Audio encoder for wind and microphone noise reduction in a microphone array system
View Patent ↗An audio system encodes and decodes audio captured by a microphone array system in the presence of wind noise. The encoder encodes the audio signal in a way that includes beamformed audio signal and a “hidden” representation of a non-beamformed audio signal. The hidden signal is produced by modulating the low frequency signal to a high frequency above the audible range. A decoder can then either output the beamformed audio signal or can use the hidden signal to generate a reduced wind noise audio signal that includes the non-beamformed audio in the low frequency range.
1. A method for encoding an audio signal captured by a microphone array system in the presence of wind noise, the method comprising:
capturing at least a first audio signal via a first microphone of a microphone array and a second audio signal via a second microphone of the microphone array;
combining the first audio signal and the second audio signal to generate a beamformed audio signal;
determining a selected audio signal having a lower wind noise metric between the first audio signal and the second audio signal;
processing the selected audio signal to modulate the selected audio signal based on a high frequency carrier signal to generate a high frequency signal; and
combining the high frequency signal and the beamformed audio signal to generate an encoded audio signal.
2. The method of claim 1 , where at least one of the first microphone and the second microphone comprise an omni-directional microphone.
3. The method of claim 1 , wherein processing the selected audio signal further comprises:
low pass filtering and level-limiting the selecting audio signal.
4. The method of claim 1 , wherein processing the selected audio signal further comprises:
applying a low pass filter having a cutoff frequency of approximately 4 kHz.
5. The method of claim 1 , wherein the high frequency carrier signal has a frequency of at least 20 kHz.
6. The method of claim 1 , wherein determining the selected audio signal having the lower wind noise metric comprises:
performing a comparison of an energy level of the first audio signal with an energy of the second audio signal within a low frequency range in which wind noise is present;
and determining the selected audio signal based on the comparison.
7. The method of claim 1 , wherein combining the first audio signal with the second audio signal to generate the beamformed audio signal comprises:
delaying the second audio signal by an amount corresponding a time for sound to travel a distance between the first microphone and the second microphone;
computing a difference signal representing a difference between the first audio signal and the delayed second audio signal; and
equalizing the difference signal to boost a low frequency component of the difference signal.
8. A non-transitory computer-readable storage medium storing instructions for encoding an audio signal captured by a microphone array system in the presence of wind noise, the instructions when executed by one or more processors cause the one or more processors to perform steps including:
capturing at least a first audio signal via a first microphone of a microphone array and a second audio signal via a second microphone of the microphone array;
combining the first audio signal and the second audio signal to generate a beamformed audio signal;
determining a selected audio signal having a lower wind noise metric between the first audio signal and the second audio signal;
processing the selected audio signal to modulate the selected audio signal based on a high frequency carrier signal to generate a high frequency signal; and
combining the high frequency signal and the beamformed audio signal to generate an encoded audio signal.
9. The non-transitory computer-readable storage medium of claim 8 , where at least one of the first microphone and the second microphone comprise an omni-directional microphone.
10. The non-transitory computer-readable storage medium of claim 8 , wherein processing the selected audio signal further comprises:
low pass filtering and level-limiting the selecting audio signal.
11. The non-transitory computer-readable storage medium of claim 8 , wherein processing the selected audio signal further comprises:
applying a low pass filter having a cutoff frequency of approximately 4 kHz.
12. The non-transitory computer-readable storage medium of claim 8 , wherein the high frequency carrier signal has a frequency of at least 20 kHz.
13. The non-transitory computer-readable storage medium of claim 8 , wherein determining the selected audio signal having the lower wind noise metric comprises:
performing a comparison of an energy level of the first audio signal with an energy of the second audio signal within a low frequency range in which wind noise is present;
and determining the selected audio signal based on the comparison.
14. The non-transitory computer-readable storage medium of claim 8 , wherein combining the first audio signal with the second audio signal to generate the beamformed audio signal comprises:
delaying the second audio signal by an amount corresponding a time for sound to travel a distance between the first microphone and the second microphone;
computing a difference signal representing a difference between the first audio signal and the delayed second audio signal; and
equalizing the difference signal to boost a low frequency component of the difference signal.
15. An audio capture device for encoding an audio signal in the presence of wind noise, the audio capture system comprising:
a microphone array including at least a first microphone to capture a first audio signal and a second microphone to capture a second audio signal;
a processor; and
a non-transitory computer-readable storage medium storing instructions that when executed by the processor cause the processor to perform steps including:
combining the first audio signal and the second audio signal to generate a beamformed audio signal;
determining a selected audio signal having a lower wind noise metric between the first audio signal and the second audio signal;
processing the selected audio signal to modulate the selected audio signal based on a high frequency carrier signal to generate a high frequency signal; and
combining the high frequency signal and the beamformed audio signal to generate an encoded audio signal.
16. The audio capture device of claim 15 , where at least one of the first microphone and the second microphone comprise an omni-directional microphone.
17. The audio capture device of claim 15 , wherein processing the selected audio signal further comprises:
low pass filtering and level-limiting the selecting audio signal.
18. The audio capture device of claim 15 , wherein processing the selected audio signal further comprises:
applying a low pass filter having a cutoff frequency of approximately 4 kHz.
19. The audio capture device of claim 15 , wherein the high frequency carrier signal has a frequency of at least 20 kHz.
20. The audio capture device of claim 15 , wherein determining the selected audio signal having the lower wind noise metric comprises:
performing a comparison of an energy level of the first audio signal with an energy of the second audio signal within a low frequency range in which wind noise is present;
and determining the selected audio signal based on the comparison.
21. The audio capture device of claim 15 , wherein combining the first audio signal with the second audio signal to generate the beamformed audio signal comprises:
delaying the second audio signal by an amount corresponding a time for sound to travel a distance between the first microphone and the second microphone;
computing a difference signal representing a difference between the first audio signal and the delayed second audio signal; and
equalizing the difference signal to boost a low frequency component of the difference signal.