Audio decoder for wind and microphone noise reduction in a microphone array system
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 decoding an encoded audio signal, the method comprising:
receiving the encoded audio signal, the encoded audio signal representing a non-beamformed audio signal modulated from a low frequency range to a high frequency range and combined with a beamformed audio signal spanning the low frequency range and a mid-frequency range between the low frequency range and the high frequency range;
responsive to receiving an input to recover the beamformed audio signal, applying a low pass filter to the encoded audio signal to filter out the non-beamformed audio signal modulated from the low frequency range to the high frequency range to generate an original audio signal; and
responsive to receiving an input to recover a reduced wind noise audio signal, processing the encoded audio signal to generate the reduced wind noise audio signal, the reduced wind noise audio signal representing the non-beamformed audio signal in the low frequency range and the beamformed audio signal in the mid-frequency range.
2. The method of claim 1 , wherein processing the encoded audio signal to generate the reduced wind noise audio signal comprises:
band-pass filtering the encoded audio signal according to a first band-pass filter corresponding to the high frequency range to obtain the band-passed non-beamformed signal;
amplifying the band-passed filtered signal to generate an amplified first band-pass filtered signal;
demodulating the amplified first band-pass filtered signal based on a carrier signal to recover the non-beamformed audio signal in the low frequency range;
band-pass filtering the encoded audio signal according to a second band-pass filter corresponding to the mid-frequency range to recover a band-passed portion of the beamformed audio signal in the mid-frequency range;
combining the recovered non-beamformed audio signal in the low frequency range with the recovered band-passed portion of the beamformed audio signal in the mid-frequency range to generate a decoded audio signal.
3. The method of claim 2 , wherein the first band pass filter has a low cutoff frequency of at least 20 kHz and a high cutoff frequency approximately 4 kHz above a frequency of the carrier signal.
4. The method of claim 2 wherein the carrier signal comprises approximately 20 kHz.
5. The method of claim 2 , wherein the second band-pass filter has a low cutoff frequency of approximately 4 kHz and a high cutoff frequency of at least 20 kHz.
6. A non-transitory computer-readable storage medium storing instructions for decoding an encoded audio signal, the instructions when executed by one or more processors cause the one or more processors to perform steps including:
receiving the encoded audio signal, the encoded audio signal representing a non-beamformed audio signal modulated from a low frequency range to a high frequency range and combined with a beamformed audio signal spanning the low frequency range and a mid-frequency range between the low frequency range and the high frequency range;
responsive to receiving an input to recover the beamformed audio signal, applying a low pass filter to the encoded audio signal to filter out the non-beamformed audio signal modulated from the low frequency range to the high frequency range to generate an original audio signal; and
responsive to receiving an input to recover a reduced wind noise audio signal, processing the encoded audio signal to generate the reduced wind noise audio signal, the reduced wind noise audio signal representing the non-beamformed audio signal in the low frequency range and the beamformed audio signal in the mid-frequency range.
7. The non-transitory computer-readable storage medium of claim 6 , wherein processing the encoded audio signal to generate the reduced wind noise audio signal comprises:
band-pass filtering the encoded audio signal according to a first band-pass filter corresponding to the high frequency range to obtain the band-passed non-beamformed signal;
amplifying the band-passed filtered signal to generate an amplified first band-pass filtered signal;
demodulating the amplified first band-pass filtered signal based on a carrier signal to recover the non-beamformed audio signal in the low frequency range;
band-pass filtering the encoded audio signal according to a second band-pass filter corresponding to the mid-frequency range to recover a band-passed portion of the beamformed audio signal in the mid-frequency range;
combining the recovered non-beamformed audio signal in the low frequency range with the recovered band-passed portion of the beamformed audio signal in the mid-frequency range to generate a decoded audio signal.
8. The non-transitory computer-readable storage medium of claim 7 , wherein the first band pass filter has a low cutoff frequency of at least 20 kHz and a high cutoff frequency approximately 4 kHz above a frequency of the carrier signal.
9. The non-transitory computer-readable storage medium of claim 7 , wherein the carrier signal comprises approximately 20 kHz.
10. The non-transitory computer-readable storage medium of claim 7 , wherein the second band-pass filter has a low cutoff frequency of approximately 4 kHz and a high cutoff frequency of at least 20 kHz.
11. A method for decoding an encoded audio signal, the method comprising:
receiving the encoded audio signal, the encoded audio signal representing a non-beamformed audio signal modulated from a low frequency range to a high frequency range and combined with a beamformed audio signal spanning the low frequency range and a mid-frequency range, the mid-frequency range between the low frequency range and the high frequency range;
band-pass filtering the encoded audio signal according to a first band-pass filter corresponding to the high frequency range to obtain a first band-pass filtered signal;
amplifying the first band-pass filtered signal to generate an amplified first band-pass filtered signal;
demodulating the amplified first band-pass filtered signal to recover the non-beamformed audio signal in the low frequency range;
band-pass filtering the encoded audio signal according to a second band-pass filter corresponding to the mid-frequency range to recover a band-passed portion of the beamformed audio signal in the mid-frequency range;
combining the recovered non-beamformed audio signal in the low frequency range with the recovered band-passed portion of the beamformed audio signal in the mid-frequency range to generate a decoded audio signal.
12. The method of claim 11 , wherein the first band pass filter has a low cutoff frequency of at least 20 kHz and a high cutoff frequency approximately 4 kHz above a frequency of the carrier signal.
13. The method of claim 11 , wherein the carrier signal comprises approximately 20 kHz.
14. The method of claim 11 , wherein the second band-pass filter has a low cutoff frequency of approximately 4 kHz and a high cutoff frequency of at least 20 kHz.
15. A non-transitory computer-readable storage medium storing instructions for decoding an encoded audio signal, the instructions when executed by one or more processors cause the one or more processors to perform steps including:
receiving the encoded audio signal, the encoded audio signal representing a non-beamformed audio signal modulated from a low frequency range to a high frequency range and combined with a beamformed audio signal spanning the low frequency range and a mid-frequency range, the mid-frequency range between the low frequency range and the high frequency range;
band-pass filtering the encoded audio signal according to a first band-pass filter corresponding to the high frequency range to obtain a first band-pass filtered signal;
amplifying the first band-pass filtered signal to generate an amplified first band-pass filtered signal;
demodulating the amplified first band-pass filtered signal to recover the non-beamformed audio signal in the low frequency range;
band-pass filtering the encoded audio signal according to a second band-pass filter corresponding to the mid-frequency range to recover a band-passed portion of the beamformed audio signal in the mid-frequency range;
combining the recovered non-beamformed audio signal in the low frequency range with the recovered band-passed portion of the beamformed audio signal in the mid-frequency range to generate a decoded audio signal.
16. The non-transitory computer-readable storage medium of claim 15 , wherein the first band pass filter has a low cutoff frequency of at least 20 kHz and a high cutoff frequency approximately 4 kHz above a frequency of the carrier signal.
17. The non-transitory computer-readable storage medium of claim 15 , wherein the carrier signal comprises approximately 20 kHz.
18. The non-transitory computer-readable storage medium of claim 15 , wherein the second band-pass filter has a low cutoff frequency of approximately 4 kHz and a high cutoff frequency of at least 20 kHz.