Signal processing circuit and method for increasing speech intelligibility

• US 6,353,671 B1
• Filed: 02/05/1998
• Issued: 03/05/2002
• Est. Priority Date: 02/05/1998
• Status: Expired due to Fees

• Current Assignee: Bioinstco Corp.
• Original Assignee: Bioinstco Corp.
• Inventors: Ostrander, Lee E., Kandel, Gillray L.
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): PENDLETON, DIONNE
• Application Number:
  US09/019,243
• Time in Patent Office: 1,489 Days
• Field of Search: 381/312, 381/317, 381/318, 381/320, 381/321, 381/81, 381/93, 381/313, 381/314, 381/104, 381/106, 381/107, 381/57, 381/316, 381/94.1, 381/94.3, 381/39, 381/58, 381/108, 381/109, 381/71.14, 381/102, 381/60, 381/71.1, 381/71.9, 404/209, 404/225, 404/234, 379/6
• US Class Current: 381/318
• CPC Class Codes: H04R 2225/43 Signal processing in hearing aids to enhance the speech intelligibility
• CPC Class Codes: H04R 2410/07 Mechanical or electrical reduction of wind noise generated by wind passing a microphone
• CPC Class Codes: H04R 25/43 Electronic input selection or mixing based on input signal analysis, e.g. mixing or selection between microphone and telecoil or between microphones with different directivity characteristics H04R25/407 takes precedence
• CPC Class Codes: H04R 25/453 electronically
• CPC Class Codes: H04R 25/505 using digital signal processing
• CPC Class Codes: H04R 25/75 Electric tinnitus maskers providing an auditory perception

Abstract

A signal processing circuit and method for increasing speech intelligibility. The invention comprises a receiving circuit for receiving an audio signal detectable by a human. A gain amplifying circuit provides gain amplification of the audio signal. A shaping filter modifies the audio signal to be in phase with a second audio signal present at the receiving circuit and which is detected by the human unprocessed by the signal processing circuit. The shaping filter further differentially amplifies first and second speech formant frequencies to restore a normal loudness relationship between them. A feedback circuit controls the gain amplification in the gain amplifying circuit for enabling the signal processing circuit to substantially prevent regenerative oscillation of the amplified audio signal. Additionally, a signal tone may be injected into the signal processing circuit for automatically controlling the gain amplifying circuit.

Claims

1. A method of processing an audio signal in a hearing aid for increasing speech intelligibility to a human comprising the steps of:

receiving an audio signal;

differentially amplifying a first frequency range that substantially comprises first speech formant frequencies and a second frequency range that substantially comprises second formant frequencies of said audio signal;

mixing an injected inaudible signal tone with said audio signal;

sensing a level of presence of the signal tone; and

automatically controlling gain amplification of only the second frequency range based on the sensed level of the injected signal tone, wherein regenerative oscillation of the audio signal is substantially prevented.

2. The method of claim 1 in which said step of amplifying comprises:

amplifying substantially only second speech formant frequencies of said audio signal to normalize a loudness relationship between said second speech formant frequencies and first speech formant frequencies.

3. The method of claim 1 further including modifying said audio signal wherein said modified audio signal is in phase with a second audio signal present at the receiving circuit and which is detectable by the human and unprocessed by the signal processing circuit.

4. The method of claim 1 wherein the step of automatically controlling comprises:

sensing an amplified audio signal; and

processing said amplified audio signal to provide a negative feedback only to the second frequency range for substantially preventing regenerative oscillation of said amplified audio signal.

5. A method of processing an audio signal in a hearing aid for increasing speech intelligibility to a human comprising the steps of:

receiving an audio signal;

passing the audio signal through a signal processing circuit having an output, and outputting a modified audio signal from the output;

phase aligning the modified audio signal with an unpassed audio signal present at the output;

amplifying frequencies of said audio signal differentially wherein a second frequency range comprising second speech formant frequencies of said audio signal has an amplified gain greater than a gain amplification of a first frequency range comprising first speech formant frequencies, regardless of a presence of noise in the first and second frequency ranges; and

controlling said amplified gain based on an inaudible signal tone, wherein the signal processing circuit substantially prevents regenerative oscillation of said amplified audio signal.

6. The method of claim 5 in which said step of amplifying comprises:

amplifying only said second frequency range of said audio signal to normalize a loudness relationship between said second speech formant frequencies and first speech formant frequencies.

7. The method of claim 5, wherein the step of phase aligning comprises:

providing first and second filters for phase aligning first and second speech formant frequencies with the unpassed audio signal present at the output.

8. The method of claim 7 further including a step of mixing a signal tone with said audio signal and wherein said step of controlling comprises sensing a level of presence of the signal tone and automatically controlling said gain amplification based on the sensed level of the signal tone.

9. The method of claim 5 wherein the step of controlling comprises:

sensing an amplified audio signal; and

processing said amplified audio signal to provide a negative feedback for substantially preventing regenerative oscillation of said amplified audio signal.

10. The method of claim 9, further including the steps of:

mixing a signal tone with said audio signal;

sensing a level of presence of the signal tone; and

controlling automatically said gain amplification based on the sensed level of the signal tone.

11. A hearing aid signal processing circuit for increasing speech intelligibility to a human, said human having at least one eardrum, comprising:

a receiving circuit for receiving an audio signal;

a gain amplifying circuit for differentially amplifying a first frequency range comprising first speech formant frequencies and a second frequency range comprising second speech formant frequencies of said audio signal as a function of the difference in decibels for restoring a sound pressure level of said second frequency range to a normal level dependent on said human and a frequency of said audio signal; and

a feedback circuit for controlling gain amplification of only one of the frequency ranges based on a sensed level of an inaudible continuous signal tone, wherein the signal processing circuit substantially prevents regenerative oscillation of the audio signal.

12. The signal processing circuit of claim 11, wherein said feedback circuit comprises a processing filter for providing a negative feedback to change gain amplification by the gain amplifying circuit as a function of sensed environmental variables.

13. The signal processing circuit of claim 12, further comprising a signal injection circuit for injecting a signal tone to mix with said audio signal.

14. The signal processing circuit of claim 13, wherein said feedback circuit comprises a gain control circuit for automatically controlling the gain amplifying circuit as a function of the presence of the signal tone.

15. The signal processing circuit of claim 11, wherein said gain amplifying circuit is manually controlled for variable gain amplification.

16. The signal processing circuit of claim 11, wherein said feedback circuit further comprises a gain control circuit for automatically controlling the gain amplifying circuit.

17. The signal processing circuit of claim 11, wherein the gain amplifying circuit comprises a first gain amplifier that amplifies only said first frequency range and a second gain amplifier that amplifies only said second frequency range.

18. The signal processing circuit of claim 11, further comprising a signal injection circuit for injecting a signal tone to mix with said audio signal.

19. The signal processing circuit of claim 18, wherein said feedback circuit comprises a gain control circuit for automatically controlling the gain amplifying circuit as a function of the sensed level of the signal tone.

20. The signal processing circuit of claim 19, wherein said feedback circuit further comprises a processing filter for providing a negative feedback to change gain amplification by the gain amplifying circuit as a function of sensed environmental variables.

21. The signal processing circuit of claim 19, further including a shaping filter for modifying said audio signal wherein said modified audio signal is in phase with a second audio signal which passes to the eardrum through a passageway and is substantially unaffected by the signal processing circuit and is detectable by said human.

22. The signal processing circuit of claim 19, comprising a hearing aid.

23. The signal processing circuit of claim 19, wherein said gain control circuit further comprises a narrow band filter that passes substantially only the signal tone and wherein the gain amplifying circuit passes only said second frequency range.

24. The signal processing circuit of claim 11, further comprising an acoustical link for passing the injected continuous tone between a receiver and a microphone.