JP2019520769A - Hearing aid intensity and phase correction - Google Patents

Abstract

A method for correcting intensity distortion and phase distortion in an open-ear hearing aid includes a step of determining an insertion effect of the hearing aid when the hearing aid (12) is inserted into the ear, substantially into the eardrum (11). The complex insertion transfer function (ITF) intensity response and phase response are corrected when the transfer function to the eardrum is approximately balanced with the transfer function of a hearing aid that is not in place. [Selected figure] Figure 1

Description

The present invention relates to a hearing device that improves the hearing ability of a person when worn by the person. However, while hearing aids are sometimes referred to as hearing aids, such names do not limit the use of the invention by the deaf person. Likewise, the invention is also usable by non-hearing persons.

  More particularly, the present invention relates to a hearing aid in which at least a portion of the hearing aid occludes the ear canal and creates an undesirable insertion effect. The invention has particular applicability to open ear hearing aids, but can also be used in conjunction with closed hearing aids.

  Insertion of all or part of the hearing aid into the ear distorts both the magnitude and phase of the sound reaching the tympanic membrane. Ideally, the hearing aid is to compensate for these effects so that the arriving sound remains undistorted after passing through the hearing aid and the ear canal. Many hearing aids compensate for intensity effects but can not cope with phase distortion well. As a result, the user often complains that the arrival sound is not natural and there are no directional cues important to the listening experience. These complaints are particularly widespread among musicians and professionals in the music industry. Although these people's ears are trained to identify subtle differences, they need hearing aids to compensate for partial hearing loss.

  U.S. Pat. No. 5,325,436 (Sigfrid Soli et al.) Proposes a solution to compensate for the insertion effect of the hearing aid, and discloses a method for determining the digital filter to compensate for the insertion effect of the hearing aid in the ear ing. In this method, the intensity and phase responses in the ear are measured for both without and with a hearing aid inserted in place, and then the required equalization (EQ) is calculated. However, the method is complex in computing, computing EQ, and in most cases making assumptions about topological elements that are not valid. Because of the assumptions made about phase, phase response tends to be invalid. This method pre-supposes an ear pierce so as to completely occlude the ear canal, in order to attenuate all outside sounds. Also, for correction, it is only intended to maintain the interaural timing difference between the two ears, not the absolute timing difference. For this reason, hearing aids require binaural devices.

  The present invention provides an apparatus and method for correcting the insertion effect of a hearing aid into the ear that is compatible with an open-ear type insertion and that does not require any assumptions about phase response, and that can be shared with monaural instruments. The present invention is particularly effective for correcting phase distortion and various abnormalities in the tympanic membrane by providing a hearing aid in the ear canal. The apparatus and method of the present invention can provide amplified sound to the tympanic membrane that is perceived as a natural sound and that also keeps a clue to the direction by improving the listening experience. That is, the device is perceived as acoustically transparent. The improved listening experience, realized by most users, will be realized by professionals in the music industry who want to regain the musical ability to identify particularly subtle musical differences.

SUMMARY OF THE INVENTION The present invention is directed to a method and apparatus for correcting for magnitude distortion and phase distortion of a hearing aid inserted into the ear when worn by a user. The method comprises the steps of determining the insertion effect of the hearing aid present in the user's ear. This insertion effect is characterized at the tympanic membrane, characterized by a complex insertion transfer function (ITF) with intensity response and phase response. Both the intensity and phase response of the ITF are corrected when the transfer function to the tympanic membrane is balanced with the transfer function of the hearing aid not in place.

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

  The correction of insertion effects in intensity and phase can be determined by incorporating the ratio of a complex head-related transfer function (HRTF): 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 a hearing aid. Or 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-phase response of the hearing aid is known, equalization to correct the ITF can be calculated for all parts of the transfer function that are minimal phase. However, in most cases, non-minimum phase regions can not be calculated because there is no analysis method to process non-minimum phase regions.

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

  Alternatively, the desired equalization to correct the ITF intensity and phase response can be subjectively determined by the user who experienced the in speech sound. The user compares the sound heard in the presence of the hearing aid with the perception of the sound heard in the absence in the ear canal. The desired equalization is achieved when the user indicates that there is no recognized difference between these two conditions.

  The hearing aid according to the preferred embodiment of the present invention is configured to correspond to less than about 120 degrees of phase at all frequencies amplified in the hearing aid. In other words, the latency of the hearing aid is preferably less than about 1/3 of the highest frequency period produced by the hearing aid. For example, if the hearing aid amplifies sound to 10 kHz, the preferred latency would be less than 30 μs.

FIG. 2 is a schematic view of an open ear hearing aid worn in the ear that produces an insertion effect, showing two sound paths to the tympanic membrane.

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

In accordance with the present invention, a method is shown that can compensate the ITF with a second order minimum phase filter. The HRTF is the same as in FIG. 2 and the aided transfer function (ATF) is the result of direct sound and amplified and equalized sound by the hearing aid. (The intensity response is shown in the upper plot and the phase response in the lower.) HRTF is the head related transfer function and ATF is the auxiliary transfer function.

FIG. 4 is a graph mathematically showing how the minimum filter can be fully compensated for attenuation, as in FIG. 3. (The intensity response is shown in the top figure and the phase response is shown in the bottom figure.) These filters are shown separately in FIG. 4A and summed together in FIG. 4B.

FIG. 6 is a graph mathematically illustrating whether a bandpass filter can not compensate for attenuation, either intensity or phase, with a delay of 1.5 ms. These filters are also shown separately in FIG. 5A and in FIG. 5B.

FIG. 6 is a general flow chart illustrating two basic steps according to the invention for compensating for the insertion effect of the hearing aid in the ear canal.

FIG. 6 is a more detailed flow chart illustrating steps in accordance with the present invention for compensating for the insertion effect of a hearing aid into the ear canal using an acoustic human anatomical model.

BEST MODE FOR CARRYING OUT THE INVENTION The presence of a hearing aid in the ear canal changes the transfer function to the tympanic membrane. This change consists of two components: the active response of the hearing aid itself and its passive effect. When the passive effects are compensated, the hearing aid becomes truly transparent and sounds natural to the user at all sound levels.

In an open hearing aid, the presence of the receiver (or loudspeaker) in the ear canal does not attenuate the incident sound completely. This is in fact the direct path around the receiver (or loudspeaker) from being provided with a plurality of holes in the rubber insert that hold in place. These instruments tend to attenuate very little low frequency (less than 500 Hz), but higher frequencies attenuate in a variable way depending on the geometry of the hearing aid, the ear tip and the user's ear canal.

  Such open hearing aids have two advantages for the user. First, for high frequency deaf (usually this type of) users, the hearing aid does not have to amplify any low frequency sounds at all, and there is less physical restraint or compression on the miniature loudspeakers used. Second, there is no occlusion effect, and when the entrance of the ear canal is occluded, the user's own speech changes.

  In a closed hearing aid, the incident sound is attenuated at all frequencies and is generally negligible. This means that the sound produced by the closed hearing aid is only the significant sound that reaches the tympanic membrane. However, since the insertion effect remains in magnitude and phase, it requires correction in the same manner as described above.

  In hearing aids without microphones, such as in-the-ear monitors, the current input signal is an electrical signal. The insertion effect of such a hearing aid can be determined from the case where the speaker plays in front of the wearer, as in the case of the closed hearing aid.

  The method according to the invention will first be described in the case of an open ear hearing aid. In this method, the acoustic human anatomical model is used for the measurements necessary to determine the equalization for the insertion effect of the hearing aid. This equalization requires effective correction. An alternative method of using a human anatomical model, i.e. one that does not use a human anatomical model but relies on a live person, will be described later. The other two examples mentioned above, namely the examples of the occlusion hearing aid and the in-ear monitor, are virtually identical and can be corrected since they use the same correction method as described above.

  The acoustic human anatomical model is designed to emulate an average human head and contains a microphone in a calibrated artificial ear. With the microphone embedded in this way, the sound pressure can be easily measured at the position of the tympanic membrane of the human model. These measurements can be used to determine complex transfer functions. These complex transfer functions indicate how the sound travels through the ear and reaches the tympanic membrane, with or without the hearing aid in place. Without a hearing aid, the ear is not occluded and the complex transfer function is usually called head-related transfer function (HRTF). In in-place and turned-off hearing aids, the ear is occluded and the complex transfer function can be called insertion transfer function (ITF). The insertion effect is the difference between HRTF and ITF, sometimes called insertion loss. Insertion loss is also due to the intensity decay associated with it, but also because any resonance or filter that changes the intensity response will necessarily change the phase as well, so the phase is also affected.

  The difference in intensity and phase between HRTF and ITF must be corrected for transparent recognition. The insertion effects of the ear canal and the hearing aid are static and passive. Thus, their resonances can be described as minimum phase. Minimal phase systems have several useful properties. That is, the effects of the system are spectrally localized. The system has a stable inverse relationship. And for a given intensity response, the minimum phase response is unique.

  All these properties mean that the insertion effect can be eliminated by adding a complementary second-order minimum phase filter to the processing of the hearing aid. When adding filters, both intensity and phase responses 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 an aided transfer function (ATF) and is identical to the HRTF without a hearing aid.

  ATF is a combination of direct sound (represented by ITF) at the tympanic membrane and amplified sound. For the proper operation of the summarization (for), the time delay between the sounds must be minimized so that the phase lag corresponds to less than 120 degrees of phase at all frequencies amplified by the hearing aid. You must. Therefore, the phase lag can be adjusted by moving the microphone close to the receiver of the hearing aid or designing the hearing aid. These changes are an integral part of the design. On the other hand, the compensation filter for ATF can be changed, for example by reprogramming the digital signal processing chip, if the hearing aid is digital. (The invention is not limited to digital embodiments.)

  To apply the method of the invention to the human ear, the in-ear response is measured with a probe microphone. A probe microphone is placed in the ear canal to accurately measure HRTF, ITF, and ATF with a model such as an acoustic human anatomical model.

  An alternative human application is to incorporate a subjective path. Using source material at levels that the subject can hear without difficulty, the subject will be asked if raw material recognition without a hearing aid (HRTF) matches 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 skilled listeners such as musicians and recording engineers.

  FIG. 1 schematically shows an example of an open ear hearing aid (12) consisting of a microphone 13, a processor 15 and a speaker 17. Here, the incident sound indicated by reference numeral 10 reaches the tympanic membrane 11 via two sound paths A and B. Direct path A is a sound path that passes around an earpiece (not shown) and features an insertion transfer function (ITF). The amplification path B passes through the microphone 13, the processor 15 (which provides equalization of correction) and the speaker 17. The recognition sound indicated by the arrow P is a summation of the sound reaching the tympanic membrane via these two sound paths.

  An example of the insertion effect resulting from the open ear hearing aid is shown in FIG. FIG. 2 shows transfer function measurements obtained from an acoustic human anatomical model. The insertion effect is the difference between HRTF and ITF. As shown in the upper graph, the intensity is different from 500 Hz or higher ("insertion loss") and, as shown in the lower graph, the phase is different at more than 500 Hz.

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

This concept is shown mathematically in the examples of the minimum phase filter in FIGS. 4A and 4B. It is generally the case for any causal 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 ("attenuation"). This filter is minimal at the center frequency and approaches unity away from the center frequency. The second-order minimum phase filter is mathematically represented by the following biquadratic equation:

Where 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, where the gain is limited to greater than one. The transfer function of this filter is shown by dashed lines in FIG. 4A.

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

The aggregate transfer function at the tympanic membrane of these filters corresponds to ATF. Several parameters shown by following formula 3 and Formula 4


A predetermined fixed attenuation filter can be analytically shown that the boost with has a single magnitude and zero phase response a (see FIG. 4B). The parameters of the filters in FIGS. 4A and 4B were chosen according to such a relationship. Such systems are completely transparent.

  It should be noted that this embodiment corresponds to multiple filters assembled in parallel. When two filters are arranged in series, one filter acts on the output of the other filter and, under simpler conditions, ie, when multiple filters are in inverse relation to each other, it can be aggregated into a single There are many. The mathematical concepts outlined above are specific examples and should be maintained for many other filter combinations, two bell filters (two fourth-order filters), high pass filters and low pass filters etc. Can.

  In the above example, it was estimated that there was no time delay between the direct sound and the amplified sound. Thus, these sounds are summed at the tympanic membrane since there is no phase shift at the peak frequency and the phase shift is negligible at ambient frequencies. Such conditions are appropriate when the hearing aid has no latency and there is little distance (or propagation time) between the microphone and the hearing aid.

  If the amplified sound is sufficiently delayed, there is a frequency that shifts the phase by about 180 degrees with respect to the direct sound. When summed at the tympanic membrane, these sounds act destructively on each other's summed sounds, eliminating them. Amplified sound at a given frequency: The relative strength of the direct sound determines whether the cancellation is complete (equivalent strength) or partial (not equal strength).

  Most hearing aids have a latency of at least 1.5 ms, and if it is not longer, significant cancellation can be performed and proper compensation of the ITF is prevented. Such an example is modeled by adding a pure delay to a pandpass filter. As shown in FIGS. 5A and 5B, the delay has a linear phase response. There are two noticeable effects on the delay of 1.5 ms. 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.

  Microphone delay can be reduced by shortening the distance between the microphone and the receiver. The microphone delay can be increased by adding a delay into the processing circuitry (the processing circuitry is not necessarily needed, but perhaps a digital processor) or moving the microphone further away from the receiver.

  The block diagram of FIG. 6 illustrates the above-described basic steps of correcting the insertion effect of a hearing aid in accordance with 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 mentioned above, the insertion effect can be achieved subjectively from the input by the wearer.) Once the insertion effect of the hearing aid into the ear canal is determined, it is possible to subsequently correct both the intensity and the phase (Block 103).

  FIG. 7 details these steps in determining this correction using an acoustic manikin. The acoustic human anatomical model is designed to simulate an average frequency response at the tympanic membrane to provide a microphone embedded behind the outside ear (block 104). The Head Transfer Function (HRTF) is measured with the hearing aid moved from the human anatomical model ear so that the ear canal is not occluded (block 105). Next, the complex insertion transfer function (ITF) can be measured with a turned off hearing aid (block 107) by placing the hearing aid in the external ear canal of a human anatomical model (block 106). With the HRTFs and ITF thus measured, the equalization necessary to correct for the insertion effect of the hearing aid in the ear canal can be determined (block 108). As mentioned above, the equalization to correction is the ratio of HRTF measurements: ITF measurements. This correction may be applied to the hearing aid (block 109). The resulting aided transfer function (ATF) can then be measured and compared to the HRTF.

  In order to correct the insertion effect by the acoustic human anatomical model, the plurality of steps shown in FIG. 7 can be adopted even using a human being. In this case, the measurement is performed with a probe microphone on the tympanic membrane.

  It will be appreciated that the steps can be repeated to fine tune the correction to reach the optimal ATF.

  While the invention has been described in considerable detail in the specification, it is to be understood that the invention is not limited to such detailed description, except as required by the claims.

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

Claims (27)

A method of correcting intensity distortion and phase distortion of a hearing aid in which at least a part of the hearing aid is inserted in the ear when the user wears the hearing aid, the method comprising
Determining the insertion effect of the hearing aid when the hearing aid is in the ear, the insertion effect characterized by a complex insertion transfer function (ITF) with an intensity response and a phase response;
Correcting the insertion effect by correcting both the intensity response and the phase response of the ITF, wherein the phase response is corrected only when the phase response is the minimum phase;
Said method comprising   The method of claim 1 wherein the insertion effect is corrected with at least one second order minimum phase filter.   3. The method of claim 2, wherein the second order minimum phase filter is an infinite impulse response (IIR) filter.   3. The method of claim 2, wherein the second order minimum phase filter is a biquad filter.   The method of claim 1 wherein the insertion effect is corrected with a plurality of second order minimum phase filters.   6. The method of claim 5, wherein the plurality of second order minimum phase filters are a plurality of infinite impulse response (IIR) filters.   6. The method of claim 5, wherein the plurality of second order minimum phase filters are a plurality of fourth order filters.   If there is no hearing aid in the ear, the sound path from the ear to the tympanic membrane is characterized by a complex HRTF, and the step of correcting for the insertion effect corrects the intensity response and phase response of the ITF. To determine the desired equalization, which is determined from the complex HRTFs and the insertion transfer functions (ITFs), the strength and phase of the desired equalization being HRTF: The method of claim 1 comprising the step of being a ratio of ITF.   The method according to claim 8, wherein the complex HRTF is determined by measuring a complex HRTF of a human anatomical model.   The method according to claim 8, wherein the complex HRTF is determined by measuring the complex HRTF of the hearing aid user.   9. The method according to claim 8, wherein the complex ITF is determined by measuring the complex ITF of a hearing aid on the ear of a human anatomical model.   The method according to claim 8, wherein the complex ITF is determined by measuring the complex ITF of the hearing aid when worn by the user.   The step of correcting for the insertion effect is a step of determining the desired equalization for correcting the intensity response and the phase response of the ITF, wherein the desired equalization comprises sounding in speech 2.) Determined subjectively by the user experienced at the time, the user compares the sound heard when wearing the hearing aid with the substantially same sound heard without the hearing aid, when there is no perceived difference between these two sounds The method according to claim 1, wherein the step comprises the step of achieving equalization.   9. The method according to claim 8, wherein if the intensity response and phase response of the hearing aid are known, equalization to correct these intensity and phase responses is calculated for all parts of the phase response that are minimal phase.   The method according to claim 8, wherein if the phase response is a minimum phase, different minimum phase filters are repeatedly introduced into the hearing aid until the desired phase correction is achieved.   The hearing aid amplifies the spectrum within the acoustic frequency, and the hearing aid is configured such that the latency of the amplified sound corresponds to a phase less than about 120 degrees of the highest frequency produced by the hearing aid. the method of.   The method according to claim 1, wherein the latency of the hearing aid is less than about 1/3 of the highest frequency period produced by the hearing aid. When worn by the user, at least a portion of the hearing aid is inserted into the ear, and when the hearing aid is worn, an insertion effect is produced characterized by a complex insertion transfer function (ITF) with an intensity response and a phase response. A method of correcting intensity distortion and phase distortion in said hearing aid, said method comprising
Configuring the hearing aid such that the waiting time of the hearing aid when worn is less than about 1/3 of the highest frequency period amplified by the hearing aid;
Correcting for complex ITF intensity response; and correcting for complex ITF phase response whenever the phase response is minimal phase;
Said method comprising   The method according to claim 18, wherein the complex ITF intensity response and phase response are corrected using at least one minimum phase second order filter.   20. The method of claim 19, wherein the minimum phase second order filter is an infinite impulse response (IIR) filter.   20. The method of claim 19, wherein the minimum phase second order filter is a fourth order filter.   If the latency 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 ITF and the frequency dependent phase delay are known, then the phase correction is for all parts of the phase response which is the minimum phase The method of claim 18, wherein the   The method according to claim 18, wherein different minimum phase filtering is repeatedly introduced into the hearing aid whose phase response is the minimum phase until the desired correction is achieved. A hearing aid which when worn by a user is at least partially inserted into the ear and produces amplified sound in one or more selected frequency bands,
Microphone;
A speaker insertable into the ear wherein the distance between the microphone and the speaker when the hearing aid is worn is selected such that the latency time of the hearing aid is less than about 1/3 of the maximum wavelength period amplified by the hearing aid The speaker; and a processor provided between the microphone and the speaker;
And at least the speaker of the hearing aid creates an insertion effect characterized by a complex insertion transfer function (ITF) having an intensity response and a phase response when the hearing aid is inserted in the ear, the processor producing an ITF intensity response Said hearing aid configured to correct for insertion effects by correcting both and phase response, but only if the phase response is a minimum phase.   25. The hearing aid according to claim 24, wherein the processor comprises at least one minimum phase second order filter, the minimum phase second order filter being used to correct complex ITF intensity and phase responses.   The hearing aid according to claim 25, wherein the minimum phase second order filter is an infinite impulse response (IIR) filter. The hearing aid according to claim 25, wherein the minimum phase second order filter is a fourth order filter.