A method and a system for generation of a calibrated sound field

CA 02396873 2010-07-07

METHOD AND A SYSTEM FOR GENERATION OF A CALIBRATED SOUND FIELD

FIELD OF THE INVENTION

The present invention generally relates to auditory prostheses. The 5 invention more particularly relates to a method and a system for calibration of a sound field. The invention still more particularly relates to an auditory prosthesis, a method and a system to be used during fine-tuning of an auditory prosthesis.

BACKGROUND OF THE INVENTION

An auditory prosthesis, such as a hearing aid, is typically fine-tuned to an individual user by placing the user with the auditory prosthesis in an auditory test room in which various sound fields are generated from a sound source. Each of the sound fields corresponds to a sound field occurring in a real life sound environment, such as in a concert hall, in an environment with party noise, with traffic noise, with no background noise, etc, etc. It is the object of the fine-tuning procedure to adjust the auditory prosthesis in such a way that the user's hearing loss is compensated as well as possible in similar real life sound environments.

hi order to perform the required auditory measurements accurately during auditory prosthesis fine-tuning, the test room and the auditory fine-tuning equipment must be calibrated to provide a predetermined sound field at the position of the user. It is well known that sound pressure in sound fields generated with equipment that is not calibrated may vary significantly. Many dispensers of hearing aids constitute rather small entities for which investment in calibration equipment represents a significant burden.

EP-A-0 341 995 discloses an auditory prostheses having a microphone, a signal processor, a signal output and an output transducer. The calibration device comprises a memory for storing information characteristic of information intrinsic to the individual auditory prosthesis and representing either a sufficient set of adjustment parameters for calculation of the transfer function of the auditory prosthesis or manufacturing information.

CA 02396873 2010-07-07

WO-A-9948323 relates to a hearing aid fitting method comprising selection of loudness levels for a plurality of frequencies and comparing each loudness level for each frequency for perceived sameness.

The present invention provides a method and a system for generation of a calibrated sound field that reduces calibration equipment requirements without substantially compromising calibration accuracy.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided an auditory prosthesis comprising: a microphone for transforming an acoustic input signal into a microphone signal; a processor with a processor output, the processor being adapted for providing at the processor output a hearing loss compensation signal; an output transducer for transforming the hearing loss compensation signal into an acoustic output signal; and a measuring signal output for providing a sound level signal other than the acoustic output signal and determined on the basis of the microphone signal.

Hearing defects may typically vary as a function of frequency in a way that is different for each individual user.

To take account of this, an advantageous embodiment of the auditory prosthesis of the invention may he provided, where the auditory prosthesis further comprises a filter bank in the signal processor connected with the microphone to receive the microphone signal therefrom, said filter bank having bandpass filters for dividing the microphone signal into a set of bandpass filtered microphone signals, wherein the signal processor is adapted to generate the processor output signal by individually processing each of the bandpass filtered microphone signals, summing the processed signals to form the processor output signal and determine sound pressures based on the set of bandpass filtered microphone signals.

According to an aspect of the present invention there is provided an auditory prosthesis that can be used in the calibration of sound fields, comprising a microphone for transforming an acoustic input signal into a microphone signal; a signal processor with a processor output, the signal processor being adapted for providing at the processor output a hearing loss compensation signal; an output transducer for

CA 02396873 2010-07-07 transforming the hearing loss compensation signal into an acoustic output signal; a memory for storage of sensitivity values of the microphone, and a pre-adjustment circuit for providing pre-adjustment of the microphone signal in order to provide a calibrated microphone signal; wherein the signal processor is further adapted to determine sound pressures based on the microphone signal, and to output through a signal output a set of sound pressure signals other than the acoustic output signal, the set of sound pressure signals representing the respective determined sound pressures to the exterior of the auditory prosthesis.

Hereby, selective calibration of the equipment for sound field generation in each of the frequency bands of the auditory prosthesis is facilitated. Further, a prosthesis according to the present invention may reduce sound pressure variations, e.g. from app. 20 dB to app. 2 dB. Typically, a 2 dB sound pressure ambiguity is sufficiently accurate for the purpose of performing an optimum fine-tuning of an auditory prosthesis.

In a preferred embodiment of the present invention, a calibration of the microphone of the auditory prosthesis is performed for determination of sensitivity values of the microphone, and the determined sensitivity values are stored in the memory. Calibration of the sound field with an auditory prosthesis according to this embodiment is substantially as accurate as the calibration accuracy of the microphone.

A method for generation of a calibrated sound field, comprising the steps of positioning in a test space a sound signal generator and an auditory prosthesis that can be used in the calibration of sound fields, the auditory prostheses having a microphone responsive to sound in the test space, a signal processor, and an output transducer for generating a sound output, operating the sound signal generator to generate a sound field in the test space, the signal processor determines sound pressures based on the microphone signal, and outputs through a signal output a set of sound pressure signals other than the acoustic output signal, the set of sound pressure signals representing the respective determined sound pressures to the exterior of the auditory prosthesis, and feeding the sound level signal to a controller in order that the controller may modify the generated sound field based on the sound level signal as appropriate to generate a calibrated sound field in the test space.

CA 02396873 2010-07-07

In a preferred embodiment of the method, the step of positioning further comprises the steps of positioning the auditory prosthesis in the ear of a user situated in the test space.

When the auditory prosthesis is positioned in the ear of a user who is situated in the test space during sound field calibration, the need for a manikin or a test dummy, an occluded ear simulator, etc, is eliminated.

The method may further comprise the step of modifying the generated sound field based on the generated set of sound pressure signals whereby a calibrated sound field is generated. Thus, in the method the step of generating a sound field may comprise the steps of providing a sound signal, modifying the sound signal according to a set of control parameters to provide a modified sound signal, and transforming the modified sound signal into a sound field in the test space. The method may further comprise the steps of supplying the set of sound pressure signals to a controller for calculation of new values of the set of control parameters for modification of the sound signal.

A method for generation of a calibrated sound field, comprising the steps of positioning in a test space a sound signal generator and an auditory prosthesis that can be used in the generation of sound fields, the auditory prostheses having a microphone responsive to sound in the test space, a signal processor, and an output transducer for generating a sound output, operating the sound signal generator to generate a sound field in the test space, the signal processor determines sound pressures based on the microphone signal, and outputs through a signal output a set of sound pressure signals other than the acoustic output signal, the set of sound pressure signals representing the respective determined sound pressures to the exterior of the auditory prosthesis, and feeding the sound level signal to a controller in order that the controller may modify the generated sound field based on the sound level signal as appropriate to generate a calibrated sound field in the test space, and storing microphone sensitivity values as specified by the manufacturer of the microphone, and determining the sound level signal based on the stored sensitivity values.

A method for generation of a calibrated sound field, comprising the steps of positioning in a test space a sound signal generator and an auditory prosthesis that can

CA 02396873 2010-07-07 be used in the generation of sound fields, the auditory prostheses having a microphone responsive to sound in the test space, a signal processor, and an output transducer for generating a sound output, operating the sound signal generator to generate a sound field in the test space, the signal processor determines sound pressures based on the microphone signal, and outputs through a signal output a set of sound pressure signals other than the acoustic output signal, the set of sound pressure signals representing the respective determined sound pressures to the exterior of the auditory prosthesis, feeding the sound level signal to a controller in order that the controller may modify the generated sound field based on the sound level signal as appropriate to generate a calibrated sound field in the test space, and storing microphone sensitivity values as specified by the manufacturer of the microphone, and determining the sound level signal based on the stored sensitivity values.

It is not required to calibrate the sound field generating equipment before every fine-tuning of an auditory prosthesis to a user. Typically, it is sufficient to calibrate at regular intervals, e.g. during the first fine-tuning of a working day. However, when the sound field is calibrated with the auditory prosthesis worn by the user to whom the auditory prosthesis is subsequently fine-tuned, the additional advantage is obtained that the sound field is calibrated at the position of the auditory prosthesis during fine-tuning whereby ambiguity of sound pressure at the auditory prosthesis during fine-tuning is minimized.

The auditory prosthesis may be a hearing aid that is adapted to be programmed by an external programming device and to be connected to the programming device with a programming cable. Preferably, the signal output is also adapted to be connected to the programming cable, in order that the set of sound level signals can be supplied to the controller via the programming cable.

The auditory prosthesis may further comprise a wireless communication link for reception of the set of sound pressure signals from the signal processor and for transmission of corresponding respective signals.

The sound signal may be generated by reproduction of a signal recorded in a storage medium.

CA 02396873 2010-07-07

The controller may be comprised in a personal computer comprising a memory for storage of the control parameters together with a computer programme for calculation of the control parameters, the computer further comprising input means for receiving the set of sound pressure signals.

According to a still further aspect of the present invention, there is provided a system for generation of a calibrated sound field, comprising a sound signal generator for generation of a sound signal, a sound signal modifier adapted to modify the sound signal in accordance with a set of control parameters for provision of a modified sound signal, a sound transducer for transforming the modified sound signal into a sound field in a test space, an auditory prosthesis that can be used in the generation of sound fields, and a controller, wherein the auditory prostheses has a microphone for transforming an acoustic input signal into a microphone signal, a signal processor with a processor output and a measuring signal output, and a transducer responsive to the processor output for generating a compensated acoustic output to the ear of a wearer of the auditory prosthesis, wherein the signal processor is further adapted to determine sound pressures based on the microphone signal, and to output a set of sound pressure signals other than the acoustic output signal, the set of sound pressure signals representing the respective determined sound pressures to the exterior of the auditory prosthesis, and wherein the controller is adapted to receive the sound level signal and to calculate a new set of control parameters based on the sound level signal.

An auditory prosthesis that can be used in the generation of sound fields, comprising a microphone for transforming an acoustic input signal into a microphone signal; a signal processor provided with a processor output and a filter bank; a transducer for providing a sound output to a user, and a measuring signal output, wherein the filter bank has bandpass filters for dividing the microphone signal into a set of bandpass filtered microphone signal derivatives, and wherein the signal processor is further adapted to determine sound pressures based on the microphone signal, and to output through a signal output a set of sound pressure signals other than the acoustic output signal, the set of sound pressure signals representing the respective determined sound pressures to the exterior of the auditory prosthesis.

CA 02396873 2010-07-07

6a

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail in conjunction with several embodiments and the accompanying drawings, in which:

Fig. 1 is a block diagram of a prior art system for generation of a calibrated sound field,

Fig. 2 is a block diagram of a first embodiment of the present invention,

Fig 3 is a block diagram of a second embodiment of the present invention,

Fig. 4 is a block diagram of an embodiment of a hearing aid according to the present invention,

Fig. 5 is a block diagram of an embodiment of the signal processor of a hearing aid according to the present invention,

Fig. 6 is a block diagram of a signal processor of the hearing aid shown in Fig.

or 3,

Fig. 7 is a block diagram of another signal processor of the hearing aid shown in Fig. 2 or 3, and

Fig. 8 is a block diagram of a hearing aid according to the present invention comprising a multichannel signal processor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF

THE INVENTION

A prior art sound field calibration system is shown in Fig. 1. A sound signal generator 1 generates a sound signal that is supplied to a sound signal modifier 2 wherein the level of the sound signal is modified as a function of frequency in accordance with a set of control parameters stored in a memory, not illustrated, in the sound signal modifier 2. The modified sound signal obtained from the signal modifier 2 is converted by a loudspeaker 3 into a sound field in a test space T.

The sound field is monitored in at least one observation point within the test space T by measuring means 4 comprising a precision calibrated microphone.

CA 02396873 2006-11-23

The measuring signal obtained from measuring means 4, including level and/or frequency spectrum information, is supplied to control means comprising a signal analyser 5 for derivation of data representing the sound characteristic of the sound field in the test space, from where the data are supplied to a control parameter calculator 6 for calculation of a new set of control parameters for use in the signal modifier 2.

In the embodiment of the present invention shown in Fig. 2, the sound signal generator 1, the signal modifier 2, and the control means including the measuring signal analyser 5 and the control parameter calculator 6 of the system illustrated in Fig. 1 have been combined into a computing device 7, such as a personal computer, comprising memory means 8, such as a hard disc, a keyboard 9, a display screen 10, and a sound interface that is connected with loudspeakers 3 for conversion of the sound signal into a sound field in the test space T.

As further shown in Fig. 2 and in accordance with the invention, monitoring of the sound field in the test space T is performed by a microphone positioned in a hearing aid that is carried by a user 13 who is seated in the test space

T. The measuring signal obtained from one of or both of the hearing aids 14 is transmitted to the computer 7 through a cable 15, preferably the programming cable 15 that is connected to a programming device 11 for programming of the hearing aid to suit various sound environments or listening situations by a computer assisted fine-tuning procedure.

Thereby the sound field calibration of the test space T and the fine-tuning procedure may be combined into a single sequential operation using the same computer system 7 for the sound field calibration of the test space and for the finetuning procedure.

In an alternative embodiment of the present invention shown in Fig. 3, the measuring signal obtained from the hearing aids 14' is supplied to the computer 7 by wireless transmission means, such as IR or radio transmission from transmitters, not shown, integrated in each hearing aid 14', to an antenna 16 connected with a receiver 17 that is also connected to the cable 15.

CA 02396873 2002-12-27

In order to avoid possible discomfort to a user 13 during the calibration procedure, a pre-adjustment of the sound signal may be performed prior to calibration. During the pre-adjustment the hearing aid is positioned at the observation point in the test space T without being carried by the user whereby the need for adjustment of the sound signal during calibration is minimised in order to minimise possible user discomfort.

In the simplified block diagram shown in Fig. 4, a hearing aid 14 for use in the implementation of the calibration method and system according to the invention comprises at least one microphone 18 connected with a signal processor

19, preferably comprising programmable signal processing parts, such as bandpass filters and amplifiers, from which a processor output signal is supplied to an output transducer 20, such as a hearing aid receiver.

It will be obvious for the person skilled in the art that the circuits shown in Fig. 4 may be realised using digital or analogue circuitry or any combination hereof. In the present embodiment, digital signal processing is employed and thus, the processor 19 comprises digital signal processing circuits. In the present embodiment, all the digital circuitry of the hearing aid may be provided on a single digital signal processing chip, or, the circuitry may be distributed on a plurality of integrated circuit chips in any appropriate way.

According to the invention, the hearing aid 14 also comprises interface means that is connected to the signal processor 19 for outputting the processor output signal. The interface means may comprise a coupling terminal 21 for connection with the cable 15 as shown in Fig. 2, and the interface means may comprise wireless interface means as illustrated in Fig. 3.

In a programmable hearing aid according to the present invention, a bidirectional communication link may be provided between the signal processor 19 and the computer 7 as shown in Figs. 2 and 3. Thus, data may flow in both directions in signal line 15 shown in Figs. 2 and 3. For a non-programmable hearing aid, it is sufficient to provide a unidirectional communication link between the processor 19 and the computer 7 for transmission of the measuring signal to the

CA 02396873 2006-11-23 computer 7 for use in the calculation of calibration control parameters.

As shown in Fig. 5, the signal processor 19 comprises a sound pressure level signal generator 22 that is connected to the coupling terminal 21 for generation of the measuring signal. In a programmable hearing aid, the sound pressure level signal generator may also serve as input/output interface for communication of programming data between the signal processor 19 and the programming computer.

As further illustrated in Fig. 6, the sound pressure level signal generator 22 may comprise an A/D converter 23 for provision of a digital measuring signal for use in further signal processing in the processor 19, as indicated by line 24, and for use in the calibration of the sound field.

The measuring signal may be provided directly from the A/D converter 23 to the interface means, e.g. the coupling terminal 21 as shown by the solid line 25, or, it may be further processed, e.g. averaged values may be calculated, and provided to the interface means. In another embodiment of the invention, a digital RMSaveraged signal is formed in a RMS-detector 26 and supplied to the interface means, e.g. the coupling terminal 21, via the dashed line 27.

As shown in Fig. 7, the sound pressure level signal generator 22 may also include a pre-adjustment circuit 28 that is interconnected between the A/D converter 23 and the RMS detector 26 to provide pre-adjustment of the digital microphone signal into a calibrated microphone signal. The pre-adjustment circuit 28 comprises a memory for storing sensitivity values, such as sound pressure level sensitivity values, of the microphone defining ratios of electronic microphone signal amplitude to sound pressure at the microphone. Typically, a set of sensitivity values is stored for a set of respective frequency ranges, and the stored sensitivity values are used in the determination of sound pressure. The sensitivity values specified on the data sheet provided by the manufacturer of the microphone may be stored in the memory, or, sensitivity values as determined by a calibration measurement of the microphone 18 may be stored in the memory.

In the embodiment of the present invention shown in Fig. 7, the measuring

CA 02396873 2010-07-07 signal obtained from the RMS detector 26 is supplied to a transmitter 29 feeding an antenna 30 positioned at the hearing aid 14,14’ for wireless transmission of the measuring signal to the antenna 16 and the receiver 17 shown in Fig. 3.

Although the hearing aid 14, 14’ in Figs. 4-7 is illustrated as a single channel hearing aid, it should be understood that a hearing aid 14,14’ according to the present invention may contain any appropriate number of channels. A multichannel hearing aid according to the present invention, as shown in Fig. 8, comprises a multichannel processor 31 wherein a digital microphone signal supplied by the A/D converter 32 is filtered by adjustable band pass filters 33, 34, and 35 into, e.g. a high frequency signal, an intermediate signal and a low frequency signal. The filtered digital signals are further processed in separate processing channels of the signal processor 31. Obviously, any number of channels may be provided in the hearing aid 14,14’. The hearing aid may comprise an RMS detector 36 that is also divided into separate processing channels for individually processing of the output signals from the band-pass filters. In the embodiment of the present invention shown in Fig. 8, the measuring signal obtained from the RMS detector 36 is supplied to a transmitter 37 feeding an antenna 38. The individually processed signals are transmitted to the computer 7 for adjustment of the control parameters.