JP6954986B2 - Hearing aid strength and phase correction - Google Patents

Description

Background Techniques The present invention relates to a hearing device that, when worn by a person, improves the person's hearing ability. However, hearing aids are sometimes referred to as hearing aids, but such names do not limit the use of the present invention by the hearing impaired. Similarly, the present invention can also be used by non-hearing impaired persons.

More specifically, the present invention relates to hearing aids in which at least a portion of the hearing aid obstructs the ear canal, creating an undesired insertion effect. The present invention has particular potential for open-ear hearing aids, but can also be used in collaboration with obstructive hearing aids.

Inserting all or part of the hearing aid into the ear distorts both the magnitude and phase of the sound reaching the eardrum. Ideally, the hearing aid compensates for these effects so that the incoming sound remains undistorted after passing through the hearing aid and the ear canal. Many hearing aids compensate for intensity effects, but cannot adequately deal with phase distortion. As a result, users often complain that the arrival sound is not natural and there are no directional cues in the listening experience. These complaints are widespread, especially among musicians and professionals in the music industry. The ears of these people are trained to identify subtle differences, but require hearing aids to compensate for partial hearing deficits.

U.S. Pat. No. 5,325,436 (Sigflide Soli et al.) Proposes a solution that compensates for the effect of hearing aid insertion and discloses a method of determining a digital filter that compensates for the effect of hearing aid insertion into the ear. ing. In this way, the intensity response and phase response of the ear was measured for both the case of inserting the case without hearing and hearing aids in position and then calculates the required equalization (equalization) (EQ). However, the method is complex when calculating, calculates EQ, and in most cases makes assumptions about non-valid phase elements. Due to the assumptions made about phase, the phase response is likely to be invalid. Since this method attenuates all outside sounds, it pre-supposes an ear pierce to completely block the ear canal. Further, the correction is intended only to maintain the mutual interaural timing difference between both ears, and is not intended to be an absolute timing difference. For this reason, hearing aids require binaural devices.

The present invention provides a device and method for correcting the effect of inserting a hearing aid into the ear, which does not require any assumptions about the phase response, can be shared with a monaural device, and is suitable for open-ear insertion. The present invention is particularly effective in correcting the phase distortion and various abnormalities caused by the presence of the hearing aid in the ear canal in the eardrum. The apparatus and method of the present invention can supply an amplified sound to the eardrum, which is recognized as a natural sound and which keeps a clue in the direction by improving the listening experience. That is, the device is perceived to be acoustically transparent. An improved listening experience will be realized for most users, but especially for professionals in the music industry who want to regain their musical ability to discern subtle musical differences.

Disclosure of the Invention The present invention is directed to methods and devices for correcting the magnitude and phase distortion of a hearing aid that, when worn by the user, at least part of the hearing aid is inserted into the ear. This method involves determining the effect of inserting a hearing aid present in the user's ear. This insertion effect is characterized by a complex insertion transfer function (ITF) with intensity and phase responses and is determined at the eardrum. Both the strength and phase response of the ITF are corrected when the transfer function to the eardrum is balanced with the transfer function of the hearing aid that is not in place.

The insertion effect is preferably corrected by at least one of a plurality of second-order minimum phase filters, preferably a plurality of second-order minimum phase filters. The second-order minimum phase filter is an indefinite impulse response (IIR) filter, more preferably a fourth-order (biquad) filter.

The correction of the insertion effect in intensity and phase can be determined by incorporating the ratio of complex head-related transfer function (ITF): complex insertion transfer function ITF, although it is rough and not perfect. These complex HRTFs and ITFs can be determined by measurement on a human anatomical model with or without hearing aids. Alternatively, it can be determined by measurement on the user of the hearing aid. The phase response is corrected only when the phase response is the minimum phase.

If the strength and phase response of the hearing aid is known, the equalization to correct the ITF can be calculated for all parts of the transfer function, which is the minimum phase. However, in most cases, the non-minimum phase region cannot be calculated because there is no analysis method for processing the non-minimum phase region.

More practically, the desired equalization is determined by the iterative method. Various minimum phase filters can be introduced into the hearing aid to correct the spectral region dominated by the minimum phase phenomenon. Intensity response may be correctable in other areas where phase cannot be corrected. This correction step is repeated until the desired phase correction is achieved.

Alternatively, the desired equalization for correcting the ITF intensity / phase response can be subjectively determined by the user who has experienced in describing sound. During the ear canal, the user compares the perception of sound heard in the presence of a hearing aid with that heard in the absence of a hearing aid. The desired equalization is achieved when the user indicates that there is no perceived difference between these two conditions.

A hearing aid according to the best embodiment of the present invention is configured to correspond to a phase of less than about 120 degrees at all frequencies amplified by the hearing aid. In other words hearing aid delay time (latency) is less than about 1/3 of the highest frequency term generated by the hearing aid is preferred. For example, if the hearing aid amplifies the sound to 10 kHz, the preferred latency would be less than 30 μs.

It is a schematic diagram of an open-ear hearing aid that is worn in the ear and produces an insertion effect, and shows two sound paths to the eardrum.

It is a graph which shows the insertion effect of the open ear type hearing aid that the head related transfer function (HRTF) and the insertion transfer function (ITF) were measured on the acoustic human body anatomical model. (The graph in the upper figure shows the intensity response, and the graph in the lower figure shows the phase response.)

According to the present invention, a method in which the ITF can be compensated by the second-order minimum phase filter is shown. The HRTF is the same as in FIG. 2, and the aided transfer function (ATF) is the result of the direct sound and the amplified and equalized sound by the hearing aid. (Intensity response is shown in the upper figure (plot) and phase response is shown in the lower figure.) HRTF is a head-related transfer function, and ATF is an auxiliary transfer function.

As in FIG. 3, it is a graph that mathematically shows how the minimum filter can completely compensate for the attenuation. (Intensity response is shown in the upper figure and phase response is shown in the lower figure.) These filters are shown separately in FIG. 4A and summarized together in FIG. 4B.

It is a graph that mathematically explains whether a bandpass filter cannot compensate for attenuation in either intensity or phase with a delay of 1.5 ms. These filters are also shown separately in FIG. 5A and assembled in FIG. 5B.

It is a comprehensive flowchart explaining two basic steps by this invention which compensates for the insertion effect of a hearing aid into the ear canal.

It is a more detailed flowchart illustrating a plurality of steps according to the present invention that compensate for the effect of inserting a hearing aid into the ear canal using an acoustic human anatomy model.

Best Mode for Practicing the Invention The presence of a hearing aid in the ear canal alters the transfer function to the eardrum. This change consists of two components: the active response of the hearing aid itself and its passive effects. When the passive effect is compensated, the hearing aid becomes truly transparent and sounds natural to the user at all sound levels.

In open hearing aids, the incident sound is not completely attenuated even if there is a receiver (or loudspeaker) in the ear canal. This is true because the direct path around the receiver (or loudspeaker) is provided by a plurality of holes in the rubber insertion chip that holds it in place. These devices tend to attenuate low frequencies (less than 500 Hz) very little, but higher frequencies are attenuated in a variable way that depends on the geometry of the hearing aid, eartips and the user's ear canal.

Such open hearing aids have two advantages for the user. First, for users with high-frequency deafness (usually almost this type), the hearing aid does not need to amplify the low-frequency sound at all, and there is less physical restraint or pressure on the miniature loudspeaker used. Secondly, when there is no occlusion effect and the entrance of the ear canal is blocked, the user's own voice changes.

In closed hearing aids, incident sound is attenuated at all frequencies and is generally negligible. This means that the only sound produced by a closed hearing aid is a significant sound that reaches the eardrum. However, since the insertion effect remains in strength and phase, it needs to be corrected in the same way as described above.

For hearing aids that do not have a microphone, such as an intraocular monitor, the current input signal is an electrical signal. The effect of inserting such a hearing aid is the same as that of the closed hearing aid, and can be determined from the case where the speaker emits sound in front of the wearer (played).

First, the method of the present invention will be described in the case of an open-ear hearing aid. In this method, an acoustic human anatomical model is used for the measurements necessary to determine the (for) equalization of the hearing aid insertion effect. Effective correction is required for this equalization. An alternative method using a human anatomy model, that is, a method that does not use a human anatomy model but depends on a live person, will be described later. The other two examples described above, namely the obstructive hearing aid and the intraoural monitor, are substantially the same and can be corrected because they use the same correction method as described above.

The acoustic human anatomy model is designed to emulate the average human head and contains a microphone in the calibrate cochlear implant. With the microphone embedded in this way, the sound pressure can be easily measured at the position of the eardrum of the human model. These measurements can be used to determine complex transfer functions. These complex transfer functions display how sound passes through the ear and reaches the eardrum, whether or not the hearing aid is in place. Without hearing aids, the ear is not obstructed and the complex transfer function is commonly referred to as the head related transfer function (HRTF). The hearing aid that have Yes Power is turned off in a predetermined location, the ear is closed, complex transfer function may be referred to as insertion transfer function (ITF). The insertion effect is the difference between the HRTF and the ITF, sometimes referred to as insertion loss. Insertion loss is due to the associated intensity attenuation, but the phase is also affected because either the resonance or the filter that changes the intensity response inevitably changes the phase as well.

Intensity and phase differences between HRTFs and ITFs must be corrected for transparent cognitive ability. The ear canal and hearing aid insertion effects are static and passive. Therefore, their resonance can be explained as the minimum phase. The minimum phase system has some useful properties. That is, the effect of the system is spectrally localized. The system has a stable inverse relationship. Also, for a given intensity response, the minimum phase response is unique.

All these characteristics mean that the insertion effect can be eliminated by adding a complementary secondary minimum phase filter to the hearing aid processing. When adding a filter, both intensity response and phase response can be corrected. If a non-minimum phase filter is used, either the intensity response or the phase response can be corrected, but not both at the same time. The transfer function that compensates for the insertion effect is called the aided transfer function (ATF) and is identical to an HRTF without a hearing aid.

ATF is a combination of direct sound (expressed by ITF) and amplified sound on the eardrum. For the summation (for) to operate properly, the time delay between the plurality of sounds must be minimized so that the phase delay corresponds to a phase of less than 120 degrees at all frequencies amplified by the hearing aid. Must be. Therefore, the phase lag can be adjusted by moving the microphone closer to the receiver of the hearing aid or by designing the hearing aid. These changes have essential design consequences. On the other hand, the compensation filter for ATF can be changed if the hearing aid is digital, for example, by reprogramming the digital signal processing chip. (The present invention is not limited to digital embodiments.)

To apply the method of the present invention to the human ear, the intraoural response is measured with a probe microphone. The probe microphone is placed in the ear canal and accurately measures HRTFs, ITFs, and ATFs with a model such as an acoustic human anatomy model.

An alternative human application is to incorporate a subjective path. Using a source material that is at a level that the subject can easily hear, the subject will be asked if raw material recognition without a hearing aid (HRTF) is commensurate with ATF. With a subject who can provide detailed guidance on the exact spectral differences between HRTFs and ATFs, one will find the same filters as these measurements. This approach works best for experienced listeners such as musicians and recording engineers.

FIG. 1 schematically shows an example of an open-ear hearing aid (12) including a microphone 13, a processor 15, and a speaker 17. Here, the incident sound indicated by reference numeral 10 reaches the eardrum 11 via the two sound paths A and B. The direct path A is a sound path that passes around an earpiece (not shown) and is characterized by an insertion transfer function (ITF). The amplification path B passes through the microphone 13, the processor 15 ( providing equalization of correction), and the speaker 17. The recognition sound indicated by the arrow P is a summation of sounds that reach the eardrum via these two sound paths.

FIG. 2 shows an example of the insertion effect generated by the open-ear hearing aid. FIG. 2 shows transfer function measurements obtained from an acoustic human anatomy model. The insertion effect is the difference between the HRTF and the ITF. As shown in the graph above, the intensities differ from above 500 Hz (“insertion loss”), and as shown in the graph below, the phases differ above 500 Hz.

3, the insertion effect is shown to be corrected by using a secondary (2 ^nd order) minimum phase filter. It should be noted that the difference between ATF and HRTF is significantly reduced over the range of 1-8 kHz in intensity and phase. The small dig at 950 Hz is not the smallest phase resonance.

式中、ｓはラプラス（Laplace）変数、Ｗは角度周波数（＝２πＦ、但しＦは中心周波数）、Ｑは品質因子、Ｇは利得で、この場合、利得は１より大に限定される。このフイルターの伝達関数を図４Ａに断続線で示した。 This idea is mathematically shown in FIGS. 4A and 4B with an example of a minimum phase filter. This is generally true for any causual filter that has a stable inverse. In this embodiment, the direct sound attenuated by the hearing aid (ITF) is modeled as a bell-shaped attenuation filter (“attenuated”). This filter is the smallest at the center frequency and approaches a single one away from the center frequency. The (that) second-order minimum phase filter is mathematically represented by the following fourth-order (biquadratic) equation.

In the equation, s is the Laplace variable, W is the angular frequency (= 2πF, where F is the center frequency), Q is the quality factor, and G is the gain. In this case, the gain is limited to greater than 1. The transfer function of this filter is shown intermittently in FIG. 4A.

The hearing aid response "boost" is modeled as a bandpass filter with gain. This filter has the highest intensity at the center frequency and approaches zero at the edges.

を有するブーストが単一強度及びゼロ位相レスポンスａ（図４Ｂ参照）となる所定の固定減衰フイルターを解析的に示すことができる。図４Ａ及び４Ｂのフイルターのパラメーターは、このような関係に従って選択した。このようなシステムは完全に透明である。 The aggregate transfer function of these filters in the eardrum corresponds to ATF. Multiple parameters represented by the following equations 3 and 4

It is possible to analytically show a predetermined fixed damping filter in which the boost having a single intensity and zero phase response a (see FIG. 4B). The filter parameters of FIGS. 4A and 4B were selected according to this relationship. Such a system is completely transparent.

It should be noted that this embodiment corresponds to a plurality of filters assembled in parallel. When two filters are placed in series, one filter acts on the output of the other filter, and under simpler conditions, i.e., if multiple filters are inversely related to each other, they can be aggregated in a single unit. many. The mathematical view outlined above is a specific example and should be maintained for many other combinations of filters, such as two bell-shaped filters (two quaternary filters), high pass filters and low pass filters. Can be done.

In the above example, it is estimated that there is no time delay between the direct sound and the amplified sound. Therefore, since there is no phase shift at the peak frequency and the phase shift is negligible at the surrounding frequencies, these sounds are added up in the eardrum. Such conditions are suitable when the hearing aid has no delay time and there is little distance (or propagation time) between the microphone and the hearing aid.

If the amplified sound is delayed sufficiently, there is a frequency that shifts the phase by about 180 degrees with respect to the direct sound. When aggregated in the eardrum, these sounds act destructively on each other and eliminate the aggregated sound. Amplified sound at a predetermined frequency: The relative intensity of the direct sound determines whether the erasure is complete (equivalent intensity) or partial (non-equivalent intensity).

Most hearing aids have at least 1.5ms delay time (latency), if not longer than, to perform important erase, preventing proper compensation of ITF. Such an example is modeled by adding a pure delay to the Pandopath filter. As shown in FIGS. 5A and 5B, the lag has a linear phase response. There are two significant effects on the 1.5 ms delay: 1) The intensity response at the center frequency is less than the amplified sound alone. 2) There is a wide range of combining around the center frequency. This comb filtering has a gain of less than -10 dB and has several notches that significantly distort the input signal.

The microphone delay can be reduced by reducing the distance between the microphone and the receiver. The microphone delay can be increased by adding a delay in the processing circuit configuration (the processing circuit configuration is not necessary, but probably a digital processor), or by moving the microphone further away from the receiver.

The block diagram of FIG. 6 shows the aforementioned basic steps of correcting the insertion effect of a hearing aid according to the present invention. As a first step, the effect of inserting the hearing aid into the ear canal must be determined (block 102). The insertion effect can be achieved by measuring both the hearing aid present in the ear canal and the hearing aid moved in the ear canal, as described above. (As described above, the insertion effect can be subjectively achieved from the input by the wearer.) Once the effect of inserting the hearing aid into the ear canal is determined, both strength and phase can be continuously corrected. (Block 103).

FIG. 7 details these steps in determining this correction using an acoustic manikin. The acoustic human anatomy model is designed to simulate an average frequency response at the eardrum and provides a microphone embedded behind the outside ear (block 104). Head-related transfer functions (HRTFs) are measured with a hearing aid that is moved from the ear of a human anatomical model so that the ear canal is not obstructed (block 105). Then, hearing aid by placing the ear canal of the human anatomy model (block 106), it can be measured power is off the (Turned off) complex insertion transfer function hearing aid (ITF) (Block 107 ). The HRTFs and ITFs thus measured can determine the equalization required to compensate for the effect of hearing aid insertion into the ear canal (block 108). As mentioned above, the equalization to the correction is the ratio of HRTF measurement value: ITF measurement value. This correction can be applied to hearing aids (block 109). The resulting aided transfer function (ATF) can then be measured and compared to the HRTF.

Since the insertion effect is corrected by the acoustic human anatomy model, the plurality of steps shown in FIG. 7 can also be adopted by using a living human being. In this case, the measurement is made with a probe microphone on the eardrum.

It is understood that the plurality of steps can be repeated in order to reach the optimum ATF by fine tune the correction.

Although the present invention has been described in considerable detail in the present specification, it will be understood that the present invention is not limited to such detailed description except that it is required within the scope of claims.

U.S. Pat. No. 5,325,436

Claims (27)

When a user wears a hearing aid, at least part of the hearing aid is a method of correcting the intensity distortion and phase distortion of the hearing aid that is inserted into the ear .
When the hearing aid is that uncut is Ri power ear near, comprising the steps of determining the insertion effect of the hearing aid, the insert effect is a complex insertion transfer function having an intensity response and phase response (ITF) and as the factory to be specific,
In the step of correcting the insertion effect by correcting both the intensity response and the phase response of the insertion transfer function (ITF), when the phase response is the minimum phase, only the phase response is corrected. Process and
The method comprising. The method of claim 1, wherein the insertion effect is corrected by at least one secondary minimum phase filter. The method according to claim 2, wherein the second-order minimum phase filter is an infinite impulse response (IIR) filter. The method according to claim 2, wherein the second-order minimum phase filter is a fourth-order (biquad) filter. The method according to claim 1, wherein the insertion effect is corrected by a plurality of second-order minimum phase filters. The method according to claim 5, wherein the plurality of second-order minimum phase filters are a plurality of infinite impulse response (IIR) filters. The method according to claim 5, wherein the plurality of second-order minimum phase filters are a plurality of fourth-order filters. When there is no hearing aid in the ear, the sound path from the ear to the tympanic membrane identifies a complex head related transfer function (HRTF), and the process of correcting for the insertion effect is the intensity response of the insertion transfer function (ITF). and a step of determining a desired equalization to compensate for the phase response, the equalized are determined from a complex head-related transfer function (HRTF) and complex insertion transfer function (ITF), the equalizing The method of claim 1, wherein the intensity and phase are head-related transfer function (HRTF) : insertion transfer function (ITF) ratios. The method of claim 8, wherein the complex head related transfer function (HRTF) is determined by measuring the complex head related transfer function (HRTF) of a human anatomical model. The method of claim 8, wherein the complex head related transfer function (HRTF) is determined by measuring the complex head related transfer function (HRTF) of the hearing aid user. Complex insert transfer function (ITF), the method according to claim 8, which is determined by measuring the complex insertion transfer function of the hearing aid that is on the ear of the human anatomy Model (ITF). Complex insert transfer function (ITF), the method according to claim 8, which is determined by the user to measure the complex insertion transfer function (ITF) of the hearing aid when worn. The step of correcting the insertion effect is a step of determining the desired equalization for correcting the intensity response and the phase response of the insertion transmission function (ITF) , and the desired equalization is the step of determining the desired equalization in words. Subjectively determined by the user who has experienced in describing sound, the user compares the sound heard when wearing the hearing aid with the approximately same sound heard without the hearing aid and is perceived between these two sounds. the method of claim 1, that when there is no difference comprising the steps are equalized was achieved. The method of claim 8, wherein if the intensity and phase responses of the hearing aid are known, the equalization to correct these intensity and phase responses is calculated for all parts of the phase response that is the minimum phase. The method of claim 8, wherein if the phase response is minimal phase, different minimum phase filters are repeatedly introduced into the hearing aid until the desired phase correction is achieved. Hearing aid amplifies the spectrum of the acoustic frequency, and the hearing aid is the delay time of the amplified sound (latency) is, according to claim 1 which is configured to correspond to approximately 120 ° less than the phase of the highest frequency to be processed by the hearing aid the method of. The method of claim 1 hearing aid delay time (latency) is less than about 1/3 of the highest frequency term generated in the hearing aid. A complex insertion transmission function (ITF) that, when worn by the user, is at least partially inserted into the ear and has a strong and phase response when the hearing aid is in the ear and turned off. ) Is a method of correcting intensity distortion and phase distortion in the hearing aid, which produces the insertion effect specified by .
The process of configuring the hearing aid so that the delay time of the hearing aid when it is in the ear and turned on is less than about 1/3 of the period of the highest frequency amplified by the hearing aid.
The process of correcting the complex ITF intensity response and
Whenever the phase response is the minimum phase, the process of correcting for the complex insertion transfer function (ITF) phase response and
The method comprising. 18. The method of claim 18, wherein the intensity and phase responses of the complex ITF are corrected using at least one minimum phase secondary filter. 19. The method of claim 19, wherein the minimum phase secondary filter is an infinite impulse response (IIR) filter. 19. The method of claim 19, wherein the minimum phase secondary filter is a quaternary filter. If the delay time of the hearing aid causes a frequency-dependent phase delay of the sound passing through the hearing aid, and the phase response of the insertion transfer function (ITF) and the frequency-dependent phase delay are known, then the phase correction is the minimum phase of the phase response. The method of claim 18, which is calculated for all parts. 18. The method of claim 18, wherein if the phase response is minimal phase, different minimum phase filters are repeatedly introduced into the hearing aid until the desired phase correction is achieved. A hearing aid that, when worn by the user, is at least partially inserted into the ear and produces amplified sound in one or more selected frequency bands .
And a microphone,
Ear-insertable speakers, the distance between the microphone and the speaker when wearing the hearing aid is selected so that the hearing aid wait time is less than about one-third of the maximum wavelength period amplified by the hearing aid. and the speaker,
The processor installed between the microphone and the speaker ,
The provided, at least when the speaker of the hearing aid is inserted in the ear hearing aid, an insertion effect, wherein a complex insertion transfer function (ITF) having an intensity response and phase response without wounds, said processor is inserted transfer function ( intensity response and the phase response both ITF), provided that only if the phase response is minimum phase, by correcting the, configured hearing aids to compensate for the insertion effect. 24. The processor has at least one minimum phase secondary filter, which is used to correct the intensity and phase response of a complex insertion transfer function (ITF). Hearing aids. The hearing aid according to claim 25, wherein the minimum phase secondary filter is an infinite impulse response (IIR) filter. The hearing aid according to claim 25, wherein the minimum phase secondary filter is a quaternary filter.

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