Programmable digital hearing aid system

• US 4,731,850 A
• Filed: 06/26/1986
• Issued: 03/15/1988
• Est. Priority Date: 06/26/1986
• Status: Expired due to Term

• Current Assignee: Energy Transportation Group Incorporated
• Original Assignee: Audimax, Inc.
• Inventors: Levitt, Harry, Dugot, Richard S., Kopper, Kenneth W.
• Primary Examiner(s): Ng, Jin F.
• Assistant Examiner(s): Schroeder, L. C.
• Application Number:
  US06/879,214
• Time in Patent Office: 628 Days
• Field of Search: 381/68.2, 381/68.4, 381/93, 381/94
• US Class Current: 381/317
• CPC Class Codes: H03G 5/16 Automatic control
• CPC Class Codes: H04R 2225/41 Detection or adaptation of hearing aid parameters or programs to listening situation, e.g. pub, forest
• CPC Class Codes: H04R 2225/43 Signal processing in hearing aids to enhance the speech intelligibility
• CPC Class Codes: H04R 25/407 Circuits for combining signals of a plurality of transducers
• CPC Class Codes: H04R 25/453 electronically
• CPC Class Codes: H04R 25/505 using digital signal processing

Abstract

A hearing aid system comprises a hearing aid that is programmable so as to have optimum electro-acoustic characteristics for the patient and acoustic environment in which it is used. Selected optimum parameter values are programmed into an electronically erasable, programmable read only memory (EEPROM) which supplies coefficients to a programmable filter and amplitude limiter in the hearing aid so as to cause the hearing aid to adjust automatically to the optimum set of parameter values for the speech level, room reverberation, and type of background noise then obtaining. The programmable filter may be a digital equivalent of a tapped delay line in which each delayed sample is multiplied by a weighting coefficient and the sum of the weighted samples generates a desired electro-acoustic characteristic. Alternatively, the programmable filter may be a tapped analog delay line in which the sum of the weighted outputs of the taps generates the desired characteristics. Acoustical feedback is reduced by an electrical feedback path in the hearing aid which is matched in both amplitude and phase to the acoustic feedback path, the two feedback signals being subtracted so as to cancel each other.

Claims

1. A hearing aid comprising at least one input microphone, an output receiver, and a signal transmission channel interposed between said microphone and said receiver in which the improvement comprises a programmable delay line filter and programmable signal limiter means interposed between the input and output of said transmission channel in a feedback path for said transmission channel, said filter being programmed to impart to the hearing aid at least one response characteristic effective to compensate for impaired hearing of the wearer of the aid.

2. A hearing aid as in claim 1 in which said filter comprises a delay line having a multiplicity of taps, first memory means for storing filter-response related coefficients therein, and means jointly responsive to said delay line taps and to coefficients stored in said memory means for providing an output having at least one response characteristic effective to compensate for impaired hearing of the wearer of the aid.

3. A hearing aid as in claim 2 in which said filter comprises a digital delay line and means for converting analog signals in said channel to digital signals for application to said delay line.

4. A hearing aid as in claim 2 in which said filter comprises an analog delay line having a multiplicity of taps, and means for periodically sampling analog signals in said channel and supplying them to said delay line.

10. A hearing aid as described in claim 1 in which said programmable delay line filter is programmed so as to effect substantial reduction of acoustic feedback from said receiver to said microphone.

5. A hearing aid comprising at least one input microphone, an output receiver, and a transmission channel interposed between said microphone and receiver, means controllable to impart different response characteristics to said hearing aid, and controlling means responsive to the level of speech signals in said transmission channel in excess of the level of noise signals in said channel for automatically controlling said controllable means to impart a selected one of said different response characteristics to said hearing aid.

6. A hearing aid as described in claim 5 in which said controlling means comprises speech detector means for determining when speech signals are in said transmission channel, a plurality of bandpass filter means for determining the noise frequency spectrum in said transmission channel, a plurality of comparator means each response to said speech detector and to respective bandpass filter means for indicating whether the speech level in each said bandpass filter exceeds the noise level therein and for actuating said controlling means to impart to the hearing aid a response characteristic effective to compensate for impaired hearing of the wearer of the aid at the noise levels obtaining in said channel.

7. A hearing aid as described in claim 6 in which said controlling means also comprises means for rectifying a portion of the signals in said transmission channel, a plurality of differently pre-biased comparators connected to receive the output of said rectifying means, and means responsive to the outputs of said comparators for generating a signal representative of the average level of the signals in said transmission channel for controlling said controllable means to impart to the hearing aid a response characteristic effective to compensate for impaired hearing of the wearer of the aid at the signal and noise levels obtaining in said channel.

8. A hearing aid as described in claim 7 in which said controllable means comprises a delay line having a multiplicity of taps, memory means for storing predetermined filter response-related coefficients therein, and means responsive to said controlling means for combining said delay line taps and coefficients to constitute a delay line filter of predetermined response characteristic in said transmission channel.

9. A hearing aid comprising at least one input microphone, an output receiver, a signal transmission channel interposed between said microphone and said receiver, and a programmable delay line filter interposed in a forward path between the input and output of said transmission channel, said programmable filter being programmed to effect substantial reduction of acoustic feedback from said receiver to said microphone.

11. A hearing aid comprising at least one input microphone, an output receiver, a signal transmission channel interposed between said microphone and said receiver, and a programmable delay line filter interposed in a forward path between the input and output of said transmission channel said filter comprising a digital delay line having a multiplicity of taps, means for converting analog signals in said channel to digital signals for application to said delay line, and first memory means for storing filter-response related coefficients therein, said digital delay line comprising second memory means arranged to receive digital signals from said analog-to-digital converting means, register means connected to receive digital signals from said second memory means, first digital-to-analog converter means connected to receive digital signals from said register means, timing means controlling the transfer of digital signals from said second memory means through said register means to said first digital-to-analog converter means, second digital-to-analog converter means connected to receive filter response related coefficients from said memory means in timed relation to the transfer of digital signals to said first digital-to-analog converter means and to supply analog signals therefrom to said first digital-to-analog converter means for combination therein with digital signals transferred thereto from said second memory means, signal summing means connected to receive the output of said first digital converter means, and sample and hold means connected to receive the output of said signal summing means and for providing an output having at least one response characteristic effective to compensate for impaired hearing of the wearer of the aid.

12. A hearing aid comprising at least one input microphone, an output receiver, a signal transmission channel interposed between said microphone and said receiver, and a programmable delay line filter interposed in a forward path between the input and output of aid transmission channel, said filter comprising an analog delay line having a multiplicity of taps, means for periodically sampling analog signals in said channel and sampling analog signals in said channel and supplying them to said delay line, and first memory means for storing filter-response related coeffients therein, digital-to-analog converter means connected to receive filter-response related coefficients from said first memory means for conversion to analog values, multiplexer means connected to supply signal samples from said sampling means to said digital converter means for combination with said respective analog values, summing means for summing said analog values and signal samples, and sample and hold means connected to receive the output of said summing means and for providing an output having at least one response characteristic effective to compensate for impaired hearing of the wearer of the aid.

13. A method of reducing acoustic feedback in a sound system comprising a microphone, a transducer and a signal transmission channel interposed between said microphone and transducer, comprising the steps of

determining the effect on the amplitude and phase of a signal in said transmission channel as a function of frequency of acoustic feedback between said transducer and microphone, and

inserting between the input and output of said transmission channel an electrical feedback path having a filter therein programmed to equalize and reduce the effect of said acoustic feedback both in amplitude and phase on a signal in said transmission channel.

14. A method of reducing acoustic feedback in a hearing aid comprising a microphone, a receiver fitted in an ear of a wearer of the aid, and a signal transmission channel interposed between said microphone and transducer, comprising the steps of

determining the effect on the amplitude and phase of a signal in said transmission channel as a function of frequency of acoustic feedback between said receiver and microphone, and

inserting between the input and output of said transmission channel a programmable filter programmed to equalize and reduce the effect of said acoustic feedback both in amplitude and phase on a signal in said transmission channel.

15. A method of reducing feedback in a hearing aid as described in claim 14 in which said programmable filter is inserted in a forward path through said transmission channel.

16. A method of reducing feedback in a hearing aid as described in claim 14 in which said programmable filter is inserted in an electrical feedback loop for said transmission channel.

17. A hearing aid comprising at least two input microphone channels, means for adjusting the amplitude and phase characteristics of each of said microphone channels, means for summing the outputs of said microphone channels, an output receiver, a signal transmission channel connected to receive the output of said summing means and to provide an output to said receiver, and a programmable filter interposed between said summing means and the output of said transmission channel, said filter being programmed to impart to the hearing aid at least one response characteristic effective to compensate for impaired hearing of the wearer of the aid and to reduce the effects of both noise and reverberation.

18. A hearing aid comprising at least one input microphone, an output receiver, and a signal transmission channel interposed between said microphone and said receiver in which the improvement comprises a signal-level dependent amplifier interposed between the input and output of said transmission channel in a feedback path for said transmission channel, said amplifier being programmed to impart to the hearing aid at least one response characteristic effective to compensate for impaired hearing of the wearer of the aid.

19. A hearing aid comprising at least one input microphone, an output receiver, a signal transmission channel interposed between said microphone and said receiver, and a programmable delay line filter interposed in a feedback path between the input and output of said transmission channel, said programmable filter being programmed to effect substantial reduction of acoustic feedback from said receiver to said microphone.