Apparatus and method to eliminate noise in portable recorder

• US 20070170992A1
• Filed: 10/13/2006
• Published: 07/26/2007
• Est. Priority Date: 01/13/2006
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: CHO, Yong-choon
• Granted Patent: US 8,108,210 B2
• Time in Patent Office: Days
• US Class Current: 330/278
• CPC Class Codes: G10L 21/0208 Noise filtering
• CPC Class Codes: H03G 5/005 of digital signals

Abstract

A noise removing apparatus and method usable in a portable recorder to remove noise and enhance a voice signal when the voice signal with noise is input to the portable recorder. The noise removing method includes dividing an input signal into a high frequency component signal and a low frequency component signal, adjusting a magnitude of the high frequency component signal by comparing the magnitude of the divided high frequency component signal and a magnitude of the low frequency component signal, enhancing a clearness of the low frequency component signal by filtering the divided low frequency component with an adaptive filter, and adding the magnitude-adjusted high frequency component signal and the clearness-enhanced low frequency component signal.

Claims

1. A noise removing method usable in a recorder, the method comprising:

dividing an input signal into a high frequency component signal and a low frequency component signal;

adjusting a magnitude of the high frequency component signal based on a comparison between the magnitude of the high frequency component signal and a magnitude of the low frequency component signal;

enhancing a clearness of the low frequency component signal by filtering the divided low frequency component signal with an adaptive filter; and

adding the magnitude-adjusted high frequency component signal and the clearness-enhanced low frequency component signal.

2. The method of claim 1, wherein the adjusting of the magnitude of the high frequency component signal comprises:

calculating the magnitude of each of the low frequency component signal and the high frequency component signal;

comparing the calculated magnitudes of the high frequency component signal and the low frequency component signal;

if the magnitude of the high frequency component signal is greater than the magnitude of the low frequency component signal, generating a gain value to reduce the magnitude of the high frequency component signal, and if the magnitude of the high frequency component signal is less than the magnitude of the low frequency component signal, generating a gain value to restore the magnitude of the high frequency component signal to a magnitude of the input signal; and

adjusting the magnitude of the high frequency component by the generated gain value.

3. The method of claim 1, wherein the enhancing of the clearness of the low frequency component signal comprises:

delaying the low frequency component signal input to the adaptive filter for a predetermined time;

comparing the divided low frequency component signal and the delayed and filtered low frequency component signal to extract a difference signal; and

extracting a signal of a tonal component having a predetermined cycle from the low frequency component signal by updating a filter coefficient of the adaptive filter with respect to the extracted difference signal.

4. The method of claim 1, wherein the enhancing of the clearness of the low frequency component signal comprises:

defining an interval in which an amount of changes in the low frequency component signal exceeds a predetermined value as a transient interval; and

replacing a portion in the low frequency component signal in the transient interval with an average value of previous portions of the low frequency component signal.

5. A method of removing noise from an audio signal, the method comprising:

dividing an input audio signal into a high frequency component and a low frequency component;

detecting a voice region of the audio signal by comparing magnitudes of the high and low frequency components;

adjusting characteristics of the high and low frequency components, respectively, based on whether the voice region is detected; and

adding the adjusted high and low frequency components to generate an output audio signal.

6. The method of claim 5, wherein the dividing, detecting, adjusting, and adding operations are performed in a time domain.

7. The method of claim 5, wherein the detecting of the voice region comprises:

calculating the magnitudes of the high and low frequency components;

determining which one of the magnitudes of the high and low frequency components is greater;

determining that the voice region exists when the magnitude of the low frequency component is greater than the magnitude of the high frequency component, and the voice region does not exist when the magnitude of the low frequency component is less than the magnitude of the high frequency component.

8. The method of claim 5, wherein the adjusting of the characteristics comprises:

reducing a level of the high frequency component when the voice region is not detected; and

enhancing a tone of the low frequency component when the voice region is detected.

9. The method of claim 8, wherein the enhancing of the tone of the low frequency component comprises:

determining a transient interval of the low frequency component; and

replacing the transient interval of the low frequency component with an average of previous intervals of the low frequency component;

delaying the low frequency component signal having the replaced transient interval for a predetermined time;

performing a least mean squares (LMS) filtering on the delayed low frequency component;

subtracting the low frequency component having the replaced transient interval from the LMS filtered low frequency component to determine an error signal; and

updating at least one filter coefficient of the LMS filtering based on the error signal.

10. The method of claim 8, wherein the reducing of the level of the high frequency component comprises updating a gain value applied to the high frequency component according to:

G_new=1−

α

(1−

G_old), when the voice region is not detected, and

G_new=G_old×

β

, when the voice region is detected,

where G_new is a current gain value, G_old is a previous gain value, a is a first predetermined coefficient, and β

is a second predetermined coefficient.

11. A method of removing noise from a voice signal, the method comprising:

receiving an input audio signal in a time domain, adjusting a first gain of a high frequency component of the audio signal in the time domain, and adjusting a second gain of a low frequency component of the audio signal in the time domain; and

combining the gain adjusted high and low frequency components as an output signal.

12. A noise removing apparatus usable with a recorder, the apparatus comprising:

a filter unit to divide an input signal into a high frequency component signal and a low frequency component signal;

a gain generation unit to detect a voice region by comparing magnitudes of the high frequency component signal and the low frequency component signal divided by the filter unit;

a gain adjusting unit to adjust the high frequency component signal with respect to a gain value generated by the gain generation unit;

a tonal enhancing unit to extract a tonal component from the divided low frequency component signal by filtering with an adaptive filter; and

an addition unit to add the high frequency component signal magnitude-adjusted by the gain adjusting unit and the low frequency component signal tone-enhanced by the tonal enhancing unit.

13. The apparatus of claim 12, wherein the tonal enhancing unit comprises:

a delay unit to delay the divided low frequency component signal for a predetermined time;

an adaptive filter unit having the adaptive filter to extract a tonal component signal having a predetermined cycle from the delayed low frequency component signal by updating an adaptive filter coefficient with respect to an extracted error signal; and

a subtraction unit to extract the error signal corresponding to a difference between the delayed low frequency component signal and the tonal component signal by comparing the delayed low frequency component signal and the tonal component signal output by the adaptive filter unit

14. The apparatus of claim 12, wherein the tonal enhancing unit comprises a transient reduction unit to define an interval in which an amount of changes in the divided low frequency component signal exceeds a predetermined value as a transient interval, and to replace the divided low frequency component signal in the transient interval with an average value of previous low frequency component signals.

15. The apparatus of claim 12, wherein the tonal enhancing unit comprises a gain adjusting unit to multiply a gain value generated by comparing the magnitudes of the high frequency component signal and the low frequency component signal divided by the filter unit.

16. A noise removing apparatus, comprising:

a filter unit to divide an input audio signal into a high frequency component and a low frequency component;

a voice region detection unit to detect a voice region of the audio signal by comparing magnitudes of the high and low frequency components;

a gain unit to adjust characteristics of the high and low frequency components, respectively, based on whether the voice region is detected; and

an addition unit to add the adjusted high and low frequency components to generate an output audio signal.

17. The apparatus of claim 16, wherein the filter unit, the voice region detection unit, the gain unit, and the addition unit each operate on time domain signals.

18. The apparatus of claim 16, wherein the voice region detection unit calculates the magnitudes of the high and low frequency components, determines which one of the magnitudes of the high and low frequency components is greater, and determines that the voice region exists when the magnitude of the low frequency component is greater than the magnitude of the high frequency component, and the voice region does not exist when the magnitude of the low frequency component is less than the magnitude of the high frequency component.

19. The apparatus of claim 16, wherein the gain unit reduces a level of the high frequency component when the voice region is not detected, and enhances a tone of the low frequency component when the voice region is detected.

20. The apparatus of claim 19, wherein the gain unit comprises:

a transient time reduction unit to determine a transient interval of the low frequency component, to replace the transient interval of the low frequency component with an average of previous intervals of the low frequency component, a delay unit to delay the low frequency component signal having the replaced transient interval output from the transient time reduction unit for a predetermined time;

an adaptive filter to perform a least mean squares (LMS) filtering on the delayed low frequency component;

subtracting the low frequency component having the replaced transient interval from the LMS filtered low frequency component to determine an error signal; and

updating at least one filter coefficient of the adaptive filter based on the error signal.

21. The apparatus of claim 16, wherein the reducing of the level of the high frequency component comprises updating a gain value applied to the high frequency component according to:

G_new=1−

α

(1−

G_old), when the voice region is not detected, and

G_new=G_old×

β

, when the voice region is detected,

where G_new is a current gain value, G_old is a previous gain value, a is a first predetermined coefficient, and β

is a second predetermined coefficient.

22. A portable recorder, comprising:

a microphone to detect an analog audio signal;

an analog to digital converter to convert the analog audio signal to a digital audio signal; and

a noise removing device to divide the digital audio signal into a high frequency component and a low frequency component, to detect a voice region of the audio signal by comparing magnitudes of the high and low frequency components, to adjust characteristics of the high and low frequency components, respectively, based on whether the voice region is detected, and to add the adjusted high and low frequency components to generate an output audio signal.

23. A computer readable medium usable in a portable recorder and containing executable code to perform a method of removing noise from a voice signal, the medium comprising:

executable code to receive an input audio signal in a time domain, to adjust a first gain of a high frequency component of the audio signal in the time domain, and to adjust a second gain of a low frequency component of the audio signal in the time domain; and

executable code to combine the gain adjusted high and low frequency components as an output signal.