Method and System for Removal of Clicks and Noise in a Redirected Audio Stream

• US 20090086987A1
• Filed: 06/30/2008
• Published: 04/02/2009
• Est. Priority Date: 10/02/2007
• Status: Active Grant

• Current Assignee: Synaptics Incorporated
• Original Assignee: Conexant Systems Incorporated (Synaptics Incorporated)
• Inventors: Kerner, Yair, Qian, Xiaoyan Vivian, Wihardja, James W., Chien, Jonathan
• Granted Patent: US 8,656,415 B2
• Time in Patent Office: Days
• US Class Current: 381/71.100
• CPC Class Codes: G10L 19/025 Detection of transients or attacks for time/frequency resolution switching
• CPC Class Codes: G10L 21/0208 Noise filtering
• CPC Class Codes: G10L 21/0232 Processing in the frequency domain

Abstract

There is provided a method of redirecting an audio stream from a first audio endpoint to a second audio endpoint in a computer operating system. The method includes directing the audio stream from a client application through a first audio resource stack to the first audio endpoint; creating an audio endpoint bridge to provide a path for the audio stream from the first audio resource stack through a second audio resource stack connected to the second audio endpoint; and redirecting the audio stream to the second audio endpoint using the audio endpoint bridge. The audio endpoint bridge can be created by forming a bridging application so as to activate the second audio stack. The bridging application can be hooked into a Windows audio engine in the second audio resource stack. The bridge can be used to intercept an audio stream and remove noise from it. Additionally, a specific type of noise with sporadic intermittent spikes has been observed in this audio framework with certain Bluetooth headsets. A system and method is described for removing this specific type of noise.

Claims

1. A method for redirecting an audio stream from a first audio endpoint to a second audio endpoint in a computer operating system, the method comprising:

directing said audio stream from a client application through a first audio resource stack to said first audio endpoint;

creating an audio endpoint bridge to provide a path for said audio stream from said first audio resource stack through a second audio resource stack connected to said second audio endpoint;

enhancing said audio stream to reduce noise;

redirecting said audio stream to said second audio endpoint using said audio endpoint bridge.

2. The method of claim 1 wherein enhancing said audio stream comprises employing an algorithm selected from application of smoothing filters, noise spectrum frequencies suppression, linear predictive noise cancellation, or any combination thereof.

3. The method of claim 1, wherein enhancing said audio stream comprises:

estimating a noise level of the audio stream;

estimating a speech signal level of the audio stream;

determining a ratio of the speech signal level to the noise level (SNR);

attenuating the audio stream in a first frequency range using a first attenuation function based on the SNR; and

attenuating the audio stream in a second frequency range using a second attenuation function based on the SNR;

wherein the first frequency range is below the second frequency range, and wherein the first attenuation function has a lower maximum attenuation level than the second attenuation function.

4. The method of claim 3, wherein enhancing said audio stream further comprises:

detecting a silence area in the audio stream; and

stopping the estimating of the noise level of the audio stream during the silence area.

5. The method of claim 1, wherein enhancing said audio stream comprises:

detecting energy from a spike in the audio stream delaying the audio stream; and

applying a spike removing procedure whenever energy from a spike is detected.

6. The method of claim 5 wherein the spike removing procedure comprises linear interpolation.

7. The method of claim 1, wherein said audio endpoint bridge is created by forming a bridging application so as to activate said second audio stack.

8. The method of claim 7, wherein said bridging application is formed by an audio processing object in said first audio resource stack.

9. A system for redirecting an audio stream from a first audio endpoint to a second audio endpoint in an operating system, the system comprising:

a first audio resource stack for directing said audio stream from a client application to said first audio endpoint, said first audio resource stack comprising an audio processing object;

a second audio resource stack connected to said second audio endpoint bridge;

an audio endpoint bridge for redirecting said audio stream from said audio processing object through said second audio resource stack to said second audio endpoint, wherein said audio processing object is configured to form a bridging application so as to activate said second audio stack, thereby creating said audio endpoint bridge and the bridging application is configured to remove noise from the audio stream.

10. The system of claim 9 wherein the bridging application comprises a smoothing filter, a noise spectrum frequency suppressor, a linear predictive noise canceller, or a combination thereof.

11. The system of claim 9, wherein the bridging application comprises:

a noise level estimator configured to estimate a noise level of the audio stream;

a speech signal level estimator configured to estimate a speech signal level of the audio stream, wherein the bridging application is configured to determine a ratio of the SNR;

a first attenuator configured to attenuate the audio stream in a first frequency range using a first attenuation function based on the SNR; and

a second attenuator configured to attenuate the audio stream in a second frequency range using a second attenuation function based on the SNR;

wherein the first frequency range is below the second frequency range, and wherein the first attenuation function has a lower maximum attenuation level than the second attenuation function.

12. The system of claim 9, wherein the bridging application comprises:

a band-pass filter receiving the audio stream;

an energy detector coupled to the band-pass filter;

a delay module receiving the audio stream;

a switch controlled by the energy detector and coupled to the delay module;

a spike remover wherein the energy detector causes the switch to divert the audio stream through the spike remover if energy from a spike is detected.

13. The system of claim 12, wherein the spike remover comprises a linear interpolator.

14. A method of removing spikes and noise from an audio stream comprising:

detecting energy from a spike in the audio stream;

delaying the audio stream; and

applying a spike removing procedure whenever energy from a spike is detected.

15. The method of claim 14 wherein the spike removing procedure comprises linear interpolation.

16. The method of claim 14, wherein the spike removing procedure comprises a median filter or a linear filter or both.

17. The method of claim 14 wherein detecting energy from a spike comprises filtering the audio stream with a band-pass filter and detecting the energy received from the band-pass filter.

18. The method of claim 14 further comprising applying an additional noise reduction system.

19. The method of claim 18 wherein the additional noise reduction system comprises a smoothing filter, a noise spectrum frequency suppressor, a linear predictive noise canceller, or a combination thereof.

20. A system for removing spikes and noise from an audio signal comprising:

a band-pass filter receiving the audio signal;

an energy detector coupled to the band-pass filter;

a delay module receiving the audio signal;

a switch controlled by the energy detector and coupled to the delay module a spike remover;

wherein the energy detector causes the switch to divert the audio signal through the spike remover if energy from a spike is detected.

21. The system of claim 20 wherein the spike remover comprises a linear interpolator.

22. The system of claim 20, wherein the spike remover comprises a median filter;

23. The system of claim 20, wherein the spike remover comprises a linear filter.

24. The system of claim 20 wherein the energy detector compares the energy received from the band-pass filter to a predetermined threshold and causes to the switch to divert the audio signal through the spike remover if the energy exceeds the predetermined threshold.

25. The system of claim 20 further comprising a noise reduction system.

26. The method of claim 25 wherein the noise reduction system comprises a smoothing filter, a noise spectrum frequency suppressor, a linear predictive noise canceller, or a combination thereof.