Diffuse noise listening

Abstract

A hearing aid includes: a first microphone system configured for conversion of sound emitted by a sound source into a first audio signal; a first matched filter configured for filtering the first audio signal into a first filtered audio signal, the first matched filter having a first matching transfer function that substantially matches a first transfer function of a first sound propagation path leading from the sound source to the first microphone system, when a user wears the hearing aid; and a hearing loss processor configured to provide a hearing loss compensated output signal that compensates for a hearing loss of the user based at least in part on the first filtered audio signal.

Claims

1. A hearing aid comprising: a first microphone system configured for conversion of sound emitted by a sound source into a first audio signal, the sound source being external to the hearing aid; a first matched filter configured for filtering the first audio signal into a first filtered audio signal; and a hearing loss processor configured to provide a hearing loss compensated output signal that compensates for a hearing loss of the user based at least in part on the first filtered audio signal; wherein the first matched filter comprises a first matching transfer function that corresponds with a first transfer function, wherein the first transfer function is associated with a first sound propagation path between the sound source that is external to the hearing aid and the first microphone system; and wherein the first matching transfer function corresponds with a complex conjugate of the first transfer function, or with the complex conjugate of the first transfer function multiplied with a complex scalar.

2. The hearing aid according to claim 1, further comprising: a second microphone system configured for providing a second audio signal; a second matched filter configured for filtering the second audio signal into a second filtered audio signal, the second matched filter having a second matching transfer function that substantially matches a second transfer function of a second sound propagation path leading from the sound source to the second microphone system, when the user wears the hearing aid; and a first adder configured for adding the first filtered audio signal and the second filtered audio signal to obtain a sum audio signal; wherein the hearing loss processor is configured to process the sum audio signal to provide the hearing loss compensated output signal.

3. The hearing aid according to claim 2, wherein the first and second matching transfer functions substantially equalize a phase of the first filtered audio signal and a phase of the second filtered audio signals, so that the first adder can add the first and second filtered audio signals in-phase.

4. The hearing aid according to claim 2, wherein the first and second matching transfer functions substantially equalize an amplitude spectrum of the first and second filtered audio signals to an amplitude spectrum of the sound emitted by the sound source.

5. The hearing aid according to claim 1, wherein the sound source resides in a forward looking direction of the user.

6. The hearing aid according to claim 1, wherein the first matched filter has an impulse response that is substantially equal to a time reversed and time shifted impulse response of the first sound propagation path.

7. The hearing aid according to claim 1, wherein the hearing aid is a multi-channel hearing aid in which the first audio signal is divided into a plurality of signal components for being processed individually in a plurality of frequency channels, respectively.

8. The hearing aid according to claim 7, wherein the first matched filter is configured to perform filtering in a selected frequency band.

9. The hearing aid according to claim 7, wherein the plurality of frequency channels includes warped frequency channels.

10. A binaural hearing aid system comprising a first hearing aid and a second hearing aid, wherein the first hearing aid is the hearing aid according to claim 1.

11. A binaural hearing aid system comprising a first hearing aid and a second hearing aid, wherein each of the first and second hearing aids is a hearing aid according to claim 1.

12. The hearing aid according to claim 1, wherein the first matching transfer function is equal or substantially equal to the complex conjugate of the first transfer function, or is equal or substantially equal to the complex conjugate of the first transfer function multiplied by the complex scalar.

13. The hearing aid according to claim 1, wherein the first matched filter comprises a causal filter.

14. The hearing aid according to claim 13, wherein the causal filter is based on the complex scalar.

15. A binaural hearing aid system comprising a first hearing aid and a second hearing aid, wherein the first hearing aid comprises: a first microphone system configured for conversion of sound emitted by a sound source into a first audio signal; a first matched filter configured for filtering the first audio signal into a first filtered audio signal, the first matched filter having a first matching transfer function that substantially matches a first transfer function of a first sound propagation path leading from the sound source to the first microphone system, when a user wears the first hearing aid, the sound source being external to the first hearing aid; and a hearing loss processor configured to provide a hearing loss compensated output signal that compensates for a hearing loss of the user based at least in part on the first filtered audio signal; wherein the second hearing aid has a first adder; wherein the first hearing aid has a second adder, the second adder having a first input that is connected to an output of the adder of the first hearing aid, and a second input that is connected to an output of the first adder of the second hearing aid; wherein the second adder of the first hearing aid comprises an output for provision of a binaural sum audio signal that is based on the sum audio signal of the first hearing aid and a sum audio signal of the second hearing aid; and wherein the hearing loss processor is configured to process the binaural sum audio signal to provide the hearing loss compensated output signal.

16. A method of increasing a signal to noise ratio of a sound signal received in an environment with diffuse noise, comprising: converting acoustic sound into an audio signal using a microphone system, and filtering the audio signal with a matched filter, wherein the matched filter comprises a matching transfer function that corresponds with a first transfer function, and wherein the first transfer function is associated with a sound propagation path between a sound source and the microphone system, the sound source being external to a hearing device comprising the microphone system; wherein the matching transfer function corresponds with a complex conjugate of the first transfer function, or with the complex conjugate of the first transfer function multiplied with a complex scalar.

17. The method according to claim 16, further comprising adding a plurality of the filtered audio signals to obtain a sum audio signal for improvement of the signal to noise ratio, wherein one of the filtered audio signals is resulted from the act of filtering the audio signal.

18. The method according to claim 16, wherein the matching transfer function is equal or substantially equal to the complex conjugate of the first transfer function, or is equal or substantially equal to the complex conjugate of the first transfer function multiplied by the complex scalar.

19. The method according to claim 16, wherein the matched filter comprises a causal filter.

20. The method according to claim 19, wherein the causal filter is based on the complex scalar.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Below, the new method and hearing aid are explained in more detail with reference to the drawings in which various examples are shown. In the drawings:

(2) FIG. 1 schematically illustrates a user wearing a hearing aid with two microphones in a listening situation,

(3) FIG. 2 schematically illustrates the new hearing aid with two microphones and two matched filters,

(4) FIG. 3 schematically illustrates a user wearing a new binaural hearing aid system with a plurality of microphones accommodated in each of the hearing aids,

(5) FIG. 4 schematically illustrates one exemplary circuitry of a new binaural hearing aid system,

(6) FIG. 5 schematically illustrates another exemplary circuitry of a new binaural hearing aid system, and

(7) FIG. 6 shows a plot of the directional characteristic of a conventional omni-directional microphone system and of the new optimized omni-directional microphone system.

DESCRIPTION

(8) The drawings illustrate the design and utility of embodiments, in which similar elements are referred to by common reference numerals. Like elements may, thus, not be described in detail with respect to the description of each figure. In order to better appreciate how the above-recited and other advantages and objects are obtained, a more particular description of the embodiments will be rendered, which are illustrated in the accompanying drawings. It should be noted that the figures are only intended to facilitate the description of the features. They are not intended as an exhaustive description of the claimed invention or as a limitation on the scope of the claimed invention. In addition, an illustrated feature needs not have all the aspects or advantages shown. An aspect or an advantage described in conjunction with a particular feature is not necessarily limited to that feature and can be practiced in any other features even if not so illustrated or explicitly described.

(9) The new hearing aid according to the appended claims may be embodied in different forms not shown in the accompanying drawings and should not be construed as limited to the examples set forth herein.

(10) FIG. 1 schematically illustrates a user 100 wearing a BTE hearing aid (only the microphones of the hearing aid are shown) on the user's right ear. The BTE hearing aid 10 has two microphones 12, 24 accommodated in the BTE hearing aid housing in such a way that a line through centres of the microphones extends in parallel with a forward looking direction of the user. In FIG. 1, the user 100 desires to listen to speaker 110; however, the user and listener 100 and the speaker 110 are surrounded by a number of other people (not shown) also engaged in various conversations. As a result, the user 100 is exposed to a diffuse noise field and as a result the hearing impaired user cannot focus the auditory attention on the selected sound source, i.e. the conversation partner 110, while suppressing speech from other talkers and other sounds.

(11) FIG. 2 shows a blocked schematic of the BTE hearing aid 10 worn by the user 100 in FIG. 1.

(12) The illustrated BTE hearing aid 10 has a front microphone 12 that converts acoustic sound into a front audio signal 14. The front audio signal 14 is pre-processed in a first pre-processing filter 16 into a pre-processed front audio signal 18. The pre-processing may include, without excluding any form of processing, adaptive and/or static feedback suppression and/or adaptive and/or fixed beamforming and/or pre-filtering. A first matched filter 20 is connected to the output of the first pre-processing filter 16 and operates to filter the pre-processed front audio signal 18 into a front filtered audio signal 22. A sound source 110, see FIG. 1, resides in the forward looking direction of the user 100 and emits sound to the microphone 12 when worn by the user 100 of the hearing aid 10.

(13) The front microphone 12 has the far field microphone related transfer function H.sub.1(ω) of the front looking direction, and the first matched filter 20 has a matching transfer function that is a equal to the complex conjugate of the far field microphone related transfer function H.sub.1*(ω) multiplied by the complex scalar e.sup.−jωT to ensure that the impulse response h.sub.1(T−t) of the first matched filter 20 is causal.

(14) Similarly, the illustrated BTE hearing aid 10 also has a rear microphone 24 that converts acoustic sound into a rear audio signal 26. The rear audio signal 26 is pre-processed in a second pre-processing filter 28 into a pre-processed rear audio signal 30. The pre-processing may include, without excluding any form of processing, adaptive and/or static feedback suppression and/or adaptive and/or fixed beamforming and/or pre-filtering. A second matched filter 32 is connected to the output of the second pre-processing filter 28 and operates to filter the pre-processed rear audio signal 30 into a rear filtered audio signal 34. The rear microphone 24 has the far field microphone related transfer function H.sub.2(ω) of the front looking direction, and the second matched filter 32 has a matching transfer function that is a equal or substantially equal to the complex conjugate of the far field microphone related transfer function H.sub.2*(ω) multiplied by the complex scalar e.sup.−jωT to ensure that the impulse response h.sub.2(T−t) of the second matched filter 32 is causal.

(15) Other embodiments of the hearing aid 10 may have a number of microphones that is larger than two.

(16) The matched filters 20, 32 operate to improve the SNR of the audio signals 14, 26 that originate from a sound source 110 in an environment with significant diffuse acoustic noise, e.g. at a gathering with a lot of simultaneous conversation.

(17) The front and rear audio signals 22, 34 are input to an adder 36 that adds the front and rear audio signals 22, 34 into the sum audio signal 38.

(18) The matched filters 20, 32 remove the phase from their respective input signals 18, 30 so that subsequently, the adder 36 adds the filtered signals 22, 34 in-phase to further improve the SNR of the sum audio signal 38.

(19) The adder 36 may form a weighted sum of the signals 22, 34 input to the adder 36.

(20) The sum audio signal 38 is input to a hearing loss processor 40 configured to process the sum audio signal 38 into a hearing loss compensated output signal 42 that is compensated for the hearing loss of the user in a way well-known in the art of hearing aids, possibly in accordance with a number of selectable hearing programmes stored in a memory (not shown) of the hearing aid 10.

(21) Finally, the hearing loss compensated output signal 42 is input to an output transducer 44 in the form of a receiver 44 for conversion of the hearing loss compensated output signal 42 into an acoustic output signal that is transmitted towards an eardrum of the user 100 wearing the hearing aid 10.

(22) For optimum performance, the microphone related transfer functions H.sub.1(ω), H.sub.2(ω) of the respective acoustic propagation paths 120, 130 from the sound source 110 in the forward looking direction of the user 100 to the respective microphones 12, 24 are determined for the individual user 100 and matched by the respective matched filters 20, 32.

(23) However, approximate microphone related transfer functions H.sub.1′(ω), H.sub.2′(ω) may be used instead. H.sub.1′(ω), H.sub.2′(ω) may be determined using an artificial head, such as a KEMAR head, whereby approximated microphone related transfer functions H.sub.1′(ω), H.sub.2′(ω) are provided of sufficient accuracy for the hearing aid user 100 to obtain an improved SNR of the sum audio signal 38 in an environment with diffuse noise.

(24) The approximate microphone related transfer functions H.sub.1′(ω), H.sub.2′(ω) may also be determined as an average of previously determined microphone related transfer functions for a group of humans. The group of humans may be selected to fit certain features of the human for which the individual microphone related transfer functions are to be determined in order to obtain approximate microphone related transfer functions that more closely match the respective corresponding individual microphone related transfer functions. For example, the group of humans may be selected according to age, race, gender, family, ear size, etc., either alone or in any combination. Averaging may also be performed over a number of directions.

(25) The approximate microphone related transfer functions may also be microphone related transfer functions previously determined for the user in question, e.g. during a previous fitting session at an earlier age.

(26) The sum audio signal 38 is provided in accordance with the equation:

(27) ${\hat{x}}_{\mathrm{ML}}\left(t\right)=g\left(t\right).Math.\left(\underset{n=1}{\overset{N}{.Math.}}{h}_n\left(T-t\right).Math.s_n\left(t\right)\right)$
where {circle around (x)} is the convolution operator, i.e. f1{circle around (x)}f2 means the convolution of functions f1 and f2, and where n is a microphone index, i.e. n=1 for the front microphone 12 and n=2 for the rear microphone 24, h.sub.n(t) is the inverse Fourier transform of H.sub.n(ω), s.sub.n(t) is the n.sup.th pre-filtered microphone signal 18, 30, and

(28) $g\left(t\right)={ℱ}^{-1}\left\{\frac{1}{h^H\left(\omega \right)h\left(\omega \right)}\right\}$
is a filter describing the amplitude equalization across frequency to compensate for the filtering operation.

(29) Alternatively, the summation is performed in the adder 36 while multiplication by g(t) is performed by the processor 40.

(30) The hearing aid 10 shown in FIG. 2 may be a multi-channel hearing aid in which audio sound signals 14, 26 to be processed are divided into a plurality of frequency channels, and wherein audio signals are processed individually in each of the frequency channels, possibly apart from the matched filters 20, 32 that may still operate in the entire frequency range of the hearing aid 10, or, may be divided into other frequency channels, typically fewer frequency channels than the remaining illustrated circuitry.

(31) For a multi-channel hearing aid 10, FIG. 2 may illustrate the circuitry and signal processing in a single frequency channel of the audio signals 14, 26.

(32) The illustrated circuitry and signal processing may be duplicated in a plurality of the frequency channels, e.g. in all of the frequency channels.

(33) For example, the signal processing illustrated in FIG. 2 may be performed in a selected frequency band.

(34) The selected frequency band may comprise one or more of the frequency channels, or all of the frequency channels. The selected frequency band may be fragmented, i.e. the selected frequency band need not comprise consecutive frequency channels.

(35) The plurality of frequency channels may include warped frequency channels, for example all of the frequency channels may be warped frequency channels.

(36) Outside the selected frequency band, the audio signals may be processed for hearing loss compensation without matched filtering 20, 32.

(37) In this way, matched filtering may be avoided in frequency channels in which no diffuse noise is present.

(38) FIG. 3 schematically illustrates a user 100 wearing a binaural hearing aid system with a left ear BTE hearing aid accommodating microphones 12B, 24B and a right ear BTE hearing aid accommodating microphones 12A, 24A.

(39) Signals may be communicated wired or wirelessly between the left ear hearing aid and the right ear hearing aid in a way well-known in the art of signal transmission.

(40) With respect to the filtering of the received acoustic signals, each of the left ear BTE hearing aid and the right ear BTE hearing aid of the binaural hearing aid system, operates in the same way as the hearing aid 10 with the blocked schematic shown in FIG. 2 apart from the fact that the filtered audio signal of each hearing aid is transmitted to the other hearing aid and added to the filtered audio signal of the other hearing aid as shown in FIG. 4.

(41) FIG. 4 shows a blocked schematic of a binaural hearing aid system 10 comprising a right ear hearing aid 10A and a left ear hearing aid 10B, each of which operates in the same way as the hearing aid 10 shown in FIG. 2 apart from the fact that the sum audio signal 38A, 38B, respectively, of each of the right ear hearing aid 10A and left ear hearing aid 10B, is transmitted to the other hearing aid 10B, 10A and added to the sum audio signal 38B, 38A of the other hearing aid 10B, 10A in the respective processor 40B, 40A. The required wired or wireless interface circuitry is not shown.

(42) Further, one or more microphones with pre-filters connected to respective matched filters may be added to the circuitry of the hearing aids 10A, 10B as indicated by the vertical lines of dots, generating filtered output audio signals input to the adder 36A, 36B for further improvement of the SNR of the sum audio signal 38A, 38B.

(43) The number of microphones in the right ear hearing aid 10A and the left ear hearing aid 10B is preferably, but need not be, the same.

(44) For example, the binaural hearing aid system 10 may comprise four microphones, namely a front microphone 12A, 12B and a rear microphone 24A, 24B, in each of the right ear hearing aid 10A and the left ear hearing aid 10B of the binaural hearing aid system 10.

(45) Each of the hearing aids 10A, 10B shown in FIG. 4 may be a multi-channel hearing aid in which audio sound signals 14A, 26A, 14B, 26B to be processed are divided into a plurality of frequency channels, and wherein audio signals are processed individually in each of the frequency channels, possibly apart from the matched filters 20A, 32A, 20B, 32B that may still operate in the entire frequency range of the respective hearing aid 10A, 10B; or, may be divided into other frequency channels, typically fewer frequency channels than the remaining illustrated circuitry.

(46) For multi-channel hearing aids 10A, 10B, FIG. 4 may illustrate the circuitry and signal processing in a single frequency channel of the audio signals 14A, 26A, 1B, 26B.

(47) The illustrated circuitry and signal processing may be duplicated in a plurality of the frequency channels, e.g. in all of the frequency channels.

(48) For example, the signal processing illustrated in FIG. 4 may be performed in a selected frequency band.

(49) The selected frequency band may comprise one or more of the frequency channels, or all of the frequency channels. The selected frequency band may be fragmented, i.e. the selected frequency band need not comprise consecutive frequency channels.

(50) The plurality of frequency channels may include warped frequency channels, for example all of the frequency channels may be warped frequency channels.

(51) Outside the selected frequency band, the audio signals may be processed for hearing loss compensation without matched filtering 20A, 32A, 20B, 32B.

(52) In this way, matched filtering may be avoided in frequency channels in which no diffuse noise is present.

(53) The circuitry of the right ear hearing aid 10A and left ear hearing aid 10B may be identical as shown in FIG. 4. However, in other embodiments the circuit components may be distributed in arbitrary ways between the two hearing aid housings in accordance with design choices well-known in the art of hearing aids.

(54) For example, as shown in FIG. 5, one of the hearing aids 10A may comprise all of the required matched filters 20A, 32A, 20B, 32B, and the processor 40A, while the other one of the hearing aids 10B does not comprise matched filters and a processor. Instead, microphone output signals, possibly pre-processed, 18B, 30B are transmitted to the hearing aid comprising the respective matched filters 20B, 32B, and wherein the processor 40A is configured to output the hearing loss compensated output signals 42A, 42B for both ears of the user. The hearing loss compensated output signal 42B for the other ear is then transmitted to the hearing aid 10B without matched filters and input to the output transducer 44B of the hearing aid 10B.

(55) The required wired or wireless interface circuitry for signal transfer between the hearing aids 10A, 10B is not shown.

(56) FIG. 6 shows a directionality plot 50 of the sum audio signal 38 of the hearing aid 10 shown in FIG. 2 in comparison with a directionality plot 60 of conventional omni-directional processing in the form the directionality 60 of the front microphone audio signal 14. It is noteworthy that the directionalities are very similar and thus, loss of environmental awareness is avoided with the matched filters.

(57) Mutually uncorrelated white noise sequences have been applied to the microphones 12, 20, and a resulting SNR of −1.28 dB has been calculated for the front microphone audio signal 14 (conventional omni response). The corresponding SNR value for the sum audio signal 38 is equal to 5.92 dB. Thus, the SNR improvement for this example amounts to approximately 7 dB and without sacrificing the environmental awareness.

(58) The disclosed method can also be used to suppress microphone noise.

(59) As used in this specification, the term “substantially matches”, or any of other similar terms (such as “substantially equal”), refers to two items that do not vary by more than 10%. For example, a description regarding an impulse response being “substantially equal” to another impulse response refers to the two impulse responses having at least one characteristic that does not vary by more than 10%. Similarly, a description regarding a matching transfer function of a matched filter that “substantially matches” a transfer function of a sound propagation path refers to the matching transfer function and the transfer function of the sound propagation path having at least one characteristic that does not vary by more than 10%. For example, “substantially matches” can refer to deviations that are less than or equal to ±10%, such as less than or equal to ±5%, such as less than or equal to ±2%, such as less than or equal to ±1%, such as less than or equal to ±0.5%, such as less than or equal to ±0.2%, such as less than or equal to ±0.1%, such as 0% (which represents an exact match).

(60) Although particular features have been shown and described, it will be understood that they are not intended to limit the claimed invention, and it will be made obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the claimed invention. The specification and drawings are, accordingly to be regarded in an illustrative rather than restrictive sense. The claimed invention is intended to cover all alternatives, modifications and equivalents.