FIELD

The present disclosure relates to a device and method for detection and compensation for an oblique ear-probe insertion in especially hearing testing diagnostic setups. More particularly the disclosure relates to detecting an oblique ear-probe insertion from an ear-probe measurement and compensating for its effect on the ear-canal reflectance.

BACKGROUND

Ear-canal reflectance has proved to be a useful quantity for identifying conductive hearing disorders, calibrating stimulus levels in situ, and estimating the pressure emitted from the ear. Measurements in the ear canal using an ear probe are affected by evanescent modes, and the ear-canal reflectance further depends on the characteristic impedance at the position of the ear probe. The characteristic impedance of a uniform waveguide is closely related to its cross-sectional area, which inherently varies between different ear canals and with insertion depth. Evanescent modes occur when an acoustic flow is injected into a waveguide (such as an ear canal) through a narrow aperture as non-propagating modes are elicited, and are closely related to a geometrical mismatch between the ear probe and the waveguide. Evanescent modes and incorrect estimates or assumptions of characteristic impedance thus introduce errors into the ear-canal reflectance and should be compensated for and estimated, respectively, to obtain accurate measurements of ear-canal reflectance, especially toward higher frequencies.

An additional factor introducing inaccuracies into the ear-canal reflectance are related to the insertion angle of the ear probe into the ear canal. Ear probes are usually inserted into the ear canal using a rubber or foam ear tip and, while the calibration procedure constitutes a controlled setup, it is difficult to take non-invasive precautions to avoid oblique ear-probe insertions into ear canals. While the ear canal in itself is inherently non-uniform, it is further not a straight waveguide. Placing the ear-probe tip at the position of a bend of the ear canal can result in an oblique insertion although it appears to be perpendicular as seen from the outside. Thus, for avoiding a contribution in the ear-canal reflectance from errors arising in, e.g., reflectance measurements due to the oblique probe insertion, there exists a need for a solution that allows for detecting and compensating for an oblique ear-probe insertion in a diagnostic setup.

SUMMARY

Accordingly, a method and diagnostic device are disclosed that can detect if the physical features (i.e., especially insertion angle of the ear probe) in front of the ear probe provide the conditions suitable for defining and estimating the characteristic impedance of the ear canal or a waveguide simulating the ear canal, and thereby obtaining a valid reflectance measure using the estimated characteristic impedance.

That is, a method for detecting an oblique ear probe insertion into an acoustic waveguide, such as an ear canal, is disclosed. The method comprises the steps of:Inserting an ear probe into a waveguide;emitting an acoustic stimulus into said waveguide via the ear probe;measuring an ear-probe response;estimating a characteristic impedance of the waveguide from the measured ear-probe response in a plurality of frequency ranges of said ear-probe response; andutilizing the estimated characteristic impedance for each of the plurality of said frequency ranges to characterize the degree of obliqueness in said ear-probe insertion.

By providing a method as presented herein, it is possible not only to provide an estimate of the degree of obliqueness of the ear-probe insertion in a waveguide, such as an ear canal, but also to compensate for such obliqueness. This is important, since a plurality of diagnostic measures in, e.g., hearing diagnostics depend on an accurate estimate of the characteristic impedance of the ear canal to calculate an accurate estimate of, e.g., ear-canal reflectance, stimulus levels, and acoustic responses emitted from the ear. Thus, with this method it is possible to evaluate an ear-probe insertion from measurements of an ear-probe response, which allows, e.g., an audiologist to evaluate, or a predefined threshold algorithm to detect, if a measurement in an ear canal is accurate enough in the view of hearing diagnostic evaluation.

It should be noted that an acoustic characteristic impedance is used to describe a transmission line, such as an ear canal, and is defined as the ratio of sound pressure and volume flow of a single wave propagating along the line; that is, a wave travelling in one direction in the absence of reflections in the other direction. The characteristic impedance is interesting in hearing diagnostics when a description of the ear canal is needed for the diagnostic setups, since it is used in a plurality of these calculations. The characteristic impedance of a uniform transmission line is closely related to the cross-sectional area of the transmission line. Thus, the characteristic impedance of an ear canal is usually unknown and needs to be estimated based on, e.g., ear-probe measurements and/or acoustic Thevenin-equivalent parameters of the ear probe characterizing the ear probe.

Accordingly, in an embodiment, the waveguide is an ear canal of a human test person, for which a hearing test or diagnosis is relevant.

In the method, it is relevant that the stimulus is configured so that an efficient ear-probe response can be recorded, thus, in an embodiment, the stimulus is configured as pure tones, chirps, sweeps, pseudo-random noise, or a similar acoustic stimulus.

In more detail, the method of detecting an oblique ear probe insertion is in an embodiment utilizing a Hilbert-transform approach to estimate the characteristic impedance. That is, in an embodiment, the characteristic impedance is estimated by using a Hilbert transform of the imaginary part and the real part of a reflectance or an impedance measure. Thus, prior to evaluating the estimated characteristic impedance, the real and imaginary parts of the reflectance or an impedance measure is calculated from a Hilbert transform. In the method described herein, the unknown characteristic impedance of the waveguide, preferably an ear canal, at a plurality of different frequencies is found by using the Hilbert transform as described in applicants co-pending published application EP3288294.

Furthermore, in an alternative setup, other methods for estimating the characteristic impedance can be considered, preferably it should be noted that methods assessing the causality of a reflectance measure or an impedance measure using, e.g., a Fourier transform, an inverse Fourier transform, or a Hilbert transform, are considered preferable methods for estimating the characteristic impedance, since such methods can separate the local physical features of an acoustic waveguide at the position of the ear probe from features further down the waveguide. However, methods for estimating the characteristic impedance, based on a different principle than assessing causality, may be used.

In order to estimate the characteristic impedance for a plurality of frequency ranges of the impedance or reflectance measure, the method is configured such that the plurality of frequencies ranges are defined from a set of truncation frequencies.

In more detail, the truncation frequencies may in an embodiment be determined from points that allow differentiability in a Hermitian-symmetric frequency spectrum of the impedance or reflectance measure. By finding the points that allow differentiability in a Hermitian-symmetric frequency spectrum of the impedance or reflectance measure, errors in the estimated of characteristic impedance due to a finite impedance measurement bandwidth may be avoided.

Alternatively, the plurality of frequency ranges may be defined from the suitable requirements of any other method for estimating the characteristic impedance or be arbitrarily predefined.

Based on the estimated characteristic impedances for a plurality of frequencies and found as described, the degree of oblique probe insertion may be found by assessing the variation in the estimated characteristic impedances across the plurality of frequency ranges.

Accordingly, in an embodiment, the variation in the estimated characteristic impedances across the frequency ranges may be found by fitting a function to the estimated characteristic impedance across the plurality of frequency ranges. Preferably the function to be fitted is a polynomial, which will become apparent in the detailed description.

In a further embodiment, when an oblique ear-probe insertion has been detected, the method furthermore comprises a compensation step for compensating for such oblique insertion. That is, in a further step, the oblique probe insertion may be compensated for by utilizing the degree of oblique probe insertion to finding a set of compensation parameters compensating for the oblique probe insertion.

In an embodiment, the method for compensating for an oblique probe insertion, includes the further steps of:inputting the set of discrete values of the estimated characteristic impedances to the signal processor;fitting a function to the set of discrete values of the estimated characteristic impedances;approximating an incident impedance from the fitted function to estimate the impedance where the waveguide terminated by its characteristic impedance; Thus, it is possible to compensate for an oblique ear-probe insertion, by merely looking at the characteristic impedance.

However, to more accurately ensure that all errors arising due to the oblique ear-probe insertion have been compensated for, the method may in an embodiment comprise further steps, wherein the contribution from evanescent modes together with the spreading flow in the obliqueness of the ear-probe insertion is also considered. Thus, in a further step an inertance contribution is calculated and compensated for by:further estimating a discrete set of inertances that minimize the non-causality in the reflectance or impedance measure at a number of truncation frequencies.inputting a set of estimated discrete values for an inertance to the signal processor;fitting a function to the set of discrete values of the estimated discrete values of inertances;combining the real and imaginary parts estimated by the approximations to fitted polynomials to describe an estimate of the incident impedance; andoutput the estimated incident impedance to be used in calculating a reflectance measure.

By applying the above-mentioned steps, it is ensured that all contributions which may arise from the oblique inserted ear probe may be compensated for.

In a further aspect of the disclosure, a diagnostic tool configured to perform the method steps for detecting and compensating for an oblique probe insertion, is provided for. The diagnostic tool may be configured as a hearing screener, diagnostic tool, or similar device, configured to measure an ear-probe response to evaluate the hearing of a test person.

The diagnostic tool comprises in more detail:An ear probe having a probe tip, the ear probe being configured to be inserted into the ear canal of a test person; and the ear probe further comprisingat least one receiver and at least one microphone, wherein at least one receiver is configured to emit a stimulus into the ear canal and the microphone is configured to measure an ear-probe response, wherein the diagnostic tool further comprisesa signal-generator configured to generate a stimulus and transmit the stimulus to the receiver for transmission of the stimulus into the ear canal; anda signal processor configured to receive the measured ear-probe response measured by the microphone, wherein the signal processor is configured to perform the steps of the method described herein.

That is, the diagnostic tool is configured to be controlled into a mode, wherein the signal generator transmits a stimulus to the receiver, whereby the receiver emits the stimulus into the ear canal via the probe tip of the ear probe. An ear-probe response is measured by the microphone and input into the signal processor of the diagnostic tool. Within the signal processor, a configuration is setup to perform the method of detecting and compensating for a potential obliquely inserted ear probe.

It should be noted that the ear-probe could be constituted by a receiver and a microphone arranged in the ear canal, where a dome-like sealing is abutting the ear canal walls.

In more detail, the signal processor is configured to calculate a degree of oblique probe insertion by assessing the variation in estimated characteristic impedance across a plurality of frequency ranges, and/or further configured to display such variation to a user via a display of the diagnostic tool. This allows the user, for example an audiologist or other hearing-care professional to evaluate if the estimated characteristic impedances can be used in further calculations of hearing related parameters, such as reflectance. In this way, the hearing care professional may be informed about an obliquely inserted ear probe which may distort the further calculations, and therefore requires a new recording or alternatively a compensation, if the results should be expected to be accurate.

Alternatively, this evaluation may also be configured as an automatic process, where the diagnostic tool processes the ear-probe response measured by the microphone and automatically evaluates the degree of obliqueness, and potentially compensates for such obliqueness as described in the following.

In a further embodiment, the diagnostic tool may be configured with a control setup, allowing the user to set the diagnostic tool into one or more modes, wherein a first mode includes; displaying to a user the variation in estimated characteristic impedances across the plurality of frequency ranges; and a second mode wherein a compensation control is presented to the user, allowing the user to set the diagnostic tool into a compensation mode, whereupon the diagnostic tool performs a compensation calculation according to the compensation steps described herein. Accordingly, the diagnostic tool is configured to output a compensated reflectance measure on the display of the diagnostic tool.

