Active noise reduction adaptive filtering
An active noise reduction system that reduces the incidence of divergence in the presence of high amplitude interfering noise. A limited frequency range threshold is established.
1. Apparatus comprising:
a feed forward active noise reduction system comprising
a vehicle cabin;
a transducer for transducing acoustic noise in the vehicle cabin to a noise signal;
circuitry for determining the amplitude of the noise signal in a limited portion of the frequency range;
circuitry for comparing the amplitude of the noise signal in the limited portion of the frequency range with a limited frequency range threshold, wherein the limited frequency range is one of
below the frequency of the first amplitude peak of the engine noise, or
between amplitude peaks of engine noise; and
circuitry for modifying the noise signal if the amplitude of the noise signal in the limited portion of the frequency range exceeds the limited frequency range threshold.
2. An apparatus according to claim 1 , further comprising:
circuitry for determining the amplitude of the noise signal over a broadband frequency range;
circuitry for comparing the amplitude of the noise signal in the broadband frequency range with a broadband threshold; and
circuitry for modifying the noise signal if the amplitude of the noise signal in the limited portion of the frequency range exceeds the limited frequency range threshold or the amplitude of the noise signal in the broadband frequency range exceeds the broadband threshold.
3. An apparatus according to claim 2 , wherein the broadband frequency range threshold is different than the limited frequency range threshold.
4. An apparatus according to claim 1 , wherein the circuitry for modifying the noise signal comprises circuitry for modifying a gain applied to the noise signal.
5. An apparatus according to claim 1 , further comprising a low pass filter for filtering the noise signal to provide a low pass filtered noise signal; and
circuitry for providing the low pass filtered noise signal to the circuitry for comparing the noise signal in the limited portion of the frequency range.
6. An apparatus according to claim 1 , further comprising:
a band pass filter for filtering the noise signal to provide a band pass filtered noise signal; and
circuitry for providing the band pass filtered noise signal to the circuitry for comparing the noise signal in the limited portion of the frequency range.
7. Apparatus comprising:
a feed-forward active noise reduction system, comprising a transducer for transducing acoustic noise at a location to a noise signal;
circuitry for determining the amplitude of the noise signal in a broadband frequency range;
circuitry for comparing the amplitude of the noise signal in the broadband frequency range with a broadband threshold;
circuitry for determining the amplitude of the noise signal over a limited portion of the broadband frequency range;
circuitry for comparing the amplitude of the noise signal in the limited portion of the broadband frequency range with a limited frequency range threshold, wherein the limited frequency range is one of
below the frequency of the first amplitude peak of the engine noise, or
between amplitude peaks of engine noise; and
circuitry for modifying the noise signal if the amplitude of the noise signal in the broadband frequency range exceeds the broadband threshold or the amplitude of the noise signal in the limited portion of broadband frequency range exceeds the limited frequency range threshold.
8. An apparatus according to claim 7 , wherein the circuitry for modifying the noise signal comprises circuitry for modifying a gain applied to the noise signal.
9. An apparatus according to claim 7 , further comprising:
a low pass filter for filtering the noise signal to provide a low pass filtered noise signal; and
circuitry for providing the low pass filtered noise signal to the circuitry for comparing the noise signal in the limited portion of the broadband frequency range.
10. An apparatus according to claim 7 , further comprising:
a band pass filter for filtering the noise signal to provide a band pass filtered noise signal; and
circuitry for providing the band pass filtered noise signal to the circuitry for comparing the noise signal in the limited portion of the broadband frequency range.
11. An apparatus according to claim 7 , wherein the active noise reduction system is for reducing acoustic noise in a vehicle cabin.
12. An apparatus according to claim 7 , wherein the broadband threshold is different than the limited frequency range threshold.
13. A method for operating a feed forward active noise reduction system, comprising:
transducing acoustic noise in a vehicle cabin to a noise signal;
determining the amplitude of the noise signal in a limited portion of the frequency range;
comparing the amplitude of the noise signal in the limited portion of the frequency range with a limited frequency range threshold, wherein the limited frequency range is one of
below the frequency of the first amplitude peak of noise resulting from operation of a vehicle engine, or
between amplitude peaks of the noise resulting from the operation of the vehicle engine; and
if the amplitude of the noise signal in the limited portion of the frequency range exceeds the limited frequency range threshold, modifying the noise signal.
14. A method according to claim 13 , further comprising:
determining the amplitude of the noise signal over a broadband frequency range;
comparing the amplitude of the noise signal in the broadband frequency range with a broadband threshold; and
if the amplitude of the noise signal in the limited portion of the frequency range exceeds the limited frequency range threshold or the amplitude of the noise signal in the broadband frequency range exceeds the broadband threshold, modifying the noise signal.
15. A method according to claim 13 , wherein the modifying the noise signal comprises modifying a gain applied to the noise signal.
16. A method according to claim 13 , further comprising low pass filtering the noise signal prior to the comparing the noise signal in the limited portion of the frequency range.
17. A method according to claim 13 , further comprising band pass filtering the noise signal prior to the comparing the noise signal in the limited portion of the frequency range.
18. The method of claim 13 , wherein the modifying prevents the feed-forward active noise reduction system from diverging in the presence of high amplitude noise not resulting from the operation of the engine of the vehicle.
19. The method of claim 13 wherein the method detects the presence of high amplitude noise not resulting from the operation of the engine of the vehicle.
20. A method for operating a feed-forward active noise reduction system, comprising:
detecting acoustic energy at a location;
transducing the acoustic noise to a noise signal;
determining the amplitude of the noise signal in a broadband frequency range;
comparing the amplitude of the noise signal in the broadband frequency range with a broadband threshold;
determining the amplitude of the noise signal over a limited portion of the broadband frequency range;
comparing the amplitude of the noise signal in the limited portion of the broadband frequency range with a limited frequency range, wherein the limited frequency range is one of
below the frequency of a first amplitude peak of noise resulting from the operation of an engine, or
between amplitude peaks of noise resulting from operation of the engine; and
if the amplitude of the noise signal in the broadband frequency range exceeds the broadband threshold or the amplitude of the noise signal in the limited portion of the broadband frequency range exceeds the limited frequency range threshold, modifying the noise signal.
21. A method according to claim 20 , wherein the modifying the noise signal comprises modifying a gain applied to the noise signal.
22. A method according to claim 20 , further comprising low pass filtering the noise signal prior to the comparing the noise signal in the limited portion of the broadband frequency range.
23. A method according to claim 20 , further comprising band pass filtering the noise signal prior to the comparing the noise signal in the limited portion of the broadband frequency range.
24. A method according to claim 20 , wherein the location is in a vehicle cabin.
25. A method according to claim 20 wherein the broadband threshold is different than the limited frequency range threshold.
26. The method of claim 20 , wherein the modifying prevents the feed-forward active noise reduction system from diverging in the presence of high amplitude noise not resulting from operation of the engine.
27. The method of claim 20 , wherein the method detects the presence of high amplitude noise not resulting from the operation of the engine.