Coupled acoustic echo cancellation system

• US 6,496,581 B1
• Filed: 09/11/1997
• Issued: 12/17/2002
• Est. Priority Date: 09/11/1997
• Status: Expired due to Term

• Current Assignee: Digisonix Incorporated
• Original Assignee: Digisonix Incorporated
• Inventors: Roe, Thomas O., Finn, Brian M.
• Primary Examiner(s): Isen, Forester W.
• Assistant Examiner(s): SINGH, RAMNANDAN P
• Application Number:
  US08/927,874
• Time in Patent Office: 1,923 Days
• Field of Search: 379/406-411, 379/388, 379/392, 379/41, 379/406.08, 379/407, 379/412, 381/71.21, 381/94, 381/71, 381/73, 381/83, 381/93, 381/71.11, 381/94.7, 381/71-- 7, 381/66, 381/107
• US Class Current: 379/406.01
• CPC Class Codes: G10L 2021/02082 the noise being echo, reverberation of the speech
• CPC Class Codes: G10L 2021/02087 the noise being separate speech, e.g. cocktail party
• CPC Class Codes: H04M 9/082 using echo cancellers echo cancellers per se H04B3/23
• CPC Class Codes: H04R 3/02 for preventing acoustic reaction , i.e. acoustic oscillatory feedback specially adapted for hearing aids H04R25/453

Abstract

Full acoustic coupling and echo cancellation is provided in implementations where there is acoustic coupling between acoustic zones. In acoustic echo cancellation systems, including active acoustic attenuation systems and communications systems, having a first model canceling the speech of a second person in the output of a first microphone otherwise present due to electrical transmission from a second microphone to a first loudspeaker and broadcast by the first loudspeaker to the first microphone, the cancellation of the speech of the second person in the output of the first microphone preventing rebroadcast thereof by the second loudspeaker, and a second model canceling the speech of the first person in the output of the second microphone otherwise present due to electrical transmission from the first microphone to the second loudspeaker and broadcast by the second loudspeaker to the second microphone, the cancellation of the speech of the first person in the output of the second microphone preventing rebroadcast thereof by the first loudspeaker, an improvement provides a third model cancelling the speech of the first person in the output of the first microphone otherwise present due to acoustic transmission from the second loudspeaker in the second zone to the first microphone in the first zone, and a fourth model cancelling the speech of the second person in the output of the second microphone otherwise due to acoustic transmission from the first loudspeaker in the first zone to the second microphone in the second zone. Further improvements and features are provided in various combinations.

Claims

1. In a communication system comprising:

a first acoustic zone;

a second acoustic zone;

a first microphone at said first zone;

a first loudspeaker at said first zone;

a second microphone at said second zone and having an output supplied to said first loudspeaker such that a first person at said first zone can hear the speech of a second person at said second zone as transmitted by said second microphone and said first loudspeaker;

a second loudspeaker at said second zone and having an input supplied from said first microphone such that said second person at said second zone can hear the speech of said first person at said first zone as transmitted by said first microphone and said second loudspeaker;

a first model canceling the speech of said second person in the output of said first microphone otherwise present due to electrical transmission from said second microphone to said first loudspeaker and broadcast by said first loudspeaker to said first microphone, the cancellation of the speech of said second person in the output of said first microphone preventing rebroadcast thereof by said second loudspeaker;

a second model canceling the speech of said first person in the output of said second microphone otherwise present due to electrical transmission from said first microphone to said second loudspeaker and broadcast by said second loudspeaker to said second microphone, the cancellation of the speech of said first person in the output of said second microphone preventing rebroadcast thereof by said first loudspeaker;

the improvement comprising;

a third model canceling the speech of said first person in the output of said first microphone otherwise present due to acoustic transmission from said second loudspeaker in said second zone to said first microphone in said first zone;

a fourth model canceling the speech of said second person in the output of said second microphone otherwise due to acoustic transmission from said first loudspeaker in said first zone to said second microphone in said second zone.

2. The invention according to claim 1 wherein:

said first model models the path from said first loudspeaker to said first microphone;

said second model models the path from said second loudspeaker to said second microphone;

said third model models the path from said second loudspeaker to said first microphone;

said fourth model models the path from said first loudspeaker to said second microphone.

3. The invention according to claim 2 wherein:

said first model has a model input from the input to said first loudspeaker from the output of said second microphone, and a model output to the output of said first microphone to the input to said second loudspeaker;

said second model has a model input from the input to said second loudspeaker from the output of said first microphone, and a model output to the output of said second microphone to the input of said first speaker;

said third model has a model input from the input to said second loudspeaker from the output of said first microphone, and a model output to the output of said first microphone to the input to said second loudspeaker;

said fourth model has a model input from the input to said first loudspeaker from the output of said second microphone, and a model output to the output of said second microphone to the input to said first loudspeaker.

4. The invention according to claim 1 comprising:

a first summer summing outputs of said first and third models and said first microphone, and supplying the resultant sum to said second loudspeaker;

a second summer summing outputs of said second and fourth models and said second microphone, and supplying the resultant sum to said first loudspeaker.

5. The invention according to claim 4 comprising:

a third summer summing the output of said first summer and a first auxiliary noise signal, and supplying the resultant sum to said second loudspeaker;

a fourth summer summing the output of said second summer and a second auxiliary noise signal, and supplying the resultant sum to said first loudspeaker.

6. The invention according to claim 5 wherein:

said first auxiliary noise signal is random and uncorrelated relative to the speech of said first person;

said second auxiliary noise signal is random and uncorrelated relative to the speech of said second person and relative to said first auxiliary random noise signal.

7. The invention according to claim 6 wherein:

said first model has an error correlator having inputs from said first summer and said second auxiliary random noise signal;

said second model has an error correlator having inputs from said second summer and said first auxiliary random noise signal;

said third model has an error correlator having inputs from said first summer and said first auxiliary random noise signal;

said fourth model has an error correlator having inputs from said second summer and said second auxiliary random noise signal.

8. The invention according to claim 5 wherein:

said first model has a model input from the output of said fourth summer, a model output to an input to said first summer, and an error input from the output of said first summer;

said second model has a model input from the output of said third summer, a model output to an input to said second summer, and an error input from the output of said second summer;

said third model has a model input from the output of said third summer, a model output to an input to said first summer, and an error input from the output of said first summer;

said fourth model has a model input from the output of said fourth summer, a model output to an input to said second summer, and an error input from the output of said second summer.

9. The invention according to claim 4 comprising:

a third summer summing the output of said first summer and a desired audio signal for said second zone, and supplying the resultant sum to said second loudspeaker;

a fourth summer summing the output of said second summer and a desired audio signal for said first zone, and supplying the resultant sum to said first loudspeaker.

10. The invention according to claim 4 wherein:

said first model has a model input from the input to said first loudspeaker from the output of said second microphone, a model output to an input to said first summer, and an error input from the output of said first summer;

said second model has a model input from the input to said second loudspeaker from the output of said first microphone, a model output to an input to said second summer, and an error input from the output of said second summer;

said third model has a model input from the input to said second loudspeaker from the output of said first summer, a model output to an input to said first summer, and an error input from the output of said first summer;

said fourth model has a model input from the input to said first loudspeaker from the output of said second summer, a model output to an input to said second summer, and an error input from the output of said second summer.

11. The invention according to claim 10 comprising:

a third summer summing the output of said first summer and a desired audio signal for said second zone, and supplying the resultant sum to said second loudspeaker;

a fourth summer summing the output of said second summer and a desired audio signal for said first zone, and supplying the resultant sum to said first loudspeaker;

and wherein;

said error input of said first model is supplied from a node between said first and third summers;

said error input of said second model is supplied from a node between said second and fourth summers;

said error input of said third model is supplied from said node between said first and third summers;

said error input of said fourth model is supplied from said node between said second and fourth summers;

the model input of said first model is supplied from the output of said fourth summer;

the model input of said second model is supplied from the output of said third summer;

the model input of said third model is supplied from the output of said third summer;

the model input of said fourth model is supplied from the output of said fourth summer.

12. The invention according to claim 1 wherein at least one or more of said models is adaptive.

13. The invention according to claim 1 comprising:

a switch having open and closed states, and conducting the output of one of said microphones therethrough in said closed state;

a voice activity detector having an input from said output of said one microphone at a node between said one microphone and said switch;

an occupant sensor sensing the presence of a person at one of said acoustic zones;

an AND function having a first input from said voice activity detector, a second input from said occupant sensor, and an output to said switch to actuate the latter between said open and closed states.

14. The invention according to claim 1 wherein the input to said first model is supplied through a variable training signal circuit providing increasing training signal levels with increasing speech signal levels from said second microphone.

15. The invention according to claim 14 wherein said training signal circuit comprises:

a summer having a first input from said second microphone, a second input from said training signal, and an output to said first loudspeaker and to said first model;

a variable gain element supplying said training signal to said second input of said summer;

a gate sensing the speech signal level from said second microphone at a node between said second microphone and said first input of said summer, and controlling the gain of said variable gain element.

16. The invention according to claim 14 wherein said variable training signal circuit maintains said training signal levels below a level perceptible to a person at said first zone.

17. The invention according to claim 1 wherein:

the input to said first model is supplied through a first variable training signal circuit providing increasing training signal levels with increasing speech signal levels from said second microphone, said first training signal circuit comprising a first summer having a first input from said second microphone, a second input from a first training signal, and an output to said first loudspeaker and to said first model, a first variable gain element supplying said first training signal to said second input of said first summer, a first gate sensing the speech signal level from said second microphone at a first node between said second microphone and said first input of said first summer, and controlling the gain of said first variable gain element;

the input to said second model is supplied through a second variable training signal circuit providing increasing training signal levels with increasing speech signal levels from said first microphone, said second training signal circuit comprising a second summer having a first input from said first microphone, a second input from a second training signal, and an output to said second loudspeaker and to said second model, a second variable gain element supplying said second training signal to said second input of said second summer, a second gate sensing the speech signal level from said first microphone at a second node between said first microphone and said first input of said second summer, and controlling the gain of said second variable gain element.

18. The invention according to claim 1 comprising a tonal noise remover sensing periodic noise and removing same from the output of said first microphone to prevent broadcast thereof by said second loudspeaker.

19. The invention according to claim 18 wherein said tonal noise remover comprises a summer having a first input from said first microphone, a second input from a tone generator generating one or more tones in response to said periodic noise, and an output to said second loudspeaker.

20. The invention according to claim 19 wherein the output of said tone generator is supplied through an adaptive filter model to said summer.

21. The invention according to claim 20 wherein said adaptive filter model has a model input from said tone generator, a model output supplying a correction signal to said second input to said summer, and an error input from said output of said summer.

22. The invention according to claim 21 wherein said tone generator receives a plurality of tach signals, and outputs a plurality of tone signals for each of said tach signals.

23. The invention according to claim 1 comprising:

a first tonal noise remover sensing periodic noise and removing same from the output of said first microphone to prevent broadcast thereof by said second loudspeaker, said first tonal noise sensor comprising a first summer having a first input from said first microphone, a second input from a first tone generator supplied through a first adaptive filter model, and an output to said second loudspeaker, said first tone generator generating one or more tones in response to periodic noise, said first adaptive filter model having a model input from said first tone generator, a model output supplying a correction signal to said second input to said first summer, and an error input from said output of said first summer;

a second tonal noise remover sensing periodic noise and removing same from the output of said second microphone to prevent broadcast thereof by said first loudspeaker, said second tonal noise sensor comprising a second summer having a first input from said second microphone, a second input from a second tone generator supplied through a second adaptive filter model, and an output to said first loudspeaker, said second tone generator generating one or more tones in response to periodic noise, said second adaptive filter model having a model input from said second tone generator, a model output supplying a correction signal to said second input to said second summer, and an error input from said output of said second summer.

24. The invention according to claim 23 comprising:

a third summer summing the outputs of said first and third models and said first summer, and supplying the resultant sum to said second loudspeaker;

a fourth summer summing the outputs of said second and fourth models and said second summer, and supplying the resultant sum to said first loudspeaker.

25. The invention according to claim 1 comprising a noise responsive high pass filter between said first microphone and said second loudspeaker and having a filter cutoff effective at elevated noise levels and reducing bandwidth and making more gain available, to improve intelligibility of speech of said first person transmitted from said first microphone to said second loudspeaker.

26. The invention according to claim 25 wherein said system is in a vehicle, and said high pass filter is vehicle speed sensitive,

such that at higher vehicle speeds and resulting higher noise levels, lower frequency speech content is blocked and higher frequency speech content is passed, the lower frequency speech content being otherwise masked at higher speeds by broadband vehicle and wind noise, so that the reduced bandwidth and the absence of the lower frequency speech content does not sacrifice the perceived quality of speech,

and such that at lower vehicle speeds and resulting lower noise levels, the cutoff frequency of said filter is lowered such that lower frequency speech content is passed, in addition to higher frequency speech content, to provide enriched low frequency performance, and overcome objections to a tinny sounding system.

27. The invention according to claim 25 comprising a summer having a first input from said first microphone, a second input from a training signal, and an output to said high pass filter, such that said training signal is variably filtered according to noise level.

28. The invention according to claim 25 comprising a summer having a first input from said high pass filter, a second input from a training signal, and an output to said second loudspeaker, such that said training signal is full bandwidth and not variably filtered according to noise level.

29. The invention according to claim 25 comprising:

a second noise responsive high pass filter between said second microphone and said first loudspeaker and having a filter cutoff effective at elevated noise levels and reducing bandwidth and making more gain available, to improve intelligibility of speech of said second person transmitted from said second microphone to said first loudspeaker;

a first summer summing the outputs of said first model and said first mentioned noise responsive high pass filter, and supplying the resultant sum to said second loudspeaker;

a second summer summing the outputs of said second model and said second noise responsive high pass filter, and supplying the resultant sum to said first loudspeaker.

30. The invention according to claim 1 comprising a feedback detector having an input from said first microphone, and an output controlling an adjustable notch filter filtering the output of said first microphone supplied to said second loudspeaker.

31. The invention according to claim 30 wherein:

said adjustable notch filter has an input from the output of said first microphone;

said feedback detector has an input from said first microphone at a node between the output of said first microphone and the input of said adjustable notch filter;

and comprising a summer summing the outputs of said first and third models and said adjustable notch filter, and supplying the resultant sum to said second loudspeaker.

32. The invention according to claim 31 comprising a second feedback detector having an input from said second microphone, and an output controlling a second adjustable notch filter filtering the output of said second microphone supplied to said first loudspeaker, said second adjustable notch filter having an input from the output of said second microphone, said second feedback detector having an input from said second microphone at a second node between the output of said second microphone and the input of said second adjustable notch filter, and comprising a second summer summing the outputs of said second and fourth models and said second adjustable notch filter, and supplying the resultant sum to said first loudspeaker.

33. The invention according to claim 1 comprising a feedback tonal canceler removing tonal noise from the output of said first microphone to prevent broadcast thereof by said second loudspeaker.

34. The invention according to claim 33 wherein said feedback tonal canceler has an input from said first microphone, and an output summed with the output of said first microphone and supplied to said second loudspeaker.

35. The invention according to claim 33 wherein said feedback tonal canceler comprises a summer having a first input from said first microphone, a second input from a tone generator, and an output supplied to said second loudspeaker, and a feedback detector having an input from said first microphone, and an output to said tone generator.

36. The invention according to claim 35 wherein the output of said tone generator is supplied through an adaptive filter model to said second input to said summer.

37. The invention according to claim 36 wherein said adaptive filter model has a model input from said tone generator, a model output supplying a correction signal to said second input to said summer, and an error input from said output of said summer.

38. The invention according to claim 35 comprising a second summer summing the outputs of said first and third models and said first mentioned summer, and supplying the resultant sum to said second loudspeaker.

39. The invention according to claim 38 comprising a second feedback tonal canceler removing tonal noise from the output of said second microphone to prevent broadcast thereof by said first loudspeaker, said second feedback tonal canceler having an input from said second microphone, and an output summed with the output of said second microphone and supplied to said first loudspeaker, said second feedback tonal canceler comprising a third summer having a first input from said second microphone, a second input from a second tone generator, and an output supplied to said first loudspeaker, and a second feedback detector having an input from said second microphone, and an output to said second tone generator, and comprising a fourth summer summing the outputs of said second and fourth models and said third summer, and supplying the resultant sum to said first loudspeaker.

40. In an active acoustic attenuation system comprising:

a first zone subject to noise;

a first speaking location in said first zone such that a first person at said first speaking location is subject to noise;

a first loudspeaker introducing sound into said first zone at said first speaking location;

a first error microphone sensing noise and speech at said first speaking location;

a first model having an error input from said first microphone, and an output outputting a correction signal to said first loudspeaker to introduce canceling sound at said first speaking location to attenuate noise at said first speaking location;

a second zone subject to noise;

a second speaking location in said second zone such that a second person at said second speaking location is subject to noise;

a second loudspeaker introducing sound into said second zone at said second speaking location;

a second error microphone sensing noise and speech at said second speaking location;

a second model having an error input from said second error microphone, and an output outputting a correction signal to said second loudspeaker to introduce canceling sound at said second speaking location to attenuate noise at said second speaking location;

a third model canceling the speech of said second person in the output of said first microphone otherwise present due to electrical transmission from said second microphone to said first loudspeaker and broadcast by said first loudspeaker to said first microphone, the cancellation of the speech of said second person in the output of said first microphone preventing rebroadcast thereof by said second loudspeaker;

a fourth model canceling the speech of said first person in the output of said second microphone otherwise present due to electrical transmission from said first microphone to said second loudspeaker and broadcast by said second loudspeaker to said second microphone, the cancellation of the speech of said first person in the output of said second microphone preventing rebroadcast thereof by said first loudspeaker;

the improvement comprising;

a fifth model canceling the speech of said first person in the output of said first microphone otherwise present due to acoustic transmission from said second loudspeaker in said second zone to said first microphone in said first zone;

a sixth model canceling the speech of said second person in the output of said second microphone otherwise present due to acoustic transmission from said first loudspeaker in said first zone to said second microphone in said second zone.

41. The invention according to claim 40 comprising:

a seventh model having an output outputting a correction signal summed at a first summer with the output of said first microphone to electrically cancel noise from said first zone in the output of said first microphone, and having an error input from the output of said first summer;

an eighth model having a model output outputting a correction signal summed at a second summer with the output of said second microphone to electrically cancel noise from said second zone in the output of said second microphone, and having an error input from the output of said second summer.

42. The invention according to claim 40 comprising:

a first summer summing the outputs of said first model and said second microphone, and supplying the resultant sum to said first loudspeaker;

a second summer summing the outputs of said second model and said first microphone, and supplying the resultant sum to said second loudspeaker;

a third summer summing the outputs of said third and fifth models and said first microphone, and supplying the resultant sum to said second loudspeaker;

a fourth summer summing the outputs of said fourth and sixth models and said second microphone, and supplying the resultant sum to said first loudspeaker;

the output of said fourth summer being supplied to an input of said first summer;

the output of said third summer being supplied to an input of said second summer;

said third model having a model input from the output of said fourth summer, a model output to an input to said third summer, and an error input from the output of said third summer;

said fourth model having a model input from the output of said third summer, a model output to an input to said fourth summer, and an error input from the output of said fourth summer;

said fifth model having a model input from the output of said third summer, a model output to an input to said third summer, and an error input from the output of said third summer;

said sixth model having a model input from the output of said fourth summer, a model output to an input to said fourth summer, and an error input from the output of said fourth summer.

43. The invention according to claim 40 comprising:

a seventh model electrically canceling noise from said first zone in the output of said first microphone;

an eighth model electrically canceling noise from said second zone in the output of said second microphone;

a fifth summer summing the outputs of said seventh model and said first microphone, and supplying the resultant sum to an input to said third summer and to an error input of said seventh model;

a sixth summer summing the outputs of said eighth model and said second microphone, and supplying the resultant sum to an input to said fourth summer and an error input to said eighth model.

44. The invention according to claim 42 comprising:

a fifth summer summing the outputs of said third summer and a first auxiliary noise signal, and supplying the resultant sum to said inputs to said fourth and fifth models and said second summer;

a sixth summer summing the outputs of said fourth summer and a second auxiliary noise signal, and supplying the resultant sum to said inputs to said third and sixth models and said first summer.

45. The invention according to claim 44 wherein:

said first auxiliary noise signal is random and uncortelated relative to said noise in said first zone, the speech of said first person, said noise in said second zone, and the speech of said second person;

said second auxiliary noise signal is random and uncorrelated relative to said noise in said first zone, the speech of said first person, said noise in said second zone, the speech of said second person, and said first random auxiliary noise signal.

46. The invention according to claim 45 wherein said third model has an error correlator having inputs from said third summer and said second random auxiliary noise signal;

said fourth model has an error correlator having inputs from said fourth summer and said first random auxiliary noise signal;

said fifth model has an error correlator having inputs from said third summer and said first random auxiliary noise signal;

said sixth model has an error correlator having inputs from said fourth summer and said second random auxiliary noise signal.

47. The invention according to claim 40 wherein at least one or more of said models is adaptive.

48. A communication system comprising:

a first acoustic zone;

a second acoustic zone;

a first microphone at said first zone;

a first loudspeaker at said first zone;

a second microphone at said second zone and having an output supplied to said first loudspeaker such that a first person at said first zone can hear the speech of a second person at said second zone as transmitted by said second microphone and said first loudspeaker;

a second loudspeaker at said second zone and having an input supplied from said first microphone such that said second person at said second zone can hear the speech of said first person at said first zone as transmitted by said first microphone and said second loudspeaker;

a switch having open and closed states, and conducting the output of one of said microphones therethrough in said closed state;

a voice activity detector having an input from said output of said one microphone at a node between said one microphone and said switch;

an occupant sensor sensing the presence of a person at one of said acoustic zones;

an AND function having a first input from said voice activity detector, a second input from said occupant sensor, and an output to said switch to actuate the latter between said open and closed states.

49. A communication system comprising:

a first acoustic zone;

a second acoustic zone;

a first microphone at said first zone;

a first loudspeaker at said first zone;

a second microphone at said second zone and having an output supplied to said first loudspeaker such that a first person at said first zone can hear the speech of a second person at said second zone as transmitted by said second microphone and said first loudspeaker;

a second loudspeaker at said second zone and having an input supplied from said first microphone such that said second person at said second zone can hear the speech of said first person at said first zone as transmitted by said first microphone and said second loudspeaker;

a first model canceling the speech of said second person in the output of said first microphone otherwise present due to electrical transmission from said second microphone to said first loudspeaker and broadcast by said first loudspeaker to said first microphone, the cancellation of the speech of said second person in the output of said first microphone preventing rebroadcast thereof by said second loudspeaker;

a second model canceling the speech of said first person in the output of said second microphone otherwise present due to electrical transmission from said first microphone to said second loudspeaker and broadcast by said second loudspeaker to said second microphone, the cancellation of the speech of said first person in the output of said second microphone preventing rebroadcast thereof by said first loudspeaker;

a variable training signal circuit supplying an input to said first model and providing increasing training signal levels with increasing speech signal levels from said second microphone.

50. The invention according to claim 49 wherein said training signal circuit comprises:

a summer having a first input from said second microphone, a second input from said training signal, and an output to said first loudspeaker and to said first model;

a variable gain element supplying said training signal to said second input of said summer;

a gate sensing the speech signal level from said second microphone at a node between said second microphone and said first input of said summer, and controlling the gain of said variable gain element.

51. The invention according to claim 50 comprising in combination a second variable training signal circuit supplying an input to said second model and providing increasing training signal levels with increasing speech levels from said first microphone, said second training signal circuit comprising a second summer having a first input from said first microphone, a second input from a second training signal, and an output to said second loudspeaker and to said second model, a second variable gain element supplying said second training signal to said second input of said second summer, a second gate sensing the speech level from said first microphone at a second node between said first microphone and said first input of said second summer, and controlling the gain of said second variable gain element, wherein said training signal circuits maintain training signal levels of said training signals below levels perceptible to persons at said first and second zones.

52. A communication system comprising:

a first acoustic zone;

a second acoustic zone;

a first microphone at said first zone;

a first loudspeaker at said first zone;

a second microphone at said second zone and having an output supplied to said first loudspeaker such that a first person at said first zone can hear the speech of a second person at said second zone as transmitted by said second microphone and said first loudspeaker;

a second loudspeaker at said second zone and having an input supplied from said first microphone such that said second person at said second zone can hear the speech of said first person at said first zone as transmitted by said first microphone and said second loudspeaker;

a first model canceling the speech of said second person in the output of said first microphone otherwise present due to electrical transmission from said second microphone to said first loudspeaker and broadcast by said first loudspeaker to said first microphone, the cancellation of the speech of said second person in the output of said first microphone preventing rebroadcast thereof by said second loudspeaker;

a second model canceling the speech of said first person in the output of said second microphone otherwise present due to electrical transmission from said first microphone to said second loudspeaker and broadcast by said second loudspeaker to said second microphone, the cancellation of the speech of said first person in the output of said second microphone preventing rebroadcast thereof by said first loudspeaker;

a first summer having a first input from said first microphone, a second input from a tone generator generating one or more tones in response to periodic noise, and an output to a second summer.

53. The invention according to claim 52 wherein the output of said tone generator is supplied through an adaptive filter model to said second input to said first summer.

54. The invention according to claim 53 wherein said adaptive filter model has a model input from said tone generator, a model output supplying a correction signal to said second input to said first summer, and an error input from said output of said first summer.

55. The invention according to claim 54 wherein said second summer has a first input from the output of said first model, a second input from the output of said first summer, a third input from the output of a third model and an output supplied to said second loudspeaker.

56. The invention according to claim 52 comprising in combination:

a first tonal noise remover sensing periodic noise and removing same from the output of said first microphone to prevent broadcast thereof by said second loudspeaker, said first tonal noise remover comprising said first summer having said first input from said first microphone, said second input from said tone generator supplied through said adaptive filter model, and said output to said second summer;

a second tonal noise remover sensing periodic noise and removing same from the output of said second microphone to prevent broadcast thereof by said first loudspeaker, said second tonal noise remover comprising a third summer having a first input from said second microphone, a second input from a second tone generator supplied through a second adaptive filter model, and an output to a fourth summer, said second tone generator generating one or more tones in response to periodic noise, said second adaptive filter model having a model input from said second tone generator, a model output supplying a correction signal to said second input to said third summer, and an error input from said output of said third summer.

57. A communication system comprising:

a first acoustic zone;

a second acoustic zone;

a first microphone at said first zone;

a first loudspeaker at said first zone;

a second microphone at said second zone and having an output supplied to said first loudspeaker such that a first person at said first zone can hear the speech of a second person at said second zone as transmitted by said second microphone and said first loudspeaker;

a second loudspeaker at said second zone and having an input supplied from said first microphone such that said second person at said second zone can hear the speech of said first person at said first zone as transmitted by said first microphone and said second loudspeaker;

a first model canceling the speech of said second person in the output of said first microphone otherwise present due to electrical transmission from said second microphone to said first loudspeaker and broadcast by said first loudspeaker to said first microphone, the cancellation of the speech of said second person in the output of said first microphone preventing rebroadcast thereof by said second loudspeaker;

a second model canceling the speech of said first person in the output of said second microphone otherwise present due to electrical transmission from said first microphone to said second loudspeaker and broadcast by said second loudspeaker to said second microphone, the cancellation of the speech of said first person in the output of said second microphone preventing rebroadcast thereof by said first loudspeaker;

a noise responsive high pass filter between said first microphone and said second loudspeaker and having a filter cutoff effective at elevated noise levels and reducing bandwidth and making more gain available, to improve intelligibility of speech of said first person transmitted from said first microphone to said second loudspeaker.

58. The invention according to claim 57 wherein said system is in a vehicle, and said high pass filter is vehicle speed sensitive,

such that at higher vehicle speeds and resulting higher noise levels, lower frequency speech content is blocked and higher frequency speech content is passed, the lower frequency speech content being otherwise masked at higher speeds by broadband vehicle and wind noise,

and such that at lower vehicle speeds and resulting lower noise levels, the cutoff frequency of said filter is lowered such that lower frequency speech content is passed, in addition to higher frequency speech content, to overcome objections to a tinny sounding system.

59. The invention according to claim 57 comprising a summer having a first input from said first microphone, a second input from a training signal, and an output to said high pass filter, such that said training signal is variably filtered according to noise level.

60. The invention according to claim 57 comprising a summer having a first input from said high pass filter, a second input from a training signal, and an output to said second loudspeaker, such that said training signal is full bandwidth and not variably filtered according to noise level.

61. The invention according to claim 57 comprising:

a second noise responsive high pass filter between said second microphone and said first loudspeaker and having a filter cutoff reducing bandwidth and making more gain available, to improve intelligibility of speech of said second person transmitted from said second microphone to said first loudspeaker;

a first summer summing the outputs of said first model and said first mentioned noise responsive high pass filter, and supplying the resultant sum to said second loudspeaker;

a second summer summing the outputs of said second model and said second noise responsive high pass filter, and supplying the resultant sum to said first loudspeaker.

62. A communication system comprising:

a first acoustic zone;

a second acoustic zone;

a first microphone at said first zone;

a first loudspeaker at said first zone;

a second microphone at said second zone and having an output supplied to said first loudspeaker such that a first person at said first zone can hear the speech of a second person at said second zone as transmitted by said second microphone and said first loudspeaker;

a second loudspeaker at said second zone and having an input supplied from said first microphone such that said second person at said second zone can hear the speech of said first person at said first zone as transmitted by said first microphone and said second loudspeaker;

a first model canceling the speech of said second person in the output of said first microphone otherwise present due to electrical transmission from said second microphone to said first loudspeaker and broadcast by said first loudspeaker to said first microphone, the cancellation of the speech of said second person in the output of said first microphone preventing rebroadcast thereof by said second loudspeaker;

a second model canceling the speech of said first person in the output of said second microphone otherwise present due to electrical transmission from said first microphone to said second loudspeaker and broadcast by said second loudspeaker to said second microphone, the cancellation of the speech of said first person in the output of said second microphone preventing rebroadcast thereof by said first loudspeaker;

a feedback detector having an input from said first microphone, and an output controlling an adjustable notch filter filtering the output of said first microphone supplied to said second loudspeaker.

63. The invention according to claim 62 wherein:

said adjustable notch filter has an input from the output of said first microphone;

said feedback detector has an input from said first microphone at a node between the output of said first microphone and the input of said adjustable notch filter;

and comprising a summer having a first input from the output of said first model, a second input from the output of said adjustable notch filter, a third input from the output of a third model, and an output supplied to said second loudspeaker.

64. The invention according to claim 63 comprising a second feedback detector having an input from said second microphone, and an output controlling a second adjustable notch filter filtering the output of said second microphone supplied to said first loudspeaker, said second adjustable notch filter having an input from the output of said second microphone, said second feedback detector having an input from said second microphone at a second node between the output of said second microphone and the input of said second adjustable notch filter, and comprising a second summer having a first input from the output of said second model, a second input from the output of said second adjustable notch filter, a third input from the output of a fourth model, and an output supplied to said first loudspeaker.

65. A communication system comprising:

a first acoustic zone;

a second acoustic zone;

a first microphone at said first zone;

a first loudspeaker at said first zone;

a second microphone at said second zone and having an output supplied to said first loudspeaker such that a first person at said first zone can hear the speech of a second person at said second zone as transmitted by said second microphone and said first loudspeaker;

a second loudspeaker at said second zone and having an input supplied from said first microphone such that said second person at said second zone can hear the speech of said first person at said first zone as transmitted by said first microphone and said second loudspeaker;

a first model canceling the speech of said second person in the output of said first microphone otherwise present due to electrical transmission from said second microphone to said first loudspeaker and broadcast by said first loudspeaker to said first microphone, the cancellation of the speech of said second person in the output of said first microphone preventing rebroadcast thereof by said second loudspeaker;

a second model canceling the speech of said first person in the output of said second microphone otherwise present due to electrical transmission from said first microphone to said second loudspeaker and broadcast by said second loudspeaker to said second microphone, the cancellation of the speech of said first person in the output of said second microphone preventing rebroadcast thereof by said first loudspeaker;

a feedback tonal canceler removing tonal noise from the output of said first microphone to prevent broadcast thereof by said second loudspeaker.

66. The invention according to claim 65 wherein said feedback tonal canceler has an input from said first microphone, and an output summed at a first summer with the output of said first microphone and supplied to a second summer.

67. The invention according to claim 66 wherein said feedback tonal canceler comprises said first summer having a first input from said first microphone, a second input from a tone generator, and an output supplied to said second summer, and a feedback detector having an input from said first microphone, and an output to said tone generator.

68. The invention according to claim 67 wherein the output of said tone generator is supplied through an adaptive filter model to said second input to said first summer.

69. The invention according to claim 68 wherein said adaptive filter model has a model input from said tone generator, a model output outputting a correction signal to said second input to said first summer, and an error input from said output of said first summer.

70. The invention according to claim 67 wherein said second summer has a first input from the output of said first model, a second input from the output of said first summer, a third input from the output of a third model and an output supplied to said second loudspeaker.

71. The invention according to claim 70 comprising a second feedback tonal canceler removing tonal noise from the output of said second microphone to prevent broadcast thereof by said first loudspeaker, said second feedback tonal canceler having an input from said second microphone, and an output summed at a third summer with the output of said second microphone and supplied to said first loudspeaker, said second feedback tonal canceler comprising said third summer having a first input from said second microphone, a second input from a second tone generator, and an output supplied to a fourth summer, and a second feedback detector having an input from said second microphone, and an output to said second tone generator, and comprising said fourth summer having a first input from the output of said second model, a second input from the output of said third summer, and an output supplied to said first loudspeaker.

72. The invention according to claim 71 wherein the output of said second tone generator is supplied through a second adaptive filter model to said second input to said third summer, said second adaptive filter model having a model input from said second tone generator, a model output supplying a correction signal to said second input to said third summer, and an error input from said output of said third summer.

73. A communication system comprising first and second acoustic zones, a microphone at said first zone, a loudspeaker at said second zone and having an input supplied from said microphone such that a person at said second zone can hear the speech of a person at said first zone, a switch having open and closed states and conducting the output of said microphone therethrough in said closed state, a voice activity detector having an input from said output of said microphone at a node between said microphone and said switch, an occupant sensor sensing the presence of a person at said first zone, an AND function having a first input from said voice activity detector, a second input from said occupant sensor, and an output to said switch to actuate the latter between said open and closed states.

74. A communication system comprising first and second acoustic zones, a microphone at said first zone, a loudspeaker at said second zone and having an input supplied from said microphone such that a person at said second zone can hear the speech of a person at said first zone, a tonal noise remover sensing periodic noise and removing same from the output of said microphone to prevent broadcast thereof by said loudspeaker.

75. The invention according to claim 74 wherein said tonal noise remover comprises a summer having a first input from said microphone, a second input from a tone generator generating one or more tones in response to said periodic noise, and an output to said loudspeaker.

76. The invention according to claim 75 wherein the output of said tone generator is supplied through an adaptive filter model to said summer.

77. The invention according to claim 76 wherein said adaptive filter model has a model input from said tone generator, a model output supplying a correction signal to said second input to said summer, and an error input from said output of said summer.

78. The invention according to claim 77 wherein said tone generator receives a plurality of tach signals, and outputs a plurality of tone signals for each of said tach signals.

79. A communication system comprising first and second acoustic zones, a microphone at said first zone, a loudspeaker at said second zone and having an input supplied from said microphone such that a person at said second zone can hear the speech of a person at said first zone, a noise responsive highpass filter between said microphone and said loudspeaker and having a filter cutoff effective at elevated noise levels and reducing bandwidth and making more gain available, to improve intelligibility of speech of said person at said first zone transmitted from said microphone to said loudspeaker.

80. A communication system comprising first and second acoustic zones, a microphone at said first zone, a loudspeaker at said second zone and having an input supplied from said microphone such that a person at said second zone can hear the speech of a person at said first zone, a switch having open and closed states and conducting the output of said microphone therethrough in said closed state, a voice activity detector having an input from said output of said microphone at a node between said microphone and said switch, a noise responsive highpass filter between said microphone and said loudspeaker and having a filter cutoff reducing bandwidth and making more gain available, to improve intelligibility of speech of said person at said first zone transmitted from said microphone to said loudspeaker when said switch is in said closed state.

81. A vehicle communication system comprising first and second acoustic zones in the vehicle, a first microphone at said first zone, a loudspeaker at said second zone and having an input supplied from said microphone such that an occupant at said second zone can hear the speech of an occupant at said first zone, a vehicle speed sensitive highpass filter between said microphone and said loudspeaker and having a filter cutoff reducing bandwidth and making more gain available, to improve intelligibility of speech of said occupant at said first zone transmitted from said microphone to said loudspeaker, such that at higher vehicle speeds, lower frequency speech content is blocked and higher frequency speech content is passed, the lower frequency speech content being otherwise masked at higher speeds by broadband vehicle and wind noise, and such that at lower vehicle speeds, the cutoff frequency of said filter is lowered such that lower frequency speech content is passed, in addition to higher frequency speech content, to overcome objections to a tinny sounding system in said vehicle.