Direction-aware active noise cancellation system
View Patent ↗Robust feedforward active noise cancellation is provided which can overcome or substantially alleviate problems associated with the diverse and dynamic nature of the surrounding acoustic environment. A multi-faceted analysis is performed to determine the direction (or directions) of propagation of noise in the surrounding acoustic environment. The direction of propagation is then utilized to determine direction-dependent characteristics of the acoustic path between a reference position where the noise is captured and a desired position where the noise is to be cancelled. These characteristics are used to form a feedforward signal adapted to cancel the noise at the desired position. By forming the feedforward signal based on direction-dependent characteristics of the acoustic path, the techniques described herein can achieve optimal noise cancellation at the desired location, regardless of the direction of propagation of the noise.
1. A method for reducing an acoustic energy level at a listening position, the method comprising:
receiving a primary acoustic wave at a first reference position to form a first reference signal;
receiving the primary acoustic wave at a second reference position to form a second reference signal;
separating each of the first reference signal and the second reference signal into a plurality of sub-band signals in the frequency domain;
determining, in the frequency domain, a direction of propagation of the primary acoustic wave for each sub-band of the first reference sub-band signal and each sub-band of the second reference sub-band signal based on the first and second reference sub-band signals;
forming, in the frequency domain, a feedforward sub-band signal based on the determined direction of propagation of the primary acoustic wave; and
generating a secondary acoustic wave based on the feedforward sub-band signal, the secondary acoustic wave adapted to reduce the acoustic energy level at the listening position.
2. The method of claim 1 , wherein determining, in the frequency domain, the direction of propagation of the primary acoustic wave is based on at least one of an amplitude difference and a phase difference between the first reference sub-band signal and the second reference sub-band signal.
3. The method of claim 1 , wherein determining, in the frequency domain, the direction of propagation of the primary acoustic wave is based on a time delay estimation between the first reference sub-band signal and the second reference sub-band signal.
4. The method of claim 1 , wherein:
the primary acoustic wave is received at the first reference position by a first reference microphone;
the secondary acoustic wave is received at the second reference position by a second reference microphone; and
the secondary acoustic wave is generated by an audio transducer proximate the listening position.
5. The method of claim 4 , wherein:
the first reference microphone is arranged on a first earpiece of a headset;
the second reference microphone is arranged on a second earpiece of the headset;
the audio transducer is arranged within the first earpiece of the headset; and
the listening position is proximate the first earpiece of the headset.
6. The method of claim 5 , further comprising:
forming a second feedforward sub-band signal based on the determined direction of propagation of the primary acoustic wave; and
generating a tertiary acoustic wave based on the second feedforward sub-band signal via a second audio transducer arranged within the second earpiece, the tertiary acoustic wave adapted to reduce an acoustic energy level at a second listening position proximate the second earpiece.
7. The method of claim 1 , wherein determining, in the frequency domain, the direction of propagation of the primary acoustic wave comprises determining a location of an acoustic source of the primary acoustic wave, and the feedforward sub-band signal is formed based on the determined location of the acoustic source.
8. The method of claim 1 , wherein:
the primary acoustic wave comprises a plurality of frequency sub-band acoustic waves from a plurality of acoustic sources;
determining, in the frequency domain, the direction of propagation of the primary acoustic wave comprises determining a direction of propagation of each of the plurality of frequency sub-band acoustic waves based on corresponding portions of the first and second reference sub-band signals;
forming the feedforward sub-band signal comprises forming a plurality of frequency sub-band feedforward signals based on the determined direction of propagation of each of the plurality of frequency sub-band acoustic waves; and
generating the secondary acoustic wave is based on the plurality of frequency sub-band feedforward signals.
9. The method of claim 1 , wherein the feedforward sub-band signal is further based on estimated sub-band transfer functions between the listening position and the first and second reference positions, the estimated sub-band transfer functions having corresponding parameters at least comprising an amplitude, at least one of the corresponding parameters being determined as a function of the direction of propagation for each sub-band of the primary acoustic wave.
10. A system for reducing an acoustic energy level at a listening position, the system comprising:
a first reference microphone for receiving a primary acoustic wave at a first reference position to form a first reference signal, receiving the primary acoustic wave comprising converting the primary acoustic wave to a frequency-domain such that the first reference signal is separated into sub-bands in the frequency domain;
a second reference microphone for receiving the primary acoustic wave at a second reference position to form a second reference signal, receiving the primary acoustic wave comprising converting the primary acoustic wave to a frequency-domain such that the second reference signal is separated into sub-bands in the frequency domain;
a feedforward module for determining, in the frequency domain, a direction of propagation of the primary acoustic wave for each sub-band of the first reference signal and each sub-band of the second reference signal based on the first and second reference signals, and to form, in the frequency domain, a feedforward sub-band signal based on the determined direction of propagation of the primary acoustic wave; and
an audio transducer for generating a secondary acoustic wave based on the feedforward sub-band signal, the secondary acoustic wave adapted to reduce the acoustic energy level at the listening position.
11. The system of claim 10 , wherein the feedforward module determines, in the frequency domain, the direction of propagation of the primary acoustic wave based on at least one of an amplitude and a phase difference between the first reference signal and the second reference signal.
12. The system of claim 10 , wherein the feedforward module determines, in the frequency domain, the direction of propagation of the primary acoustic wave based on a time delay estimation between the first reference signal and the second reference signal.
13. The system of claim 10 , wherein:
the first reference microphone is arranged on a first earpiece of a headset;
the second reference microphone is arranged on a second earpiece of the headset;
the audio transducer is arranged within the first earpiece of the headset; and
the listening position is proximate the first earpiece of the headset.
14. The system of claim 13 , wherein the feedforward module further forms a second feedforward signal based on the determined direction of propagation of the primary acoustic wave, and further comprising a second audio transducer to generate a tertiary acoustic wave based on the second feedforward signal, the tertiary acoustic wave adapted to reduce the energy level at a second listening position proximate the second earpiece.
15. The system of claim 10 , wherein the feedforward module determines, in the frequency domain, the direction of propagation by determining a location of an acoustic source of the primary acoustic wave, and the feedforward sub-band signal is formed based on the determined location of the acoustic source.
16. The system of claim 10 , wherein:
the primary acoustic wave comprises a plurality of frequency sub-band acoustic waves from a plurality of acoustic sources;
the feedforward module determines, in the frequency domain, the direction of propagation by determining a direction of propagation of each of the plurality of frequency sub-band acoustic waves based on corresponding portions of the first and second reference signals, and forms a plurality of frequency sub-band feedforward signals based on the determined direction of propagation of each of the plurality of frequency sub-band acoustic waves; and
the audio transducer generates the secondary acoustic wave based on the plurality of frequency sub-band feedforward signals.
17. The system of claim 10 , wherein the feedforward module forms the feedforward sub-band signal further based on estimated sub-band transfer functions between the listening position and the first and second reference positions, the estimated sub-band transfer functions having corresponding parameters at least comprising an amplitude, at least one of the corresponding parameters being determined as a function of the direction of propagation for each sub-band of the primary acoustic wave.
18. A non-transitory computer readable storage medium having embodied thereon a program, the program being executable by a processor to perform a method for reducing an acoustic energy level at a listening position, the method comprising:
receiving a primary acoustic wave at a first reference position to form a first reference signal;
receiving the primary acoustic wave at a second reference position to form a second reference signal;
separating each of the first reference signal and the second reference signal into a plurality of sub-band signals in the frequency domain;
determining, in the frequency domain, a direction of propagation of the primary acoustic wave for each sub-band of the first reference signal and each sub-band of the second reference signal based on the first and second reference signals;
forming, in the frequency domain, a feedforward sub-band signal based on the determined direction of propagation of the primary acoustic wave; and
generating a secondary acoustic wave based on the feedforward sub-band signal, the secondary acoustic wave adapted to reduce the acoustic energy level at the listening position.
19. The non-transitory computer readable storage medium of claim 18 , wherein determining, in the frequency domain, the direction of propagation of the primary acoustic wave is based on at least one of an amplitude difference and a phase difference between the first reference signal and the second reference signal.
20. The non-transitory computer readable storage medium of claim 19 , wherein determining, in the frequency domain, the direction of propagation of the primary acoustic wave is based on a time delay estimation between the first reference signal and the second reference signal.