WO2010015027A1

WO2010015027A1 - Sound processor for fluctuating hearing

Info

Publication number: WO2010015027A1
Application number: PCT/AU2009/000996
Authority: WO
Inventors: Peter Blamey
Original assignee: Peter Blamey
Priority date: 2008-08-06
Filing date: 2009-08-04
Publication date: 2010-02-11

Abstract

In one embodiment, a device for processing sound includes a means for acquiring an input sound signal; a means for amplifying the signal with gain under the control of a control module in accordance with a set of control parameters; a means for setting, storing, and adjusting at least two sets of control parameters suitable for a "good hearing day" when hearing is a maximum and a "bad hearing day" when hearing is at a minimum; one or more continuously variable means for interpolating and extrapolating a set of control parameters from the "good hearing day" and "bad hearing day" fittings; a means for setting the control module parameters to the interpolated or extrapolated set of control parameters; and a means of converting the amplified input sound to an acoustic output signal. The device allows a user with fluctuating hearing loss to easily adapt the fitting of the device to an arbitrary "bad hearing day" fitting, an arbitrary "good hearing day" fitting or any fitting in between. The apparatus may be implemented in dedicated hardware embodiment or by software running on a microprocessor.

Description

SOUND PROCESSOR FOR FLUCTUATING HEARING

Field of the Invention:

The present invention relates to sound processing devices for people with impaired hearing that may change over a timescale that is measured in hours, days, weeks, or months rather than years, which is more common. These are devices in which an acoustic sound input or an electric or digital representation of an acoustic sound input is processed and converted to an acoustic sound output to improve speech intelligibility, sound quality and/or naturalness of the sound. Sound processing devices are often used in hearing aids, assistive listening devices (ALD), and consumer audio devices such as radios, television sets, CD players, MP3 players, stereo systems, headsets, telephones, and mobile phone handsets. The Global Medical Device Nomenclature Agency

(GMDNS) definition of an ALD is an amplifying device, other than a hearing aid, for use by a hard of hearing person.

Background of the invention: Sound processing devices for people with impaired hearing are commonly customised or fitted to suit their individual hearing loss. This is often a time consuming process and may also be expensive if it is carried out by a professional person with specialized skills. It is impractical for a person whose hearing fluctuates on a relatively short time-scale to use conventional fitting techniques to compensate for their changing hearing. The options currently available to these people are to use a volume control, to select from amongst a variety of program settings stored in their hearing aid, or to select from a variety of different devices. None of these alternatives is completely satisfactory because they provide relatively crude approximations to the changes that may be required to compensate optimally for the changes in hearing that are taking place.

Customization or fitting of hearing aids is typically carried out by a professional person with specialized skills, and the results of the customization are stored as control parameters in the hearing aid. Typically, an initial fitting is based on audiometric measures of the client's hearing thresholds at multiple frequencies in the range 125 Hz to 8 kHz, and then the fitting is fine-tuned to more closely accommodate the client's preferences, individual differences in the acoustic properties of the ear, hearing needs, and usual acoustic environments. The fitting process may take several sessions and a total of several hours to achieve an acceptable fitting. There may be several fittings or programs in the hearing aid, for listening in quiet, in noisy situations, for music, for the telephone, etc.

Fittings are usually characterized by a set of parameters derived from the hearing loss and individually adjusted for the client. For example, a multichannel wide dynamic range compression hearing aid fitting (WDRC) may be characterized by the prescribed gain for sounds with particular input levels, such as 50, 70, and 90 dB SPL in each frequency channel. Another way of characterizing a WDRC fitting would be to specify the gains, kneepoints, and compression ratios in each frequency channel. See Dillon 2001 for further details of WDRC systems and fittings. In another example of an adaptive dynamic range optimization hearing aid fitting (ADRO), the parameters consist of the maximum output levels, comfort targets, audibility targets, and maximum gains in each frequency channel. See Blarney et al (US patent 6,731 ,767) for a description of an adaptive dynamic range optimization sound processor.

Typically, assistive listening devices are not fine-tuned to the hearing loss of the user.

However, there may be a selection of settings designed to compensate for hearing losses of various shapes (such as flat, gently sloping, steeply sloping) and degrees (such as mild, moderate, and severe hearing loss) and a volume control. Typically, the setting selection is made once and not changed thereafter.

Some people suffer from fluctuating hearing thresholds, and thus the normal fitting procedures based on a single measure of hearing thresholds on a particular day are unlikely to provide a fitting that is optimal on days when the hearing is different. Fluctuating hearing loss may arise from a variety of causes, such as Meniere's disease which affects the static pressure of fluid in the cochlea, which in turn can affect the resting position of the basilar membrane and the threshold of neural excitation arising from the motion of the basilar membrane in response to a sound. Another common cause of fluctuating hearing loss is middle-ear disease which affects the efficiency of conduction of sound from the ear drum to the cochlea. Figure 2 shows an example of the hearing thresholds for a person with Meniere's disease observed on different days. It should be noted that in this case, the fluctuation is not just a uniform raising or lowering of thresholds by an equal amount at each frequency, and therefore a volume control that adjusts intensity by a uniform amount at each frequency and each input level will not compensate adequately for these fluctuations.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.

Throughout this specification the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

Summary of the invention: According to a first aspect the present invention provides a method for customizing and controlling a sound processing device for a person with fluctuating hearing, the method comprising: providing at least one fitting of the device that is suitable for a "good hearing day" when hearing is at a maximum and at least one other fitting that is suitable for a "bad hearing day" when hearing is at a minimum; setting, storing, and adjusting the at least two fittings; providing a calculation that interpolates between the "good hearing" and "bad hearing" fittings and extrapolates beyond these fittings; selecting an interpolated or extrapolated fitting by means of at least one continuously variable control mechanism; and controlling the operation of the sound processing device in accordance with the interpolated or extrapolated fitting.

According to a second aspect the present invention provides a sound processing device suitable for a person with fluctuating hearing, the sound processing device comprising: a means of acquiring an input sound signal; an amplifier with gain under the control of a control module; a control module that controls the gain and the output of the device in accordance with a set of control parameters; a means for setting, storing, and adjusting at least two sets of control parameters suitable for a "good hearing day" when hearing is a maximum and a "bad hearing day" when hearing is at a minimum; one or more continuously variable means for interpolating and extrapolating a set of control parameters from the "good hearing day" and "bad hearing day" fittings; a means for setting the control module parameters to the interpolated or extrapolated set of control parameters; and a means of converting the amplified input sound to an acoustic output signal.

According to a third aspect the present invention provides a computer program product comprising computer program code means to make a computer execute a sound processing procedure suitable for a person with fluctuating hearing, the computer program product comprising: computer program means for acquiring an input sound signal; computer program means for providing amplification of the signal with gain under the control of a control module; computer program means for controlling the gain and the output of the device in accordance with a set of control parameters; computer program means for setting, storing, and adjusting at least two sets of control parameters suitable for a "good hearing day" when hearing is a maximum and a "bad hearing day" when hearing is at a minimum; computer program means for interpolating and extrapolating a set of control parameters from the "good hearing day" and "bad hearing day" fittings; computer program means for setting the computer control module parameters to the interpolated or extrapolated set of control parameters; and computer program means for converting the amplified input sound signal into an acoustic output signal.

The amplifier and control module preferably comprise a conventional WDRC or ADRO sound amplifier with gain control modified to accept continuously varying settings from the interpolation and extrapolation module.

The appropriate settings for the "good hearing day" fitting and the "bad hearing day" fitting are preferably determined by conventional fitting of the device on days when the device user feels that their hearing capability is at a maximum and when their hearing capability is at a minimum respectively. It is not usually predictable when the device user will experience "good hearing days" or "bad hearing days" so it is preferable that means should be provided for self-fitting or adjustment of the fittings on "good hearing days" and "bad hearing days" by the device user without the need for professional intervention or assistance. When the device user prefers a setting of the interpolation and extrapolation control to a value that extrapolates beyond the "good hearing day" setting it is likely that they are experiencing an extremely "good hearing day" and it may be appropriate to adjust the "good hearing day" fitting. Conversely, when the device user prefers a setting of the interpolation and extrapolation control to a value that extrapolates beyond the "bad hearing day" setting it is likely that they are experiencing an extremely "bad hearing day" and it may be appropriate to adjust the "bad hearing day" fitting.

The interpolation and extrapolation control module preferably interpolates and extrapolates all sound processing settings in the device that are different between the "good hearing day" and "bad hearing day" fittings. Preferably, these include settings for the amplification module (e.g.

WDRC or ADRO), limiting settings for loud sounds (e.g. Maximum Power Output), noise reduction settings, feedback canceller settings, etc. It is possible that some of these settings may not be continuously variable, and in this case, the interpolation and extrapolation control module may need additional information, such as the setting of the interpolation and extrapolation control at which the non-continuous control settings change from the "good hearing day" setting to the "bad hearing day" setting.

If the sound processor contains programs for special situations such as listening to music, speech in noise, telephone, etc, the special settings for these situations are preferably derived by interpolation or extrapolation from the "good hearing day" and "bad hearing day" fittings for these special situations. Alternatively a fixed "offset" may be applied to the interpolated "general purpose" program settings to derive the "special purpose" program settings.

By means of a physical control on the device, the device user can interactively optimize the performance of the device according to whether they are experiencing a "good hearing day", a "bad hearing day", or anything in between or slightly beyond this range of hearing capabilities.

Brief description of the drawings:

Figure 1 illustrates a block diagram for a sound processor for fluctuating hearing.

Figure 2 illustrates hearing thresholds measured on different days for a person with Meniere's disease (McNeill & Blarney, in preparation)

Figure 3 is a flow diagram illustrating one embodiment of the interpolation and extrapolation process.

Figure 4 is a flow diagram illustrating a second embodiment of the interpolation and extrapolation process. Figure 5 is a flow diagram illustrating a third embodiment of the interpolation and extrapolation process.

Figure 6 is a flow diagram illustrating one embodiment of the fitting and adjustment process.

Description of the preferred embodiments: Figure 1 illustrates a device architecture for sound signal processing incorporating the invention for fluctuating hearing. One or more input signals 101 are passed to a sound processor 102. The input signals are usually provided by one or more microphones or by signals transmitted from a remote microphone as in a telephone for example or from a signal store as in an MP3 player for example. The sound processor 102 amplifies and otherwise processes the sound signals under the control of the control module 105. In one embodiment of the present invention, the sound processor 102 is a wide dynamic range compression processor (WDRC) and the control module 105 determines the gains applied in each frequency channel of the sound processor according to parameter values set in the control module. These parameters may represent the gains to be applied as a function of signal intensity in each channel, or equivalently they may represent the kneepoints and compression ratios of the input/output function to be applied in each frequency channel. In another embodiment of the present invention, the sound processor 102 is an adaptive dynamic range optimization processor (ADRO) and the control module 105 determines the gains applied in each frequency channel of the sound processor according to parameter values set in the control module. These parameters may represent the maximum output levels, comfort targets, audibility targets and maximum gains to be applied in each frequency channel. Additional parameters may be applied by the control module 105 if the sound processor 102 includes noise reduction, feedback cancellation, and/or other sound processing algorithms. The control module

105 may optionally apply adaptive processing parameters according to information passed from the sound processing module 102 to the control module 105. See Blarney et al 2004 for a description of a sound processor with adaptive processing parameters. The sound signal passes from the sound processor 102 via an optional volume control 103 to one or more output signals 104. The function of the volume control 103 is to give the user a physical means to control the final loudness of the output signal(s). The output signals 104 are usually converted to sound or transmitted to a remote location where they are converted to sound by a loudspeaker or similar transducer. The parameter values in the control module 105 are set by the interpolation and extrapolation module 106 which accepts a control signal from a physical interpolation control 107. The interpolation control may be a potentiometer, a switch, or other physical means whereby the device user may indicate that they wish to change the value of the device settings towards or away from the "good hearing day" settings. The interpolation and extrapolation module 106 has access to one or more "good hearing day" fittings 108 and one or more "bad hearing day" fittings 109 which include values for all of the parameter settings used by the control module 105 and are suitable for processing sounds according the device user's hearing capabilities on "good hearing days" and "bad hearing days" respectively. If there are more than one fittings of each type, the interpolation and extrapolation module also has access to program select information 110 that determines which set of fitting parameters id to be used. Interpolation and extrapolation module 106 combines the information from the physical interpolation control 107, the fittings 108 and 109, and the program selection 110 to calculate the settings for the control module 105. By this means the device user may interactively optimize the performance of the sound processor according to whether they are experiencing a "good hearing day", a "bad hearing day" or anything in between or slightly beyond this range of fluctuation.

Figure 2 illustrates a hypothetical example of the audiograms representing the hearing of a person with a fluctuating hearing loss on a "good hearing day" 201, a "bad hearing day" 202, and on an intermediate hearing day. The "good hearing day" fitting 108 comprises suitable hearing aid fitting parameters for the hearing loss represented by the threshold curve 201 and the "bad hearing day" fitting 109 comprises hearing aid fitting parameters suitable for the hearing loss represented by the audiogram curve 202. By interpolating between these two sets of fitting parameters 108 and 109, the device user can set the device to a fitting suitable for the intermediate threshold curve 203.

Figure 3 illustrates the steps carried out by the interpolation and extrapolation module in one preferred embodiment of the invention. In step 301, the device checks at regular intervals to see whether the interpolation and extrapolation control 107 has changed since it was last checked. If the control has not changed, no further action is taken. If the control has changed, its value is read at step 303 and converted to a number I such that I is greater than or equal to -0.1 and I is less than or equal to 1.1. The value 1 = 0 corresponds to a "bad hearing day" and the value I = I corresponds to a "good hearing day". At step 305, a counter J is set to zero. This counter will step through each of the parameters that is to be interpolated or extrapolated. At step 306, the value of J is compared with N, the number of parameters to be interpolated or extrapolated. If J is greater or equal to N, no further action is taken. If J is less than N, then V_GJ, the value of the J* parameter for the "good hearing day" fitting is read from the device memory at step 307. At step 308, V_Bj, the value of the J* parameter for the "bad hearing day" fitting is read from the device memory. At step 309, Vj, the interpolated value of the J* parameter is calculated using the formula v_J = v_GJ * i + v_BJ * (i-i) At step 312, the value Vj is passed to the control module 105 to be used in the subsequent sound processing. At step 313, the value of J is incremented, and the process repeats from step 306.

Figure 4 illustrates the steps carried out by the interpolation and extrapolation module in a second preferred embodiment of the invention. In this embodiment, there is more than one "good hearing day" program or fitting and more than one "bad hearing day" program or fitting. In step 401, the device checks at regular intervals to see whether the interpolation and extrapolation control 107 has changed since it was last checked. If the control has not changed, then the device checks to see whether the device user has changed the program in step 402. If the device user has not changed the program or the interpolation and extrapolation control, then no further action is taken. If the control has changed or the program has been changed, the interpolation value is read at step 403 and converted to a number I such that I is greater than or equal to -0.1 and I is less than or equal to 1.1. The value 1 = 0 corresponds to a "bad hearing day" and the value I = I corresponds to a "good hearing day". The program number, P, is read at step 404. At step 405, a counter J is set to zero. This counter will step through each of the parameters that is to be interpolated or extrapolated. At step 406, the value of J is compared with N_P, the number of parameters to be interpolated or extrapolated in program P. If J is greater or equal to N_P, no further action is taken. If J is less than N_P, then V_Gpj, the value of the J^Λ parameter for the "good hearing day" fitting in program P is read from the device memory at step 407. At step 408, V_Bpj, the value of the J* parameter for the "bad hearing day" fitting in program P is read from the device memory. At step 409, Vj, the interpolated value of the J* parameter is calculated using the formula

(1 -I) At step 412, the value Vj is passed to the control module 105 to be used in the subsequent sound processing. At step 413, the value of J is incremented, and the process repeats from step 406.

Figure 5 illustrates the steps carried out by the interpolation and extrapolation module in a third preferred embodiment of the invention. In this embodiment, there is only one "good hearing day" fitting and only one "bad hearing day" fitting. Parameters for special situations or programs are derived from the "general purpose" program by adding fixed offsets to the interpolated fitting parameters. In step 501, the device checks at regular intervals to see whether the interpolation and extrapolation control 107 has changed since it was last checked. If the control has not changed, then the device checks to see whether the device user has changed the program in step 502. If the device user has not changed the program or the interpolation and extrapolation control, then no further action is taken. If the control has changed or the program has been changed, the interpolation value is read at step 503 and converted to a number I such that I is greater than or equal to -0.1 and I is less than or equal to 1.1. The value 1 = 0 corresponds to a "bad hearing day" and the value I = I corresponds to a "good hearing day". The program number, P, is read at step 504. At step 505, a counter J is set to zero. This counter will step through each of the parameters that is to be interpolated or extrapolated. At step 506, the value of J is compared with N, the number of parameters to be interpolated or extrapolated. If J is greater or equal to N, no further action is taken. If J is less than N, then V_Gj, the value of the J* parameter for the "good hearing day" fitting in the "general purpose" program is read from the device memory at step 507. At step 508, Vj_3J, the value of the J* parameter for the "bad hearing day" fitting in the "general purpose" program is read from the device memory. At step 509, O_PJ, the offset value for parameter J in program P is read from the device memory. At step 510, Vj, the interpolated value of the J* parameter is calculated using the formula

V_J = V_GJ * I + V_BJ * (1 -I) + O_PJ At step 512, the value Vj is passed to the control module 105 to be used in the subsequent sound processing. At step 513, the value of J is incremented, and the process repeats from step 506.

Figure 6 illustrates a process that may be used to alert the device user that it may be advantageous to refit the device. To enable this process, the interpolation control is checked at regular intervals at step 601. If the interpolation control is not at one of its extreme values, the a timer is set to zero at step 602. If the interpolation control is at one of its extreme values, the timer is checked to determine whether at least one hour has elapsed at step 603. If less than one hour has elapsed since the timer was last set to zero, the timer is incremented at step 604. Otherwise, if the interpolation control is at its minimum value, the device user is informed at step 606 that this may be an extreme "bad hearing day" and it may be advantageous to adjust the "bad hearing day" fitting for the relevant program number(s). The device user may be informed using a predetermined signal such as a pattern of beeps, or a voice message played from the device memory. If the interpolation control is at its maximum value, the device user is informed at step 608 that this may be an extreme "good hearing day" and it may be advantageous to adjust the "good hearing day" fitting for the relevant program number(s). The device user may be informed using a predetermined signal such as a pattern of beeps, or a voice message played from the device memory.

The advantages of these embodiments of the present invention include the flexibility of the system to adjust to arbitrary hearing loss configurations for "good hearing days" and "bad hearing days" in an arbitrary number of "general purpose" or "special purpose" situations. Furthermore, the device user can adjust the fitting to any intermediate or extrapolated fitting using a single control on the device. If the device user is provided with the additional capability to reprogram the "good hearing day" fitting and "bad hearing day" fitting, the device may be optimized to cover the full range of hearing fluctuations for the individual user without further recourse to the audiologist or professional fitter. Furthermore, the device may be configured to automatically inform the device user when they are experiencing a very good or very poor hearing day, based on their setting of the interpolation control. This may quickly alert them to any temporary or permanent change in their hearing status.

Some portions of this detailed description are presented in terms of algorithms and symbolic representations of operations on data bits within a computer memory. These algorithmic descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent series of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.

As such, it will be understood that such acts and operations, which are at times referred to as being computer-executed, include the manipulation by the processing unit of the computer of electrical signals representing data in a structured form. This manipulation transforms the data or maintains it at locations in the memory system of the computer, which reconfigures or otherwise alters the operation of the computer in a manner well understood by those skilled in the art. The data structures where data are maintained are physical locations of the memory that have particular properties defined by the format of the data. However, while the invention is described in the foregoing context, it is not meant to be limiting as those of skill in the art will appreciate that various of the acts and operations described may also be implemented in hardware.

It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the description, it is appreciated that throughout the description, discussions utilizing terms such as "processing" or "computing" or "calculating" or "determining" or "displaying" or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission or display devices.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

References:

Dillon, H., Hearing aids, Boomerang Press, 2001 US patent 6,731,767; Adaptive Dynamic Range of Optimization Sound Processor; Blarney PJ,

James CJ, Wildi K, McDermott HJ, Martin LFA. PCT/AU2004/001691; Method and Apparatus for Adaptive Sound Processing Parameters; Blarney

PJ, Dickson B, Steele BR, Steinberg MJ.

McNeill, C, Blarney, PJ. Patterns of hearing fluctuation - towards a hearing aid prescription for clients with Meniere's syndrome, (manuscript in preparation).

Claims

CLAIMS:The invention claimed is:

1. a method for customizing and controlling a sound processing device for a person with fluctuating hearing, the method comprising: providing at least one fitting of the device that is suitable for a "good hearing day" when hearing is at a maximum and at least one other fitting that is suitable for a "bad hearing day" when hearing is at a minimum; setting, storing, and adjusting the at least two fittings; providing a calculation that interpolates between the "good hearing" and "bad hearing" fittings and extrapolates beyond these fittings; selecting an interpolated or extrapolated fitting by means of at least one continuously variable control mechanism; and controlling the operation of the sound processing device in accordance with the interpolated or extrapolated fitting.

2. a sound processing device suitable for a person with fluctuating hearing, the sound processing device comprising: a means of acquiring an input sound signal; an amplifier with gain under the control of a control module; a control module that controls the gain and the output of the device in accordance with a set of control parameters; a means for setting, storing, and adjusting at least two sets of control parameters suitable for a "good hearing day" when hearing is a maximum and a "bad hearing day" when hearing is at a minimum; one or more continuously variable means for interpolating and extrapolating a set of control parameters from the "good hearing day" and "bad hearing day" fittings; a means for setting the control module parameters to the interpolated or extrapolated set of control parameters; and a means of converting the amplified input sound to an acoustic output signal.

3. the sound processing device of claim 2 in which the amplifier is a wide dynamic range compression amplifier with at least one frequency channel and the control parameters include the gains, kneepoints, compression ratios, maximum output limits and time constants of the frequency channels.

4. the sound processing device of claim 2 in which the amplifier is an Adaptive Dynamic Range

Optimisation (ADRO) amplifier with at least one frequency channel and the control parameters include the maximum gains, comfort targets, audibility targets, and maximum output limits of the frequency channels.

5. the sound processing device of claim 2 in which the means of setting, storing, and adjusting the "bad hearing day" and "good hearing day" control parameters is a computer program running on a computer attached to the sound processing device by a wired or wireless programming interface and the program is designed to be used by an unskilled person such as the user of the sound processing device with fluctuating hearing loss.

6. the sound processing device of claim 2 in which the continuously varying means for interpolation and extrapolation of the control parameters has a range that extends beyond the range of the "bad hearing day" and "good hearing day" parameters by at least ten percent of the range.

7. the sound processing device of claim 6 in which the continuously varying means for interpolation and extrapolation of the control parameters can alert the sound device user if it is set to its minimum or maximum value for an extended period of time as an indicator that the "bad hearing day" parameters or the "good hearing day" parameters respectively may need to be updated.

8. the sound processing device of claim 2 in which a record of the value of the continuously varying means for interpolation and extrapolation of the control parameters is stored in a memory of the sound processing device from time to time, and said records may be read from the sound processing device memory to help in adjusting the "bad hearing day" and "good hearing day" control parameters.

9. the sound processing device of claim 2 in which there are more than one pair of "bad hearing day" and "good hearing day" control parameter sets for different purposes and the user may switch between the pairs of control parameter sets while the value of the continuously varying means for interpolation and extrapolation of the control parameters is maintained.

10. the sound processing device of claim 2 in which there are more than one set of offsets that are applied to the control parameters after the interpolation or extrapolation has been applied and the user may switch between the offsets for different listening situations while the value of the continuously varying means for interpolation and extrapolation of the control parameters is maintained.

1. the sound processing device of claim 2 in which the device is a digital hearing aid that has been reprogrammed so that the physical volume control is used to perform the interpolation and extrapolation instead of its usual function; pairs of "bad hearing day" and "good hearing day" fittings are stored instead of conventional fittings in the memory of the hearing aid; and the fitting software for the hearing aid is modified to set, store, and adjust the "bad hearing day" and "good hearing day" fittings by the hearing aid user with fluctuating hearing loss.