METHOD FOR ADJUSTING A SYSTEM FOR PROVIDING HEARING ASSISTANCE TO A USER

Abstract

There is provided a method for adjusting a system for providing hearing assistance to a user (101), the system comprising a microphone arrangement (26) for capturing audio signals, a transmission unit (102) for transmitting the audio signals via a wireless link (107) to a receiver unit (103) worn by the user, a gain control unit (126) located in the receiver unit for setting the gain applied to the audio signals, and means (38) worn at or in a user's ear (39) for stimulating the hearing of the user according to the audio signals from the receiver unit (103), said method comprising: generating test audio signals, transmitting said test audio signals at a pre-defined level from the transmission unit via the wireless link to the receiver unit and stimulating the user's hearing with said test audio signals via said stimulating means; simultaneously transmitting gain control commands from the transmission unit to the gain control unit in order to selectively change the gain set by the gain control unit; repeating these steps until an optimum value of the gain set by the gain control unit has been determined; and transmitting a store command from the transmission unit to the receiver unit in order to store that determined optimum value of the gain.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of the use of an embodiment of a hearing assistance system according to the invention;

FIG. 2 is a schematic view of the transmission unit of the system of FIG. 1;

FIG. 3 is a diagram showing the signal amplitude versus frequency of the common audio signal/data transmission channel of the system of FIG. 1;

FIG. 4 is a block diagram of one embodiment of the receiver unit of the system of FIG.

FIG. 5 is a block diagram of one embodiment of the transmission unit of the system of FIG. 1;

FIG. 6 is a block diagram of another embodiment of the transmission unit of the system of FIG. 1;

FIG. 7 is a diagram showing an example of the gain set by the gain control unit versus time;

FIG. 8 shows schematically an example in which the receiver unit is connected to a separate audio input of a hearing aid; and

FIG. 9 shows schematically an example in which the receiver unit is connected in parallel to the microphone arrangement of a hearing aid.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows schematically the use of a system for hearing assistance comprising an FM radio transmission unit 102 comprising a directional microphone arrangement 26 consisting of two omnidirectional microphones M1 and M2 which are spaced apart by a distance d, an FM radio receiver unit 103, and hearing instrument 104 comprising a microphone arrangement 36. The audio output of the receiver unit 103 is connected to an audio input of the hearing instrument 104 via an audio shoe (not shown). The transmission unit 102 is worn by a speaker 100 around his neck by a neck-loop 121 acting as an FM radio antenna, with the microphone arrangement 26 capturing the sound waves 105 carrying the speaker's voice. Audio signals and control data are sent from the transmission unit 102 via radio link 107 to the receiver unit 103 worn by a user/listener 101. In addition to the voice 105 of the speaker 100 background/surrounding noise 106 may be present which will be both captured by the microphone arrangement 26 of the transmission unit 102 and microphone arrangement 36 of the hearing instrument 104. Typically the speaker 100 will be a teacher and the user 101 will be a hearing-impaired person in a classroom, with background noise 106 being generated by other pupils.

FIG. 8 is a block diagram of an example in which the receiver unit 103 is connected to a high impedance audio input of the hearing instrument 104. The receiver unit 103 contains a module 31 for demodulation and signal processing for processing the FM signal received by the antenna 123 from the antenna of the transmission unit 102 (these audio signals resulting from the microphone arrangement 26 of the transmission unit 102 in the following also will be referred to as “first audio signals”). The processed first audio signals are amplified by variable gain amplifier 126. The output of the receiver unit 103 is connected to an audio input of the hearing instrument 104 which is separate from the microphone 36 of the hearing instrument 15 (such separate audio input has a high input impedance).

The first audio signals provided at the separate audio input of the hearing instrument 104 may undergo pre-amplification in a pre-amplifier 33, while the audio signals produced by the microphone 36 of the hearing instrument 104 (in the following referred to “second audio signals”) may undergo pre-amplification in a pre-amplifier 37. The hearing instrument 104 further comprises a digital central unit 35 into which the first and second audio signals are supplied as a mixed audio signal for further audio signal processing and amplification prior to being supplied to the input of the output transducer 38 of the hearing instrument 104. The output transducer 38 serves to stimulate the user's hearing 39 according to the combined audio signals provided by the central unit 35.

FIG. 9 shows a modification of the embodiment of FIG. 8, wherein the output of the receiver unit 103 is not provided to a separate high impedance audio input of the hearing instrument 104 but rather is provided to an audio input of the hearing instrument 104 which is connected in parallel to the hearing instrument microphone 36. Also in this case, the first and second audio signals from the remote microphone arrangement 26 and the hearing instrument microphone 36, respectively, are provided as a combined/mixed audio signal to the central unit 35 of the hearing instrument 104. The gain applied to first audio signals can be adjusted by the variable gain amplifier 126 of the receiver unit 103. Further, also the gain ratio for the first and second audio signals can be controlled by the receiver unit 103 by accordingly controlling the signal at the audio output of the receiver unit 103 and the output impedance Z1 of the audio output of the receiver unit 103.

FIG. 2 is a schematic view of the transmission unit 102 which, in addition to the microphone arrangement 26, comprises a digital signal processor 122, an FM transmitter 120, an antenna 149 for establishing a short distance bidirectional inductive link 54 with an antenna 151 of the receiver unit 103, a button 50 for activating an FM advantage adjustment mode of the transmission unit 102 and the receiver unit 103, a button 51 to read identification information stored in the receiver unit 103 via the inductive link 54, a button 52 for causing a “volume up” command being transmitted to the receiver unit 103, and a button 53 for causing a “volume down” command being transmitted to the receiver unit 103.

According to FIG. 3, the channel bandwidth of the FM radio transmitter, which, for example, may range from 100 Hz to 7 kHz, is split in two parts ranging, for example from 100 Hz to 5 kHz and from 5 kHz to 7 kHz, respectively. In this case, the lower part is used to transmit the audio signals (i.e. the first audio signals) resulting from the microphone arrangement 26, while the upper part is used for transmitting data from the FM transmitter 120 to the receiver unit 103. The data link established thereby can be used for transmitting control commands relating to the gain from the transmission unit 102 to the receiver 103, and it also can be used for transmitting general information or commands to the receiver unit 103.

The internal architecture of the FM transmission unit 102 is schematically shown in FIG. 5. As already mentioned above, the spaced apart omnidirectional microphones M1 and M2 of the microphone arrangement 26 capture both the speaker's voice 105 and the surrounding noise 106 and produce corresponding audio signals which are converted into digital signals by the analog-to-digital converters 109 and 110. M1 is the front microphone and M2 is the rear microphone. The microphones M1 and M2 together associated to a beamformer algorithm form a directional microphone arrangement 26 which, according to FIG. 1, is placed at a relatively short distance to the mouth of the speaker 100 in order to insure a good SNR at the audio source and also to allow the use of easy to implement and fast algorithms for voice detection as will be explained in the following. The converted digital signals from the microphones M1 and M2 are supplied to the unit 111 which comprises a beam former implemented by a classical beam former algorithm and a 5 kHz low pass filter. The first audio signals leaving the beam former unit 111 are supplied to a gain model unit 112 which mainly consists of an automatic gain control (AGC) for avoiding an overmodulation of the transmitted audio signals. The output of a gain model unit 112 is supplied to an adder unit 113 which mixes the first audio signals, which are limited to a range of 100 Hz to 5 kHz due to the 5 kHz low pass filter in the unit 111, and DTMF (dual-tone multi-frequency) encoded data signals supplied from a control unit 162 within a range from 5 kHz and 7 kHz. The combined audio/data signals are converted to analog by a digital-to-analog converter 119 and then are supplied to the FM transmitter 120 which uses the neck-loop 121 as an FM radio antenna.

The transmission unit 102 further comprises a voice memory 160 in which test audio signals are stored which can be retrieved by request of a control unit 162 and which are then supplied to the gain model unit 112. The control unit 162 generates commands for controlling the transmission unit 102 and the receiver unit 103 according to operation of the buttons 50 to 53 by the user 100. Such control commands are transmitted via the FM transmitter 120 and the antenna 121 to the receiver unit 103. The units 109, 110, 111, 112, 113, 119 and 162 all can be realized by the digital signal processor 122 of the transmission unit 102.

The receiver unit 103 is schematically shown in FIG. 4. The audio signals produced by the microphone arrangement 26 and processed by the units 111 and 112 of transmission unit 102 and the command signals produced by the control unit 162 of the transmission unit 102 are transmitted from the transmission unit 102 over the same FM radio channel to the receiver unit 103 where the FM radio signals are received by the antenna 123 and are demodulated in an FM radio receiver 124. An audio signal low pass filter 125 operating at 5 kHz supplies the audio signals to a variable gain amplifier 126 from where the audio signals are supplied to the audio input of the hearing instrument 104. The output signal of the FM radio receiver 124 is also filtered by a high pass filter 127 operating at 5 kHz in order to extract the commands from the control unit 162 contained in the FM radio signal. A filtered signal is supplied to a unit 128 including a DTMF and digital demodulator/decoder in order to decode the command signals from the control unit 162.

The command signals decoded in the unit 128 are provided to a parameter update unit 129 in which the parameters of the commands are updated according to information stored in an EEPROM 130 of the receiver unit 103. The output of the parameter update unit 129 is used to control the audio signal amplifier 126 which is gain and output impedance controlled. Thereby the audio signal output of the receiver unit 103 can be controlled according to the commands from the control unit 162 in order to control the gain (and also the gain ratio, i.e. the ratio of the gain applied to the audio signals from the microphone arrangement 26 of the transmission unit 102 and the audio signals from the hearing instrument microphone 36) according to the commands from the control unit 162.

The inductive antenna 151 of the receiver unit 103 is connected via a unit 150 to the EEPROM 130 and is used for reading identification information stored in the EEPROM 130, which serves to identify the receiver unit 103, via the inductive link 54 by the transmission unit 102. In addition, the inductive link 54 may have additional functions such as reading other receiver parameters, programming the receiver unit 103, monitoring battery status, the receiver unit 103 and monitoring the quality of the link.

The desired gain determined by the amplifier 126 may be adjusted according to the following procedure.

First, the user 100 selects the respective receiver unit 103, which is to be adjusted by approaching the receiver unit 103 with the transmission unit 102 so close that the receiver unit 103 comes within the reach of the inductive link 54. Then the button 51 is pushed whereby the control unit 162 causes the transmission unit 102 to read the identification code via the inductive link 54 from the EEPROM 130 of the receiver unit 103. Once the identification code has been read by the transmission unit 102, this particular identification code is coded over the data link of the transmission unit 102 in order to address in the further adjustment procedure only the specified receiver unit 103. If the user 101 uses two hearing instruments 104, two receiver units 103 must be addressed by the transmission unit 102. If the user 101 is the only one within the reach distance of the transmission unit 102, the receiver identification step can be omitted.

As a next step, the user 100 will enter an adjustment mode of the transmission unit 102 by pushing the button 50.

In the FM advantage adjustment procedure then test audio signal is generated, for example, by retrieving a test signal from the voice memory 160. Alternatively, the test audio signals may be generated by the voice of the user 100 which is captured by the microphone arrangement 26. In the latter case, the voice of the user 100 also will be captured by the hearing instrument microphone 36. In any case, the test audio signal preferably will be transmitted to the receiver unit 103 at the maximum audio level of the transmission unit 102, which is typical for the case when the user 100 is speaking. The test audio signals provided by the low pass filter 125 will be amplified by the amplifier 126 according to the presently set gain in the EEPROM 130 and then will be supplied to the hearing instrument 104 for being reproduced by the speaker 38.

As a next step, perception of the test audio signals by the user 101 will be evaluated, and according to the result of this evaluation the volume-up-button 52 will be pushed if the user 101 feels that the volume of the audio test signals is too low, or the volume-down-button 53 will be pushed if the user 101 feels that the volume of the test audio signals is too high. Upon operation of the respective button 52 or 53 the control unit 162 will cause a corresponding control command to be transmitted to the receiver unit 103 where it is demodulated in the unit 128 and serves to correspondingly increase or reduce the gain applied by the amplifier 126 via the unit 129.

Such change of the gain applied by the amplifier 126 is continued until an optimum value—which corresponds then to the optimum value of the individual FM advantage—has been found. Thereupon that determined optimum gain value will be stored in the EEPROM 130 of the receiver unit upon receipt of a respective command sent by the transmitting unit 102. Such store command signal may be generated by the control unit 162 of the transmission unit 102 upon corresponding operation of the buttons at the transmission unit 102, for example by again pushing the “A”-button 50, or it may be generated automatically, if a certain time period without operation of the volume up or volume down-buttons 52, 53 has lapsed.

After having terminated the FM advantage adjustment procedure, the transmission unit 102 and the receiver unit 103 will resume the normal operation mode. This normal operation mode may be such that the determined optimum gain value stored in the EEPROM 130 will be continuously applied to the amplifier 126, i.e. the amplifier 126 will be operated at constant gain.

According to an alternative embodiment which is shown in FIGS. 6 and 7, the transmission unit 102 and the receiver unit 103 may be designed such that in the normal operation mode the gain presently applied by the amplifier 126 may be changed according to the result of an auditory scene analysis permanently performed by the transmission unit 102 by analysing the audio signal captured by the microphone arrangement 26. The receiver unit 103 shown in FIG. 4 may be used also with the transmission unit 102 of FIG. 6.

To this end, the transmission unit 102 is provided with classification unit 134, the functions of which may be implemented by the digital signal processor 122. The classification unit 134 shown in FIG. 6 includes units 114, 115, 116, 117 and 118, as will be explained in detail in the following.

The unit 114 is a voice energy estimator unit which uses the output signal of the beam former unit 111 in order to compute the total energy contained in the voice spectrum with a fast attack time in the range of a few milliseconds, preferably not more than 10 milliseconds. By using such short attack time it is ensured that the system is able to react very fast when the speaker 11 begins to speak. The output of the voice energy estimator unit 114 is provided to a voice judgement unit 115 which decides, depending on the signal provided by the voice energy estimator 114, whether close voice, i.e. the speaker's voice, is present at the microphone arrangement 26 or not.

The unit 117 is a surrounding noise level estimator unit which uses the audio signal produced by the omnidirectional rear microphone M2 in order to estimate the surrounding noise level present at the microphone arrangement 26. However, it can be assumed that the surrounding noise level estimated at the microphone arrangement 26 is a good indication also for the surrounding noise level present at the microphone 36 of the hearing instrument 104, like in classrooms for example. The surrounding noise level estimator unit 117 is active only if no close voice is presently detected by the voice judgement unit 115 (in case that close voice is detected by the voice judgement unit 115, the surrounding noise level estimator unit 117 is disabled by a corresponding signal from the voice judgment unit 115). A very long time constant in the range of 10 seconds is applied by the surrounding noise level estimator unit 117. The surrounding noise level estimator unit 117 measures and analyzes the total energy contained in the whole spectrum of the audio signal of the microphone M2 (usually the surrounding noise in a classroom is caused by the voices of other pupils in the classroom). The long time constant ensures that only the time-averaged surrounding noise is measured and analyzed, but not specific short noise events. According to the level estimated by the unit 117, a hysteresis function and a level definition is then applied in the level definition unit 118, and the data provided by the level definition unit 118 is supplied to the unit 116 in which the data is encoded by a digital encoder/modulator and is transmitted continuously with a digital modulation having a spectrum a range between 5 kHz and 7 kHz. That kind of modulation allows only relatively low bit rates and is well adapted for transmitting slowly varying parameters like the surrounding noise level provided by the level definition unit 118.

The estimated surrounding noise level definition provided by the level definition unit 118 is also supplied to the voice judgement unit 115 in order to be used to adapt accordingly to it the threshold level for the close voice/no close voice decision made by the voice judgement unit 115 in order to maintain a good SNR for the voice detection.

If close voice is detected by the voice judgement unit 115, a very fast DTMF (dual-tone multi-frequency) command is generated by a DTMF generator included in the unit 116. The DTMF generator uses frequencies in the range of 5 kHz to 7 kHz. The benefit of such DTMF modulation is that the generation and the decoding of the commands are very fast, in the range of a few milliseconds. This feature is very important for being able to send a very fast “voice ON” command to the receiver unit 103 in order to catch the beginning of a sentence spoken by the speaker 11. The command signals produced in the unit 116 (i.e. DTMF tones and continuous digital modulation) are provided to the adder unit 113, as already mentioned above.

FIG. 7 illustrates an example of how the gain in the normal operation mode may be controlled according to the determined present auditory scene category.

As already explained above, the voice judgement unit 115 provides at its output for a parameter signal which may have two different values:

“Voice ON”: This value is provided at the output if the voice judgement unit 115 has decided that close voice is present at the microphone arrangement 26. In this case, fast DTMF modulation occurs in the unit 116 and a control command is issued by the unit 116 and is transmitted to the amplifier 126, according to which the gain is set to a given value which, for example, may result in an FM advantage of 10 dB under the respective conditions of for example, the ASHA guidelines.

“Voice OFF”: If the voice judgement unit 115 decides that no more close voice is present at the microphone arrangement 26, a “voice OFF” command is issued by the unit 116 and is transmitted to the amplifier 126. In this case, the parameter update unit 129 applies a “hold on time” constant 131 and then a “release time” constant 132 defined in the EEPROM 130 to the amplifier 126. During the “hold on time” the gain set by the amplifier 126 remains at the value applied during “voice ON”. During the “release time” the gain set by the amplifier 126 is progressively reduced from the value applied during “voice ON” to a lower value corresponding to a “pause attenuation” value 133 stored in the EEPROM 130. Hence, in case of “voice OFF” the gain of the microphone arrangement 26 is reduced relative to the gain of the hearing instrument microphone 36 compared to “voice ON”. This ensures an optimum SNR for the hearing instrument microphone 36, since at that time no useful audio signal is present at the microphone arrangement 26 of the transmission unit 102.

The control data/command issued by the surrounding noise level definition unit 1118 is the “surrounding noise level” which has a value according to the detected surrounding noise level. As already mentioned above, the “surrounding noise level” is estimated only during “voice OFF” but the level values are sent continuously over the data link. Depending on the “surrounding noise level” the parameter update unit 129 controls the amplifier 126 such that according to definition stored in the EEPROM 130 the amplifier 126 applies an additional gain offset or an output impedance change to the audio output of the receiver unit 103.

The application of an additional gain offset is preferred in case that there is the relatively low surrounding noise level (i.e. quiet environment), with the gain of the hearing instrument microphone 36 being kept constant. The change of the output impedance is preferred in case that there is a relatively high surrounding noise level (noisy environment), with the signals from the hearing instrument microphone 36 being attenuated by a corresponding output impedance change. In both cases, a constant SNR for the signal of the microphone arrangement 26 compared to the signal of the hearing instrument microphone 36 is ensured.

A preferred application of the systems according to the invention is teaching of pupils with hearing loss in a classroom. In this case the speaker 100 is the teacher, while a user 101 is one of several pupils, with the hearing instrument 104 being a hearing aid.

The FM advantage adjustment procedure in the adjustment mode may be similar to that described above with regard to the system of FIGS. 4 and 5. In the case of the embodiment of FIGS. 6 and 7 the optimum gain value determined and stored in the adjustment mode will be used to the calibrate the gain variation based on the auditory scene analysis in the normal operation mode. In present case, for example, the value of the gain applied in the “Voice ON” regime will correspond to the optimum gain value determined and stored in the adjustment mode.

While in the embodiments described so far the receiver unit is separate from the hearing instrument, in some embodiments it may be integrated with the hearing instrument.

The microphone arrangement producing the second audio signals may be connected to or integrated within the hearing instrument. The second audio signals may undergo an automatic gain control prior to being mixed with the first audio signals. The microphone arrangement producing the second audio signals may be designed as a directional microphone comprising two spaced apart microphones.

While various embodiments in accordance with the present invention have been shown and described, it is understood that the invention is not limited thereto, and is susceptible to numerous changes and modifications as known to those skilled in the art. Therefore, this invention is not limited to the details shown and described herein, and includes all such changes and modifications as encompassed by the scope of the appended claims.

Claims

1. A method for adjusting a system for providing hearing assistance to a user, said system comprising a microphone arrangement for capturing audio signals, a transmission unit for transmitting said audio signals via a wireless link to a receiver unit worn by said user, a gain control unit located in said receiver unit for setting a gain applied to said audio signals, and means worn at or in a user's ear for stimulating a hearing of said user according to said audio signals from said receiver unit, said method comprising:(a) generating test audio signals, transmitting said test audio signals at a pre-defined level from said transmission unit via said wireless link to said receiver unit and stimulating said user's hearing with said test audio signals via said stimulating means;(b) simultaneously transmitting gain control commands from said transmission unit to said gain control unit in order to selectively change said gain set by said gain control unit;(c) repeating steps (a) and (b) until an optimum value of said gain set by said gain control unit has been determined; and(d) transmitting a store command from said transmission unit to said receiver unit in order to store that determined optimum value of said gain.

2. The method of claim 1, wherein said system comprises a hearing instrument which is worn at or in said user's ear and which is connected to said receiver unit, said hearing instrument comprising said stimulating means, a second microphone arrangement for capturing second audio signals, and means for mixing said audio signals from said gain control unit and said second audio signals prior to stimulating said user's hearing with the mixed audio signals via said stimulating means.

3. The method of claim 1, wherein said system comprises a hearing instrument which is worn at said user's ear and comprises said receiver unit, said hearing instrument comprising said stimulating means, a second microphone arrangement for capturing second audio signals, and means for mixing said audio signals from said gain control unit and said second audio signals prior to stimulating said user's hearing with the mixed audio signals via said stimulating means.

4. The method of claim 2, wherein in step (a) said test audio signals are generated by retrieving audio signals from an audio signal memory.

5. The method of claim 4, wherein said audio signal memory is integrated in said transmission unit.

6. The method of claim 2, wherein in step (a) said test audio signals generated by an audio signal synthesizer.

7. The method of claim 6, wherein said audio signal synthesizer is integrated within said transmission unit.

8. The method of claim 2, wherein in step (a) said test audio signals are generated by generating a test sound and capturing said test sound as said test audio signals by said microphone arrangement.

9. The method of claim 8, wherein said test sound is a voice of a person using the transmission unit.

10. The method of claim 9, further comprising: capturing said test sound as said second audio signals by said second microphone arrangement, mixing said audio signals from said gain control unit and said second audio signals according to a presently set gain and stimulating said user's hearing with the mixed audio signals via said stimulating means of said hearing instrument.

11. The method of claim 1, wherein in step (d) said determined optimum value of said gain is stored in a memory which is integrated within said receiver unit.

12. The method of claim 2, wherein in step (d) said determined optimum value of said gain is stored in a memory which is integrated within said hearing instrument.

13. The method of claim 1, wherein prior to step (a) said receiver unit is identified.

14. The method of claim 13, wherein said receiver unit is identified by reading an identification information stored in said receiver unit by said transmission unit via an inductive link.

15. The method of claim 14, wherein said receiver unit is specifically addressed by said transmission unit by transmitting a signal coded according to said identification information read by said transmission unit.

16. The method of claim 1, wherein in step (a) said test signal is transmitted at a maximum level of said audio signals of said transmission unit.

17. The method of claim 2, wherein said gain control unit comprises an amplifier which is at least one of gain controlled and output impedance controlled and which is located in said receiver unit.

18. The method of claim 1, wherein a data link for transmitting said gain control commands and said store command and said audio signal link are realized by a common transmission channel.

19. The method of claim 18, wherein a lower portion of a bandwidth of said transmission channel is used by said audio signal link and an upper portion of said bandwidth of said transmission channel is used by said data link.

20. The method of claim 2, wherein an output of said receiver unit is connected in parallel with said second microphone arrangement.

21. The method of claim 2, wherein said audio signals from said receiver unit are supplied to said hearing instrument via an audio input separate from said second microphone arrangement.

22. The method of claim 1, wherein said audio signal link is a Frequency Modulated radio link

23. The method of claim 2, wherein said hearing instrument is a hearing aid having an electroacoustic output transducer as said stimulating means.

24. The method of claim 1, wherein said audio signals in said transmission unit undergo an automatic gain control treatment in a gain model unit prior to being transmitted to said receiver unit.

25. A method for operating a system for providing hearing assistance to a user having been adjusted according to the method of claim 1, wherein said gain control unit sets said gain to a constant value, with said constant value corresponding to said stored optimum value of said gain.

26. A method for operating a system for providing hearing assistance to a user having been adjusted according to the method of claim 1, comprising (a) capturing audio signals by said microphone arrangement and transmitting said audio signals by said transmission unit via said wireless audio signal link to said receiver unit;(b) analyzing said audio signals prior to being transmitted by a classification unit in order to determine a present auditory scene category from a plurality of auditory scene categories;(c) setting by said gain control unit a gain applied to said audio signals according to said present auditory scene category determined in step (b).(d) stimulating said user's hearing by said stimulating means according to said audio signals from said gain control unit;wherein said stored optimum value of said gain is used to calibrate said gain control unit.

27. The method of claim 26, wherein said gain applied for at least one of said auditory scenes is said stored optimum value of said gain.

28. The method of claim 27, wherein said gain control unit sets said gain to a constant value as long as said classification unit determines a level of said audio signals above a given threshold, wherein said constant value corresponds to said stored optimum value.

29. A system for providing hearing assistance to a user, comprising a microphone arrangement for capturing audio signals, a transmission unit for transmitting said audio signals via a wireless link to a receiver unit to be worn by said user, a gain control unit located in said receiver unit for setting a gain applied to said audio signals, and means worn at or in an ear of said user for stimulating a hearing of said user according to said audio signals from said gain control unit, means for generating test audio signals and transmitting said test audio signals at a pre-defined level from said transmission unit via said wireless audio signal link to said receiver unit;means for simultaneously transmitting gain control commands from said transmission unit to said gain control unit in order to selectively change said gain set by said gain control unit in order to determine an optimum value of said gain;means for storing optimum value said gain; andmeans for transmitting a store command from said transmission unit to said receiver unit in order to store that determined optimum value of said gain in said storing means.

30. The system of claim 29, wherein said microphone arrangement is integrated within said transmission unit.