Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R25/00—Deaf-aid sets, i.e. electro-acoustic or electro-mechanical hearing aids; Electric tinnitus maskers providing an auditory perception
  • H04R25/50—Customised settings for obtaining desired overall acoustical characteristics
  • H04R25/505—Customised settings for obtaining desired overall acoustical characteristics using digital signal processing
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R1/00—Details of transducers, loudspeakers or microphones
  • H04R1/10—Earpieces; Attachments therefor ; Earphones; Monophonic headphones
  • H04R1/1016—Earpieces of the intra-aural type
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
  • H04R2460/00—Details of hearing devices, i.e. of ear- or headphones covered by H04R1/10 or H04R5/033 but not provided for in any of their subgroups, or of hearing aids covered by H04R25/00 but not provided for in any of its subgroups
  • H04R2460/05—Electronic compensation of the occlusion effect
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04S—STEREOPHONIC SYSTEMS 
  • H04S2420/00—Techniques used stereophonic systems covered by H04S but not provided for in its groups
  • H04S2420/01—Enhancing the perception of the sound image or of the spatial distribution using head related transfer functions [HRTF's] or equivalents thereof, e.g. interaural time difference [ITD] or interaural level difference [ILD]

Definitions

• the present invention generally relates to hearing devices worn by a person to improve the person's ability to hear sounds. Reference will sometimes be made herein to "hearing aids;” however, such references are not intended to limit the invention to use by persons having hearing loss. The invention could as well be used by persons without hearing impairments.
• the invention more particularly relates to hearing devices wherein at least a portion of the device occludes the ear canal and creates undesirable insertion effects.
• the invention has particular applicability to open ear hearing devices, but could also be used in conjunction with closed ear devices.
• Soli pre-supposes an ear piece that fully occludes the ear canal so as to attenuate all outside sounds. Also, the correction described in Soli is intended only to preserve the interaural timing difference between the ears, not the absolute timing difference: because of this, Soli requires binaural fittings of the hearing aids.
• the present invention provides a device and method for correcting the insertion effect of a hearing device in an ear, which requires no assumptions about the phase response, can be used with monaural fittings, and is suited for open ear inserts.
• the invention is particularly effective in correcting, at the ear drum, phase distortion and anomalies in sound caused by the presence of the hearing device in the ear canal.
• the device and method of the invention are capable of providing, to the ear drum, amplified sound that is perceived as natural and which retains directional cues for an improved listening experience; that is, the device is perceived to be acoustically transparent. Improvements to the listening experience will be realized by most users, but will be realized in particular by music industry professionals who wish to regain their capability to discern subtle musical differences.
• the invention is directed to a method and device for correcting magnitude and phase distortion in hearing devices wherein at least a portion of the hearing device is inserted in the ear when worn by the user.
• the method comprises determining the insertion effect of the hearing device when in the ear of a user.
• the insertion effect is characterized by a complex insertion transfer function (ITF) having a magnitude and a phase response and is determined at the ear drum. Both the magnitude and phase response of the ITF is corrected when the transfer function to the ear drum matches the transfer function without the hearing device in place.
• ITF complex insertion transfer function
• the insertion effect is corrected by at least one and suitably a plurality 2 nd order minimum phase filters.
• the 2 nd order minimum phase filters are preferably infinite impulse response (IIR) filters, and still more preferably biquad filters.
• Correcting for the insertion effect in both magnitude and phase involves determining an appropriate equalization, which can roughly but not entirely be determined by taking the ratio of a complex head-related transfer function (HRTF) and a complex insertion transfer function (ITF).
• HRTF head-related transfer function
• ITF complex insertion transfer function
• the complex HRTF and ITF can be determined by measurements on a manikin with and without the hearing device, or can be determined by measurements directly on the user of the hearing device.
• the phase response is only corrected where the phase response is minimum phase.
• the equalization for correcting the ITF could be computed for all portions of the transfer function that are minimum phase. However, in most cases this will not be possible, since there is no analytic way to deal with non-minimum phase regions.
• the desired equalization can be determined through an iterative process. Different minimum phase filtering can be introduced to the hearing device to correct those spectral regions dominated by minimum phase phenomena: in other regions where the phase cannot be corrected, it may be possible to correct the magnitude response. This is done iteratively until a desired phase correction is achieved.
• the desired equalization for correcting the ITF magnitude and phase response can be determined subjectively by a user experienced in describing sound. The user compares her perception of sound heard with and without the presence of a hearing device in her ear canal. The desired equalization is achieved when the user indicates that there is no perceived difference between the two conditions.
• the hearing device is configured such that the latency of the sound amplified by the hearing device corresponds to less than about 120 degrees of phase at all frequencies amplified by the hearing device.
• the latency of the hearing device will preferably be less than about one third of the period of the highest frequency produced by the hearing device. For example, if the device amplifies sounds up to 10 kHz, the preferred latency will be less than 30 ⁇ .
• Fig. 1 is a diagrammatic representation an open ear hearing aid worn in the ear where it produces an insertion effect, and showing two sound paths to the ear drum.
• Fig. 2 are graphs that show the insertion effects of an open ear hearing device where the head related transfer function (HRTF) and insertion transfer function (ITF) were measured on an acoustic manikin. (Magnitude response is shown on the upper graph, and phase response is shown on the lower graph.)
• HRTF head related transfer function
• ITF insertion transfer function
• Fig. 3 are graphs that show how the ITF can be compensated with 2 nd order minimum phase filters in accordance with the invention.
• the HRTF is identical to Fig. 2, while the aided transfer function (ATF) is the result of the direct sound and the sound amplified and equalized by the hearing device.
• ATF aided transfer function
• HRTF head related transfer function
• ATF aided transfer function
• Figs. 4A and 4B are graphs that mathematically demonstrate how a minimum phase filter can completely compensate for attenuation, in analogy to Fig. 3. (Magnitude response is shown above; phase response is shown below.) The filters are shown separately in Fig. 4A and are shown summed together in Fig. 4B.
• Figs. 5A and 5B are graphs that mathematically demonstrate how a 1.5 ms delay makes it impossible for a bandpass filter to compensate an attenuation in either magnitude or phase. Again, the filters are shown separately in Fig. 5A and are shown summed together in Fig. 5B.
• Fig. 6 is a generalized flow chart illustrating the two basic steps in accordance with the invention for correcting for the insertion effects of a hearing device in an ear canal.
• Fig. 7 is a more detailed flow chart illustrating steps for correcting for the insertion effects of a hearing device in an ear canal using an acoustic manikin. Best Mode for Carrying Out the Invention
• the presence of a hearing device in the ear canal changes the transfer function to the ear drum. This change consists of two components: the active response of the device itself, and its passive acoustic effect. If the passive effect is compensated, then the hearing device becomes truly transparent and will sound natural to a user at all sound levels.
• the incident sound is not completely attenuated by the presence of the receiver in the ear canal: this is true because a direct path around the receiver (or loudspeaker) is provided by holes in the rubber insertion tip that holds the receiver in place.
• Such devices tend to attenuate low frequencies (below 500 Hz) very little, but attenuate higher frequencies in a variable way that depends on the geometry of the hearing aid, the ear tip, and the user's ear canal.
• Such an open aid has two advantages for the user: first, for those with high frequency hearing loss (the most common kind), the hearing aid doesn't need to amplify low frequency sounds at all, which places fewer physical constraints on the miniature loudspeaker used. Second, there is no occlusion effect, which is the change in the perception of one's own voice when the entrance to the ear canal is blocked.
• the input signal is now an electrical signal.
• the insertion effect of such devices is identical to the previous case, and can be determined from the case when the sound is played through loudspeakers in front of the wearer.
• the method of the invention is first described for the case of an open-ear hearing aid, wherein an acoustic manikin is used for measurements needed to determine the equalization that will be needed to effectively correct for the insertion effects of the hearing aid.
• Alternatives to using a manikin are later described, namely, the method which does not use a manikin but relies on a live person.
• closed hearing aids and in-ear monitors are practically identical and can be corrected for using the same method described herein.
• An acoustic manikin contains a microphone in an artificial ear that is designed and calibrated to emulate the average human head.
• the embedded microphone makes it possible to easily measure sound pressure at the ear drum position of the manikin. Such measurements can be used to determine the complex transfer functions that describes how sound passes through the ear to the ear drum, with or without the hearing device in place. Without the hearing device, the ear is unoccluded and the complex transfer function is commonly referred to as the Head Related Transfer Function (HRTF). With the hearing device in place and turned off, the ear is occluded and the complex transfer function can be referred to as the Insertion Transfer function. (ITF).
• the insertion effect is the difference between the HRTF and the ITF. This is sometimes called "insertion loss," because of the magnitude attenuation associated with it, but the phase is also affected since any resonance or filter that changes magnitude response will necessarily change the phase as well.
• the magnitude and phase difference between the HRTF and the ITF must be corrected for transparent perception.
• the ear canal and the device's insertion effect are static and passive. Thus, their resonances can be described as minimum phase.
• Minimum phase systems possess several useful properties: their effects are spectrally localized; they have stable inverses; and, for a given magnitude response, the minimum phase response is unique.
• ATF Aided Transfer Function
• the ATF is the combination, at the ear drum, of the direct sound
• the time delay between the sounds must be minimized so that the phase delay corresponds to less than 120 degrees phase at all frequencies amplified by the hearing aid.
• the phase delay can be adjusted by moving the microphone closer to the hearing aid's receiver and by designing the hearing aid accordingly. Such changes tend to be integral to the design.
• the compensation filters for the ATF can be changed, such as by reprogramming a digital signal processor chip if the hearing aid is digital. (It will be understood that the invention is not limited to a digital implementation.)
• the in-ear response is measured with a probe microphone.
• the probe microphone is positioned in the ear canal, and the HRTF, ITF, and ATF measured exactly as with an acoustic manikin.
• An alternative human application is to take a subjective path: using source material at a level such that the subject can hear it without difficulty, the subject would be asked if source perception without an aid (the HRTF) matches the ATF. With a subject able to provide detailed guidance as to the exact spectral difference between the HRTF and the ATF, one would find the same filters as the measurement methods. This approach works best for trained listeners, such as musicians or recording engineers.
• Fig. 1 schematically shows an example of an open ear hearing aid (12) comprised of a microphone 13, processor 15, and speaker 17, wherein incident sound denoted by the numeral 10 arrives at the ear drum 11 via two sound paths denoted A and B.
• the direct path A goes around the earpiece (not shown) and is characterized by the Insertion Transfer Function (ITF).
• the amplified path B goes through the microphone 13, the processor 15 (providing the correction equalization), and the speaker 17.
• the perceived sound denoted arrow P is the summation of the sound arriving at the ear drum via these two paths.
• FIG. 2 An example of an insertion effect from an open ear hearing aid is shown in Fig. 2, which shows transfer function measurements from an acoustic manikin.
• the insertion effect is the difference between the HRTF and the ITF: as shown in the top graph, the magnitude is different from 500 Hz and above ("insertion loss"); as shown in the bottom graph, the phase differs above 500 Hz.
• the hearing aid's response (“boost”) is modeled as a bandpass filter with gain, which has a magnitude maximum at the center frequency and approaches zero at the edges:
• Fig. 4B results in unity magnitude and zero phase response a shown in Fig. 4B.
• the filter parameters in Figs. 4A and 4B were chosen according to such a relationship. Such a system is completely transparent.
• this embodiment corresponds to filters that sum in parallel.
• two filters are placed in series, one acting on the output of the other, they sum to unity under much simpler conditions, namely when the filters are inverses of each other.
• the mathematical argument outlined above is a specific case, and can be shown to hold for many other filter combinations: two bell- shaped filters (two biquads), a high pass and a low pass, etc.
• the amplified sound is delayed sufficiently, there will be a frequency where the phase is shifted by 180° with respect to the direct sound.
• the phase is shifted by 180° with respect to the direct sound.
• summing at the ear drum such sounds will sum destructively with each other and cancel.
• the relative magnitude of the amplified to the direct sound at a given frequency determines whether the cancellation will be complete (equal magnitudes) or partial (unequal magnitudes).
• Most hearing aids have latencies of at least 1.5 ms, if not longer, which results in significant cancellation and prevents proper compensation of the ITF.
• Such a case is modeled by adding pure delay to a bandpass filter; delay has a linear phase response, as shown in Figs. 5A and 5B.
• delay has a linear phase response, as shown in Figs. 5A and 5B.
• the comb filtering includes several notches with a gain less than -10 dB, which distort the input signal significantly.
• the microphone delay can be reduced by shortening the separation distance between microphone and receiver; it can be increased by adding delay in the processing circuitry (which is presumably, but not necessarily, a digital processor) or by moving the microphone further away from the receiver.
• the block diagram of Fig. 6 illustrates the basic steps described above for correcting the insertion effects of a hearing device in accordance with the invention.
• the insertion effects of the hearing device in the canal must be determined (block 102). This can be achieved as described above, by taking measurements with the device both removed from and present in the ear canal. (The effects can also be achieved subjectively from input from the wearer as also above-described.)
• the insertion effect of the hearing device in the ear canal is determined, it can then be then corrected for both magnitude and phase (block 103).
• Fig. 7 illustrates these steps in greater detail where the correction is determined using an acoustic manikin.
• An acoustic manikin provides a microphone embedded behind the outer ear that is designed to simulate the average frequency response at the eardrum (block 104).
• HRTF complex head related transfer function
• the complex insertion transfer function (ITF) can be measured (block 107) with the hearing device turned off.
• the equalization needed to correct for the insertion effect of the hearing device in the ear canal can be determined (block 108).
• the correcting equalization will be the ratio of the measured HRTF to the measured ITF.
• This correction can then be applied to the hearing device (block 109).
• the resultant aided transfer function (ATF) can then be measured and compared to the HRTF.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Acoustics & Sound (AREA)
• Signal Processing (AREA)
• Health & Medical Sciences (AREA)
• General Health & Medical Sciences (AREA)
• Neurosurgery (AREA)
• Otolaryngology (AREA)
• Headphones And Earphones (AREA)
• Circuit For Audible Band Transducer (AREA)
• Measurement Of The Respiration, Hearing Ability, Form, And Blood Characteristics Of Living Organisms (AREA)
• Soundproofing, Sound Blocking, And Sound Damping (AREA)

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• 2016
  • 2016-07-07 JP JP2019500379A patent/JP6954986B2/ja active Active
  • 2016-07-07 MX MX2019000303A patent/MX2019000303A/es unknown
  • 2016-07-07 CN CN201680088987.4A patent/CN109716792B/zh active Active
  • 2016-07-07 KR KR1020197003508A patent/KR102596749B1/ko active IP Right Grant
  • 2016-07-07 CA CA3032573A patent/CA3032573A1/en active Pending
  • 2016-07-07 WO PCT/US2016/041298 patent/WO2018009194A1/en active Search and Examination
  • 2016-07-07 AU AU2016413718A patent/AU2016413718A1/en not_active Abandoned
  • 2016-07-07 EP EP16908313.6A patent/EP3482572A4/en not_active Withdrawn

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