EP2584795A2 - Method for determining a compression characteristic curve - Google Patents

Abstract

The method involves determining (15) a maximum audible frequency of a hearing device. The knee point is determined by predefined rule in dependence on the maximum audible frequency. The parameters of frequency compression characteristic are constituted on a basis of frequency groups such that number of frequency groups is determined based on the maximum audible frequency. The maximum compression rate is set to be 4. An independent claim is included for method for adjusting a binaural hearing system.

Description

The present invention relates to a method for determining a knee point of a frequency compression characteristic for a hearing device. Moreover, the present invention relates to a method for determining a frequency compression characteristic and a method for adjusting a binaural hearing system. The term hearing device here is understood to mean any device which can be worn in or on the ear and triggers a sound stimulus, in particular a hearing device, headphones and the like.

Hearing aids are portable hearing aids that are used to care for the hearing impaired. In order to meet the numerous individual needs, different types of hearing aids such as behind-the-ear hearing aids (BTE), hearing aid with external receiver (RIC: receiver in the canal) and in-the-ear hearing aids (ITE), e.g. Concha hearing aids or canal hearing aids (ITE, CIC). The hearing aids listed by way of example are worn on the outer ear or in the ear canal. In addition, bone conduction hearing aids, implantable or vibrotactile hearing aids are also available on the market. The stimulation of the damaged hearing takes place either mechanically or electrically.

Hearing aids have in principle as essential components an input transducer, an amplifier and an output transducer. The input transducer is usually a sound receiver, z. As a microphone, and / or an electromagnetic receiver, for. B. an induction coil. The output transducer is usually used as an electroacoustic transducer, z. As miniature speaker, or as an electromechanical transducer, z. B. bone conduction, realized. The amplifier is usually integrated in a signal processing unit. This basic structure is in FIG. 1 shown using the example of a behind-the-ear hearing aid. In a hearing aid housing 1 for Carrying behind the ear, one or more microphones 2 are installed for recording the sound from the environment. A signal processing unit 3, which is also integrated in the hearing aid housing 1, processes the microphone signals and amplifies them. The output signal of the signal processing unit 3 is transmitted to a loudspeaker or earpiece 4, which outputs an acoustic signal. The sound is optionally transmitted via a sound tube, which is fixed with an earmold in the ear canal, to the eardrum of the device carrier. The power supply of the hearing device and in particular the signal processing unit 3 is effected by a likewise integrated into the hearing aid housing 1 battery. 5

Frequency compression is a relatively new technology in hearing aids. Frequency compression makes high-frequency information audible that can not be heard without this procedure. This is achieved by an algorithm that maps high frequency information from higher frequencies to lower frequencies. Originally low frequencies are replaced with the new information.

In order for the frequency compression algorithm to be profitable in terms of speech intelligibility, this algorithm must be parameterized in a special way. However, there is currently no way to reliably demonstrate that speech frequency benefits can be expected through a frequency compression algorithm. In particular, there is a lack of a defined strategy to parameterize a frequency compression algorithm in such a way that there is a profit in terms of speech intelligibility. Since speech intelligibility is very important for hearing-impaired people to be able to participate satisfactorily in daily conversations, and for them to be satisfied with their hearing aid, it is correspondingly important to be able to obtain better speech intelligibility with hearing aids.

Currently common techniques for setting frequency compression algorithms do not consider the acoustic Fine structure of consonants and vowels such as their center frequency or other characteristics, eg. B. formants. Today's fitting strategies applied during initial fitting are aimed at increased feedback stability rather than speech intelligibility benefits. Only through a very tedious and time-consuming, manual fine adjustment can be an additional benefit in terms of speech intelligibility reach.

The US 2011/0249843 A1 describes a method for determining a knee point of a frequency compression characteristic for a hearing aid. A critical frequency in the frequency domain is determined, the input signal is analyzed, a cutoff frequency is defined, a source frequency above the cutoff frequency is identified, and a target frequency band below the cutoff frequency is identified.

The DE 10 2009 058 415 A1 describes that in a hearing aid existing sounds and in particular their fundamental frequencies are to be determined in the input signal and the frequency transpositions are to be executed in dependence on the determined fundamental frequencies. The transposed harmonics are again placed on the frequency raster of the fundamental frequency, so that the sound property is retained even after the frequency transposition.

In the article "Improved audibility for people with severe hearing loss" by O. Bürkli-Halevy et al., Published in Hörakustik 3, 2008, pages 8-14 It is described that in hearing aids a frequency compression with a compression ratio between 1.5: 1 and 4: 1 should be used.

The object of the present invention is therefore to be able to adjust the frequency compression of a hearing device in a simple manner so that it is possible to achieve advantages in terms of speech intelligibility.

• Ermitteln einer maximal hörbaren Frequenz eines Nutzers der Hörvorrichtung, und
• Ermitteln des Kniepunkts mittels einer vorgegebenen Vorschrift in Abhängigkeit von der maximal hörbaren Frequenz, wobei
• Parameter der Frequenzkompressionskennlinie auf der Basis von Frequenzgruppen gebildet werden.

According to the invention, this object is achieved by a method for determining a knee point of a frequency compression characteristic curve for a hearing device

• Determining a maximum audible frequency of a user of the hearing device, and
• Determining the knee point by means of a predetermined rule as a function of the maximum audible frequency, wherein
• Parameters of the frequency compression characteristic are formed on the basis of frequency groups.

Advantageously, therefore, the knee point of the frequency compression characteristic is determined as a function of the maximum audible frequency of the user (ie the highest frequency audible by the user) of the hearing device. It is assumed that a frequency compression characteristic has at least two legs, which are connected to each other at the knee point. By suitable displacement of the knee point in accordance with the prescribed rule, it is thus possible to optimize the information that can be transmitted in the audible range to the user of the hearing device.

Preferably, the knee point is always set above 1.5 kHz. Since below the knee point the frequencies are typically transmitted uncompressed, in the case of the knee point above 1.5 kHz, all essential spectral components are transmitted unchanged, allowing the user to distinguish female voices from male voices.

The knee point can be calculated using the Bark scale. The Bark scale represents a psychoacoustic scale for the perceived pitch (tonality).

berechnet, wobei f_max_bark die maximale hörbare Frequenz umgerechnet in einen Bark-Wert und no_bands_down eine in Abhängigkeit von der maximal hörbaren Frequenz festgelegte Anzahl an Frequenzgruppen (critical bands) bedeutet. Damit muss in einer Zuordnungsvorschrift lediglich noch festgelegt werden, wie hoch der Wert no bands down in Einheiten von Frequenzgruppen (critical bands) in Abhängigkeit von der maximal hörbaren Frequenz ist. Dieser Wert lässt sich analytisch für jede Frequenz oder aber beispielsweise tabellarisch für einzelne Frequenzkanäle festlegen.Advantageously, a coordinate f_cutoff of the knee point is calculated using the formula $$\mathrm{f\_cutoff}=1960\cdot (\left(\mathrm{f\_max\_bark}-\mathrm{no\_bands\_down}+0.53\right)/\left(26.28-\left(\mathrm{f\_max\_bark}-\mathrm{no\_bands\_down}\right)\right)$$

where f_max_bark is the maximum audible frequency converted into a bark value and no_bands_down is a number of critical bands defined as a function of the maximum audible frequency. Thus, in an assignment rule, it is only necessary to determine what the value no bands down in units of frequency bands (critical bands) is as a function of the maximum audible frequency. This value can be determined analytically for each frequency or, for example, in tabular form for individual frequency channels.

Thus, in a further development, a method for determining a frequency compression characteristic according to which an input value is mapped into an output value can be provided by determining a knee point according to the above methods, wherein below the knee point each input value is equal to the respective output value. Thus, in any case, the lower part of a frequency compression characteristic is set from zero to the knee-point frequency. There is no compression in this frequency range.

Above the knee point, compression typically occurs. Here the compression rate should maximally reach the value 4. Higher compression rates lead to irritating transmissions.

Again, the input value f_source_max can be calculated to the output value f_max, which corresponds to the maximum audible frequency, using the Bark scale. Thus, the algorithm for adjusting the frequency compression is closer to the psychoacoustic magnitude of the actual perceptible pitch.

berechnet werden, wobei f_max_bark die maximal hörbare Frequenz umgerechnet in einen Bark-Wert und no_bands_up eine in Abhängigkeit von der maximal hörbaren Frequenz festgelegte Anzahl an Frequenzgruppen (critical bands) bedeutet. Auch hier ist dann nur noch für jede maximal hörbare Frequenz f_max bzw. den höchsten hörbaren Kanal eine Anzahl an Frequenzgruppen festzulegen, deren Gesamtbreite den Abstand vom Kniepunkt (f_cutoff) zur Originalfrequenz f_source_max bildet, die entsprechend der Kompressionskennlinie auf die maximal hörbare Frequenz f_max abgebildet wird.In order to specify the frequency compression characteristic above the knee point, the input value f_source_max for the maximum audible output value f_max can be determined using the formula $$\mathrm{f\_source\_max}=1960\cdot \left(\left(\mathrm{f\_max\_bark}+\mathrm{no\_bands\_up}\right)+0.53\right)/\left(26.28-\left(\mathrm{f\; max\; bark}+\mathrm{no\; bands\; up}\right)\right)$$

where f_max_bark is the maximum audible frequency converted to a bark value and no_bands_up is a number of frequency bands (critical bands) determined as a function of the maximum audible frequency. Here, too, a number of frequency groups whose total width forms the distance from the knee point (f_cutoff) to the original frequency f_source_max, which is mapped to the maximum audible frequency f_max in accordance with the compression characteristic, is only then defined for each maximum audible frequency f_max or the highest audible channel ,

With the inventive determination of the frequency compression characteristic shown above, a method for automatic adjustment of a binaural hearing system can be provided. It is particularly advantageous if the just described frequency compression characteristic is determined for that ear of the user of the hearing devices, which has the lower hearing loss. This ensures that the user of the hearing devices is not lost information that the user could still hear.

FIG 1

den prinzipiellen Aufbau eines Hörgeräts gemäß dem Stand der Technik;

FIG 2

ein Blockschaltdiagramm zur Bestimmung einer Frequenzkompressionskennlinie und

FIG 3

eine erfindungsgemäße Frequenzkompressionskennlinie.

The present invention will now be explained in more detail with reference to the accompanying drawings, in which:

FIG. 1

the basic structure of a hearing aid according to the prior art;

FIG. 2

a block diagram for determining a frequency compression characteristic and

FIG. 3

a frequency compression characteristic according to the invention.

The embodiments described in more detail below represent preferred embodiments of the present invention.

With the adjustment algorithm described below, a frequency compression algorithm of a hearing aid or other hearing device is to be adjusted to provide a benefit in terms of speech intelligibility as compared to the case of a hearing aid without frequency compression. All other parameters of the hearing aid except the frequency compression are not changed (gain, level compression, etc.).

In the hearing aid, a frequency compression algorithm is implemented whose frequency compression characteristic 10 (cf. FIG. 3 ) represents the mapping of an input frequency f_in (= f_source) to an output frequency f_out (= f_destination). Usually, this frequency compression characteristic 10 has the in FIG. 3 illustrated structure. It has two linear sections 11 and 12, of which the first section 11 leads from the origin of the diagram to a knee point 13, and the second linear section 12 from the knee point 13 to an end point 14. The first linear section 11 has the slope one, so that no frequency compression takes place in the frequency range from zero to the knee point 13 or the frequency f_cutoff.

The frequency compression characteristic is therefore characterized by three parameters: the frequency f_cutoff, which represents the two coordinates of the knee point 13 and the starting point of the actual frequency compression algorithm (all frequencies below f_cutoff are not affected by the algorithm), the frequency f_max, which is the maximum audible frequency and the frequency f_source_max corresponding to the original input frequency which is mapped to the output frequency f_max by the frequency compression characteristic. Thus, the information in the original frequency range between f_cutoff and f_source_max is mapped to the area between f_cutoff and f_max. This reduction in bandwidth results in the audibility of high frequency information at lower frequencies at the expense of loss of original low frequency information.

1. 1. Die Hörbarkeit von Reibelauten (Frikative) ist erhöht. Insbesondere soll bei aktiviertem Frequenzkompressionsalgorithmus die Mittenfrequenz des Lauts "s" von derjenigen des Lauts "sch" verschieden sein.
2. 2. Eine Vokalverwechslung zwischen den Vokalen "e" und "i" soll minimiert sein. Bei aktiviertem Frequenzkompressionsalgorithmus sollen die verschobenen Frequenzen des zweiten Vokalformanten von "e" und "i" voneinander verschieden sein, vorzugsweise unabhängig von der Erfüllung der anderen Anforderungen.
3. 3. Es soll so viel Originalinformation wie möglich erhalten bleiben. Anders ausgedrückt: der Verlust an Originalfrequenzinformation soll minimiert werden. Daher soll der Kniepunkt bzw. f_cutoff möglichst hoch sein, und die resultierende Frequenzkompressionsrate soll mit Rücksicht auf die anderen Anforderungen so klein wie möglich sein. Insbesondere sollte die Frequenzkompressionsrate jedoch maximal den Wert 4 erreichen.
4. 4. Der Frequenzkompressionsalgorithmus soll bei binauraler Versorgung immer an das Ohr angepasst werden, das das bessere Hörvermögen besitzt.
5. 5. Bei binauraler Versorgung soll in beiden Hörgeräten die gleiche Einstellung des Frequenzkompressionsalgorithmus angewandt werden, um einen konsistenten Schalleindruck an beiden Ohren zu erreichen, so dass ein kortikales Neuerlernen der auditorischen Wahrnehmung möglich ist.
6. 6. Die Unterscheidbarkeit von Sprachbeispielen der beiden Geschlechter soll gegeben sein. Daher soll die Frequenz f_cutoff des Kniepunkts 13 nicht unter 1,5 kHz liegen.

However, an advantageous adaptation formula for the frequency compression algorithm fulfills the following audiological requirements:

1. 1. The audibility of fricatives is increased. In particular, when the frequency compression algorithm is activated, the center frequency of the sound "s" should be different from that of the sound "sch".
2. 2. A vocal confusion between the vowels "e" and "i" should be minimized. With the frequency compression algorithm enabled, the shifted frequencies of the second vowel formant of "e" and "i" should be different from each other, preferably independent of meeting the other requirements.
3. 3. Keep as much original information as possible. In other words, the loss of original frequency information should be minimized. Therefore, the knee point or f_cutoff should be as high as possible, and the resulting frequency compression rate should be as small as possible in view of the other requirements. In particular, however, the frequency compression rate should maximally reach the value 4.
4. 4. The frequency compression algorithm should always be adapted for binaural supply to the ear, which has the better hearing.
5. 5. For binaural care, the same frequency compression algorithm setting should be used in both hearing aids to achieve a consistent sound impression on both ears so that cortical re-learning of auditory perception is possible.
6. 6. The distinction of language examples of the two sexes should be given. Therefore, the frequency f_cutoff of the knee point 13 should not be less than 1.5 kHz.

The fact whether a user of a hearing device is suitable for the frequency compression according to the invention can be estimated reliably with two measurements. These measurements should be performed on the ear with better residual hearing. The first measurement corresponds to an audiogram and the second measurement concerns the presence of a so-called dead region in the user's ear. Based solely on the audiogram, it is usually not possible to reliably determine the maximum audible frequency. This is because, for example, on the basilar membrane hairs are not excited by the sound waves directly to vibrate, but also by vibrations of the basilar membrane itself. Thus, for example, sound is heard, which is beyond an actual maximum audible frequency. In order to better determine the maximum audible frequency, for example, a dead area or its lower limit is determined by the so-called TEN test (see below).

On the basis of a given audiogram and a chosen fitting formula (eg ConnexxFit), a benefit achievable by a hearing aid can be calculated. The calculation of the hearing aid output spectrum allows an estimate of the maximum audible frequency with the respective setting. The intersection of the hearing aid output spectrum with the hearing loss (audiogram) determines the so-called maximum audible frequency f_max.

• a) Bestimmen des 99%-Perzentils eines sprachmodulierten 65 dB Störgeräusches (z. B. ISTS-Störgeräusch (internationales Sprachtestsignal) gemäß der internationalen Norm IEC 60118-15).
• b) Berechnen der Verstärkung des Hörgeräts im eingesetzten Zustand (insertion gain) für einen vorliegenden Hörverlust mit Hilfe eines Anpassalgorithmus oder statischen Modells für ein spezifisches Hörgerät.
• c) Addieren der Resultate von a) und b). Diese Summe entspricht dem Frequenzspektrum (aided speech spectrum) am Trommelfell.
• d) Berechnen des Schnittpunkts des vorliegenden Audiogramms mit dem Ergebnis von c), was zu der maximal hörbaren Frequenz f_max führt.

The maximum audible frequency f_max can be estimated, for example, with the following steps:

• a) Determine the 99% percentile of a speech-modulated 65 dB noise (eg, ISTS noise (international speech test signal) in accordance with international standard IEC 60118-15).
• b) calculating the gain of the hearing aid in the inserted state (insertion gain) for an existing hearing loss using a fitting algorithm or static model for a specific hearing aid.
• c) adding the results of a) and b). This sum corresponds to the frequency spectrum (aided speech spectrum) on the eardrum.
• d) calculating the intersection of the present audiogram with the result of c) resulting in the maximum audible frequency f_max.

If other percentiles or other ISTS noise levels are used in a), the frequency compression adjustment may be adjusted to specific needs (other hearing aid categories or specific subgroups of hearing impaired persons).

When a so-called dead region is estimated on the basis of the audiogram or measured with another diagnostic test (eg, the TEN test), the calculated maximum audible frequency f_max can be changed to the resultant value. A dead region may be present if hearing loss at a particular frequency is at least 80 dB (HL = Hearing Level) and the difference between two adjacent octaves is at least 50 dB (HL).

The following is based on FIG. 2 and FIG. 3 shown how a frequency compression characteristic can be determined automatically. For this purpose, the parameters of the frequency compression characteristic f_cutoff and f_source_max are preferably determined on the basis of frequency groups (critical bands), cf. Bark-Skala and Eberhard Zwicker: "Subdivision of the audible frequency range into critical bands", J. Acoust Soc. At the. Volume 33, page 248, Feb. 1961 ). The starting point for the calculations is the maximum audible frequency f_max, which also corresponds to the lower frequency of a dead region. In step 15, therefore, the maximum audible frequency f_max is determined from the audiogram, which itself was measured in step 16, and possibly the TEN test, which was carried out in step 17. Depending on this frequency f_max, the frequency f_cutoff in step 18, which represents the coordinates of the knee point 13. Furthermore, in step 19, the maximum source frequency f_source_max is determined as a function of the frequency f_max, which is mapped to the same frequency f_max. Finally, from the parameters f_max, f_cutoff and f_source_max in step 20, a frequency compression characteristic curve 10 is determined with which the frequency compression algorithm is set.

The algorithm thus formed results in a frequency compression setting which ensures improved speech intelligibility.

Preferably, the value of f_max becomes a bark value f_max_bark according to a method of H. Traunmuller (1990) "Analytical expressions for the tonotopic sensory scale" J. Acoust Soc. At the. 88: pages 97 to 100 transformed.

The transformation takes place according to the formula $$\mathrm{f\; max\; bark}=26.81\cdot \mathrm{f\; max}/\left(1960+\mathrm{f\; max}\right)-0.\mathrm{53rd}$$

Optionally, the value f_max_bark should be changeable, for example if a lower frequency compression is desired. It should then be ensured, for example for a given filter bank, that the changed value f_max_bark represents a frequency between 2 kHz and 8 kHz.

Using the formula below and the no bands down values representing a number of frequency groups, the frequency f_cutoff of the knee point can be calculated. The knee point is therefore at a certain distance (counted in frequency groups) below the maximum audible frequency f_max. The corresponding formula is: $$\mathrm{f\_cutoff}=1960\cdot \left(\left(\mathrm{f\_max\_bark}-\mathrm{no\_bands\_down}\right)+0.53\right)/\left(26.28-\left(\mathrm{f\; max\; bark}-\mathrm{no\; bands\; down}\right)\right)$$

With the illustrated algorithm, values for f_max <2 kHz would lead to f_cutoff values <1.5 kHz, which should be avoided from an audiological point of view. Therefore, values for f_max <2 kHz are always set to 2 kHz, regardless of the actual measured value.

f max in [Hz] No bands down in [CB] No bands up in [CB] 1500 3 7 1750 2 6 2000 2 5,5 2250 2 4, 8 2500 1, 8 4 2750 2 3, 8 3000 2 3,2 3250 2 3 3500 2 2,5 3750 2 2,3 4000 2 2,2 4250 1, 8 2 4500 2 2 4750 2 1, 8 5000 1, 8 1, 7 5250 2 1, 6 5500 1, 8 1,5 5750 1, 8 1, 6 6000 1, 6 1,5 6250 1, 6 1,5 6500 1, 6 1,4 6750 1, 6 1,4 7000 1, 8 1,5 7250 1, 8 1,4 7500 2 1,3 7750 2 1,2 8000 2 1,2 With the following formula and the values no_bands_up listed in the following table also in the unit "CB" (frequency groups), the further characteristic parameter f_source_max can be calculated for a current frequency f_max: $$\mathrm{f\_source\_tmp}=1960\cdot \left(\left(\mathrm{f\_max\_bark}+\mathrm{no\_bands\_up}\right)+0.53\right)/\left(26.28-\left(\mathrm{f\_max\_bark}+\mathrm{no\_bands\_up}\right)\right)$$

f max in [Hz] No bands down in [CB] No bands up in [CB] 1500 3 7 1750 2 6 2000 2 5.5 2250 2 4, 8 2500 1, 8 4 2750 2 3, 8 3000 2 3.2 3250 2 3 3500 2 2.5 3750 2 2.3 4000 2 2.2 4250 1, 8 2 4500 2 2 4750 2 1, 8 5000 1, 8 1, 7 5250 2 1, 6 5500 1, 8 1.5 5750 1, 8 1, 6 6000 1, 6 1.5 6250 1, 6 1.5 6500 1, 6 1.4 6750 1, 6 1.4 7000 1, 8 1.5 7250 1, 8 1.4 7500 2 1.3 7750 2 1.2 8000 2 1.2

The above calculations ensure that audiological requirements 1 and 2 (see above) are met. These requirements are the basis for improving speech intelligibility through the frequency compression algorithm. The values in the table here refer to a filter bank with 48 channels, each with a bandwidth of 250 Hz.

The illustrated fitting strategy for a frequency compression algorithm combines several hearing aid fitting steps, which were typically done manually (eg, measurements on 2 cm ³ test volumes). For example, the hearing threshold resulting from wearing the hearing aid is used for the estimation of the maximum audible frequency, as is the usual manual unbundling of the center frequencies of the fricatives "s" and "sch" in the hearing aid fitting. This manual method for separating "s" and "sch" is now automated in the manner according to the invention. The concept of critical bandwidths (frequency groups according to the Bark scale) is preferably also used in the presented automatic adaptation, so that ultimately there are clear advantages in the automatic adaptation of frequency compression with regard to speech intelligibility. Already after a short period of getting used to the changed sound impression due to the frequency compression, the hearing impaired subjects show an improved speech intelligibility.

Advantageously, the adaptation strategy according to the invention of a frequency compression algorithm on the one hand shows a measurable improvement in speech intelligibility when frequency compression is activated and, on the other hand, a faster one Adaptation of hearing aids with frequency compression algorithms. In particular, the adaptation can now be automated and does not require long measurements and fitting sessions. Furthermore, it is also possible to predict an additional benefit with regard to speech intelligibility with frequency compression. Another advantage is that improved speech intelligibility already sets up after initial adaptation.

Claims (10)

Method for determining a knee point (13) of a frequency compression characteristic (10) for a hearing device, by Determining a maximum audible frequency (f_max) of a user of the hearing device, and Determining the knee point (13) by means of a predetermined rule as a function of the maximum audible frequency (f_max),
characterized in that - Parameters of the frequency compression characteristic (10) are formed on the basis of frequency groups. The method of claim 1, wherein the knee point (13) is set in any case above 1.5 kHz. Method according to claim 1 or 2, wherein the knee point (13) is calculated by means of values of the Bark scale. Method according to claim 3, wherein a coordinate f_cutoff of the knee point (13) is given by the formula $$\mathrm{f\_cutoff}=1960\cdot \left(\left(\mathrm{f\_max\_bark}-\mathrm{no\_bands\_down}\right)+0.53\right)/\left(26.28-\left(\mathrm{f\; max\; bark}-\mathrm{no\; bands\; down}\right)\right)$$

and wherein f_max_bark means the maximum audible frequency converted into a bark value and no_bands_down means a number of frequency groups determined in dependence on the maximum audible frequency. A method for determining a frequency compression characteristic (10) according to which an input value is mapped into an output value by determining a knee point (13) according to one of the preceding claims, wherein below the knee point (13) each input value is equal to the respective output value. The method of claim 5, wherein the maximum compression rate is 4. A method according to claim 5 or 6, wherein an input value f_source_max is calculated to the output value f_max corresponding to the maximum audible frequency using the Bark scale. The method of claim 7, wherein the input value f_source_max using the formula $$\mathrm{f\_source\_max}=1960\cdot \left(\left(\mathrm{f\_max\_bark}+\mathrm{no\_bands\_up}\right)+0.53\right)/\left(26.28-\left(\mathrm{f\; max\; bark}+\mathrm{no\; bands\; up}\right)\right)$$

and wherein f_max bark means the maximum audible frequency (f_max) converted into a bark value and no_bands_up a number of frequency groups defined as a function of the maximum audible frequency. Method for adjusting a binaural hearing system with two hearing devices, comprising the step of determining a frequency compression characteristic (10) according to one of Claims 5 to 8. A method according to claim 9, wherein the frequency compression characteristic according to one of claims 5 to 8 is determined for the ear of the user of the hearing devices which has the lower hearing loss.

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