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