Wearable digital hearing aid and method for improving hearing ability

• US 4,791,672 A
• Filed: 10/05/1984
• Issued: 12/13/1988
• Est. Priority Date: 10/05/1984
• Status: Expired due to Term

• Current Assignee: M-E Manufacturing and Services, Inc.
• Original Assignee: Audiotone Incorporated
• Inventors: Nunley, James A., Steadman, John W., Wechsler, Perry J.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Byrd, Danita R.
• Application Number:
  US06/658,117
• Time in Patent Office: 1,530 Days
• Field of Search: 381/68, 381/68.2, 381/68.4, 381/23.1, 381/94, 381/111, 381/120, 381/122, 364/148, 364/178, 364/572
• US Class Current: 381/317
• CPC Class Codes: H04R 25/505 using digital signal processing

Abstract

A hearing aid to be worn by an individual of impaired hearing ability producing analog output signals of improved intelligibility. The hearing aid includes a wearable, programmable digital signal processor for processing digital samples of the analog signals coupled thereto in real time and providing analog output signals having the processed characteristics. The hearing aid program stored in the signal processor is continuously executed and modifies the analog signals coupled thereto by digital filtering in real time in accordance with the varying noise levels contained in the received audible signals. The modification of the signals includes noise supression.

Claims

1. A hearing aid adapted to be worn by an individual of impaired hearing ability comprising a hearing aid microphone means for receiving audio signals including speech signals and any noise and for continuously converting the received audio signals to corresponding analog electrical signals;

low pass filtering circuit means coupled to receive the analog signals from said microphone means for transmitting only those received analog signals falling within a preselected frequency band necessary for good fidelity and intelligibility of the audio signals and rejecting the signals of a frequency higher than the preselected frequency band;

circuit means coupled to receive the signals from said low pass filtering circuit means and continuously deriving analog signals representative of the level of any noise present in the received audio signals;

a wearable, programmable digital signal processing means having a memory and a plurality of signal input terminals and a signal output terminal, said signal processing means being capable of digitally processing the analog signals coupled thereto in real time and providing processed analog output signals therefrom;

means for continuously coupling the signals from said low pass filtering circuit means to a first input terminal for said digital signal processing means;

means for continuously coupling the signals from said circuit means providing the signals representative of the level of any noise in the received audio signals to a second input terminal for said digital signal processing means;

means for providing an analog signal representative of a reference noise level for the received audio signals and coupling said reference signals to a third input terminal for said digital signal processing means, a signal processing program stored in the processor memory for continuous execution in the digital processor;

said program being defined to continuously generate a plurality of adaptive digital filters for processing digital samples of the signals coupled to said first input terminal for said signal processing means to selectively modify the digital signals including suppressing the noise therein in accordance with changes in the levels of the noise in the samples of the signals coupled to the first input terminal of the signal processor, the program being further defined to continuously compare the signals coupled to the second and third input terminals for said signal processing means and adapting said digital filters for selectively modifying the signals including suppressing the noise therein coupled to said first input terminal based on the comparisons of the noise signals, the program providing continuous analog-to-digital signal conversion of the signals coupled to said first input terminal at a preselected sampling rate to permit each digital sample to be digitally filtered by said signal processor, the timing execution of the digital samples being defined to be sufficiently rapid to completely process each digital sample before the subsequent digital sample occurs, the signal processing means stored program including program steps to convert each of the filtered digital samples to corresponding analog signals appearing at said output terminal for the signal processing means;

circuit means coupled to said signal processing means to smooth out said received analo signals for accurately reproducing the electrical signals representative of the intelligible speech signals, and hearing aid speaker means coupled to said circuit means for smoothing out the electrical signals for continuously converting the coupled signals to the corresponding signals having the improved characteristics in accordance with the execution of the stored program.

2. A hearing aid as adapted to be worn by an individual of impaired hearing ability as defined in claim 1 wherein said signal processor modifies the digital samples in accordance with the stored program, the signal processor executes a Fourier analysis on the digital samples, and said low pass filtering circuit means eliminates the frequency components of the analog signals introducing aliasing errors into the Fourier analysis of the digital samples at the digital sampling rate utilized to thereby permit proper digital processing of the analog signals within said digital signal processing means.

3. A hearing aid as adapted to be worn by an individual of impaired hearing ability as defined in claim 1 or 2 wherein said digital signal processing means is a microprocessor.

4. A hearing aid as adapted to be worn by an individual of impaired hearing aility as defined in claim 1 wherein said digital signal processing means comprises an Intel 2920 microprocessor.

5. A hearing aid adapted to be worn by an individual of impaired hearing ability comprising a hearing aid microphone means for receiving audio signals including any noise therein and converting the received audio signals to corresponding analog electrical signals;

anti-aliasing filtering and preamplification circuit means coupled to receive the analog electrical signals from said microphone means, said filtering means being constructed and defined to cut off the received signals having a preselected high frequency and frequencies above said high frequency while continuously transmitting all signals therethrough below said high frequency and amplifying the filtered signals;

programmable signal processing means having a plurality of signal input terminals and an output terminal, a first input terminal being coupled to continuously receive said amplified and filtered analog signals from said anti-aliasing filtering means, low pass filter circuit means coupled to continuously receive said amplified and filtered analog signals from said anti-aliasing filtering circuit means, said low pass filter means being constructed and defined to transmit all received signals below a preselected low frequency and to attenuate all received signals above said low frequency;

circuit means coupled to said low pass filter means for receiving the signals transmitted through said filter means and providing signals having a voltage level representative of the level of any noise in the received signals;

said signal processing means including a second input signal terminal coupled to receive the signals representative of the noise level content in the received signals, means for providing an analog signal representative of a reference noise level for the received audio signals and coupling said reference iignals to a third input terminal for said digital signal processing means;

said signal processing means including a memory having a program stored therein to be executed for continuously digitally processing the analog signals continuously coupled to said first input terminal for said signal processing means in real time in accordance with the measurement of comparison of the signals coupled to said second and third input terminals for improving the signal-to-noise ratio of the signals coupled to said first input terminal for said signal processing means and continuously providing the processed signals as analog output signals from said output terminal for said signal processing means;

smoothing filter circuit means coupled to said output terminal for said signal processing means for removing the effects of the digital processing on said analog output signals, and a hearing aid speaker and amplifying circuit means coupled to receive the analog signals from said smoothing filter circuit means and continuously providing corresponding audio signals having improved clarity of intelligibility of speech.

6. A hearing aid adapted to be worn by an individual of impaired hearing ability as defined in claim 5 wherein said antialiasing filtering circuit means is constructed and defined as a low pass electrical filter having a cut off frequency of approximately 6100 Hertz.

7. A hearing aid adapted to be worn by an individual of impaired hearing ability as defined in claim 5 or 6 wherein said low pass filter circuit means is constructed and defined to transmit analog signals below approximately 750 Hertz and to attenuate analog signals above 750 Hz.

8. A hearing aid adapted to be worn by an individual of impaired hearing ability as defined in claim 5 wherein said programmable signal processing means is a programmable microprocessor signal means.

9. A hearing aid adapted to be worn by an individual of impaired hearing ability as defined in claim 8 wherein said microprocessor signal means is an Intel 2920 microprocessor.

10. A hearing aid adapted to be worn by an individual of impaired hearing ability as defined in claim 5 wherein said stored program functions to convert the analog signals coupled to its input terminals to digital signals at a preselected sampling rate and to digitally filter the analog signals to improve the signal-to-noise ratio thereof in accordance with the detected noise level in the analog signal and to reconvert the digitally filtered signals to analog signals in real time.

11. A hearing aid adapted to be worn by an individual of impaired hearing ability as defined in claim 5 wherein said stored program functions to convert the analog signals coupled to said first input terminal to corresponding digital signals at a preselected sampling rate and to convert the analog signals coupled to said second input terminal to corresponding digital signals at said preselected sampling rate;

said stored program functioning to continuously form a plurality of second order digital filters having varying digital signal filtering capabilities varying from no filtering to a high pass filter and functioning to select one of the digital filters based on the result of said measurement of the noise signals derived from the second and third input terminals and to direct the digital signals derived from the analog signals coupled to said first input terminal to the selected digital filter and then converting the digitally filtered signals to corresponding analog signals that are outputted from the signal processing means.

12. A hearing aid adapted to be worn by an individual of impaired hearing ability comprising a hearing aid microphone means for receiving audio signals including any noise therein and ocntinuously converting them to corresponding analog output electrical signals;

anti-aliasing filtering circuit means coupled to receive the analog signals from said microphone means for transmitting only those analog signals low enough in frequency so as not to introduce errors in the digital processing of the analog signals;

circuit means coupled to receive the signals from said anti-aliasing filtering circuit means and continuously deriving analog signals representative of level of any noise present in the received audio signals;

a wearable, programmable digital signal processing means having a memory and a plurality of signal input terminals and a signal output terminal, said signal processing means being capable of digitally processing the analog signals coupled thereto in real time and providing processed analog output signals therefrom;

means for continuously coupling the signals from said anti-aliasing filtering circuit means to a first input terminal for said digital signal processing means;

means for continuously coupling the signals representative of any noise in the received audio signals from said circuit means to a second input terminal for said digital processing means;

means for providing an analog signal representative of a reference noise level for the received audio signal and coupling said reference signals to a third input terminal for said digital signal processing means;

a signal processing program stored in said memory for continuous execution in the digital processor, said program being defined to continuously convert the analog signals coupled to said first input terminal to digital signals representative thereof and to internally continuously compare the noise signals coupled to said second and third input terminals for determining the manner of processing the digital signals representative of the microphone output signals, the program, upon execution, being effective to suppress any noise in the signals undergoing processing in accordance with the noise comparisons and providing processed analog output signals representative of the micorphone output signals, and hearing aid speaker circuit means coupled to receive the processed analog output signals and continuously converting them to corresoponding audio signals of improved intelligibility.

13. A hearing aid adapted to be worn by an individual of impaired hearing ability as defined in claim 12 wherein said digital signal processing means is a microprocessor.

14. A digital signal processor for a hearing aid comprising a programmable digital signal processor having a memory for storing a program to be continuously executed, the digital signal processor having a plurality of input terminals and at least a single output terminal, said digital signal processor being capable of continuously digitally processing analog signals representative of continuous audio signals including speech and any noise therein to improve the signal-to-noise ratios thereof in real time and continuously provide the processed signals as analog output signals at the output terminal thereof;

one of said input terminals is adapted to continuously receive analog signals representative of continuous audio signals;

a second of said input terminals is adapted to continuously receive analog signals representative of the level of the noise in said continuous audio signals;

a third of said input terminals is adapted to continuously receive precision oscillator signals of a preselected high frequency;

a fourth of said input terminals is adapted to continuously receive analog signals represnntative of a reference noise level, said program to be continuously executed stored in said processor memory, said program upon execution causing (1) clock pulses to be generated at a preselected rate in response to the oscillator signals coupled to said third input terminal for digitally sampling the analog signals coupled to said one of the input terminals, (2) the analog signals coupled to the input terminals to be converted to corresponding digital signals;

(3) the continuous generation of a plurality of second order digital filters adapted to improve the signal-to-nose ratio of the signals coupled to said first input terminal with increasing noise levels, (4) continuously comparing the signals received at said second and fourth terminals, (5) continuously selecting one of the digital filters in accordance with the result of the noise comparision, (6) continuously coupling the digital signals corresponding to the signals coupled to said first input terminal to the selected digital filter, (7) continuously converting the digitally filtered signals to corresponding analog signals and emitting the analog signals at said output terminal whereby the clarity of intelligibility of speech in the audio signals corresponding to the emitted analog signals is maximized as a result of hhe digital filtering.

15. A digital signal processor for a hearing aid as defined in claim 14 comprising a wearable microprocessor.

16. A digital signal processor for a hearing aid as defined in claim 15 wherein said microprocessor comprises an Intel 2920 microprocessor.

17. A digital signal processor for use with a hearing aid comprising a very high speed, programmable microprocessor permitting audio bandwidth digital filtering in real time, said microprocessor having a memory for storing a program to be continuously executed;

said program stored in the memory to be continuously executed in response to analog signals corresponding to the audio signals including any noise received by a hearing aid, the program being defined to continuously generate (1) digital signals corresponding to the analog signals coupled thereto at a preselected sampling rate, (2) a plurality of digital filters for selectively modifying each of the generated digital signals in an individual manner including improving the signal-to-noise ratios with increasing signal noise levels, the individual digital filters being selected in accordance with the detected noise levels, and (3) analog signals from the digital signals subjected to the digital filtering whereby the analog signals result in corresponding audio signals of improved audibility.

18. A digital signal processor for use with a hearing aid as defined in claim 17 wherein said microprocessor comprises an Intel 2920.

19. A method of improving the hearing ability of an individual with impaired hearing capability including the steps of receiving audio signals having any noise therein by an ear worn hearing aid and converting them to corresponding analog output signals;

providing analog signals representative of the noise levels in said audio signals;

coupling the analog output signals and the noise level analog signals to a programmable digital signal processing device, the digital signal processor having a program stored therein to continuously digitally process the analog signals coupled thereto to selectively modify said audio signals including suppressing any noise therein in accordance with the noise levels in said audio signals for improving the ability of an individual to hear the signals and providing corresponding analog output signals therefrom, the program is executed in real time;

converting the analog output signals from the digital signal processing device to corresponding more intelligible audio signals in the hearing aid, and coupling the audio signals by means of said hearing aid to the ear of the hearing aid wearer.

20. A method of improving the hearing ability of an individual of impaired hearing ability by means of a hearing aid, the steps including positioning a hearing aid in and/or adjacent the ear canal of an individual having impaired hearing ability for receiving audible sound and continuously converting the audible sound to corresponding electrical analog signals;

continuously filtering the resulting analog signals for limiting the frequency band of the received signals for preventing aliasing upon the digital filtering of the digital signals corresponding to the resulting analog singals, continuously deriving an analog signal representative of the noise level present in the received audible sound from the corresponding analog signal;

positioning a wearable, programmable, digital signal processor on said individual of impaired hearing ability, the signal processor having a prbgram stored therein for improving the signal-to-noise ratio of the received audible signals, the stored program including the necessary sequence of instructions that are continuously executed by the processor in real time for converting the analog signals coupled thereto to corresponding preselected digital samples thereof and continuously generating a pluraltty of second order digital filters for reducing the noise content of the received signals, and continuously converting the digitally filtered signals to corresponding analog signals;

continuously coupling the analog signals representative of the noise level of the received analog signals to said digital signal processor;

continuously measuring the signals representative of the noise levels of the audible signals and continuously selecting the digital filter to be utilized in accordance with the result of the noise level signal measurements;

continuously coupling the filtered analog signals to said digital signal processor; and

continuously receiving the analog signals corresponding to the digitally filtered signals from the digital signal processor at said hearing aid;

continuously converting the analog signals to corresponding audible sound signals and continuously coupling the sound signals to said individual'"'"'s ear.

21. A method of improving the signal-to-noise ratio of audible sounds in real time including the steps of receiving audible signals including any noise at adjacent a human ear of an individual with impaired hearing ability and converting the signals to corresponding electrical analog signals;

filtering the resulting analog signal to limit the frequency aand thereof to a preselected frequency band for preventing aliasing in any digital filtering of the resulting filtered signals;

continuossly converting said filtered analog signals to digital signals occurring at a preselected rate;

continuously deriving analog signals from the filtered analog signals representative of the noise level content of the received audible signals;

continuously providing a plurality of second order digital filters for filtering the digital signals in real time, the digital filters each providing different filtering capabilities ranging from no filtering to a high pass filter with a roll off below a preselected noise frequency and some enhancement frequencies above a preselected frequency for continuously improving the signal-oo-noise ratios of the received signals;

continuously converting the digital signals from the digital filters to corresponding analog output signals, continuously and automatically selecting one of the digital filters for coupling the digital signals thereto in accordance with the result of said comparison of the noise level signals, and continuously reconverting the electrical analog signals to audible signals whereby the audible signals have iproved signal-to-noise ratios, and coupling the audible signals into the ear of said invdividual to thereby increase the individual'"'"'s hearing capability.

22. A method of improving the hering ability of an individual having impaired hearing capability by means of a hearing aid, the steps including continuously band limiting the analog signals having any noise therein provided by the hearing aid corresponding to audio signals continuously received at the hearing aid;

continuously generating analog signals representative of the noise levles of the audio signals continuously received at the hearing aid;

providing a high speed, digital signal processor capable of executing digital filtering of signals coupled thereto in real time, the signal processor having a memory for storing a computer program to be continuously executed by the signal processor;

storing a computer program in the memory of the digital iignal processor, the computer program being characterized as including the sequence of instructions to be executed within said processor for continuously (1) converting the band limited analog signals to corresponding digital signals occurring at a preselected rate, (2) generating a plurality of digital filters with each filter having an individual filtering characteristic for improving the audibility of the audio output signal of the hearing aid, (3) selecting an individual filter for filtering the digital signals based on the measurement of the generated noise level signals, (4) digitally filtering the digital signals at the preselected digital filter for selectively modifying the signals including suppressing the noise therein, (5) converting the filtered digital signals to corresponding output analog signals from the signal processor, the processing of the individual digital signals being completed before a subsequent digital signal occurs with all digital signals being processed with very little time delay;

the digital processing of the band limited analog signals being effective for improving the signal-to-noise ratios of the audio signals received at the hearing aid from the signal processor, and continuously coupling the band limited analog signals to the digital signal processor;

continuously coupling the noise level signals to the digital signal processor, and continuously coupling the output analog signals to the hearing aid.