METHOD AND APPARATUS FOR ADAPTING THE TRANSFER FUNCTION IN A HEARING AID

Abstract: A digitally controlled hearing aid containing sound detectors (1, 2, 3), after which there are filters (5, 6, 7, 8) which divide the signal received into several frequency ranges. In each frequency range is calculated the average value (13, 14, 15, 16), and this value is converted to digital values. A measure of the user's hearing deficiency is read into a memory (21) in the hearing aid. This stored information is used to change the measured average values in order to obtain correction signals which, by means of a digital-analog converter (22), are used to regulate the amplification of the amplifiers (32, 33, 34, 35) which are disposed in each frequency range. The calculation by the apparatus of the average values and the control of the amplifiers can be effected in multiplex mode (17, 23). By merely reading a new storage content into the memory (21), the hearing aid's transfer function can be changed, thus enabling the hearing aid to be adapted to the user in a simple manner. By means of a control circuit (47), the information which is read into the apparatus can also be used to regulate the cut-off frequencies of the filters (5, 6, 7, 8), or by means of a control circuit (45) to adjust the output attenuators (36, 37, 38, 39).

Description: METHOD AND APPARATUS FOR ADAPTING THE TRANSFER FUNCTION IN A HEARING AID This invention relates to a method of adapting the transfer function between the sound input and the sound output in a hearing aid to different hearing deficiencies, whereby one measures the hearing defi¬ ciency and produces a digital signal which indicates the hearing deficiency or the desired correction of the transfer function, after which the digital signal produced is introduced into a memory in the hearing aid, and this method can be effected in a hearing aid with a sound detecting amplifier, an amplifier cir¬ cuit and sound reproducing device, said apparatus having a memory in which a measure of the user's hearing deficiency or the desired correction of the transfer function of the apparatus is stored as a digital signal. Developments within the field of medicine have resul¬ ted in some of the hearing impairments, which have hitherto given rise to the use of hearing aids, now being able to be helped in other ways. For example, a conductive hearing loss can be helped through an operation in the middle ear. The remaining hearing ailments, which are of a predominantly perceptive nature, are unfortunately of those types which can be helped only to a slight degree with conventional hearing aids. Moreover, conventional hearing aids based on analogue circuit technique provide only lim¬ ited possibilities of carrying out individual adap¬ tion of the hearing aid to the user. Over recent years, the digital technique has gained ground in a large number of areas within sound recor¬ ding and transmission, areas which have otherwise been dominated by analogue circuit technique. As ex¬ amples can be mentioned tape recorders and the dig- ital transmission of telephone conversations. One of the most important characteristics of digital sound processing systems is that the system's mode of operation is determined by a series of digital code words which allow themselves to be changed in a sim¬ ple manner, as opposed to analogue systems where the system's mode of operation is changed by the replace¬ ment of physical components. Moreover, with a digital system it is possible to undertake a long series of transformations of the audio signal, a process which with the analogue circuit technique can be carried into effect only with difficulty. The use of digital technique in connection with hear- ing aids appears to open possibilities for a hitherto, unknown degree of adaption to individual hearing losses. At the same time that an optimum individual adaption can be realized, one also achieves the res¬ ult that the same hearing aid can be used for many different kinds of hearing losses. A method and apparatus which uses the digitalization of au io, signals for use in hearing aids is known from the USA patent no. 4,187,413. With the technique known from this patent one converts the whole of the desired audible signal to digital signals, and cor¬ rects the signal by means of a programme which is supplied to the hearing aid in the form of a digital signal. The corrected digital signal is then conver— ted to an analogue signal which is amplified and re¬ produced in the hearing aid's receiver. This tech¬ nique is excellent from the theoretical point of view, but if the audible signal to be reproduced is 5 to have a good quality, what is involved is much greater quantities of digital signals which must be converted, corrected and again converted, which is very power-demanding, thus rendering the technique difficult to utilize in a hearing aid which is driven Q by a battery with modest capacity. The object of the invention according to the present application is to be able to digitalize the whole of the control and regulation function, without the nec- essity of having to convert the whole of the audible signal to digital values, whereby the desired effect can be achieved with a modest power consumption, thus making it possible to build the whole of the appara¬ tus into an ordinary hearing aid. This is achieved by a method as characterized in claim 1, and can be effected in practice with a hear¬ ing aid as presented and characterized in claim 4. one contents oneself simply with dividing the audible signal into a series of suitable frequency ranges, all depending on the patient's hearing deficiency, and then one merely digitalizes the average value of the signal in each frequency range. The audible sig- nal, that is the signal which the user must have am- - plified or changed, is processed in the hearing aid as an ordinary analogue signal, i.e., it is subjected to suitable amplification, while the whole of the control takes place digitally. If one proceeds as presented in claim 2, one can also use the digital hearing deficiency signal to control the filter limits for each frequency range, which provides increased possibilities of adaption. If one proceeds as presented in claim 3, one can also control an attenuator inserted one in each of the frequency ranges, thus providing even greater possi¬ bilities of adaption. The apparatus for the execution of the method is ex¬ pediently driven in multiplex operation as presented in the claims 5 and 6. It is thus possible to use the same circuit to convert the average values for all the frequency ranges to signals for use in the con¬ trol of the amplifiers. That digital signal which is indicative of the hear¬ ing deficiency or the desired correction of the tran- sfer function can also be used to control the cutoff frequencies of the filters and the adjustments of the attentuators, as presented in claims 8 and 9. This can be effected simply by having a small memory for adjusting the relevant circuits. The contents of the memory can be changed when desired by reading a new programme into the hearing aid. In the following the invention is described with reference to the drawing, which shows a hearing aid according to the invention. The drawing shows a schematic block diagram covering the whole of the hearing aid with associated digital regulation circuit. It comprises sound inputs 1, 2 and 3, where 1 shows the audio input from radio, 2 shows the audio input through an ordinary microphone and 3 shows the audio input by means of a so-called telecoil. The audio signal received is first ampli- fied in a normal amplifier 4, after which it is fed to an analogue filter bank 5, 6, 7 and 8. The filter, bank shown here as an example consists of four fil¬ ters which divide the signals received into four fre¬ quency ranges. The individual filters 5, 6, 7 and 8 are digitally controllable, i.e. their filter limits can be changed as a function of digital signals sup¬ plied to the filters from a control circuit 47, in which information can be stored concerning the filter limits. The control circuit 47 thus contains a store for digital data. The frequency ranges co ing from the filters are fed to each their channel 9, 10, 11 and 12 which lead to the amplification circuit 32, 33, 34 and 35, which will be explained later. By means of rectification circuit 13, 14, 15 and 16, from each of the channels 9, 10, 11 and 12 there is taken a signal which repre¬ sents the average value of the signal in each of said channels. The circuits 13, 14, 15 and 16 each contain a full-wave rectifier and a circuit which calculates the average value of the signal. This average value is fed to an analogue multiplexer 17 which is con¬ trolled by a control circuit 46. The multiplexer 17 feeds the average values alternately to a logarithmic amplifier 18. The logarithmic amplifier 18 converts the average values to signals which represent the signal value in deciBel. This conversion of the cal¬ culated average values to measures indicated in dB is undertaken because the normal dynamic range for ordinary audible sound is of 80/90 dB. It is there¬ fore easier to carry out the subsequent regulation on the basis of a measurement in dB than on the basis of a measurement indicated in linear values. From the logarithmic amplifier 18 the signal is fed to a cir¬ cuit 19 which is a so-called sample and hold circuit. This circuit is included in order to hold the signals while they are being supplied to the analog-digital converter 20, in that the signal must be held for a as long as the .converter is operating. The circuit 19 and 20 are controlled from the same control circuit 46 as the control multiplexer. The signal from the analog-digital converter is fed to a correction cir¬ cuit 21 which contains a memory. In this memory is stored a table covering the dynamic conditions for. each channel. This stored information indicates the hearing deficiency of the user of the hearing aid or indicates the desired correction of the hearing aid's transfer function. The information is read into the store at point B, from where through a circuit 44 which, for example, can be a series to parallel con¬ verter, it is transferred to the correction circuit 21. From the drawing it will be seen that the control circuit 46 not only controls the multiplexer 17, but also the correction circuit 21 with memory. In the correction circuit the measured average value signals are compared with the stored data for the user's hearing deficiency, thus giving rise to correction data dependent upon the hearing deficiency. This cor- rection data is fed to a digital-analog converter 22, from where it is fed to a second analog-multiplexer 23. From here the data is distributed to sample and_ hold circuits 24, 25, 26 and 27. Here one must bear in mind that the analogue signal is still an indica- ._:- o ' tion in dB, which explains the inclusion of exponen¬ tial amplifiers 28, 29, 30 and 31 which control the above-mentioned amplifiers 32, 33, 34 and 35. These amplifiers which are inserted in each their channel have adjustable amplification as a function of the signals arriving from the circuits 28, 29, 30 and 31. One thus has the amplifier inserted in each channel controlled as a function of the stored information concerning the user's hearing deficiencies. The thus amplified signals ' are fed to • a summation amplifier 40 where they are added and fed, for example, through a gain control 41 to a speech amplifier 42 before being fed to the normal sound-reproducing earphone in the hearing aid. For further adjustment of the apparatus to the user's hearing deficiency, an attenuator 36, 37, 38 and 39 can be inserted in each amplification channel between the controllable amplifiers 32, 33, 34 and 35 and the summation amplifier 40. These attenuators are simil¬ arly adjustable by means of an adjusting circuit 45, and said adjusting circuit can also contain a store for digital information. As will be seen from the diagram, the information which is read in at B can be fed direct to the memory of adjusting circuit 45 through the series to parallel converter 44. In the memory of adjusting circuit 45 is thus stored infor¬ mation concering the adjustment of the attenuators 36, 37, 38 and 39. Similarly, the information which is read in at point • B can be fed to the control circuit 47, which also contains a store with information concerning the ad- justment of the filter bank. This transfer of inform¬ ation is effected by connecting the two points marked A to each other. When a hearing aid of this type is to be used, one carries out the customary measurement of the user's hearing deficiencies. The hearing deficiency is con¬ verted to digital values which, in the form of a dig¬ ital electrical signal, are read into the hearing aid at point B. The information concerning the hearing deficiency is thus stored partly in the memory of correction circuit 21 and partly in the memories of the two -.circuits 45 and 47. The store of information in 45 provides for the adjustment of the attenuators 36, 37, 38 and 39, and the store 47 with control cir¬ cuit provides for the adjustment of the filter limits in the filter bank 5, 6, 7 and 8. The memory contained in the correction circuit 21 can be a so-called EEPROM (electrically erasable program¬ mable read only memory) , i.e. a read memory, the con¬ tents of which can be changed. If the user's hearing deficiency changes, for example with age, or if for example someone else is to use the hearing aid, it is adjusted merely by reading new information into the hearing aid at-.point B. The in¬ formation is stored in the correction circuit 21 as a kind of table covering the dynamic conditions for each channel. Although, in the description and in the drawing there is described and shown a hearing aid with four chan¬ nels, i.e. an apparatus in which the signal to be %u ' ■&■ «. ζj f " O PΪ • amplified and corrected is divided into four fre¬ quency ranges, there is naturally nothing to prevent the use of other numbers of channels. In cases where the hearing deficiency does not demand such a high degree of correction, a smaller number of channels can be used, and if severe hearing deficiences dem¬ anding greater corrections are involved, it can be presumed that a larger number of channels can be used. Since by means of the information read into the hear¬ ing aid's memories one can both change the limits for the crossover frequencies, adjust the degree of amp¬ lification of the amplifiers and adjust the attenua- ' tors inserted after the amplifiers, the hearing aid thus achieved is one which can be adapted to almost all hearing deficiences.

Claims: C L A I M S 1. Method for adapting the transfer function between the sound input and the sound output of a hearing aid to different hearing deficiencies, whereby one meas¬ ures the hearing deficiency and produces a digital signal which is indicative of the hearing deficiency or the desired correction of the transfer function, after which the digital signal produced is fed into a memory in the hearing aid, c h a r a c t e r i z ¬ e d in that a) one divides the signal received at the sound input into several frequency ranges (0-fl, fl-f2, f2-fn, fn-fro), . b) one calculates the average value of the sig¬ nal in each frequency range and converts each average value signal to digital signals, c) one hereafter, by means of a computation cir- cuit, changes the middle—value-representing digital signals as a function of the intro¬ duced hearing-deficiency-representing signals to digital adaption signals, d) which are used to change the transfer func¬ tion between the sound input and the sound output in the frequency range corresponding to the signal. 2. Method according to claim 1, c h a r a c t e r ¬ i z e d in that the digital signal which describes the hearing deficiency is also used to statically adjust the cut-off frequencies of the frequency ran¬ ges into which the signal received at the sound input is divided. 3. Method according to claims 1 or 2, c h a r a c ¬ t e r i z e d in that the digital signal which des¬ cribes the hearing deficiency is also used to static¬ ally adjust the attenuators in each of the frequency ranges. 4. Hearing aid for the application of the method ac¬ cording to claim 1, with sound detector (1, 2, 3), amplification circuit (32, 33, 34, 35) and sound re¬ ceiver (43) , said hearing aid having a memory (21) in which a measure of the user's hearing deficiency or of the desired correction of the aid's transfer func¬ tion is stored as a digital signal, c h a r a c t ¬ e r i z e d in that a) the signal from the sound detector (1, 2, 3) is fed to at least two filters (5, 6, 7, 8) which divide the signal into at least two frequency ranges, b) after which the signals are fed to at least one rectifier circuit (13, 14, 15, 16), where the average value of each signal is formed, c) said average values then being transformed into digital signals via the converter cir¬ cuit (19, 20) and supplied to a correction circuit (21) , which corrects the formed aver¬ age values by means of information stored in u said circuit (21) , d) whereupon the corrected middle values, via a second converter circuit (22) , are again transformed into analogue signals and fed to amplification circuits (32, 33, 34, 35) for the control of their transfer function, e) whereby the frequency-range-divided signals from the sound detector are corrected before being summed up and fed to the receiver (43) . 5. Apparatus according to claim 4, c h a r a c t ¬ e r i z d in that the conversion circuits (13, 14, 15, 16) which form the average values are coupled in cyclically by a multiplexer (17) controlled by a- con¬ trol circuit (46) . 6. Apparatus according to claim 5, c h a r a c t - e r i z e d in that the corrected average values are fed to the amplification circuits (32, 33, 34, 35) cyclically by a multiplexer (23) , which is also con¬ trolled by said control circuit (46) . 7. Apparatus according to claims 4 - 6, c h a r a c¬ t e r i z e d in that an attenuator (36, 37, 38, 39) is coupled in after each amplifier circuit (32, 33, 34, 35) . 8. Apparatus according to claim 7, c h a r a c t ¬ r i z e d in that the attenuators (36, 37, 38, 39) are statically controllable by means of a digital ad¬ justing circuit (45) . 9. Apparatus according to claims 4 - 8, c h a r ¬ a c t e r i z e d in that the filters (5, 6, 7, 8) after the sound detector (1, 2, 3) are statically controllable by means of a digital adjustment cir- cuit (47) . 10. Apparatus according to claims 8 - 9, c h a r ¬ a c t e r i z e d in that the control circuits (45, 47) which respectively control the attenuators (36, 37, 38, 39) and the filters (5,. 6, 7, 8) are digital storage couplings in which adjustment information is stored in an exchangeable manner.

Inventors: BISGAARD PETER NIKOLAI, ELBAEK JOERGEN FINK, BISGAARD, PETER, NIKOLAI, ELBAEK, JOERGEN, FINK
Applicants: DANAVOX AS, DANAVOX A/S
Application year: 1982
Main classification: H04R25
IPC codes: H04R25