Note: Descriptions are shown in the official language in which they were submitted.
<br/> CA 02446465 2004-07-28<br/>1<br/>HEARING AID AND A METHOD FOR TESTING A HEARING AID<br/>The present invention relates to hearing aids. The invention further relates <br/>to a method of<br/>testing hearing aids. More specifically, the invention relates to a hearing <br/>aid having a<br/>self-test capability.<br/> Background of the invention<br/>It is well-known in the art of hearing aids that a large fraction of hearing <br/>aids turned in for<br/>repair later prove to operate correctly. Thus in many cases, a perceived <br/>problem with a<br/>hearing aid does not relate to a defect in the hearing aid, rather it relates <br/>to an adjustment<br/>and use of the hearing aid. A lot of time and other resources are wasted in <br/>shipping and<br/>diagnosing hearing aids that are not defective.<br/>It is therefore desirable to provide a hearing aid with a self-test <br/>capability, permitting an<br/>operator of the hearing aid to verify proper functioning of the hearing aid. <br/>The operator<br/>of the hearing aid may be the hearing impaired user of the hearing aid or an <br/>audiologist<br/>engaged in fitting, fine tuning or otherwise working with the hearing aid.<br/> Summary of the invention<br/>According to an aspect of the present invention, there is provided a hearing <br/>aid having an<br/>input transducer for transforming an acoustic input signal into a first <br/>electrical signal, a<br/>signal processor for compensating a hearing deficiency by generation of a <br/>second<br/>electrical signal based on the first electrical signal, an output transducer <br/>for conversion of<br/>the second electrical signal into sound, a probe for determination of a signal <br/>parameter, a<br/>plurality of signal switches at respective points in a signal path of the <br/>hearing aid<br/>extending through the input transducer, the signal processor and the output <br/>transducer,<br/>and a test manager adapted to control the settings of the signal switches to <br/>connect the<br/><br/> CA 02446465 2004-07-28<br/>2<br/>probe to a selected first point of the signal path in order to conduct a test <br/>procedure of a<br/>selected section of the signal path.<br/>According to a further aspect of the present invention, there is provided a <br/>method for<br/>verifying functioning of a hearing aid, the hearing aid having an input <br/>transducer for<br/>transforming an acoustic input signal into a first electrical signal, a signal <br/>processor for<br/>compensating a hearing deficiency by generation of a second electrical signal <br/>based on<br/>the first electrical signal, an output transducer for conversion of the second <br/>electrical<br/>signal into sound, and a probe for determination of a signal parameter, the <br/>method<br/>comprising providing a plurality of signal switches at respective points in a <br/>signal path of<br/>the hearing aid extending through the input transducer, the signal processor <br/>and the output<br/>transducer, and using a test manager to control the settings of the signal <br/>switches to<br/>connect the probe to a selected first point of the signal path in order to <br/>conduct a test<br/>procedure of a selected section of the signal path.<br/>Further the hearing aid may comprise a test controller or a test manager for <br/>detection of a<br/>state of malfunction in the hearing aid. The test manager may be connected <br/>with a test<br/>stimulus generator, such as a tone generator, a noise generator, a digital <br/>word generator,<br/>or the like, with a probe means for determination of a signal parameter, such <br/>as signal<br/>level, frequency spectrum, phase characteristic, auto-correlation, cross-<br/>correlation, or the<br/>like and with a signal switch provided in the hearing aid. The signal switch <br/>is provided<br/>for connecting a test stimulus generator or a probe to a selected point in the <br/>signal path<br/>for testing of a selected part of the hearing aid. Further signal switches may <br/>be provided<br/>for coupling hearing aid components into or out of the signal path of the <br/>hearing aid.<br/>The signal path comprises components and transmission paths of the hearing aid <br/>that<br/>receive, process and transmit signals that are derived from the first <br/>electrical signal of the<br/>hearing aid.<br/>For example, the test manager may be adapted to operate respective signal path <br/>switches<br/>to disconnect the input transducer from the signal path at the entry to the <br/>hearing aid<br/><br/> CA 02446465 2004-07-28<br/>3<br/>processor and to activate a probe means for determination of the signal level <br/>at a selected<br/>or predetermined point at a later stage of the signal path whereby the noise <br/>level<br/>generated by parts of the hearing aid processor such as the input circuitry <br/>may be<br/>determined.<br/>The value of a signal parameter as determined by the probe may be compared to <br/>a<br/>reference value that may be retrieved from memory in the hearing aid or from a <br/>device<br/>external to the hearing aid. If the detected value lies outside a <br/>predetermined range<br/>comprising the reference value, the test manager may alert the operator of the <br/>hearing aid<br/>that the hearing aid is malfunctioning. The type of defect may also be <br/>signalled. For<br/>example, a tone or a sequence of tones may be generated by the output <br/>transducer to<br/>signify to the hearing impaired user that the hearing aid is defective. A <br/>specific tone or a<br/>specific sequence of tones may correspond to a specific defect.<br/>If the hearing aid is connected to a hearing aid programming device equipped <br/>with a<br/>display, the fact that the hearing aid is malfunctioning may be indicated on <br/>the display<br/>and, further, an indication of the type of defect may be displayed. For <br/>example, if the<br/>noise level is greater than a predetermined reference value, it may be <br/>signalled that the<br/>hearing aid is malfunctioning.<br/>Typically, hearing deficiency is frequency dependent in a way that is specific <br/>for each<br/>individual user. It is known in the art to provide a multichannel hearing aid, <br/>wherein the<br/>processor is divided into a plurality of channels so that individual frequency <br/>bands may be<br/>processed differently, for example, amplified with different gains. A <br/>multichannel<br/>hearing aid may further comprise a filter bank with bandpass filters for <br/>dividing the first<br/>electrical signal into a set of bandpass filtered first electrical signal <br/>derivatives, and the<br/>processor may be adapted to generate the second electrical signal by <br/>individual processing<br/>of the respective first electrical signal filter derivatives and adding the <br/>processed filter<br/>derivatives together to provide the second electrical signal. For a <br/>multichannel hearing<br/>aid, the test manager may be adapted to selectively connect a desired test <br/>stimulus<br/>generator or a desired probe to the output of a selected bandpass filter. For <br/>example, a<br/><br/> CA 02446465 2004-07-28<br/>4<br/>probe for level detection may be connected to the output of a selected <br/>bandpass filter in<br/>order to determine the noise level in a respective frequency band.<br/>In one embodiment of the invention, a test stimulus generator is provided that <br/>is<br/>controlled by the test manager for generation of a predetermined test stimulus <br/>that is fed<br/>to the output transducer of the hearing aid for conversion into a sound <br/>signal. For one<br/>type of test, the hearing aid will be placed in a compartment with hard walls, <br/>wherein a<br/>part of the generated acoustic signal will be reflected to be received by the <br/>acoustic input<br/>transducer. The test manager is further adapted to operate a signal switch to <br/>connect a<br/>selected probe, such as a level detector, or the like, to the input transducer <br/>for<br/>determination of a signal parameter, such as the signal level, of the <br/>respective generated<br/>first electrical signal.<br/>The determined value of the signal parameter may be compared to a reference <br/>value that<br/>may be retrieved from a memory in the hearing aid, and if the detected value <br/>deviates<br/>from the reference value, the test manager may, as previously described, alert <br/>the operator<br/>of the hearing aid that the hearing aid is malfunctioning. The type of defect <br/>may also be<br/>signalled. For example, the display of a programming device may show a message <br/>saying<br/>that the port to the input transducer in question should be checked for ear <br/>wax.<br/>One of the input transducers connected to the signal path may be the pick-up <br/>coil. The<br/>pick-up coil in the hearing aid may be tested in a way similar to the one <br/>described<br/>previously for an acoustic input transducer, since the output transducer <br/>typically generates<br/>a significant magnetic field that is picked up by the pick-up coil.<br/>In an embodiment with a filter bank, the probe may be connected to the output <br/>of a<br/>selected bandpass filter to determine the signal level of the first electrical <br/>signal filter<br/>derivative in the corresponding frequency band. The probe may be sequentially<br/>connected to the output of one or more of the bandpass filters to determine <br/>the signal<br/>parameter in question in more or all frequency bands. In this way the <br/>frequency spectrum<br/>of the generated first electrical signal may be determined, or harmonic <br/>distortion may be<br/><br/> CA 02446465 2004-07-28<br/>determined. For example, the test manager may be adapted to connect a selected <br/>probe<br/>for level detection to the output of a bandpass filter that picks out a third <br/>harmonic of the<br/>output of the test stimulus generator for determination of harmonic <br/>distortion.<br/>Signal switches may be provided for connecting a test stimulus generator, such <br/>as a tone<br/>5 generator to the input of the signal processor, and for connecting a probe <br/>to the output of<br/>the signal processor whereby the gain of the signal processor may be <br/>determined.<br/>Further, the gain of the signal processor may be determined as a function of <br/>the<br/>frequency.<br/>Further, the compression of the signal processor, defined as gain as a <br/>function of input<br/>level, may be determined, as a function of frequency.<br/>It is known in the art to include in the hearing aid an adaptive feedback <br/>canceller<br/>comprising an adaptive filter to compensate for acoustic feedback. Acoustic <br/>feedback<br/>may occur in case the input transducer of a hearing aid receives and detects <br/>the acoustic<br/>output signal generated by the output transducer. Amplification of the <br/>detected signal<br/>may lead to generation of a stronger acoustic output signal, which may loop to <br/>the input,<br/>and eventually the hearing aid may oscillate. The adaptive filter estimates <br/>the transfer<br/>function from output to input of the hearing aid including the acoustic <br/>propagation path<br/>from the output transducer to the input transducer. The input of the adaptive <br/>filter is<br/>connected to the output of the hearing aid and the adaptive filter works out <br/>an appropriate<br/>countersignal, which is subtracted from the input transducer signal to cancel <br/>out any<br/>acoustic feedback. A hearing aid of this type is disclosed in US 5,402,496.<br/>The test manager may be adapted to verify operation of the adaptive feedback <br/>canceller.<br/>For example, the test manager may control a signal switch to disconnect the <br/>feedback<br/>canceller from the signal path and increase the gain of the signal processor <br/>until<br/>oscillation occurs. During this test, the hearing aid is preferably placed in <br/>a<br/><br/> CA 02446465 2004-07-28<br/>6<br/>compartment with hard walls. The test manager may further be adapted to <br/>reconnect the<br/>adaptive feedback canceller to the signal path whereby oscillation should <br/>cease if the<br/>adaptive feedback canceller operates correctly.<br/>In an embodiment, the hearing aid comprises a test stimulus generator for <br/>injection of a<br/>digital signal at a selected second point in the digital part of the signal <br/>path of the hearing<br/>aid, which could be at the input of the signal processor.<br/>In response to the signal injected at the second point, a properly functioning <br/>hearing aid<br/>will generate a signal with certain parameter values at the selected first <br/>point in the signal<br/>path. The parameters may relate to frequency, amplitude, spectrum, modulation, <br/>phase,<br/>or the like. These parameter values may be compared to canonic values obtained <br/>by<br/>subjecting a known good hearing aid to a similar test. The test manager may <br/>further be<br/>adapted to compare the parameter values of the actual response signal with the <br/>canonic<br/>values to determine whether the hearing aid is malfunctioning. If a detected <br/>value lies<br/>outside a predetermined range comprising the respective canonic value, it may <br/>be<br/>concluded that the tested hearing aid is malfunctioning. The presence of a <br/>defect may be<br/>signalled to the operator of the hearing aid as previously described.<br/>A self-test procedure may be initiated by user activation of a switch <br/>positioned on the<br/>hearing aid housing, on a hearing aid programming device, on a remote control <br/>unit for<br/>the hearing aid, or on a fitting system, or the like. Preferably two switches <br/>must be<br/>activated simultaneously or sequentially to avoid accidental activation of the <br/>self-test.<br/>Still other objects of the present invention will become apparent to those <br/>skilled in the art<br/>from the following description wherein the invention will be explained in <br/>greater detail.<br/>By way of example, there is shown and described a preferred embodiment of this<br/>invention. As will be realized, the invention is capable of other embodiments, <br/>and its<br/>2 5 details are capable of modification in various, obvious aspects all <br/>without departing from<br/>the invention.<br/><br/> CA 02446465 2004-07-28<br/>7<br/>Brief description of the drawinas.<br/>The invention will now be described in more detail in conjunction with several<br/>embodiments and the accompanying drawings, in which:<br/> Figure 1 shows a blocked schematic of a hearing aid according to the present<br/>invention;<br/>Figures 2-5 show respective self-test messages as displayed on a programming <br/>device<br/>for the hearing aid according to the present invention, and<br/> Figure 6 shows a test set-up according to an embodiment of the invention.<br/>Figure 1 shows a hearing aid 10 having as input transducers two acoustic <br/>microphones<br/>12, 14 and an electromagnetic pick-up coil 16, also referred to as a telecoil. <br/>A signal<br/>switch matrix 18 selectively connects each of the input transducers 12, 14, 16 <br/>to a<br/>selected A/D converter 20, 22. For simplicity, the connections of the output <br/>of the second<br/>A/D converter 22 are not shown. The output signal 24 from A/D converter 20 is <br/>split by<br/>a set 26 of bandpass filters into a set of bandpass filtered signal <br/>derivatives 24,,<br/>242,...,24,,. The processor 28 is divided into a plurality of channels so that <br/>individual<br/>frequency bands may be processed differently, for example, amplified with <br/>different<br/>gains. The processor 28 generates the second electrical signal 30 by <br/>individual processing<br/>of each of the first electrical signal filter derivatives 241, 242,...,24õ and <br/>adding together<br/>the processed electrical signals to provide the second electrical signal 30. A <br/>D/A<br/>converter 32 converts the digital output signal 30 to an analogue signal 34. <br/>An output<br/>transducer 38 converts the analogue signal 34 into sound.<br/>It will be obvious for the person skilled in the art that the circuits <br/>indicated in Figure 1<br/>may be implemented using digital or analogue circuitry or any combination <br/>hereof. In the<br/>present embodiment, digital signal processing is employed and thus, the signal <br/>processor<br/>28 and the filter bank 26 are digital signal processing circuits. In the <br/>present<br/>embodiement, all the digital circuitry of the hearing aid 10 may be <br/>implemented on a<br/>single digital signal processing chip or, the circuitry may be distributed on <br/>a plurality of<br/>integrated circuit chips in another way.<br/><br/> CA 02446465 2004-07-28<br/>8<br/>Signal switches 36,, 362,...,36p are provided at a number of points of the <br/>signal path of the<br/>hearing aid circuitry for connecting a test stimulus or tone generator 40, or <br/>a probe or<br/>level detector 42, to the various points in the signal path of the hearing aid <br/>10. A test<br/>manager 44 controls the settings of the signal switches 36,, 36z,...,36p for <br/>conducting a test<br/>procedure in various sections of the signal path of the hearing aid 10. For <br/>simplicity, the<br/>control lines connecting the test manager 44 with each of the respective <br/>signal switches<br/>361, 362,...,36p are not shown in Figure 1. The test manager 44 further <br/>controls the signal<br/>switch matrix 18 for connecting microphones 12, 14 and pick-up coil 16 to and<br/>disconnecting them from the signal path of the hearing aid 10. Further, the <br/>test manager<br/>44 is adapted to control the test stimulus generator 40. For example, to <br/>generate an<br/>electrical signal of a selected frequency, such as 1 kHz, with a selected <br/>amplitude and/or<br/>frequency modulation, and to control the probe 42 for determination of a <br/>selected signal<br/>parameter, such as the rms value.<br/>The test manager 44 may comprise a memory for the storage of data such as <br/>identification<br/>of the type of hearing aid, calibration data of the transducers and canonic <br/>values of test<br/>parameters.<br/>For example, the noise level in the second frequency band may be determined by <br/>the test<br/>manager 44 by controlling the signal switch matrix 18 to disconnect all of the <br/>input<br/>transducers 12, 14, 16 from the A/D converters 20, 22 and connecting the level <br/>detector<br/>42 to the output 24Z of a bandpass filter 262 . Then, a first one of the <br/>acoustic transducers<br/>is connected to the respective input and the output signal level is <br/>determined.<br/>Subsequently, the first acoustic transducer is disconnected and a second one <br/>of the<br/>acoustic transducers is connected to the respective input and the output <br/>signal level is<br/>determined. The levels may be compared. Assuming a steady noise background, <br/>the<br/>levels should be similar, and thus a difference would signify a calibration <br/>error or a<br/>malfunction in one of the acoustic input transducers or the respective <br/>associated input<br/>stage.<br/><br/> CA 02446465 2004-07-28<br/>9<br/>In a further test stage, the telecoil is connected to its respective A/D <br/>converter 20, 22 and<br/>the output signal 24 level detected. As the telecoil will normally be able to <br/>pick up<br/>electromagnetic background noise, the output signal 24 level may be expected <br/>to be<br/>different from the level without the telecoil. If no difference is <br/>established, it may be<br/>assumed that there is a malfunction in the telecoil or the related input <br/>stage.<br/>In general, the test manager 44 may control the signal switch 36, to connect <br/>the test<br/>stimulus generator 40 to the input of the signal processing circuitry 26, 28 <br/>and<br/>simultaneously disconnect the input from other signal sources, and the signal <br/>switch 364<br/>to connect the probe 42 to the output signal 30 of the signal processor 28 <br/>facilitating test<br/>of any of the signal processing algorithms performed in the signal processing <br/>circuitry 26,<br/>28. For any particular test stimulus to be generated by the test stimulus <br/>generator 40,<br/>canonic values of the output signal obtained by applying a similar test <br/>stimulus to a<br/>known good signal processor may be stored in a memory (not shown) in the <br/>hearing aid<br/>10. Thus, during a test procedure the test manager 44 may compare the <br/>parameters of the<br/>detected output signal 30 of the signal processor 28 with the corresponding <br/>canonic<br/>values in order to determine whether the hearing aid 10 is malfunctioning.<br/>A signal switch 363 for interrupting the path of the signal 30 before the <br/>signal switch 362,<br/>and controlled by the test manager 44 is further provided. Having intercepted <br/>the signal<br/>30, the test manager activates the tone generator 40 to generate a signal of a <br/>selected<br/>frequency, for example, 1 kHz, that is fed to the output transducer 38 of the <br/>hearing aid<br/>10 for conversion into a sound signal. During this test, the hearing aid 10 <br/>will be placed<br/>in a compartment with hard walls so that a substantial part of the generated <br/>acoustic<br/>signal is received by the acoustic input transducers 12, 14. The test manger <br/>44 further<br/>controls signal switch 36, to connect probe 42 to one of the acoustic input <br/>transducers 12,<br/>14 for determination of the signal level of the respective first electrical <br/>signal derivative<br/>in the respective frequency band i.<br/>Reference is now made to Figure 6 for a description of a test set-up according <br/>to an<br/>embodiment of the invention. In this set-up, the hearing aid 10 is connected <br/>to a<br/><br/>CA 02446465 2004-07-28<br/>programming device 50 by way of a cable 53 and placed in an upwards open<br/>compartment 51 with hard walls. The compartment 51 may basically be any<br/>compartment with the capability of reflecting at least part of the transducer <br/>output signal<br/>to the microphone. A cup-like structure of stainless steel in the shape of a <br/>cylinder with<br/>5 open top and a flat, closed bottom, with a diameter of 70 mm, a height of <br/>100 mm and a<br/>wall thickness of 0.3 mm, has been found well suited. The hearing aid 10 is <br/>simply<br/>placed in random orientation on the bottom of the compartment 51.<br/>The self-test is initiated upon reception of a signal 48 from the activation <br/>means 46. The<br/>activation means may be constituted by one or more switches positioned on the <br/>housing<br/>10 of the hearing aid 10 or the activation means 46 may comprise interface <br/>means that is<br/>adapted to receive a command 49 for initiation of the self-test from an <br/>external device,<br/>such as a remote control unit, a hearing aid programming device 50, a fitting <br/>device, a<br/>personal computer, or the like.<br/>For example, the hearing aid 10 may be connected to a hearing aid programming <br/>device<br/>50 with a display 52. The operator may initiate the self-test by pressing a <br/>specific key or<br/>set of keys 54 on the programming device 50. Then the device 50 displays that <br/>it is ready<br/>to perform a self-test procedure as shown in Figure 2. The self-test is then <br/>launched upon<br/>activation of key 56. The programming device transmits a corresponding command <br/>to the<br/>activation means 46 of the hearing aid 10 and indicates that the self-test is <br/>in progress as<br/>shown in Figure 3.<br/>During the test, messages may be displayed on the display 52. The messages may <br/>call for<br/>user interaction. For example, the test described in the previous section may <br/>reveal that<br/>the signal picked up by one of the microphones 12, 14 is lacking. A probable <br/>cause may<br/>be that the input port to the respective microphone has been occluded by ear <br/>wax. Thus<br/>the operator is asked to check if this is the problem see Figure 4. If no <br/>problems have<br/>been revealed during the self-test, a corresponding message is displayed, as <br/>shown in<br/>Figure 5.<br/><br/> CA 02446465 2004-07-28<br/>11<br/>The input transducer connected to the signal path may be the pick-up coil 16. <br/>The pick-<br/>up coil 16 in the hearing aid 10 may be tested like an acoustic input <br/>transducer 12, 14,<br/>since the output transducer 38 typically generates a significant magnetic <br/>field that may be<br/>picked up by the pick-up coil 16.<br/>The test manager 44 controls the signal switch matrix 18 to disconnect all of <br/>the input<br/>transducers 12, 14, 16 from the signal path, and connects the test stimulus <br/>generator 40 to<br/>the signal path through signal switch 36,. The probe 42 is connected to the <br/>output 30 of<br/>the signal processor 28 through signal switch 364. By controlling the test <br/>stimulus<br/>generator 40 to generate a sequence of signals with different frequencies, the <br/>gain of the<br/>signal processor 28 is determined as a function of the frequency.<br/>Further, the compression of the signal processor 28, defined as gain as a <br/>function of input<br/>level, may be determined as a function of frequency.<br/>
