Automatic sensitivity control

• US 6,151,400 A
• Filed: 04/23/1997
• Issued: 11/21/2000
• Est. Priority Date: 10/24/1994
• Status: Expired due to Term

• Current Assignee: Cochlear Limited
• Original Assignee: Cochlear Limited
• Inventors: Seligman, Peter
• Primary Examiner(s): Kuntz, Curtis A.
• Assistant Examiner(s): Barnie, Rexford N
• Application Number:
  US08/817,686
• Time in Patent Office: 1,308 Days
• Field of Search: 381/316, 381/317, 381/318, 381/321, 381/320, 381/94.1, 381/94.3, 381/94.8, 381/101, 381/93, 381/104, 381/106, 381/83, 381/71.14, 381/102, 381/107, 381/108
• US Class Current: 381/317
• CPC Class Codes: A61N 1/36038 Cochlear stimulation
• CPC Class Codes: H03G 3/3005 in amplifiers suitable for low-frequencies, e.g. audio amplifiers H03G3/32, H03G3/34 take precedence
• CPC Class Codes: H03G 3/344 Muting responsive to the amount of noise (noise squelch) H03G3/345 takes precedence
• CPC Class Codes: H04R 25/356 Amplitude, e.g. amplitude shift or compression
• CPC Class Codes: H04R 25/505 using digital signal processing
• CPC Class Codes: H04R 25/606 acting directly on the eardrum, the ossicles or the skull, e.g. mastoid, tooth, maxillary or mandibular bone, or mechanically stimulating the cochlea, e.g. at the oval window

Abstract

Again control arrangement for an auditory prosthesis, such as a hearing aid or cochlear prosthesis, is disclosed. The output of a controlled amplifier 11 is processed so as to derive an average noise floor level. This is compared to a predetermined level, and the gain adjusted slowly up or down in response to the comparison. Hardware and software implementations are disclosed.

Claims

1. A method for processing in an auditory prosthesis an audio signal to optimize the intelligibility of an output of said auditory prosthesis as perceived by a user of said auditory prosthesis, comprising the steps of:

a) amplifying said audio signal by means of a gain adjustable amplifier to produce a gain adjusted audio signal;

b) determining an average noise floor of said audio signal wherein said average noise floor is indicative of the lowest noise level within a predetermined period;

c) adjusting the gain of said gain adjustable amplifier by means of a feedback control arrangement responsive to said gain adjusted audio signal and said average noise floor; and

d) conveying said gain adjusted audio signal to the remainder of said auditory prosthesis for further processing.

2. A method according to claim 1, wherein the step of adjusting the gain of said gain adjustable amplifier by means of a feedback control arrangement responsive to said gain adjusted audio signal comprises the further steps of:

a) extracting the envelope of said gain adjusted audio signal to produce an envelope signal;

b) monitoring said envelope signal to produce a noise floor signal indicative of said envelope signal'"'"'s minimum value during a period of time;

c) comparing said noise floor signal with a breakpoint set by said auditory prosthesis user; and

d) decreasing the gain of said gain adjustable amplifier if said noise floor signal is greater than said breakpoint set by said user of said auditory prosthesis or increasing the gain of said gain adjustable amplifier if said noise floor signal is less than said breakpoint set by said user of said auditory prosthesis.

3. A method according to claim 2, wherein the step of extracting the envelope of said gain adjusted audio signal to produce said envelope signal is accomplished by means of a diode detector circuit.

4. A method according to claim 3, wherein the step of monitoring said envelope signal to produce a signal indicative of the minimum value of said envelope signal during said period of time is implemented by means of a dip detector.

5. A method according to claim 1, wherein the gain of said gain adjustable amplifier is increased relatively slowly in response to a decrease in said average noise floor and is decreased relatively rapidly in response to an increase in said average noise floor.

6. A method according to claim 1, wherein said auditory prosthesis is a hearing aid.

7. A method according to claim 1, wherein said auditory prosthesis is a cochlear prosthesis.

8. A method for processing a digital audio signal in an auditory prosthesis by means of a microprocessor and software in order to maximize the intelligibility of sounds delivered to a user, comprising the steps of:

a) performing computations on said digital audio signal to apply gain to said digital audio signal thereby generating a gain adjusted digital audio signal wherein the degree of gain applied is subject to increment or decrement;

b) performing computations on said gain adjusted digital audio signal to produce a digital envelope signal;

c) performing computations on said digital envelope signal to generate a noise floor value characteristic of a minimum of said digital envelope signal during a preset period of time;

d) comparing said minimum of said digital envelope signal with a breakpoint value set by a user; and

e) increasing the gain applied to said digital audio signal if said noise floor value is less than said breakpoint value or decreasing the gain applied to said digital audio signal if said noise floor value is greater than said breakpoint value.

9. A method according to claim 8, wherein said computations performed on said digital audio signal to apply gain to said digital audio signal increase the gain relatively slowly in response to a decrease in said noise floor value and decrease the gain relatively rapidly in response to an increase in said noise floor value.

10. A method according to claim 8, wherein said auditory prosthesis is a hearing aid.

11. A method according to claim 8, wherein said auditory prosthesis is a cochlear prosthesis.

12. An apparatus for processing in an auditory prosthesis an audio signal which includes a noise component to optimize the intelligibility of the output of said auditory prosthesis as perceived by a user of said auditory prostheses, comprising:

a) a gain adjustable amplifier to operatively amplify said audio signal thereby producing a gain adjusted audio signal;

b) a feedback control arrangement responsive to said gain adjusted audio signal to operatively adjust the gain of said gain adjustable amplifier, including;

means for determining an average noise floor of said gain adjusted audio signal, said average noise floor corresponding to the lowest level of said noise component; and

means for providing a control signal to said gain adjustable amplifier so as to vary the gain of said gain adjustable amplifier; and

c) means for conveying said gain adjusted audio signal to the remainder of said auditory prosthesis for further processing.

13. An apparatus according to claim 12, wherein said feedback control arrangement responsive to said gain adjusted audio signal, comprises:

a) means for extracting the envelope of said gain adjusted audio signal to produce an envelope signal;

b) means for monitoring said envelope signal to produce a noise floor signal indicative of said envelope signal'"'"'s minimum value during a period of time;

c) means for comparing said noise floor signal with a breakpoint set by said auditory prosthesis user;

d) means for decreasing the gain of said gain adjustable amplifier if said noise floor signal is greater than said breakpoint set by said user of said auditory prosthesis; and

e) means for increasing the gain of said gain adjustable amplifier if said noise floor signal is less than said breakpoint set by said user of said auditory prosthesis.

14. An apparatus according to claim 13, wherein said means for extracting the envelope of said gain adjusted audio signal to produce said envelope signal is accomplished by means of a diode detector circuit.

15. An apparatus according to claim 14, wherein said means for monitoring said envelope signal to produce a signal indicative of the minimum value of said envelope signal during said period of time is implemented by means of a dip detector.

16. An apparatus according to claim 12, wherein said gain adjustable amplifier comprises a voltage controlled amplifier.

17. An apparatus according to claim 12, wherein said gain adjustable amplifier comprises a fixed gain stage and a variable attenuation stage.

18. An apparatus according to claim 17, wherein said variable attenuation stage is implemented by means of a field effect transistor.

19. An apparatus in accordance with claim 12 wherein said feedback control arrangement further includes means for comparing said average noise floor to a predetermined level;

and wherein said means for providing a control signal is responsive to said means for comparing by increasing said gain when said noise floor is below said predetermined level and by decreasing said gain when said noise floor is above said predetermined level.

20. An apparatus according to claim 12, wherein said means for providing said control signal to said gain adjustable amplifier comprises an integrator.

21. An apparatus according to claim 12, wherein the gain of said gain adjustable amplifier is increased relatively slowly in response to a decrease in said average noise floor and is decreased relatively rapidly in response to an increase in said average noise floor.

22. An apparatus according to claim 12, wherein said auditory prosthesis is a hearing aid.

23. An apparatus according to claim 12, wherein said auditory prosthesis is a cochlear prosthesis.

28. An apparatus according to claim 19, wherein said mean for comparing said average noise floor to said predefined level comprises an operational amplifier.

24. An apparatus for processing a digital audio signal in an auditory prosthesis by means of a microprocessor and software in order to maximize the intelligibility of sounds delivered to a user, said software containing instructions comprising the steps of:

a) performing computations on said digital audio signal to apply gain to said digital audio signal thereby generating a gain adjusted digital audio signal wherein the degree of gain applied is subject to increment or decrement;

b) performing computations on said gain adjusted digital audio signal to produce a digital envelope signal;

c) performing computations on said digital envelope signal to generate a noise floor value characteristic of a minimum of said digital envelope signal during a preset period of time;

d) comparing said minimum of said digital envelope signal with a breakpoint value set by said user; and

e) increasing the gain applied to said digital audio signal if said noise floor value is less than said breakpoint value or decreasing the gain applied to said digital audio signal if said noise floor value is greater than said breakpoint value.

25. An apparatus according to claim 24, wherein said computations performed on said digital audio signal to apply gain to said digital audio signal increases said gain relatively slowly in response to a decrease in said noise floor value and decreases said gain relatively rapidly in response to an increase in said noise floor value.

26. An apparatus according to claim 24, wherein said auditory prosthesis is a hearing aid.

27. An apparatus according to claim 24, wherein said auditory prosthesis is a cochlear prosthesis.

29. An apparatus for processing in an auditory prosthesis an audio signal having a noise component to optimize the intelligibility of the output of said auditory prosthesis as perceived by a user of said auditory prosthesis, comprising:

an amplifier having a variable gain controlled by a gain control signal, said amplifier receiving said audio signal and producing in response a gain adjusted audio signal;

a noise floor detector receiving said audio signal and being constructed to detect a noise floor of said noise component by determining the lowest level of said noise component over a predetermined time period;

a gain control circuit coupled to said noise floor detector and generating said gain control signal responsive to said noise floor; and

an output terminal transmitting said gain adjusted audio signal for perception by the user.

30. The apparatus of claim 29 wherein said gain control circuit includes a comparator coupled to said noise floor detector, said comparator being constructed to compare said noise floor to a predetermined value and to increase the gain of said amplifier if said noise floor is below said predetermined value and to decrease said gain if said noise floor is above said predetermined value.

31. The apparatus of claim 29 wherein said noise floor detector includes an envelope detector arranged to receive said audio signal and to detect an envelope of said audio signal, and a minima detector for detecting a minimum value of said envelope, said minimum value corresponding to said noise floor.