AUDIO NOISE CANCELLING

• US 20120057720A1
• Filed: 05/04/2010
• Published: 03/08/2012
• Est. Priority Date: 05/11/2009
• Status: Active Grant

• Current Assignee: Shenzhen TCL Creative Cloud Technology Co., Ltd.
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Van Leest, Adriaan Johan
• Granted Patent: US 9,165,549 B2
• Time in Patent Office: Days
• US Class Current: 381/71.11
• CPC Class Codes: G10K 11/17825 Error signals
• CPC Class Codes: G10K 11/17833 by using a self-diagnostic function or a malfunction prevention function, e.g. detecting abnormal output levels
• CPC Class Codes: G10K 11/17854 the filter being an adaptive filter
• CPC Class Codes: G10K 11/17875 using an error signal without a reference signal, e.g. pure feedback
• CPC Class Codes: G10K 2210/1081 Earphones, e.g. for telephones, ear protectors or headsets
• CPC Class Codes: G10K 2210/3026 Feedback
• CPC Class Codes: G10K 2210/3028 Filtering, e.g. Kalman filters or special analogue or digital filters
• CPC Class Codes: G10K 2210/503 Diagnostics; Stability; Alarms; Failsafe
• CPC Class Codes: G10K 2210/51 Improving tonal quality, e.g. mimicking sports cars
• CPC Class Codes: H04R 1/1083 Reduction of ambient noise active noise reduction per se G10K11/175; protective devices for the ear, e.g. providing acoustic protection A61F11/06
• CPC Class Codes: H04R 3/02 for preventing acoustic reaction , i.e. acoustic oscillatory feedback specially adapted for hearing aids H04R25/453

Abstract

A noise canceling system comprises a microphone (103) for generating a captured signal representing sound in an audio environment and a sound transducer (101) for radiating a sound canceling audio signal in the audio environment. A feed-back path (105, 107, 109, 111, 113) exists from the microphone (103) to the sound transducer (101) and comprises a feedback filter (109). A tone processor (119) determines a tone component characteristic for a tone component of a feedback signal of the feedback path (105, 107, 109, 111, 113) and an adaptation processor (121) adapts the feedback path in response to the tone component characteristic. The invention allows detection of the onset of instability and dynamic compensation to mitigate or prevent such instability. Accordingly increased design freedom for the feedback filter is achieved resulting in improved noise cancellation.

Claims

1. A noise canceling system comprising:

a microphone (103) for generating a captured signal representing sound in an audio environment;

a sound transducer (101) for radiating a sound canceling audio signal in the audio environment;

a feedback path (105, 107, 109, 111, 113) from the microphone (103) to the sound transducer (101), the feedback path (105, 107, 109, 111, 113) receiving the captured signal and generating a drive signal for the sound transducer (101) and comprising a feedback filter (109);

a tone processor (119) for determining a tone component characteristic for a tone component of a feedback signal of the feedback path (105, 107, 109, 111, 113); and

adaptation circuit (121) for adapting the feedback path in response to the tone component characteristic.

2. The noise canceling system of claim 1 wherein the tone component characteristic is a level indication of a signal level of the tone component.

3. The noise canceling system of claim 1 wherein the adaptation circuit (121) is arranged to adapt the feedback filter (109) in response to the tone component.

4. The noise canceling system of claim 1 wherein the tone processor comprises an Adaptive Line Enhancer.

5. The noise canceling system of claim 4 wherein the Adaptive Line Enhancer comprises:

an adaptive filter (401, 403) for delaying and filtering an input signal to generate a modified signal;

a comparator (405) for generating a difference indication by comparing the input signal to the modified signal; and

circuit (407) for adapting the adaptive filter to minimize the difference indication.

6. The noise canceling system of claim 5 wherein the tone processor (119) is arranged to generate the tone component characteristic in response to a characteristic of the modified signal.

7. The noise canceling system of claim 5 wherein the tone processor (119) is arranged to generate the tone component characteristic in response to a characteristic of at least one coefficient of the adaptive filter (401, 403).

8. The noise canceling system of claim 1 wherein the adaptation circuit (121) is arranged to adapt a gain of the feedback filter (109) in response to the tone component characteristic.

9. The noise canceling system of claim 8 wherein the adaptation circuit (121) is arranged to bias the gain towards lower gains for a tone component characteristic indicative of an increasing signal level of the tone signal component.

10. The noise canceling system of claim 1 further comprising a filter (501) to generate a filtered signal and wherein the tone processor (119) is arranged to generate the tone component characteristic in response to the filtered signal.

11. The noise canceling system of claim 1 wherein the adaptation circuit (119) is arranged to adapt a frequency response of the feedback filter (109).

12. The noise canceling system of claim 1 further comprising suppression circuit (405) for suppressing a signal component of the feedback signal, the signal component having a characteristic corresponding to the tone component characteristic.

13. The noise canceling system of claim 1 wherein the tone processor (119) and the adaptation circuit (121) are part of an Adaptive Line Enhancer inserted in the feedback path (105, 107, 109, 111, 113).

14. The noise canceling system of claim 1 wherein the feedback path (105, 107, 109, 111, 113) is an analog feedback path and at least part of the tone processor (119) is implemented digitally.

15. A method of operation for a noise canceling system including:

a microphone (103) for generating a captured signal representing sound in an audio environment;

a sound transducer (101) for radiating a sound canceling audio signal in the audio environment;

a feedback path (105, 107, 109, 111, 113) from the microphone (103) to the sound transducer (101), the feedback path (105, 107, 109, 111, 113) receiving the captured signal and generating a drive signal for the sound transducer (101) and comprising a feedback filter (109);

the method comprising;

determining a tone component characteristic for a tone component of a feedback signal of the feedback path (105, 107, 109, 111, 113); and

adapting the feedback path (105, 107, 109, 111, 113) in response to the tone component characteristic.