A METHOD OF OPERATING A BINAURAL EAR LEVEL AUDIO SYSTEM AND A BINAURAL EAR LEVEL AUDIO SYSTEM

Abstract

A method (600) of operating a binaural ear level audio system in order to improve speech intelligibility and a binaural ear level audio system adapted to carry out said method.

Claims

1. A method of operating a binaural ear level audio system comprising the steps of: providing a first and a second monaurally beamformed signal from a first and a second ear level audio device of the binaural ear level audio system; providing a binaurally beamformed signal by combining said first and second monaurally beamformed signal; using a first and a second frequency dependent parameter to control the first and the second monaurally beamformed signals, and additionally a third frequency dependent parameter to control the binaurally beamformed signal wherein said frequency dependent parameters are selected in order to provide: an optimized directivity index, for at least one first direction and for at least one first frequency range and an optimized presence of binaural cues for at least one second frequency range.

2. The method of operating a binaural ear level audio system according to claim 1, wherein said frequency dependent parameters are selected in order to provide: optimized directivity indices, for at least two directions and for at least one first frequency range and an optimized presence of binaural cues for at least one second frequency range.

3. The method of operating a binaural ear level audio system according to claim 1, wherein said first frequency range is below a frequency threshold and wherein said second frequency range is above the frequency threshold and wherein the frequency threshold is in the range between 500 Hz and 3 kHz.

4. The method of operating a binaural ear level audio system according to claim 1, wherein the values of the third frequency dependent parameter are constrained during the optimization in order to ensure that the binaurally beamformed signal is different in the two ear level audio devices and to ensure that the ipse-lateral part of the binaurally beamformed signal is weighted higher than the contra-lateral part.

5. The method of operating a binaural ear level audio system of claim 2, wherein the directivity indices for said at least two directions are optimized by determining the maximum sum of said at least two directivity indices.

6. A binaural ear level audio system comprising a first ear level audio device and a second ear level audio device and wherein at least one of the first and the second ear level audio device comprises a digital processor adapted to perform the method of claim 1.

7. The binaural ear level audio system according to claim 6, wherein the binaural ear level audio system is a binaural hearing aid system

8. A computer program product with instructions which, when executed on a computer, perform the method of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] By way of example, there is shown and described a preferred embodiment of this invention. As will be realized, the invention is capable of other embodiments, and its several details are capable of modification in various, obvious aspects, all without departing from the invention. Accordingly, the drawings and descriptions will be regarded as illustrative in nature and not as restrictive. In the drawings:

[0037] FIG. 1 illustrates a plurality of (free field) directional polar patterns provided by a monaural beamformer of a conventional hearing aid;

[0038] FIG. 2 illustrates directional polar patterns provided by a binaural beamformer of a conventional hearing aid system for a plurality of frequencies;

[0039] FIG. 3 illustrates directivity index as a function of frequency provided by a binaural beamformer of a conventional hearing aid system for two different directions;

[0040] FIG. 4 illustrates directional polar patterns provided by a binaural beamformer of a hearing aid system according to the invention for a plurality of frequencies;

[0041] FIG. 5 illustrates directivity index as a function of frequency provided by a binaural beamformer of a hearing aid system according to the invention for two different directions; and

[0042] FIG. 6 illustrates highly schematically a method of operating a binaural ear level audio system according to an embodiment of the invention.

DETAILED DESCRIPTION

[0043] In the present context the terms “binaural ear level audio system” and “binaural hearing aid system” as well as the corresponding terms “ear level audio device” and “hearing aid” may be used interchangeably because the methods of the present invention function independently on the considered systems and devices.

[0044] Furthermore, in the present context the term “direction of arrival” may also simply be denoted “direction” or “incident direction”.

[0045] In the present context the directivity index (DI) for a particular (incident) direction is determined as the ratio (typically measured in dB) between the sensitivity at a particular direction divided by the average sensitivity for the remaining (or alternatively all) incident directions. Thus the DI for a particular (incident) direction, that will be used in the following unless specifically noted otherwise, differs from the, e.g. within the field of hearing aid systems, also generally accepted DI that is independent on a specific direction and as such is determined, from a directional polar pattern, as the ratio (also typically in dB) between the area of a circle with a radius corresponding to the maximum sensitivity compared to the area within the directional polar pattern. Thus an omni-directional polar pattern has a DI of zero (see e.g. the outermost left polar pattern of FIG. 1) while the various cardioids have higher directivity indices.

[0046] As mentioned in the introduction, a monaural beamformer used in contemporary hearing aid systems may be realized by providing an omnidirectional signal and a bidirectional signal and combining them to provide a locator signal as already explained and shown in the introduction in equation (1):

locator=α.Math.omni+(1−α).Math.bidir  (1)

[0047] Wherein “locator” represents the output signal provided by the monaural beamformer. It is noted that monaural beamforming in variations may be based on combinations of signal pairs other than omnidirectional and bidirectional signals such as e.g. two cardioids pointing in opposite directions.

[0048] As also explained and shown above in the introduction a binaural beamformer may be realized by mixing the monaural beamformer signals from the local and opposite sides of a users head (which in the following also may be denoted ipse-lateral and contra-lateral sides) in accordance with equation (2):

BBout=β.Math.loc.sub.local+(1−β).Math.loc.sub.opposite  (2)

[0049] Both equations also form the basis for the present invention. Thus, equation (2) describes the binaurally beamformed signal of one of a pair of hearing aids from a binaural hearing aid system. The other hearing aid will receive an analogously generated signal. Both equations (1) and (2) will in the following unless otherwise noted be considered frequency dependent and consequently also the parameters α.sub.local, α.sub.opposite and β. According to an embodiment the binaural system comprises a filter bank adapted to provide a plurality of frequency band signals wherefrom the frequency dependence of the beamforming parameters may be determined. However, according to variations the filter bank, the associated frequency bands and the corresponding frequency dependent beamforming parameters may be implemented in alternative ways such as e.g. by using an adaptive filter as will be well known for the skilled person.

[0050] It is a particular insight of the inventors that the values of the frequency dependent parameters α.sub.local, α.sub.opposite and β may be selected (as part of an optimization) to provide optimized DI values at some predefined incident directions while at the same time maintaining binaural cues.

[0051] Generally, it is possible to preserve some amount of spatial cues if β is constrained to be larger than 0.5. The closer β is constrained to be to 1, the better the spatial cues will be preserved, but at the cost of a lower DI. Thus according to an embodiment a desired trade-off may be realized by selecting a specific constraint for β.

[0052] As discussed in the introduction, a setup in which the monaural beamformer uses α=0.25 and β=0.5 provides a narrow beam at the cost of losing all binaural cues, and furthermore there is a large drop in the DI at 30 degrees.

[0053] The present invention enables the DI to be optimized at selected angles such as 0° and 30° while at the same time preserving some binaural cues.

[0054] In one example according to the present invention, the following steps are performed in order to provide a binaurally beamformed signal based on the equations (1) and (2) defined above and wherein the directivity index is optimized for at least two directions: [0055] 1. Select at least two incident directions ω1, ω2. [0056] 2. Calculate the DI for ω1 and for ω2 for at least one frequency range and for every combination of α.sub.local, α.sub.opposite and β. This calculation may employ any mathematical procedure which is appropriate for such an optimization. [0057] 3. The result of the calculation will provide the frequency dependent combination of parameters α.sub.local, α.sub.opposite and β which provide the largest value of the sum of the directivity indices for the two selected directions and the considered frequency range. This may include an optimization criterion directed at ensuring that the difference between the directivity indices for the more than one direction is minimized. A further optimization criterion may be directed at ensuring that the directivity index for the forward pointing direction is the largest. [0058] 4. Ensure that some binaural cues are preserved either by optimizing the binaural parameter β in at least one frequency range, wherein the DI has not been optimized or by constraining the binaural parameter β, in at least one frequency range, to be larger than a threshold. A specific example will be discussed in the following.

[0059] As a specific example a case is considered where the DI is optimized for both 0° and 30° while also preserving binaural cues by putting a constraint on β during the optimization. Thus according to this example DI is optimized as the sum of the DI at 0° and 30° and in this example the constraint is β>0.69. The result of the optimization is given in the table below. The numbers in the table are obtained by calculating the DI at 0° and 30° for every frequency band and every combination of α.sub.local, α.sub.opposite and β and finding the combination that provides the largest DI for the selected frequency bands (i.e. the center frequencies of the frequency bands) angles.

TABLE-US-00001 Frequency Band 1 2 3 4 5 6 7 8 β 0.75 0.81 0.75 0.69 0.69 0.69 0.69 0.75 α.sub.local 0.13 0.25 0.25 0.31 0.31 0.31 0.19 0.19 α.sub.opposite 0.5 0.5 0.5 0.5 0.5 0.31 0 0 Frequency Band 9 10 11 12 13 14 15 β 0.88 0.81 0.75 0.69 0.69 0.81 0.69 α.sub.local 0.25 0.19 0.19 0.19 0.19 0.19 0.25 α.sub.opposite 0.06 0.19 0.06 0.13 0.13 0.19 0.13

[0060] The performance of the binaural beamforming obtained with the optimized parameter set given in the table above are illustrated in FIG. 4 and FIG. 5. FIG. 4 illustrates a directional polar pattern in accordance with the present invention and obtained with an ear level audio system positioned on a manikin for testing of hearing aid systems (such a manikin is often denoted a Kemar) and when compared with FIG. 2 it can be seen, that the decrease in sensitivity at 30°, which is present in FIG. 2, most notably in the frequency band around 2 kHz, has disappeared in FIG. 4 for the halfplane pointing away from the users head. This is also clearly visible for the directivity index at 30° obtained with the optimized parameter set as given in the table above and as illustrated by the curve 501 in FIG. 5.

[0061] The directional polar patterns in FIG. 4 also show that binaural cues have returned. Especially in the frontal plane the difference in sensitivity for the left and right side is now clearly visible, which will provide the user with binaural cues. For example, in the frequency band of 2 kHz the directional polar pattern for the left side (dashed line) clearly shows a higher sensitivity on the left side, whereas the opposite is the case for the right side (dotted line). These directional polar patterns also illustrate that the sensitivity is higher towards the frontal direction compared to the rear direction.

[0062] According to an embodiment the strength of the binaural cues are optimized for at least one binaural cue frequency range below a frequency threshold in the range between 500 Hz and 3 kHz, while at least one directivity index is optimized for a frequency range above said frequency threshold. According to a variation the binaural beamformer is fixed below said frequency threshold in the range between 500 Hz and 3 kHz and adaptive above. According to a more specific variation the strength of the binaural cues below the frequency threshold is optimized by providing directional polar patterns that are adapted to provide a lower sensitivity for sounds incident from the direction towards the other ear of the user as opposed to sounds incident from the directly opposite direction, whereby the binaural cues in the form of interaural level differences are optimized.

[0063] In summary, the optimization according to the present invention provides a balanced combination of optimized directivity and binaural cues.

[0064] Reference is now given to FIG. 6, which illustrates highly schematically a method 600 of operating a binaural ear level audio system according to an embodiment of the invention.

[0065] The first step 601 of the method comprises providing a first and a second monaurally beamformed signal from a first and a second ear level audio device of the binaural ear level audio system;

[0066] The second step 602 of the method comprises providing a binaurally beamformed signal by combining said first and second monaurally beamformed signal;

[0067] The third step 603 of the method comprises using a first and a second frequency dependent parameter to control the first and the second monaurally beamformed signals, and additionally a third frequency dependent parameter to control the binaurally beamformed signal

[0068] The fourth step 604 of the method comprises selecting said frequency dependent parameters in order to provide: an optimized directivity index, for at least one first direction and for at least one first frequency range and an optimized presence of binaural cues for at least one second frequency range.

[0069] According to a variation of the present invention, a personalization procedure may be carried out as part of an initial fitting or as part of a subsequent fine tuning. Initially the personalization procedure will test, for a plurality of sound environments, how much the speech intelligibility depends on the availability of binaural cues as opposed to having a high DI for a given range of specific directions (typically primarily towards the frontal halfplane). Based on the result of these tests an optimum trade off between directivity and binaural cues can be obtained by optimizing the parameter set required for binaural beam forming parameters (i.e. α.sub.local, α.sub.opposite and β).

[0070] According to a more specific variation of the present invention the impact of the availability of binaural cues, as opposed to having a high DI with respect to speech intelligibility for an individual user is determined by testing the users speech intelligibility in various sound environments. This may include an optimization criterion directed at ensuring that the difference between the directivity indices for the more than one direction is minimized. A further optimization criterion may be directed at ensuring that the directivity index for the forward pointing direction is the largest.

[0071] According to an even more specific variation this process of finding the optimum binaural beam forming parameters for the individual user with respect to speech intelligibility may be carried out using the methods disclosed in WO-A1-2016004983 by the same applicant. More specifically reference may be given to the method steps of claim 1 as given in page 22, line 1—page 23, line 4 of the referenced document, with the minor adjustment that instead of the user providing a rating of her preference for either of two sounds differing with respect to a set of parameters then according to this specific variation the speech intelligibility for the user is determined for each of such two sounds to be compared and based hereon a relative rating is obtained that may be used directly in the method of the referenced document.

[0072] However, according to another specific variation this process of finding the optimum binaural beam forming parameters for the individual user may also be carried out using the methods disclosed in WO-A1-2016004983 but based simply on the users preferences when comparing optimized settings based on e.g. different selected at least first and second directions and/or different weighting of the optimized directivity indices compared to the maintenance of the binaural cues.

[0073] According to an even more specific variation, the individualization procedure is based on a measurement of the amount of cognitive resources required by the user with the different parameter settings and in various sound environments. More specifically the required amount of cognitive resources may according to a variation be determined using Electroencephalography (EEG) monitoring equipment.

[0074] According to yet another advantageous aspect the individualization procedure includes testing in various sound environments that at least differ in the number and positions of present talkers.

[0075] According to a specific embodiment the term binaural cues may be interpreted as the same as the interaural level difference.

[0076] According to an embodiment said at least first and second directions for which directivity is optimized are selected adaptively and automatically based on direction of arrival (i.e. DOA) methods, e.g. by using the specific methods disclosed in WO-A1-2019086435 or WO-A1-2019086439 by the same applicant. More specifically reference may be given to the method steps of claim 1 for the two patent applications.

[0077] It is generally noted that even though many features of the present invention are disclosed in embodiments comprising other features then this does not imply that these features by necessity need to be combined.

[0078] As one example the various disclosed features for individualizing a system according to the invention such as using EEG monitoring and using the methods disclosed in WO-A1-2016004983—is generally independent of the specific values selected for the binaural beamforming parameters α.sub.local, α.sub.opposite and β.

[0079] Other modifications and variations of the structures and procedures will be evident to those skilled in the art.