Patent Application
20160205482
The present invention is related to a method for fitting a hearing device employing frequency transposition as well as to an apparatus capable of performing the method.
Various approaches for frequency lowering have been pursued in order that hearing impaired patients with high frequency hearing loss can benefit, especially in those cases where the amplification of the original high frequency sound is not useful—e.g. due to dead regions—or not possible—due to potential feedback problems when applying high gain or due to limited bandwidth of applied gain.
Known teachings describing frequency lowering schemes are for instance disclosed in WO 2007/000161 A1, U.S. Pat. No. 7,248,711 B2, AU 2002300314 A1 and EP 1 686 566 A2. The known teachings have one or several of the following disadvantages:
It is therefore desirable to overcome at least one of the above-mentioned disadvantages. In the international application WO 2012/175134 A1 of the present applicant—herewith incorporated by reference—an improved method is proposed for operating a hearing device applying a frequency transposition scheme, whereby signal components of a source region of the input signal spectrum are adaptively selected taking into account current characteristics of the input signal, and the selected signal components are transposed to a destination (also referred to as target) region. As part of the improved method it is for instance further proposed to apply a pre-weighting function to signal components of the source region before adaptively selecting the source region.
In the frequency transposition scheme described in AU 2002300314 A1 only two physical parameters can be adjusted, namely a cut-off frequency and a compression ratio. Fitting methods suitable for adjusting a hearing system applying such a scheme to the hearing preferences of its user are for instance disclosed in EP 1 538 868 A2 as well as in WO 2007/135198 A2. Moreover, EP 2 026 601 A1 discloses another method for configuring a frequency transposition scheme.
However, these known fitting methods demand a considerable level of experience and expertise with adjusting frequency transposition hearing devices from the person charged with performing the process, i.e. a fitter, e.g. a hearing health care professional such as an audiologist or an acoustician. The complexity of the fitting process is further increased when the frequency transposition scheme involves more than two parameters, as is the case with the improved scheme proposed by the present applicant in the international application WO 2012/175134 A1.
It is therefore an object of the present invention to provide an alternative, simpler fitting method for hearing devices employing frequency transposition, which can be performed by a fitter with little experience and limited expertise in dealing with such hearing devices capable of frequency transposition.
In the context of the present invention, the term “transposition” or “transpose” is defined as having at least one of the following meanings:
Furthermore, the term “hearing device” is not only directed to hearing aids (also referred to as hearing instruments or hearing prostheses) that are used to improve the hearing of hearing impaired patients but also to any communication device, be it wired or wireless, or to hearing protection devices. Hearing aids may also be implantable, such as direct acoustic cochlear stimulation (DACS) middle ear implants and cochlear implants (CI), or bone anchored hearing aids (BAHA) attached to the skull.
The present invention is first directed to a method for adjusting a hearing device comprising frequency transposition means to hearing preferences of a user of said hearing device, said frequency transposition means being configurable by at least two frequency modification parameters, said method comprising the steps of:
The present invention also provides an alternative method for adjusting a hearing device comprising frequency transposition means to hearing preferences of a user of said hearing device, said frequency transposition means being configurable by at least two frequency modification parameters, said method comprising the steps of:
The at least two frequency modification parameters can then be automatically set based on the determined qualitative prediction values, each of which is associated with one of the at least two auditory perceptive dimensions.
In a specific embodiment of the present invention, the alternative method further comprises the step of displaying said qualitative prediction value for at least one of, preferably for each of, said at least two auditory perceptive dimensions, and optionally automatically adjusting a further control element (or further control elements, each one being) associated with one of said at least two auditory perceptive dimensions.
In further embodiments of the present invention, the alternative method further comprises the step of performing an auditory performance test (as defined below) to assess the auditory performance of the user for at least one of the at least two auditory perceptive dimensions, and subsequently repeating steps a2) and b2).
In further embodiments of the present invention, each of said at least two auditory perceptive dimensions is a dimension in which an auditory performance of said user can be influenced by changing said at least two frequency modification parameters.
In further embodiments of the present invention, each of said at least two auditory perceptive dimensions is a dimension for which said user's auditory perception can be or is assessed by means of an auditory performance test, an auditory performance test being a test which allows to compare the auditory performance of two individuals or of two different aided conditions (i.e. using a hearing device) for the same individual.
In further embodiments of the present invention, the method further comprises the step of performing an auditory performance test to assess the auditory performance of the user for at least one of the at least two auditory perceptive dimensions, and subsequently performing or repeating steps a1) and b1), step a1) then being based on the outcome of the auditory performance test.
In further embodiments of the present invention, said auditory perceptive dimension is selected from a group comprising at least two of:
Thereby, harmonics protection aims at maintaining the relationship between a fundamental tone and its harmonics, such that especially the timbre of a person's voice or of a musical instrument is not noticeably altered. Distinction is for instance related to being able to distinguish between different fricatives, such as the consonants “f”, “s”, “x” and “z”. Audibility generally pertains to providing sufficient audible sound (i.e. frequency range) to an ear drum or sufficient stimulus to a middle ear or cochlear of a person by means of a hearing device (BTE, ITE or implanted), which will depend on the frequency range within which the hearing impaired person can still perceive sounds. Recognition generally relates to providing a sufficient level of sound (i.e. sound pressure level) to an ear drum or sufficient stimulus to a middle ear or cochlear of a person by means of a hearing device (BTE, ITE or implanted), which will depend on the level of hearing loss the person has at different frequencies. Furthermore, vowel information protection is directed to preserving the highest vowel formants, so that a hearing impaired user of a hearing device (BTE, ITE or implanted) is capable of distinguishing between different vowel sounds, such as “a”, “e”, “i”, “o” and “u”.
In further embodiments of the present invention, said audibility pertains to one or more of:
In further embodiments of the present invention, said distinction pertains to one or more of:
In further embodiments of the present invention, said recognition pertains to one or more of:
In further embodiments of the present invention, said group comprises at least a vowel dimension, in particular one or more of:
In further embodiments of the present invention, said frequency modification parameters comprise at least two of the following:
The latter may comprise multiple frequency weighting factors Wi for i=1, 2, . . . (e.g. a (multi-)step function) or be a continuous frequency-dependent function w(f).
In further embodiments of the present invention, the lower cut-off frequency Fk is 1′500 Hz or less and/or the upper cut-off frequency FHL is 2 kHz or less.
In further embodiments of the present invention, settings of said at least two frequency modification parameters are derived from settings of said at least two control elements by means of a look-up table.
In further embodiments of the present invention, settings of said at least two frequency modification parameters are derived from settings of said at least two control elements by means of interpolation, in particular linear interpolation, particularly between settings of said at least two frequency modification parameters corresponding to extreme settings for each of said at least two control elements, in particular maximum and/or minimum settings of each of said at least two control elements.
In further embodiments of the present invention, settings of said at least two frequency modification parameters are derived from settings of said at least two control elements by means of a weighted sum, the weighting being dependent on the setting of each of said at least two control elements.
Furthermore, the present invention is directed to an apparatus for adjusting a hearing device comprising frequency transposition means to hearing preferences of a user of said hearing device, said frequency transposition means being configurable by at least two frequency modification parameters, said apparatus comprising:
The present invention also provides an alternative apparatus for adjusting a hearing device comprising frequency transposition means to hearing preferences of a user of said hearing device, said frequency transposition means being configurable by at least two frequency modification parameters, said apparatus comprising:
The means for automatically determining a qualitative prediction value for each of the at least two auditory perceptive dimensions may comprise one or more estimators. The one or more estimators determine the qualitative prediction value associated with each auditory perceptive dimension by for instance applying a test signal (e.g. a speech sample or music) to a model of the hearing device having a transfer function, especially a frequency transposition function adaptable by the frequency modification parameters, which is set by the at least one control element. The output signal from the model is then further processed, e.g. according to the audiogram of the hearing impaired user of the hearing device to yield a signal as perceived by the user (i.e. a modelled perceived signal). Subsequently, the qualitative prediction value is derived by an analysis of the modelled perceived signal or a difference between the modelled perceived signal and the test signal. Alternatively, such qualitative prediction values may also be derived from data stored in a database comprising results of (qualitative and/or quantitative) assessments, e.g. of auditory performance tests, performed by hearing impaired persons having various degrees of hearing impairment, the assessment results being provided from tests using various hearing devices with different settings, especially of the frequency modification parameters.
In a specific embodiment the apparatus according to the present invention further comprises presentation means for displaying said qualitative prediction value for at least one of, preferably for each of, said at least two auditory perceptive dimensions.
In further embodiments the apparatus according to the present invention comprises a further control element (or further control elements, each one being) associated with one of said at least two auditory perceptive dimensions and automatically adjustable to one of said qualitative prediction values of one of said at least two auditory perceptive dimensions.
In further embodiments of the apparatus according to the present invention, each of said at least two auditory perceptive dimensions is a dimension in which an auditory performance of said user can be influenced by changing said at least two frequency modification parameters.
In further embodiments of the apparatus according the present invention, each of said at least two auditory perceptive dimensions is a dimension for which said user's auditory perception can be assessed by means of an auditory performance test, an auditory performance test being a test which allows to compare the auditory performance of two individuals or of two different aided conditions for the same individual.
In further embodiments of the apparatus according to the present invention, said perceptive dimension is selected from a group comprising at least two of:
In further embodiments of the apparatus according to the present invention, said audibility pertains to one or more of: general audibility;
In further embodiments of the apparatus according to the present invention, said distinction pertains to one or more of:
In further embodiments of the apparatus according to the present invention, said recognition pertains to one or more of:
In further embodiments of the apparatus according to the present invention, said group comprises at least a vowel dimension, in particular one or more of:
In further embodiments of the apparatus according to the present invention, said frequency modification parameters comprise at least two of the following:
In further embodiments of the apparatus according to the present invention, the lower cut-off frequency Fk is 1′500 Hz or less and/or the upper cut-off frequency FHL is 2 kHz or less.
In further embodiments the apparatus according to the present invention further comprises a look-up table configured to derive settings of said at least two frequency modification parameters from settings of said at least two control elements.
In further embodiments the apparatus according to the present invention further comprises interpolation means configured to derive settings of said at least two frequency modification parameters from settings of said at least two control elements, in particular configured to perform linear interpolation, particularly configured to perform interpolation between settings of said at least two frequency modification parameters corresponding to extreme settings for each of said at least two control elements, in particular maximum and/or minimum settings of each of said at least two control elements.
In further embodiments the apparatus according to the present invention further comprises weighting means for providing weighted sums configured to derive settings of said at least two frequency modification parameters from settings of said at least two control elements, the weighting being dependent on the setting of each of said at least two control elements.
It is expressly pointed out that the above-mentioned embodiments can be arbitrarily combined to yield further specific embodiments of the method and apparatus according to the present invention.
The present invention is further illustrated by way of exemplified embodiments shown in the accompanying drawings and described in detail in the following. It is pointed out that these embodiments are for illustrative purposes only and shall not limit the present invention as set out by the claims.
In the figures like reference signs refer to like elements.
In
In case a signal processing algorithm, which is implemented in the signal processing unit 3, is applied in the frequency domain, a transformation function, such as a Fast Fourier Transformation (FFT), is used to transform the input signal i from the time domain into the frequency domain. Consequently, an inverse transformation function must be applied in order to transform an output spectrum into the time domain after implementing the signal processing algorithm. Instead of a Fourier transformation function and its inverse function, any other transformation function may be implemented, such as a Hadamard, a Paley or Slant transformation.
As part of the signal processing the signal processing unit 3 in particular performs a frequency transposition, which is implemented in the frequency transposition means 6. Within the context of the present invention, the frequency transposition means 6 is configurable by at least two frequency modification parameters. The frequency transposition means 6 is for instance adapted to transpose selected frequency ranges, which are important for the hearing perception of a user of the hearing device HD but in which frequency ranges the user is not able to perceive an acoustic signal due to a complete hearing loss, to another frequency range in which the hearing device user can perceive an acoustic signal.
A known approach is to employ a mapping between the input frequencies fin and the output frequencies fout for different spectral regions defined by a cut-off frequency FC and a compression ratio CR as depicted in the graph of
Furthermore, known frequency transposition algorithms distort the harmonic structure of the input sound. Therefore, it is also not very useful for transposing music where it introduces unpleasant pitch distortions.
In connection with known frequency transposition schemes, it has been pointed out that the cut-off frequency FC must be equal or larger than 1500 Hz in order not to distort vowels and non-fricative sounds which have a strong format structure in a frequency region below 1500 Hz. Therefore, signal components below the cut-off frequency FC are not changed, i.e. a so called lower source region 10 on the x-axis directly corresponds to a lower target region 12 on the y-axis (one-to-one mapping). Above the cut-off frequency FC, a linear transposition is implemented in that signal components of a so called higher source region 11 are transposed to a higher target region 13 that has a smaller bandwidth than the higher source region 11. The known technique does not enable a hearing impaired person to benefit from a frequency lowering algorithm having a cut-off frequency FC below 1500 Hz, while offering acceptable sound quality and minimal distortion of vowels and non-transposed sounds, which are otherwise audible without much distortion.
A new frequency transposition scheme proposed by the present applicant in the international application WO 2012/175134 A1 adaptively selects signal components of a source region taking into account current characteristics of the input signal i.
In embodiments of the new frequency transposition scheme, a so called frequency stacking algorithm is implemented.
If a frequency range of a source region being transposed is equal to a frequency range of a destination region, a mere frequency shifting takes place. If, on the other hand, a frequency range of a source region being transposed is greater than a frequency range of a destination region, a compressive frequency transposition takes place.
In
wherein
The determination of the optimal values of parameters in the above equation for a given hearing loss could be based on audiological experiments that are described, for example, in a publication entitled “Modified Verification Approaches for Frequency Lowering Devices” by Danielle Glista & Susan Scollie (National Centre for Audiology, the University of Western Ontario, Sep. 11, 2009). This publication can be retrieved from the internet under http://www.audiologyonline.com/articles/article_detail.asp?artic le_id=2301.
In this frequency transposition scheme the compression does not start at the lower cut-off frequency FC but at the upper cut-off frequency FHL. The compression ends at the upper frequency Fu, above which no relevant information is expected. The second source stack 23—defined between the upper cut-off frequency FHL and the upper frequency Fu—is transposed as well to the destination stack 32, in which a replacement and/or superposition of spectral energy of the first source stack 22 and/or the second source stack 23 takes place. For example, a biased peak picking algorithm or a weighting function w with subsequent superposition is applied to emphasize relevant spectral information in the second source stack 23 or in the first source stack 22.
A biased peak picking method is used to respect the auditory expectation of the hearing device user and is achieved by using an appropriate spectral weighting function.
The weighting function w (also referred to as expectation bias function) is used to adaptively choose different parts of the input spectrum—e.g. the first source stack 22 or the second source stack 23 (cf.
The weighting function w weights the input spectrum in such a way that the already available low frequency information is given more significance. If a frequency transposition scheme then selects the most important information from a given source region 20 to be transposed to a destination region 30, auditory expectations are respected more and information is transposed only if it is considerably significant in comparison to what is already accessible to the hearing impaired user in the lower source region 21 or the lower destination region 31.
An advantage of using a weighting function w is that an adaptive lowering can be accomplished without any explicit real time detection of phonemes themselves. This is accomplished by a careful choice of weights and by exploiting the fact that fricatives have proportionally much larger energy in the higher frequencies compared to vowels. This keeps the vowels from getting distorted while still lowering high frequency information in fricatives.
The frequency transposition scheme according to this embodiment ensures two things. First, it separates the second source stack 23 from the first source stack 22 in the frequency transposition context. The second difference is that the final output of the frequency transposition scheme in the destination stack 32 is chosen with a biased peak picking algorithm between the spectral energies of the first source stack 22 and the second source stack 23. This results in the final input/output curve becoming signal dependent unlike in the previously known frequency transposition scheme shown in
The separation of the second source stack 23 and the destination stack 32 in the compression scheme, together with a biased peak picking allows for transposing energies only when they are significant compared to what is already there in the first source stack 22. This leaves the already audible harmonic structure of the vowels intact while still transposing fricatives and other phonemes dominated by high frequency energies. As the harmonic relationship of the notes of western instrumental music is similar to vowels, this frequency transposition scheme also distorts music less in comparison to the known techniques.
According to the fitting method of the present invention, first the following non-adjustable parameters are determined:
Then, the fitter adjusts at least two of the following perception based macro controls:
“vowel information protection” V; and
These perception based macro controls automatically control the following four parameters of the frequency transposition means 6:
The mapping from the control settings H, D, V, A to the set of frequency modification parameters CR, Fk, FHL, W may be achieved by means of a lookup table 9. Alternatively, the parameter set CR, Fk, FHL, W can be determined by interpolating between predetermined values of the parameter set CR, Fk, FHL, W associates with extreme settings of the control settings H, D, V, A, i.e. settings of CR, Fk, FHL, W for H, D, V and A either being 0 (minimum) or 100% (maximum). Moreover, weights can be applied to pre-determined settings CR, Fk, FHL, W associated with certain predefined values of the settings H, D, V, A, where the weights are dependent on the current settings of the perception based macro controls.
In the following examples, the frequency above which amplification is not sufficient is assumed to be 2 kHz.
Finally,
The perceptive dimension “recognition” is one commonly measured in speech tests. For example a phoneme such as “ABA” or “AFA” is presented to an individual and the individual has to indicate which one it was. In a recognition test, it is not sufficient if the individual indicates the pure fact that a phoneme was perceived or that it was different from the last one. Generally frequency stacking and strong frequency compression is detrimental to recognition. However, since audibility is a prerequisite for recognition, a moderate compression may even be necessary for recognition. Further, it is to be noted, that recognition test results may depend on learning effects. Since hearing aid fitting is targeted to long term performance, it is best to define the dimension based on a recognition test applied after the individual had time to get accustomed to the new processing.
There are also further perceptive dimensions for which no performance tests exist, for example “naturalness”, “familiarity” and “comfort”. For these dimensions there are only subjective tests, which for instance employ a rating scale. Therefore these further perceptive dimensions cannot be utilised in connection with the present invention. However, if a control element such as a slider associated with a perceptive dimension “familiarity” were to be used, a high setting value thereof could for instance adjust the fitting such that it more closely resembles a previous fitting with which the user is familiar from prior experience.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2013/063675 | 6/28/2013 | WO | 00 |
