extracted signal, and wherein in step i) applying the gain to the filtered second audio signal is dependent on the comparing the first and the second extracted signal, in particular applying a gain of zero if a difference between the first and the second extracted signal, or a difference between processed versions of the first and second extracted signals, is outside of a predefined interval or greater than a
predefined value.
In a further embodiment of the method step hi) comprises bandpass filtering the combined audio signal with a first bandpass filter having a passband for a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60 Hz, and step h2) comprises bandpass filtering the second audio signal with a second bandpass filter having a passband for a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60 Hz.
In a further embodiment the method further comprises detecting whether a body sound of the user is present or not with an own voice (own body sound) detection unit, and wherein at least one of steps d) to i) is not carried out if no body sound of the user is detected.
In a further embodiment of the method the filtering unit has a frequency response with a notch, a centre frequency of the notch being in a range from 100 Hz to 300 Hz and an attenuation of the notch at the centre frequency being at least 10 dB.
In a further embodiment of the method the filtering unit comprises up to 5 bi-quad sections which can be
individually activated.
In a further embodiment of the method the low frequency signal is one of a sinusoidal tone, a multisine signal or a narrowband noise. In a further embodiment of the method the magnitude and/or the frequency of the low frequency signal is selected dependent on the user's hearing loss or hearing ability.
In a further embodiment of the method the magnitude and/or the frequency of the low frequency signal is adjusted dependent on at least one of:
- a transfer function from an output of the receiver to the input of the ear canal microphone measured during fitting of the hearing device, in particular a magnitude of the transfer function within a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60 Hz;
- a value derived from the second audio signal (for
instance representative of a sound pressure level within the ear canal) ;
- a value derived from the first audio signal.
In a further embodiment of the method prior to comparing in step h3) at least one of the following operations is applied to the first and/or second extracted signal:
- absolute value;
- conversion to a logarithmic scale, for instance
conversion to decibel scale; - low-pass filtering, in particular yielding a measure of the power of the first and/or second extracted signal.
In a further embodiment of the method step h3) comprises performing a range check on a difference between the first and the second extracted signal or a processed version of first and the second extracted signal, and step i) is dependent on the outcome of the range check.
In a further embodiment the method further comprises monitoring over time of the first and/or second extracted signals and/or of processed versions of the first and second extracted signals.
In a further embodiment the method further comprises the step of changing the frequency response of the filtering unit dependent on the monitoring over time, in particular if a difference between the first and the second extracted signal or between processed versions of the first and the second extracted signal is outside of a predefined interval or greater than a predefined value during most (e.g. during more than 50%, preferably during more than 80%) of a period of time, in particular during a period of time of at least 10 seconds.
In a further embodiment of the method a rate of repeating at least one of steps e) , h) and j) is dependent on the step hi) . It is a further object of the present invention, as a second aspect, to provide a method for operation a hearing device with active occlusion control (AOC) where unpleasant sounding artefacts resulting from combining a processed version of an audio signal picked up by an ambient micro and a filtered version of an audio signal picked up by an ear canal microphone are prevented.
This object of the invention is especially achieved by the method according to claim 15 and by the hearing device according to claim 36.
In a further embodiment, especially directed to the second aspect of the invention, the method further comprises as part of step f) calculating a first sum of the processed first audio signal and the filtered second audio signal with a first adder having a first range of representable output values, and determining if the first sum is within the first range of representable output values for
detecting clipping/saturation of the first adder output.
In a further embodiment the method further comprises as part of step f) calculating a second sum of the processed first audio signal and the filtered second audio signal with a second adder having a second range of representable output values which is a sub-range of the first range of representable output values, and determining if the second sum is within the second range of representable output values for detecting clipping/saturation of the second adder output.
In a further embodiment the method further comprises monitoring a spectrum of at least one of the following signals :
- processed first audio signal or a filtered/time-averaged version of the processed first audio signal; - filtered second audio signal or a further filtered/time- averaged version of the filtered second audio signal;
- a further filtered or time-averaged version of the
second audio signal;
- a sum of the processed first audio signal and the
filtered second audio signal or a filtered/time-averaged version of the sum,
in particular for detecting clipping/saturation of the combined audio signal.
In a further embodiment the method further comprises monitoring a rate of change of the spectrum, in particular for helping to detect clipping/saturation of the combined audio signal.
In a further embodiment the method further comprises estimating a level of the combined audio signal, in particular for detecting clipping/saturation of the
combined audio signal, and in particular by performing at least one of monitoring a level of the first audio signal, estimating a (frequency-dependent) gain to be applied when processing the first audio signal in the signal processing unit, and monitoring the second audio signal.
In a further embodiment the method further comprises reducing the gain applied to the filtered second audio signal dependent on if clipping/saturation (or a nearness to clipping/saturation) of at least one of the first adder output, the second adder output, and the combined audio signal is detected.
It is a further object of the present invention, as a third aspect, to provide a method for operation a hearing device with active occlusion control (AOC) where the computational load can be reduced and power can be saved.
This object of the invention is especially achieved by the method according to claims 4 and 21 and by the hearing device according to claims 25 and 42.
In a further embodiment, especially directed to the third aspect of the invention, the method further comprises determining at least one of the following signal
characteristics of the first and the second audio signal: - broadband level;
- fluctuation or rise/decay rate of broadband level;
- bandpass filtered level;
- fluctuation or rise/decay rate of bandpass filtered
level;
- magnitude of at least one low-frequency spectral
component below 100 Hz, in particular below 60 Hz;
- fluctuation of or rise/decay rate of magnitude of at
least one low-frequency spectral component below 100 Hz, in particular below 60 Hz,
comparing the determined signal characteristics of the first and the second audio signal, and deactivating, in particular switching to a lower-power state, more
particularly powering off, at least one of the filtering units, the signal generator, the first bandpass filter, the second bandpass filter, and the own voice detection unit, if the result of comparing indicates that the determined signal characteristics of the first and the second audio signal differ by less than a predetermined threshold value. Alternatively, instead of completely switching off the filtering unit configured to reduce the perceived level of body sounds produced by the user, the number of active bi- quad stages comprising the filtering unit can be reduced dependent on the result of comparing in order to save power. Moreover, the present invention is directed to a hearing device adapted for being worn at least partially within an ear canal of a user, the hearing device comprising:
- an ambient microphone for picking up an ambient sound at an input of the ambient microphone and providing a first audio signal representing the ambient sound at an output of the ambient microphone;
- a signal processing unit adapted to process the first audio signal provided at an input of the signal
processing unit and to provide a processed first audio signal at an output of the signal processing unit;
- an ear canal microphone for picking up an ear canal
internal sound at an input of the ear canal microphone and providing a second audio signal representing the ear canal internal sound at an output of the ear canal microphone ;
- a filtering unit for filtering the second audio signal provided at an input to the filtering unit configured to reduce a perceived level of body sounds produced by the user, and providing a filtered second audio signal at an output of the filtering unit;
- a signal generator adapted to generate a low frequency signal, which is preferably not audible for the user, in particular within a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60
Hz, and having a low magnitude within a magnitude range from 30 dB to 60 dB, in particular within a magnitude range from 40 dB to 50 dB; - a signal combiner adapted to combine the processed first audio signal provided at a first input of the signal combiner, the filtered second audio signal provided at a second input of the signal combiner, and the low
frequency signal provided at a third input of the signal combiner, and to provide a combined audio signal at an output of the signal combiner;
- a receiver for outputting the combined audio signal
provided at an input of the receiver as sound into an ear canal of the user;
- a signal analysis unit adapted to analyse the combined audio signal and the second audio signal; and
- a gain element adapted to apply . a gain to the filtered second audio signal provided at an input to the gain element dependent on the outcome of analysing the combined audio signal and the second audio signal.
In an embodiment of the hearing device the signal analysis unit comprises: - a first signal extraction unit adapted to perform low frequency signal extraction on the combined audio signal provided at an input to the first signal extraction unit and providing a first extracted signal at an output of the first signal extraction unit; - a second signal extraction unit adapted to perform low frequency signal extraction on the second audio signal provided at an input to the second signal extraction unit and providing a second extracted signal at an output of the second signal extraction unit; and
- a signal comparator adapted to compare the first and the second extracted signal, respectively, provided at a first and second input, respectively, of the signal comparator and to provide a comparison result at an output of the signal comparator, and
wherein the gain element is adapted to apply a gain to the filtered second audio signal provided at an input to the gain element dependent on the comparison result provided at a further input of gain element, in particular adapted to apply a gain of zero if the comparison result indicates that a difference between the first and the second
extracted signal, or a difference between processed
versions of the first and second extracted signals, is outside of a predefined interval or greater than a
predefined value.
In a further embodiment of the hearing device the first signal extraction unit comprises a first bandpass filter having a passband for a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60 Hz, and wherein the second signal extraction unit comprises a second bandpass filter having a passband for a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60 Hz. In a further embodiment the hearing device further
comprising an own voice (own body sound) detection unit adapted to detect whether a body sound of the user is present or not and to deactivate, in particular to switch to a lower-power state, more particularly power off, at least one of the filtering unit, the signal generator, the first bandpass filter, and the second bandpass filter, if no body sound of the user is detected.
In a further embodiment of the hearing device the filtering unit has a frequency response with a notch, a centre frequency of the notch being in a range from 100 Hz to 300 Hz and an attenuation of the notch at the centre frequency being at least 10 dB.
In a further embodiment of the hearing device the filtering unit comprises up to 5 bi-quad sections which are
individually activatable.
In a further embodiment of the hearing device the low frequency signal is one of a sinusoidal tone, a multisine signal or a narrowband noise.
In a further embodiment of the hearing device the magnitude and/or the frequency of the low frequency signal is selectable dependent on the user' s hearing loss or hearing ability . In a further embodiment of the hearing device the magnitude and/or the frequency of the low frequency signal is adapted to be adjusted dependent on at least one of: - a transfer function from an output of the receiver to the input of the ear canal microphone measured during fitting of the hearing device, in particular a magnitude of the transfer function within a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60 Hz;
- a value derived from the second audio signal (for
instance representative of a sound pressure level within the ear canal) ;
- a value derived from the first audio signal.
In a further embodiment the hearing device further
comprises one or more operational units for performing at least one of the following operations to the first and/or second extracted signal or to signals derived from the first and/or second extracted signal:
- absolute value;
- conversion to a logarithmic scale, for instance
conversion to decibel scale;
- low-pass filtering,
in particular for providing a measure of the power of the first and/or second extracted signal. In a further embodiment the hearing device further
comprises a range checking unit adapted to perform a range check on a difference between the first and the second extracted signal, respectively, or a processed version of first and the second extracted signal, respectively, provided to a first and to a second input of the range checking unit, and to provide an outcome of the of the range check at an output of the range checking unit, and wherein the gain element is adapted to apply the gain to the filtered second audio signal provided at the input to the gain element dependent on the outcome of the range check provided at the further input of gain element.
In a further embodiment the hearing device further
comprises a monitoring unit adapted to monitor over time the first and/or second extracted signals and/or processed versions of the first and second extracted signals.
In a further embodiment of the hearing device the
monitoring unit is adapted to change the frequency response of the filtering unit dependent on the monitoring over time, in particular if a difference between the first and the second extracted signal or between processed versions of the first and the second extracted signal is greater than a predefined value during most of a period of time, in particular during a period of time of at least 10 seconds. In a further embodiment of the hearing device at least one of the signal generator, the first bandpass filter, the second bandpass filter, the signal comparator (14), and the gain element is adaptable such that an operating frequency thereof is dependent on the comparison result.
In a further embodiment of the hearing device the signal combiner comprises a first adder having a first range of representable output values, and adapted to calculate a first sum of the processed first audio signal and the filtered second audio signal and to determine if the first sum is within the first range of representable output values for detecting clipping/saturation of the first adder output .
In a further embodiment of the hearing device the signal combiner comprises a second adder having a second range of representable output values which is a sub-range of the first range of representable output values, and adapted to calculate a second sum of the processed first audio signal and the filtered second audio signal and to determine if the second sum is within the second range of representable output values for detecting clipping/saturation of the second adder output.
In a further embodiment the hearing device further
comprises a spectrum monitoring unit adapted to monitor a spectrum of at least one of the following signals: - processed first audio signal or a filtered/time-averaged version of the processed first audio signal;
- filtered second audio signal or a further filtered/time- averages version of the filtered second audio signal; - a further filtered or time-averaged version of the
second audio signal;
- a sum of the processed first audio signal and the
filtered second audio signal or a filtered/time-averaged version of the sum,
in particular for detecting (nearness to)
clipping/saturation of the combined audio signal.
In a further embodiment of the hearing device the spectrum monitoring unit is further adapted to monitor a rate of change of the spectrum, in particular for helping to detect clipping/saturation of the combined audio signal.
In a further embodiment the hearing device further
comprises a level estimator adapted to estimate a level of the combined audio signal, in particular for detecting clipping/saturation of the combined audio signal, and in particular by performing at least one of monitoring a level of the first audio signal, estimating a (frequency- dependent) gain to be applied when processing the first audio signal in the signal processing unit, and monitoring the second audio signal. In a further embodiment of the hearing device the gain element is adapted to reduce the gain applied to the filtered second audio signal dependent on if
clipping/saturation of at least one of the first adder output, the second adder output, and the combined audio signal is detected.
In a further embodiment of the hearing device the signal analysis unit is further adapted to determine at least one of the following signal characteristics of the first and the second audio signal:
- broadband level;
- fluctuation or rise/decay rate of broadband level;
- bandpass filtered level; - fluctuation or rise/decay rate of bandpass filtered
level;
- magnitude of at least one low-frequency spectral
component below 100 Hz, in particular below 60 Hz;
- fluctuation of or rise/decay rate of magnitude of at
least one low-frequency spectral component below 100 Hz, in particular below 60 Hz,
to compare the determined signal characteristics of the first and the second audio signal, and deactivate, in particular switch to a lower-power state, more particularly power off, at least one of the filtering unit, the signal generator, the first bandpass filter, the second bandpass filter, and the own voice detection unit, if the result of comparing indicates that the determined signal characteristics of the first and the second audio signal differ by less than a predetermined threshold value.
It is to be pointed out that combinations of the above- mentioned embodiments give rise to even further, more specific embodiments according to the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is further explained below by means of non-limiting specific embodiments and with reference to the accompanying drawings. What is shown in the figures i the following:
a schematic block diagram of an exemplary hearing device according to the present invention;
a graph of a transfer function (magnitude & phase response) for an exemplary bandpass filter with a centre frequency of 55 Hz;
a schematic signal flow diagram of a further exemplary hearing device especially according to the second aspect of the present invention; and a schematic signal flow diagram of another exemplary hearing device especially according to the second aspect of the present invention. In the figures, like reference signs refer to like parts.
DETAILED DESCRIPTION OF THE INVENTION
Fig. 1 depicts a schematic high-level block diagram of an exemplary hearing device 1 according to the present
invention. As is usual in many hearing devices ambient sound from the surroundings of the user are picked up by the ambient microphone 2 of the hearing device 1. The output signal from the ambient microphone 2 is then
processed, e.g. by applying frequency-dependent
amplification, in the signal processing unit 3, and the processed signal is subsequently output by the receiver 4 into the ear canal of the user. In order to reduce the level of occlusion experienced by the user, when the user's own voice or other body sounds are present within the ear canal, the ear canal microphone 5 picks up the sound present within the ear canal an applies the output signal of the ear canal microphone 5 to the filtering unit 6, which is configured to modify the input signal
representative of the sound within the ear canal such that the filtered signal will reduce the level of the own voice sound within the ear canal, by superposition of sound produced by the receiver 4 based on the filtered signal and own voice sound produced by the user. This is achieved by combining the filtered signal from the filtering unit 6 with the processed signal from the signal processing unit 1 by means of the signal combiner 13 and outputting the combined signal via the receiver 4 into the ear canal. In order to ensure that the closed feedback loop extending from the receiver 4 through the ear canal to the ear canal microphone 5 and back to the receiver 4 through the
filtering unit 6 remains stable, the present invention adapts the gain of the signal output by the filtering unit 6 by means of the gain element 15. The gain depends on the low-frequency transfer function of the sound path from the receiver output to the ear canal microphone input. If this transfer function exhibits a high level of low-frequency gain, the gain at the output of the filtering unit is reduced accordingly. In order to determine the low- frequency gain of the sound path from the receiver 4 through the ear canal to the ear canal microphone 5 a low- frequency "watermark" signal is generated within the hearing device 1 by the signal generator 7 and combined with the processed signal and the filtered signal and then output via the receiver 4 into the ear canal. The
frequency of the "watermark" signal is chosen to be lower than the lowest frequency components of human speech. This frequency can be chosen dependent on the lowest frequency components of the specific user's speech. The watermark signal is amplified within the ear canal. The level of amplification experienced by the "watermark" signal can then be determined by comparing the level of the
"watermark" signal applied to the receiver 4 with the level of the "watermark" signal picked up by the ear canal microphone 5. Because the frequency of the "watermark" signal is chosen such that no own voice sound components interfere with the "watermark" signal in the ear canal, the "watermark" signal can easily be extracted from the sound within the ear canal picked up by the ear canal microphone 5 by means of appropriate first bandpass filter 8. The signal applied to the receiver 4 is also bandpass filtered by means of a second bandpass filter 9 which is preferably identical to the first bandpass filter 8 (see for instance the exemplary magnitude response depicted in Fig. 2) . The low-frequency gain of the sound path from the receiver 4 through the ear canal to the ear canal microphone 5 can then be determined by comparing the level of the output signals of the first and second bandpass filters 8, 9 by means of the signal comparator 14. If the low-frequency gain determined out the output of the signal comparator 14 is outside of a certain range, e.g. larger than a
predetermined value the gain provided by the gain element 15 is set to zero, so that the output signal of the
filtering unit 6 has no effect of the sound generated by the receiver 4, and therefore the feedback loop is
interrupted in order to maintain stable operation of the hearing device and thus avoid unpleasant sounding
artefacts. In order to improve the accuracy with which the low-frequency gain is estimated further processing can be applied after bandpass filtering by means of the bandpass filters 8, 9, such as for instance by applying an absolute value 16, a linear to dB converter 17 and/or a low-pass filter 18 before the signal comparator 14. The level of the "watermark" signal will preferably be chosen such that it is inaudible for the user. The presence of own voice sound or other body sounds can for instance be determined by the own voice detection (OVD) unit 10. In case no own voice sound or other body sounds are detected by the OVD unit 10, it can for example stop the one or more of the filtering unit 6, the signal
generator 7, and the first and second bandpass filters 8, 9 (via the connections a-d) , as well as any one or more of the further units 14 to 19 in order to save power.
Fig. 3 illustrates a schematic signal flow diagram of a further exemplary embodiment of a hearing device especially according to the second aspect of the present invention, which aims to prevent saturation when combining the output of the signal processing unit 3 and the output of the filtering unit 6 in the signal combiner 13. The sum of environmental sound and own voice conducted through the air is picked up by an ambient microphone rMiCExt and applied to hearing device amplification and pre-equalised, yielding the signal uHi . Ear canal sound is picked up by the ear canal microphone located in the ear canal, yielding the signal y ic- This ear canal signal is then filtered by AOC filter C, yielding the signal uAOc- The two signals uHi and UAOC are then added to give uRec, and applied to the
receiver. In order to prevent saturation when adding the signals uHi and uAoc to yield uRec one or more of the
following is performed. The behaviour of the adder is directly monitored, for example by detecting if a
"saturation" flag has been set. The output of said adder is passed to a saturation block with upper and lower limits closer to zero than the signal range allowed. If there is a tendency towards clipping, this adder would clip first without causing artefacts on the actual adder. This could be detected by monitoring an additional saturation flag. The spectrum or bandpass-filtered (or otherwise filtered) versions of one or several of the following signals are investigated:
- the canal microphone signal yMicr
- the output of the signal processing unit uHi , - the combined output of the signal processing unit uHi and the AOC filter uAoc -
The rate of change of the absolute value of the
aforementioned signals, or bandpass-filtered (or otherwise filtered) versions thereof, or of their spectrum are monitored. The level of the external sound is monitored and together with an estimate of the amplification applied in the signal processing unit an estimate of the level of the receiver signal is determined. If any of these methods indicates a nearness to clipping, the gain applied to the AOC filter and the associated blocks will be adjusted, for example reduced.
Fig. 4 illustrates a further schematic signal flow diagram of another exemplary embodiment of a hearing device especially according to the third aspect of the present invention, which aims to turn off automatic occlusion control if the hearing device is for instance not inserted into the ear canal or when level of own voice sound is too low. To achieve this one of more of the following is performed. The ear canal and ambient microphone signals are applied to the signal processing unit. Their signal characteristics are compared, for example:
- broadband levels;
- bandpass filtered levels;
- level fluctuations, or rise/decay rates;
- bandpass filtered level fluctuations, or rise/decay
rates ;
- some spectral components;
- some fluctuations, or rise/decay rates, of spectral
components .
If the comparison is unfavourable, for instance if some characteristics are equal, or differ by a certain amount, or are similar, then the hearing device is probably not inserted, or no signal such as own voice is present to be cancelled. In this case, the activity of the AOC system is changed, for example reduced to a lower value or zero, i.e. disabled.

Claims

1. A method for operating a hearing device (1) adapted for being worn at least partially within an ear canal of a user, the hearing device (1) comprising an ambient
microphone (2), a signal processing unit (3), a receiver (4), and an ear canal microphone (5), the method comprising the steps of:
a) picking up an ambient sound at an input of the ambient microphone (2) which provides a first audio signal representing the ambient sound;
b) processing the first audio signal in the signal
processing unit (3) which provides a processed first audio signal;
c) picking up an ear canal internal sound at an input of the ear canal microphone (5) which provides a second audio signal representing the ear canal internal sound; d) filtering the second audio signal with a filtering unit (6) configured to reduce a perceived level of body sounds produced by the user, the filtering unit (6) providing a filtered second audio signal;
e) generating with a signal generator (7) a low frequency signal, which is preferably not audible for the user, in particular within a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60
Hz, and having a low magnitude within a magnitude range from 30 dB to 60 dB, in particular within a magnitude range from 40 dB to 50 dB; f) combining the processed first audio signal, the filtered second audio signal and the low frequency signal
yielding a combined audio signal;
g) applying the combined audio signal to an input of a
receiver (4) which outputs sound into an ear canal of the user;
h) analysing at least the second audio signal and for
instance also the combined audio signal; and
i) applying a gain to the filtered second audio signal
dependent on the outcome of analysing at least the second audio signal and for instance also the combined audio signal.
2. The method of claim 1, wherein step h) comprises the steps:
hi) performing low frequency signal extraction on the
combined audio signal providing a first extracted signal;
h2) performing low frequency signal extraction on the
second audio signal providing a second extracted signal; and
h3) comparing the first and the second extracted signal, and wherein in step i) applying the gain to the filtered second audio signal is dependent on the comparing the first and the second extracted signal, in particular applying a gain of zero if a difference between the first and the second extracted signal, or a difference between processed versions of the first and second extracted signals, is outside of a predefined interval.
3. The method of claim 2, wherein step hi) comprises bandpass filtering the combined audio signal with a first bandpass filter (8) having a passband for a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60 Hz, and wherein step h2) comprises bandpass filtering the second audio signal with a second bandpass filter (9) having a passband for a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60 Hz.
4. The method of one of claims 1 to 3, further comprising detecting whether a body sound of the user is present or not with an own voice detection unit (10) , and wherein at least one of steps d) to i) is not carried out if no body sound of the user is detected.
5. The method of one of claims 1 to 4, wherein the filtering unit (6) comprises up to 5 bi-quad sections which can be individually activated.
6. The method of one of claims 1 to 5, wherein the low frequency signal is one of a sinusoidal tone, a multisine signal or a narrowband noise.
7. The method of one of claims 1 to 6, wherein the magnitude and/or the frequency of the low frequency signal is selected dependent on the user' s hearing loss or hearing ability.
8. The method of one of claims 1 to 7, wherein the magnitude and/or the frequency of the low frequency signal is adjusted dependent on at least one of:
- a transfer function from an output of the receiver (4) to the input of the ear canal microphone (5) measured during fitting of the hearing device (1), in particular a magnitude of the transfer function within a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60 Hz; - a value derived from the second audio signal (for
instance representative of a sound pressure level within the ear canal) ;
- a value derived from the first audio signal.
9. The method of one of claims 3 to 8, wherein the first and/or the second bandpass filter, in particular the passband, is adjusted dependent on at least one of:
- the magnitude of the low frequency signal;
- the frequency of the low frequency signal; - a value derived from the second audio signal (for instance representative of a sound pressure level within the ear canal) ;
- a value derived from the first audio signal.
10. The method of one of claims 2 to 9, wherein prior to comparing in step h3) at least one of the following operations is applied to the first and/or second extracted signal : - absolute value;
- conversion to a logarithmic scale, for instance
conversion to decibel scale;
- low-pass filtering,
in particular yielding a measure of the power of the first and/or second extracted signal.
11. The method of one of claims 2 to 10, wherein step h3) comprises performing a range check on a difference between the first and the second extracted signal or a processed version of first and the second extracted signal, and wherein step i) is dependent on the outcome of the range check.
12. The method of one of claim 1 to 11, further comprising monitoring over time of the first and/or second extracted signals and/or of processed versions of the first and second extracted signals.
13. The method of claim 12, further comprising the step of changing the frequency response of the filtering unit (6) dependent on the monitoring over time, in particular if a difference between the first and the second extracted signal or between processed versions of the first and the . second extracted signal is outside of a predefined interval during most of a period of time, in particular during a period of time of at least 10 seconds.
14. The method of one of claims 2 to 13, wherein a rate of repeating at least one of steps e) , h) and j) is dependent on the step hi) .
15. The method of one of claims 1 to 14, further
comprising as part of step f) calculating a first sum of the processed first audio signal and the filtered second audio signal with a first adder having a first range of representable output values, and determining if the first sum is within the first range of representable output values for detecting clipping/saturation of the first adder output .
16. The method of claim 15, further comprising as part of step f) calculating a second sum of the processed first audio signal and the filtered second audio signal with a second adder having a second range of representable output values which is a sub-range of the first range of
representable output values, and determining if the second sum is within the second range of representable output values for detecting clipping/saturation of the second adder output.
17. The method of one of claims 1 to 16, further
comprising monitoring a spectrum of at least one of the following signals:
- processed first audio signal or a filtered/time-averaged version of the processed first audio signal;
- filtered second audio signal or a further filtered/time- averaged version of the filtered second audio signal; - a further filtered or time-averaged version of the
second audio signal;
- a sum of the processed first audio signal and the
filtered second audio signal or a filtered/time-averaged version of the sum,
in particular for detecting clipping/saturation of the combined audio signal.
18. The method of claim 17, further comprising monitoring a rate of change of the spectrum, in particular for helping to detect clipping/saturation of the combined audio signal.
19. The method of one of claims 1 to 18, further comprising estimating a level of the combined audio signal, in particular for detecting clipping/saturation of the combined audio signal, and in particular by performing at least one of monitoring a level of the first audio signal, estimating a (frequency-dependent) gain to be applied when processing the first audio signal in the signal processing unit (3), and monitoring the second audio signal.
20. The method of one of claims 15 to 19, further
comprising reducing the gain applied to the filtered second audio signal dependent on if clipping/saturation of at least one of the first adder output, the second adder output, and the combined audio signal is detected.
21. The method of one of claims 1 to 20, further
comprising determining at least one of the following signal characteristics of the first and the second audio signal:
- broadband level; - fluctuation or rise/decay rate of broadband level;
- bandpass filtered level;
- fluctuation or rise/decay rate of bandpass filtered
level ;
- magnitude of at least one low-frequency spectral
component below 100 Hz, in particular below 60 Hz; - fluctuation of or rise/decay rate of magnitude of at least one low-frequency spectral component below 100 Hz, in particular below 60 Hz,
comparing the determined signal characteristics of the first and the second audio signal, and deactivating, in particular switching to a lower-power state, more
particularly powering off, at least one of the filtering unit (6), the signal generator (7), the first bandpass filter (8), the second bandpass filter (9), and the own voice detection unit (10), if the result of comparing indicates that the determined signal characteristics of the first and the second audio signal differ by less than a predetermined threshold value.
22. A hearing device (1) adapted for being worn at least partially within an ear canal of a user, the hearing device (1) comprising:
- an ambient microphone (2) for picking up an ambient
sound at an input of the ambient microphone (2) and providing a first audio signal representing the ambient sound at an output of the ambient microphone (2);
- a signal processing unit (3) adapted to process the
first audio signal provided at an input of the signal processing unit (3) and to provide a processed first audio signal at an output of the signal processing unit
(3) ;
- an ear canal microphone (5) for picking up an ear canal internal sound at an input of the ear canal microphone (5) and providing a second audio signal representing the ear canal internal sound at an output of the ear canal microphone (5) ; a filtering unit (6) for filtering the second audio signal provided at an input to the filtering unit (6) configured to reduce a perceived level of body sounds produced by the user, and providing a filtered second audio signal at an output of the filtering unit (6); a signal generator (7) adapted to generate a low
frequency signal, which is preferably not audible for the user, in particular within a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60 Hz, and having a low magnitude within a magnitude range from 30 dB to 60 dB, in particular within a magnitude range from 40 dB to 50 dB; a signal combiner (13) adapted to combine the processed first audio signal provided at a first input of the signal combiner (13), the filtered second audio signal provided at a second input of the signal combiner (13) , and the low frequency signal provided at a third input of the signal combiner (13), and to provide a combined audio signal at an output of the signal combiner (13) ; a receiver (4) for outputting the combined audio signal provided at an input of the receiver (4) as sound into an ear canal of the user; a signal analysis unit (23) adapted to analyse the combined audio signal and the second audio signal; and - a gain element (15) adapted to apply a gain to the filtered second audio signal provided at an input to the gain element (15) dependent on the outcome of analysing the combined audio signal and the second audio signal.
23. The hearing device (1) of claim 22, wherein the signal analysis unit (23) comprises:
- a first signal extraction unit (8) adapted to perform low frequency signal extraction on the combined audio signal provided at an input to the first signal
extraction unit (8) and providing a first extracted signal at an output of the first signal extraction unit
(8) ;
- a second signal extraction unit (9) adapted to perform low frequency signal extraction on the second audio signal provided at an input to the second signal
extraction unit (9) and providing a second extracted signal at an output of the second signal extraction unit
( 9 ) ; and
- a signal comparator (14) adapted to compare the first and the second extracted signal, respectively, provided at a first and second input, respectively, of the signal comparator (14) and to provide a comparison result at an output of the signal comparator (14), and
wherein the gain element (15) is adapted to apply a gain to the filtered second audio signal provided at an input to the gain element (15) dependent on the comparison result provided at a further input of gain element (15), in particular adapted to apply a gain of zero if the
comparison result indicates that a difference between the first and the second extracted signal, or a difference between processed versions of the first and second
extracted signals, is outside of a predefined interval.
24. The hearing device (1) of claim 23, wherein the first signal extraction unit comprises a first bandpass filter (8) having a passband for a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60 Hz, and wherein the second signal extraction unit comprises a second bandpass filter (9) having a passband for a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60 Hz.
25. The hearing device (1) of one of claims 22 to 24, further comprising an own voice detection unit (10) adapted to detect whether a body sound of the user is present or not and to deactivate, in particular to switch to a lower- power state, more particularly power off, at least one of the filtering unit (6), the signal generator (7), the first bandpass filter (8), and the second bandpass filter (9), if no body sound of the user is detected.
26. The hearing device (1) of one of claims 22 to 25, wherein the filtering unit (6) comprises up to 5 bi-quad sections which are individually activatable.
27. The hearing device (1) of one of claims 22 to 26, wherein the low frequency signal is one of a sinusoidal tone, a multisine signal or a narrowband noise.
28. The hearing device (1) of one of claims 22 to 22, wherein the magnitude and/or the frequency of the low frequency signal is selectable dependent on the user' s hearing loss or hearing ability.
29. The hearing device (1) of one of claims 22 to 28, wherein the magnitude and/or the frequency of the low frequency signal is adapted to be adjusted dependent on at least one of:
- a transfer function from an output of the receiver (4) to the input of the ear canal microphone (5) measured during fitting of the hearing device (1), in particular a magnitude of the transfer function within a frequency range from 25 Hz to 75 Hz, in particular within a frequency range from 50 Hz to 60 Hz; - a value derived from the second audio signal (for
instance representative of a sound pressure level within the ear canal) ;
- a value derived from the first audio signal.
30. The hearing device (1) of one of claims 23 to 29, wherein the first and/or the second bandpass filter, in particular the passband, . is adapted to be adjusted
dependent on at least one of:
- the magnitude of the low frequency signal;
- the frequency of the low frequency signal; - a value derived from the second audio signal (for
instance representative of a sound pressure level within the ear canal ) ;
- a value derived from the first audio signal.
31. The hearing device (1) of one of claims 22 to 30, further comprising one or more operational units for performing at least one of the following operations to the first and/or second extracted signal or to signals derived from the first and/or second extracted signal: - absolute value (16);
- conversion to a logarithmic scale, for instance
conversion to decibel scale (17);
- low-pass filtering (18),
in particular for providing a measure of the power of the first and/or second extracted signal.
32. The hearing device (1) of one of claims 23 to 31, further comprising a range checking unit (19) adapted to perform a range check on a difference between the first and the second extracted signal, respectively, or a processed version of first and the second extracted signal, respectively, provided to a first and to a second input of. the range checking unit (19) , and to provide an outcome of the of the range check at an output of the range checking unit (19) , and wherein the gain element (15) is adapted to apply the gain to the filtered second audio signal provided at the input to the gain element (15) dependent on the outcome of the range check provided at the further input of gain element (15) .
33. The hearing device (1) of one of claims 22 to 32, further comprising a monitoring unit (20) adapted to monitor over time the first and/or second extracted signals and/or processed versions of the first and second extracted signals .
34. The hearing device (1) of claim 33, wherein the monitoring unit (20) is adapted to change the frequency response of the filtering unit (6) dependent on the
monitoring over time, in particular if a difference between the first and the second extracted signal or between processed versions of the first and the second extracted signal is greater than a predefined value during most of a period of time, in particular during a period of time of at least 10 seconds.
35. The hearing device (1) of one of claims 22 to 34, wherein at least one of the signal generator (7) , the first bandpass filter (8), the second bandpass filter (9), the signal comparator (14), and the gain element (15) is adaptable such that an operating frequency thereof is dependent on the comparison result.
36. The hearing device (1) of one of claims 22 to 35, wherein the signal combiner (13) comprises a first adder having a first range of representable output values, and adapted to calculate a first sum of the processed first audio signal and the filtered second audio signal and to determine if the first sum is within the first range of representable output values for detecting
clipping/saturation of the first adder output.
37. The hearing device (1) of claim 36, wherein the signal combiner (13) comprises a second adder having a second range of representable output values which is a sub-range of the first range of representable output values, and adapted to calculate a second sum of the processed first audio signal and the filtered second audio signal and to determine if the second sum is within the second range of representable output values for detecting
clipping/saturation of the second adder output.
38. The hearing device (1) of one of claims 22 to 35, further comprising a spectrum monitoring unit (21) adapted to monitor a spectrum of at least one of the following signals : - processed first audio signal or a filtered/time-averaged version of the processed first audio signal;
- filtered second audio signal or a further filtered/time- averages version of the filtered second audio signal;
- a further filtered or time-averaged version of the
second audio signal;
- a sum of the processed first audio signal and the
filtered second audio signal or a filtered/time-averaged version of the sum,
in particular for detecting clipping/saturation of the combined audio signal.
39. The hearing device (1) of claim 38, wherein the spectrum monitoring unit (21) is further adapted to monitor a rate of change of the spectrum, in particular for helping to detect clipping/saturation of the combined audio signal.
40. The hearing device (1) of one of claims 22 to 39, further comprising a level estimator (22) adapted to estimate a level of the combined audio signal, in
particular for detecting clipping/saturation of the
combined audio signal, and in particular by performing at least one of monitoring a level of the first audio signal, estimating a (frequency-dependent) gain to be applied when processing the first audio signal in the signal processing unit (3), and monitoring the second audio signal.
41. The hearing device (1) of one of claims 36 to 40, wherein the gain element (15) is adapted to reduce the gain applied to the filtered second audio signal dependent on if clipping/saturation of at least one of the first adder output, the second adder . output, and the combined audio signal is detected.
42. The hearing device (1) of one of claims 22 to 41, the signal analysis unit (23) is further adapted to determine at least one of the following signal characteristics of the first and the second audio signal:
- broadband level;
- fluctuation or rise/decay rate of broadband level;
- bandpass filtered level; - fluctuation or rise/decay rate of bandpass filtered
level ;
- magnitude of at least one low-frequency spectral
component below 100 Hz, in particular below 60 Hz;
- fluctuation of or rise/decay rate of magnitude of at
least one low-frequency spectral component below 100 Hz, in particular below 60 Hz,
to compare the determined signal characteristics of the first and the second audio signal, and deactivate, in particular switch to a lower-power state, more particularly power off, at least one of the filtering unit (6), the signal generator (7), the first bandpass filter (8), the second bandpass filter (9), and the own voice detection unit (10), if the result of comparing indicates that the determined signal characteristics of the first and the second audio signal differ by less than a predetermined threshold value.
PCT/EP2013/062078 2013-06-12 2013-06-12 Method for operating a hearing device capable of active occlusion control and a hearing device with active occlusion control WO2014198307A1 (en)

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