Apparatus and methods for including codes in audio signals

• US 20030081781A1
• Filed: 07/12/2002
• Published: 05/01/2003
• Est. Priority Date: 03/31/1994
• Status: Active Grant

• Current Assignee: The Nielsen Company LLC (MOOD Media Corporation)
• Original Assignee: James M. Jensen, Michael M. Perelshteyn, Robert B. Graybill, Sayed Hassan, Wayne Sabin, Wendell D. Lynch
• Inventors: Graybill, Robert B., Lynch, Wendell D., Jensen, James M., Perelshteyn, Michael M., Sabin, Wayne, Hassan, Sayed
• Granted Patent: US 6,996,237 B2
• Time in Patent Office: Days
• US Class Current: 380/253
• CPC Class Codes: H04H 20/14 for monitoring programmes
• CPC Class Codes: H04H 20/31 using in-band signals, e.g. subsonic or cue signal
• CPC Class Codes: H04H 60/13 Arrangements for device control affected by the broadcast information
• CPC Class Codes: H04H 60/17 on recording information
• CPC Class Codes: H04H 60/37 for identifying segments of broadcast information, e.g. scenes or extracting programme ID
• CPC Class Codes: H04H 60/40 for identifying broadcast time
• CPC Class Codes: H04H 60/44 for identifying broadcast stations
• CPC Class Codes: H04H 60/45 for identifying users
• CPC Class Codes: H04H 60/58 of audio determination or detection of speech characteristics in general G10L25/00; speech recognition in general G10L15/00
• CPC Class Codes: H04H 60/63 for services of sales data processing systems or methods specially adapted for electronic commerce G06Q30/00
• CPC Class Codes: H04H 60/66 for using the result on distributors' side
• CPC Class Codes: H04K 1/02 by adding a second signal to make the desired signal unintelligible
• CPC Class Codes: H04L 27/10 Frequency-modulated carrier systems, i.e. using frequency-shift keying H04L27/32 takes precedence
• CPC Class Codes: H04L 27/30 wherein each code element is represented by a combination of frequencies

Abstract

Apparatus and methods for including a code having at least one code frequency component in an audio signal are provided. The abilities of various frequency components in the audio signal to mask the code frequency component to human hearing are evaluated and based on these evaluations an amplitude is assigned to the code frequency component. Methods and apparatus for detecting a code in an encoded audio signal are also provided. A code frequency component in the encoded audio signal is detected based on an expected code amplitude or on a noise amplitude within a range of audio frequencies including the frequency of the code component.

Claims

1. An apparatus for including a code having at least one code frequency component with an audio signal having a plurality of audio signal frequency components, comprising:

first masking evaluation means for evaluating a masking ability of a first set of the plurality of audio signal frequency components to mask the at least one code frequency component to human hearing to produce a first masking evaluation;

second masking evaluation means for evaluating a masking ability of a second set of the plurality of audio signal frequency components different from the first set thereof to mask the at least one code frequency component to human hearing to produce a second masking evaluation;

amplitude assigning means for assigning an amplitude to the at least one code frequency component based on a selected one of the first and second masking evaluations; and

code inclusion means for including the at least one code frequency component with the audio signal.

2. The apparatus of claim 1, wherein the first set of the plurality of audio signal frequency components is selected from a first frequency range and the second set of the plurality of audio signal frequency components is selected from a second frequency range narrower than the first frequency range.

3. The apparatus of claim 2, wherein the second set of the plurality of audio signal frequency components is limited substantially to a single audio signal frequency component.

4. The apparatus of claim 2, wherein the means for including the at least one code frequency component is operative to include a plurality of code frequency components with the audio signal.

5. The apparatus of claim 4, wherein the plurality of code frequency components includes a first component and a second component having a minimum frequency and a maximum frequency, respectively, among all frequencies of the plurality of code frequency components and the first frequency range extends at least from the minimum frequency of the plurality of code signal components to the maximum frequency thereof.

6. The apparatus of claim 4, wherein the second set of the plurality of audio signal frequency components comprises a plurality of second sets of audio signal frequency components, each of the plurality of second sets being selected from a respective frequency range narrower than the first frequency range, the second masking evaluation means being operative to evaluate the ability of each of the plurality of second sets to mask at least a respective one of the plurality of code signal components to produce corresponding second masking evaluations, the amplitude assigning means being operative to assign a corresponding amplitude to each of the plurality of code signal components based on at least one of the corresponding second evaluations, the code inclusion means being operative to include the plurality of code signal components with the audio signal.

7. The apparatus of claim 6, wherein each of the plurality of second sets of audio signal frequency components is limited substantially to a single audio signal frequency component.

8. The apparatus of claim 7, wherein the first set of the plurality of audio signal frequency components is selected from a range of audio signal frequencies having a bandwidth corresponding to that of a critical band for the at least one code frequency component.

9. The apparatus of claim 1, wherein the code comprises a plurality of code frequency component sets, each of the code frequency component sets representing a respectively different code symbol and including a plurality of respectively different code frequency components, the code frequency components of the code frequency component sets forming component clusters spaced from one another within the frequency domain, each of the component clusters having a respective predetermined frequency range and consisting of one frequency component from each of the code frequency component sets falling within its respective predetermined frequency range, component clusters which are adjacent within the frequency domain being separated by respective frequency amounts, and wherein the predetermined frequency range of each respective component cluster is smaller than the frequency amounts separating the respective component cluster from its adjacent component clusters.

10. The apparatus of claim 1, wherein the first masking evaluation means is operative to detect signal power of audio signal frequency components of the first set within a specified frequency range, to determine first and second masking factors on the conditions that the signal power is at each of first and second frequencies, respectively, within the specified frequency range, the second frequency being different than the first frequency, to select that one of the first and second masking factors which represents a smaller amplitude of the at least one code frequency component, and to determine the masking ability of the first set of the plurality of audio signal frequency components based on the selected masking factor.

11. The apparatus of claim 1, in combination with means for decoding the encoded audio signal to detect the at least one code frequency component.

12. The apparatus of claim 1, wherein the amplitude assigning means is operative to select said one of the first and second masking evaluations based on relative abilities of the first and second sets of the plurality of audio signal frequency components to mask the at least one code frequency component.

13. A method for including a code having at least one code frequency component with an audio signal having a plurality of audio signal frequency components, comprising the steps of:

evaluating a masking ability of a first set of the plurality of audio signal frequency components to mask the at least one code frequency component to human hearing to produce a first masking evaluation;

evaluating a masking ability of a second set of the plurality of audio signal frequency components to mask the at least one code frequency component to human hearing to produce a second masking evaluation;

assigning an amplitude to the at least one code frequency component based on a selected one of the first and second masking evaluations; and

including the at least one code frequency component with the audio signal.

14. The method of claim 13, further comprising the step of decoding the encoded audio signal to detect the at least one code frequency component.

15. The method of claim 13, further comprising the step of producing the at least one code frequency component in response to data representing at least one of a broadcast source, an audio and/or video program source and an audio and/or video program identification.

16. The method of claim 13, wherein the code comprises a plurality of code frequency component sets, each of the code frequency component sets representing a respectively different code symbol and including a plurality of respectively different code frequency components, the code frequency components of the code frequency component sets forming component clusters spaced from one another within the frequency domain, each of the component clusters having a respective predetermined frequency range and consisting of one frequency component from each of the code frequency component sets falling within its respective predetermined frequency range, component clusters which are adjacent within the frequency domain being separated by respective frequency amounts, and wherein the predetermined frequency range of each respective component cluster is smaller than the frequency amounts separating the respective component cluster from its adjacent component clusters.

17. The method of claim 13, wherein the step of evaluating the masking ability of the first set includes detecting signal power of audio signal frequency components of the first set within a specified frequency range, determining first and second masking factors on the conditions that the signal power is at each of first and second frequencies, respectively, within the specified frequency range, the second frequency being different than the first frequency, selecting that one of the first and second masking factors which represents a smaller amplitude of the at least one code frequency component, and determining the masking ability of the first set of the plurality of audio signal frequency components based on the selected masking factor.

18. An apparatus for including a code having at least one code frequency component with an audio signal having a plurality of audio signal frequency components, comprising:

a digital computer having an input for receiving the audio signal, the digital computer being programmed to evaluate respective masking abilities of first and second sets of the plurality of audio signal frequency components to mask the at least one code frequency component to human hearing to produce respective first and second masking evaluations, the second set of the plurality of audio signal frequency components differing from the first set thereof, the digital computer being further programmed to assign an amplitude to the at least one code frequency component based on a selected one of the first and second masking evaluations; and

means for including the at least one code frequency component with the audio signal.

19. The apparatus of claim 18, wherein the digital computer is operative to select the first set of the plurality of audio signal frequency components as those of said plurality of audio signal frequency components within a first group of audio frequencies, and is further operative to select the second set of the plurality of audio signal frequency components from a second group of audio frequencies including at least one frequency outside the first group of audio frequencies.

20. The apparatus of claim 18, wherein the digital computer includes an input for receiving data representing at least one of a broadcast source, an audio and/or video program source and an audio and/or video program identification and is programmed to produce the at least one code frequency component in response to said data.

21. The apparatus of claim 18, in combination with a decoder having an input for receiving the encoded audio signal and operative to detect the at least one code frequency component.

22. The apparatus of claim 18, wherein the digital computer is programmed to produce the code as a plurality of code frequency component sets, each of the code frequency component sets representing a respectively different code symbol and including a plurality of respectively different code frequency components, the code frequency components of the code frequency component sets forming component clusters spaced from one another within the frequency domain, each of the component clusters having a respective predetermined frequency range and consisting of one frequency component from each of the code frequency component sets falling within its respective predetermined frequency range, component clusters which are adjacent within the frequency domain being separated by respective frequency amounts, and wherein the predetermined frequency range of each respective component cluster is smaller than the frequency amounts separating the respective component cluster from its adjacent component clusters.

23. The apparatus of claim 18, wherein the digital computer is programmed to detect signal power of audio signal frequency components of the first set within a specified frequency range, to determine first and second masking factors on the conditions that the signal power is at each of first and second frequencies, respectively, within the specified frequency range, the second frequency being different than the first frequency, to select that one of the first and second masking factors which represents a smaller amplitude of the at least one code frequency component, and to assign the amplitude to the at least one code frequency component based on the selected masking factor.

24. An apparatus for including a code having a plurality of code frequency components with an audio signal having a plurality of audio signal frequency components, the plurality of code frequency components including a first code frequency component having a first frequency and a second code frequency component having a second frequency different from the first frequency, comprising:

first masking evaluation means for evaluating a masking ability of at least one of the plurality of audio signal frequency components to mask a code frequency component having the first frequency to human hearing to produce a first respective masking evaluation;

second masking evaluation means for evaluating a masking ability of at least one of the plurality of audio signal frequency components to mask a code frequency component having the second frequency to human hearing to produce a second respective masking evaluation;

amplitude assigning means for assigning a respective amplitude to the first code frequency component based on the first respective masking evaluation and for assigning a respective amplitude to the second code frequency component based on the second respective masking evaluation; and

code inclusion means for including the plurality of code frequency components with the audio signal.

25. The apparatus of claim 24, wherein the first and second respective masking evaluations comprise signal level data corresponding to respective levels of the first and second code frequency components.

26. The apparatus of claim 24, wherein the code comprises a plurality of code frequency component sets, each of the code frequency component sets representing a respectively different code symbol and including a plurality of respectively different code frequency components, the code frequency components of the code frequency component sets forming component clusters spaced from one another within the frequency domain, each of the component clusters having a respective predetermined frequency range and consisting of one frequency component from each of the code frequency component sets falling within its respective predetermined frequency range, component clusters which are adjacent within the frequency domain being separated by respective frequency amounts, and wherein the predetermined frequency range of each respective component cluster is smaller than the frequency amounts separating the respective component cluster from its adjacent component clusters.

27. The apparatus of claim 24, wherein the first masking evaluation means is operative to detect signal power of audio signal frequency components of the at least one of the plurality of audio signal frequency components within a specified frequency range, to determine first and second masking factors on the conditions that the signal power is at each of first and second frequencies, respectively, within the specified frequency range, the second frequency being different than the first frequency, to select that one of the first and second masking factors which represents a smaller amplitude of the at least one code frequency component, and to determine the masking ability of the at least one of the plurality of audio signal frequency components based on the selected masking factor.

28. The apparatus of claim 24, in combination with means for decoding the encoded audio signal to detect the first and second code frequency components.

29. The apparatus of claim 24, further comprising means for producing the first code frequency component to represent a first information symbol and for producing the second code frequency component to represent a second information symbol different from the first information symbol.

30. The apparatus of claim 29, wherein the code inclusion means is operative to include the first and second code frequency components in a common interval of the audio signal.

31. The apparatus of claim 24, further comprising means for producing the first and second code frequency components in response to data representing at least one of a broadcast source, an audio and/or video program source and an audio and/or video program identification.

32. A method for including a code having a plurality of code frequency components with an audio signal having a plurality of audio signal frequency components, the plurality of code frequency components including a first code frequency component having a first frequency and a second code frequency component having a second frequency different from the first frequency, comprising the steps of:

evaluating a masking ability of at least one of the plurality of audio signal frequency components to mask a code frequency component having the first frequency to human hearing to produce a first respective masking evaluation;

evaluating a masking ability of at least one of the plurality of audio signal frequency components to mask a code frequency component having the second frequency to human hearing to produce a second respective masking evaluation;

assigning a respective amplitude to the first code frequency component based on the first respective masking evaluation and a respective amplitude to the second code frequency component based on the second respective masking evaluation; and

including the plurality of code frequency components with the audio signal.

33. The method of claim 32, further comprising the step of decoding the encoded audio signal to detect the first and second code frequency components.

34. The method of claim 32, further comprising the step of producing the first and second code frequency components in response to data representing at least one of a broadcast source, an audio and/or video program source and an audio and/or video program identification.

35. The method of claim 32, wherein the code comprises a plurality of code frequency component sets, each of the code frequency component sets representing a respectively different code symbol and including a plurality of respectively different code frequency components, the code frequency components of the code frequency component sets forming component clusters spaced from one another within the frequency domain, each of the component clusters having a respective predetermined frequency range and consisting of one frequency component from each of the code frequency component sets falling within its respective predetermined frequency range, component clusters which are adjacent within the frequency domain being separated by respective frequency amounts, and wherein the predetermined frequency range of each respective component cluster is smaller than the frequency amounts separating the respective component cluster from its adjacent component clusters.

36. The method of claim 32, wherein the step of evaluating the masking ability of at least one of the plurality of audio signal frequency components to mask a code frequency component having the first frequency includes detecting signal power of audio signal frequency components within a specified frequency range, determining first and second masking factors on the conditions that the signal power is at each of first and second frequencies, respectively, within the specified frequency range, the second frequency being different than the first frequency, selecting that one of the first and second masking factors which represents a smaller amplitude of the at least one code frequency component, and determining the masking ability of the at least one of the plurality of audio signal frequency components to mask a code frequency component having the first frequency based on the selected masking factor.

37. An apparatus for including a code having a plurality of code frequency components with an audio signal having a plurality of audio signal frequency components, the plurality of code frequency components including a first code frequency component having a first frequency and a second code frequency component having a second code frequency different from the first frequency, comprising:

a digital computer having an input for receiving the audio signal, the digital computer being programmed to evaluate a masking ability of at least one of the plurality of audio signal frequency components to mask a code frequency component having the first frequency to human hearing to produce a first respective masking evaluation and to evaluate a masking ability of at least one of the plurality of audio signal frequency components to mask a code frequency component having the second frequency to human hearing to produce a second respective masking evaluation;

the digital computer being further programmed to assign a corresponding amplitude to the first code frequency component based on the first respective masking evaluation and to assign a corresponding amplitude to the second code frequency component based on the second respective masking evaluation; and

means for including the plurality of code frequency components with the audio signal.

38. The apparatus of claim 37, wherein the first and second respective masking evaluations comprise signal level data corresponding to respective levels of the first and second code frequency components.

39. The apparatus of claim 37, in combination with a decoder having an input for receiving the encoded audio signal and operative to detect the first and second code frequency components.

40. The apparatus of claim 37, wherein the digital computer includes an input to receive data representing at least one of a broadcast source, an audio and/or video program source, and an audio and/or video program identification and is programmed to produce the first and second code frequency components in response to said data.

41. The apparatus of claim 37, wherein the means for including the plurality of code frequency components in the audio signal comprises a summing circuit having a first input for receiving the audio signal and a second input coupled with the digital computer to receive the plurality of code frequency components and an output for providing the encoded audio signal.

42. The apparatus of claim 37, wherein the means for including the plurality of code frequency components in the audio signal comprises said digital computer, said digital computer being programmed to add the plurality of code frequency components with the audio signal to include the plurality of code frequency components therewith.

43. The apparatus of claim 37, wherein the digital computer is programmed to produce the code as a plurality of code frequency component sets, each of the code frequency component sets representing a respectively different code symbol and including a plurality of respectively different code frequency components, the code frequency components of the code frequency component sets forming component clusters spaced from one another within the frequency domain, each of the component clusters having a respective predetermined frequency range and consisting of one frequency component from each of the code frequency component sets falling within its respective predetermined frequency range, component clusters which are adjacent within the frequency domain being separated by respective frequency amounts, and wherein the predetermined frequency range of each respective component cluster is smaller than the frequency amounts separating the respective component cluster from its adjacent component clusters.

44. The apparatus of claim 37, wherein the digital computer is programmed to evaluate the masking ability of the at least one of the plurality of audio signal frequency components by detecting signal power of audio signal frequency components within a specified frequency range, to determine first and second masking factors with respect to the code frequency component having the first frequency on the conditions that the signal power is at each of first and second frequencies, respectively, within the specified frequency range, the second frequency being different than the first frequency, and to select that one of the first and second masking factors which represents a smaller amplitude of the at least one code frequency component, the digital computer being programmed to assign the amplitude to the first code frequency component based on the selected masking factor.

45. An apparatus for including a code having at least one code frequency component with an audio signal including a plurality of audio signal frequency components, comprising:

masking evaluation means for evaluating an ability of at least one of the plurality of audio signal frequency components within a first audio signal interval on a time scale of the audio signal when reproduced as sound during a corresponding first time interval to mask the at least one code frequency component to human hearing when reproduced as sound during a second time interval corresponding to a second audio signal interval offset from the first audio signal interval to produce a first masking evaluation;

amplitude assigning means for assigning an amplitude to the at least one code frequency component based on the first masking evaluation; and

code inclusion means for including the at least one code frequency component with a portion of the audio signal within the second audio signal interval.

46. The apparatus of claim 45, wherein the second audio signal interval follows the first audio signal interval on the time scale of the audio signal.

47. The apparatus of claim 45, wherein the second audio signal interval precedes the first audio signal interval on the time scale of the audio signal.

48. The apparatus of claim 45, in combination with means for decoding the encoded audio signal to detect the at least one code frequency component.

49. The apparatus of claim 45, further comprising means for producing the at least one code frequency component in response to data representing at least one of a broadcast source, an audio and/or video program source and an audio and/or video program identification.

50. A method for including a code having at least one code frequency component with an audio signal including a plurality of audio signal frequency components, comprising the steps of:

evaluating an ability of at least one of the plurality of audio signal frequency components within a first audio signal interval on a time scale of the audio signal when reproduced as sound during a corresponding first time interval to mask the at least one code frequency component to human hearing when reproduced as sound during a second time interval corresponding to a second audio signal interval offset from the first audio signal interval to produce a first masking evaluation;

assigning an amplitude to the at least one code frequency component based on the first masking evaluation; and

including the at least one code frequency component with a portion of the audio signal within the second audio signal interval.

51. The method of claim 50, further comprising the step of decoding the encoded audio signal to detect the at least one code frequency component.

52. The method of claim 50, further comprising the step of producing the at least one code frequency component in response to data representing at least one of a broadcast source, an audio and/or video program source and an audio and/or video program identification.

53. An apparatus for including a code having at least one code frequency component with an audio signal including a plurality of audio signal frequency components, comprising:

a digital computer having an input for receiving the audio signal, the digital computer being programmed to evaluate an ability of at least one of the plurality of audio signal frequency components within a first audio signal interval on a time scale of the audio signal when reproduced as sound during a corresponding first time interval to mask the at least one code frequency component to human hearing when reproduced as sound during a second time interval corresponding to a second audio signal interval offset from the first audio signal interval, to produce a first masking evaluation;

the digital computer being further programmed to assign an amplitude to the at least one code frequency component based on the first masking evaluation; and

means for including the at least one code frequency component with a portion of the audio signal within the second audio signal interval.

54. The apparatus of claim 53, in combination with a decoder having an input for receiving the encoded audio signal and operative to detect the first and second code frequency components therein.

55. The apparatus of claim 53, wherein the digital computer includes an input for receiving data representing at least one of a broadcast source, an audio and/or video program source, and an audio and/or video program identification and is programmed to produce the at least one code frequency component in response to said data.

56. An apparatus for including a code having at least one code frequency component with an audio signal having a plurality of audio signal frequency components, comprising:

tonal signal producing means for producing a first tonal signal representing a first substantially single one of the plurality of audio signal frequency components;

masking evaluation means for evaluating a masking ability of the first substantially single one of the plurality of audio signal frequency components to mask the at least one code frequency component to human hearing based on the first tonal signal to produce a first masking evaluation;

amplitude assigning means for assigning an amplitude to the at least one code frequency component based on the first masking evaluation; and

code inclusion means for including the at least one code frequency component with the audio signal.

57. The apparatus of claim 56, wherein the tonal signal producing means is operative to produce a second tonal signal representing a second substantially single one of the plurality of audio signal frequency components different from the first substantially single one thereof, the masking evaluation means is operative to evaluate the ability of the second substantially single one of the plurality of audio signal frequency components to mask the at least one code frequency component to human hearing based on the second tonal signal to produce a second masking evaluation, and the amplitude assigning means is operative to assign an amplitude to the at least one code frequency component based on a selected one of the first and second masking evaluations.

58. The apparatus of claim 57, wherein the amplitude assigning means is operative to select said one of the first and second masking evaluations as that one of the first and second masking evaluations which indicates a greater ability of a corresponding one of the first and second substantially single ones of the plurality of audio signal frequency components to mask the at least one code frequency component to human hearing.

59. The apparatus of claim 56, in combination with decoding means for decoding the encoded audio signal to detect the at least one code frequency component.

60. The apparatus of claim 56, further comprising means for producing the at least one code frequency component in response to data representing at least one of a broadcast source, an audio and/or video program source and an audio and/or video program identification.

61. The apparatus of claim 56, wherein the code comprises a plurality of code frequency component sets, each of the code frequency component sets representing a respectively different code symbol and including a plurality of respectively different code frequency components, the code frequency components of the code frequency component sets forming component clusters spaced from one another within the frequency domain, each of the component clusters having a respective predetermined frequency range and consisting of one frequency component from each of the code frequency component sets falling within its respective predetermined frequency range, component clusters which are adjacent within the frequency domain being separated by respective frequency amounts, and wherein the predetermined frequency range of each respective component cluster is smaller than the frequency amounts separating the respective component cluster from its adjacent component clusters.

62. The apparatus of claim 56, wherein the masking evaluation means is operative to detect signal power of the first substantially single one of the plurality of the audio signal frequency components within a specified frequency range, to determine first and second masking factors on the conditions that the signal power is at each of first and second frequencies, respectively, within the specified frequency range, the second frequency being different than the first frequency, to select that one of the first and second masking factors which represents a smaller amplitude of the at least one code frequency component, and to determine the masking ability of the first substantially single one of the plurality of the audio signal frequency components based on the selected masking factor.

63. The apparatus of claim 56, wherein said masking evaluation means is operative to produce said first masking evaluation only when said at least one code frequency component is within a critical band of said first substantially single one of the plurality of audio signal frequency components.

64. The apparatus of claim 56, wherein said code includes a plurality of code frequency components, and said amplitude assigning means is operative to assign the amplitude to the at least one code frequency component based on a number of the code frequency components within a critical band of the at least one code frequency component.

65. The apparatus of claim 56, wherein said tonal signal producing means is also operative to produce a second tonal signal representing a second substantially single one of the plurality of audio signal frequency components;

said masking evaluation means is also operative to evaluate an ability of said second substantially single one of the plurality of audio signal frequency components to mask the at least one code frequency component to human hearing based on the second tonal signal to produce a second masking evaluation; and

said amplitude assigning means is operative to assign said amplitude to the at least one code frequency component based on the first and second masking evaluations.

66. The apparatus of claim 65, wherein said amplitude assigning means is operative to assign the amplitude to the at least one code frequency component based on a distribution of power between said first and second tonal signals.

67. A method for including a code having at least one code frequency component with an audio signal having a plurality of audio signal frequency components, comprising the steps of:

producing a first tonal signal representing a first substantially single one of the plurality of audio signal frequency components;

evaluating a masking ability of the first substantially single one of the plurality of audio signal frequency components to mask the at least one code frequency component to human hearing based on the first tonal signal to produce a first masking evaluation;

assigning an amplitude to the at least one code frequency component based on the first masking evaluation; and

including the at least one code frequency component with the audio signal.

68. The method of claim 67, further comprising the step of decoding the encoded audio signal to detect the at least one code frequency component.

69. The method of claim 67, further comprising the step of producing the at least one code frequency component in response to data representing at least one of a broadcast source, an audio and/or video program source and an audio and/or video program identification.

70. The method of claim 67, wherein the code comprises a plurality of code frequency component sets, each of the code frequency component sets representing a respectively different code symbol and including a plurality of respectively different code frequency components, the code frequency components of the code frequency component sets forming component clusters spaced from one another within the frequency domain, each of the component clusters having a respective predetermined frequency range and consisting of one frequency component from each of the code frequency component sets falling within its respective predetermined frequency range, component clusters which are adjacent within the frequency domain being separated by respective frequency amounts, and wherein the predetermined frequency range of each respective component cluster is smaller than the frequency amounts separating the respective component cluster from its adjacent component clusters.

71. The method of claim 67, wherein the step of evaluating the masking ability of the first substantially single one of the plurality of audio signal frequency components includes detecting signal power of the first substantially single one of the plurality of audio signal frequency components within a specified frequency range, determining first and second masking factors on the conditions that the signal power is at each of first and second frequencies, respectively, within the specified frequency range, the second frequency being different than the first frequency, selecting that one of the first and second masking factors which represents a smaller amplitude of the at least one code frequency component, and determining the masking ability of the first substantially single one of the plurality of audio signal frequency components based on the selected masking factor.

72. The method of claim 67, wherein the step of evaluating a masking ability occurs only when said at least one code frequency component is within a critical band of said first substantially single one of the plurality of audio signal frequency components.

73. The method of claim 67, wherein said code includes a plurality of code frequency components, and the step of assigning an amplitude to the at least one code frequency component is based on a number of the code frequency components within a critical band of the at least one code frequency component.

74. The method of claim 67, further including the steps of:

producing a second tonal signal representing a second substantially single one of the plurality of audio signal frequency components;

evaluating a masking ability of said second substantially single one of the plurality of audio signal frequency components to mask the at least one code frequency component to human hearing based on the second tonal signal to produce a second masking evaluation; and

wherein the step of assigning assigns the amplitude to the at least one code frequency component based on the first and second masking evaluations.

75. The method of claim 74, wherein the step of assigning assigns the amplitude to the at least one code frequency component based on a distribution of power between said first and second tonal signals.

76. An apparatus for including a code having at least one code frequency component with an audio signal having a plurality of audio signal frequency components, comprising:

a digital computer having an input for receiving the audio signal, the digital computer being programmed to produce a first tonal signal representing a first substantially single one of the plurality of audio signal frequency components and to evaluate a masking ability of the first substantially single one of the plurality of audio signal frequency components to mask the at least one code frequency component to human hearing based on the first tonal signal to produce a first masking evaluation, the digital computer being further programmed to assign an amplitude to the at least one code frequency component based on the first masking evaluation; and

code inclusion means for including the at least one code frequency component with the audio signal.

77. The apparatus of claim 76, wherein the digital computer includes an input for receiving data representing at least one of a broadcast source, an audio and/or video program source and an audio and/or video program identification and is programmed to produce the at least one code frequency component in response to said data.

78. The apparatus of claim 76, in combination with a decoder having an input for receiving the encoded audio signal and operative to detect the at least one code frequency component.

79. The apparatus of claim 76, wherein the digital computer is programmed to produce the code as a plurality of code frequency component sets, each of the code frequency component sets representing a respectively different code symbol and including a plurality of respectively different code frequency components, the code frequency components of the code frequency component sets forming component clusters spaced from one another within the frequency domain, each of the component clusters having a respective predetermined frequency range and consisting of one frequency component from each of the code frequency component sets falling within its respective predetermined frequency range, component clusters which are adjacent within the frequency domain being separated by respective frequency amounts, and wherein the predetermined frequency range of each respective component cluster is smaller than the frequency amounts separating the respective component cluster from its adjacent component clusters.

80. The apparatus of claim 76, wherein the digital computer is programmed to detect signal power of the first substantially single one of the plurality of the audio signal frequency components within a specified frequency range, to determine first and second masking factors on the conditions that the signal power is at each of first and second frequencies, respectively, within the specified frequency range, the second frequency being different than the first frequency, and to select that one of the first and second masking factors which represents a smaller amplitude of the at least one code frequency component, the digital computer being further programmed to assign the amplitude to the at least one code frequency component based on the selected masking factor.

81. The apparatus of claim 76, wherein the digital computer is programmed to produce said first masking evaluation only when said at least one code frequency component is within a critical band of said first substantially single one of the plurality of audio signal frequency components.

82. The apparatus of claim 76, wherein said code includes a plurality of code frequency components, and said digital computer is programmed to assign the amplitude to the at least one code frequency component based on a number of the code frequency components within a critical band of the at least one code frequency component.

83. The apparatus of claim 76, wherein said digital computer is programmed to produce a second tonal signal representing a second substantially single one of the plurality of audio signal frequency components;

to evaluate an ability of said second substantially single one of the plurality of audio signal frequency components to mask the at least one code frequency component to human hearing based on the second tonal signal to produce a second masking evaluation; and

to assign said amplitude to the at least one code frequency component based on the first and second masking evaluations.

84. The apparatus of claim 83, wherein said digital computer is programmed to assign the amplitude to the at least one code frequency component based on a distribution of power between said first and second tonal signals.

85. An apparatus for encoding an audio signal, comprising:

means for generating a code comprising a plurality of code frequency component sets, each of the code frequency component sets representing a respectively different code symbol and including a plurality of respectively different code frequency components, the code frequency components of the code frequency component sets forming component clusters spaced from one another within the frequency domain, each of the component clusters having a respective predetermined frequency range and consisting of one frequency component from each of the code frequency component sets falling within its respective predetermined frequency range, component clusters which are adjacent within the frequency domain being separated by respective frequency amounts, the predetermined frequency range of each respective component cluster being smaller than the frequency amounts separating the respective component cluster from its adjacent component clusters; and

code inclusion means for combining the code with the audio signal.

86. A method for encoding an audio signal, comprising:

generating a code comprising a plurality of code frequency component sets, each of the code frequency component sets representing a respectively different code symbol and including a plurality of respectively different code frequency components, the code frequency components of the code frequency component sets forming component clusters spaced from one another within the frequency domain, each of the component clusters having a respective predetermined frequency range and consisting of one frequency component from each of the code frequency component sets falling within its respective predetermined frequency range, component clusters which are adjacent within the frequency domain being separated by respective frequency amounts, the predetermined frequency range of each respective component cluster being smaller than the frequency amounts separating the respective component cluster from its adjacent component clusters; and

combining the code with the audio signal.

87. An apparatus for encoding an audio signal, comprising:

a digital computer having an input for receiving the audio signal, the digital computer being programmed to produce a code comprising a plurality of code frequency component sets, each of the code frequency component sets representing a respectively different code symbol and including a plurality of respectively different code frequency components, the code frequency components of the code frequency component sets forming component clusters spaced from one another within the frequency domain, each of the component clusters having a respective predetermined frequency range and consisting of one frequency component from each of the code frequency component sets falling within its respective predetermined frequency range, component clusters which are adjacent within the frequency domain being separated by respective frequency amounts, the predetermined frequency range of each respective component cluster being smaller than the frequency amounts separating the respective component cluster from its adjacent component clusters; and

means for combining the code with the audio signal.

88. An apparatus for detecting a code in an encoded audio signal, the encoded audio signal including a plurality of audio frequency signal components and at least one code frequency component having an amplitude and an audio frequency selected for masking the code frequency component to human hearing by at least one of the plurality of audio frequency signal components, comprising:

means for establishing an expected code amplitude of the at least one code frequency component based on the encoded audio signal; and

means for detecting the code frequency component in the encoded audio signal based on the expected code amplitude.

89. The apparatus of claim 88, further comprising means for detecting a first component of the encoded audio signal at the audio frequency of the at least one code frequency component, and wherein the means for detecting the code frequency component is operative to determine whether an amplitude of the detected first component corresponds with the expected code amplitude.

90. The apparatus of claim 88, wherein the means for detecting the first component of the encoded audio signal comprises means for separating the encoded audio signal into frequency component groups each including one or more components within a corresponding frequency range, a first one of the frequency component groups having a corresponding frequency range including the audio frequency of the at least one code frequency component.

91. A method for detecting a code in an encoded audio signal, the encoded audio signal including a plurality of audio frequency signal components and at least one code frequency component having an amplitude and an audio frequency selected for masking the code frequency component to human hearing by at least one of the plurality of audio frequency signal components, comprising the steps of:

establishing an expected code amplitude of the at least one code frequency component based on the encoded audio signal; and

detecting the code frequency component in the encoded audio signal based on the expected code amplitude.

92. A programmed digital computer for detecting a code in an encoded audio signal, the encoded audio signal including a plurality of audio frequency signal components and at least one code frequency component having an amplitude and an audio frequency selected for masking the code frequency component to human hearing by at least one of the plurality of audio frequency signal components, comprising:

an input for receiving the encoded audio signal;

a processor programmed to establish an expected code amplitude of the at least one code frequency component based on the encoded audio signal, to detect the code frequency component in the encoded audio signal based on the expected code amplitude and to produce a detected code output signal based on the detected code frequency component; and

an output coupled with the processor for providing the detected code output signal.

93. An apparatus for detecting a code in an encoded audio signal, the encoded audio signal having a plurality of frequency components including a plurality of audio frequency signal components and at least one code frequency component having a predetermined audio frequency and a predetermined amplitude for distinguishing the at least one code frequency component from the plurality of audio frequency signal components, comprising:

means for determining an amplitude of frequency components of the encoded audio signal within a first range of audio frequencies including the predetermined audio frequency of the at least one code frequency component;

means for establishing a noise amplitude for the first range of audio frequencies; and

means for detecting the presence of the at least one code frequency component in the first range of audio frequencies based on the established noise amplitude thereof and the determined amplitude of frequency components therein.

94. A method for detecting a code in an encoded audio signal, the encoded audio signal having a plurality of frequency components including a plurality of audio frequency signal components and at least one code frequency component having a predetermined audio frequency and a predetermined amplitude for distinguishing the at least one code frequency component from the plurality of audio frequency signal components, comprising the steps of:

determining an amplitude of a frequency component of the encoded audio signal within a first range of audio frequencies including the predetermined audio frequency of the at least one code frequency component;

establishing a noise amplitude for the first range of audio frequencies; and

detecting the presence of the at least one code frequency component in the first range of audio frequencies based on the established noise amplitude thereof and the determined amplitude of the frequency component therein.

95. A digital computer for detecting a code in an encoded audio signal, the encoded audio signal having a plurality of frequency components including a plurality of audio frequency signal components and at least one code frequency component having a predetermined audio frequency and a predetermined amplitude for distinguishing the at least one code frequency component from the plurality of audio frequency signal components, comprising:

an input for receiving the encoded audio signal;

a processor coupled with the input to receive the encoded audio signal and programmed to determine an amplitude of a frequency component of the encoded audio signal within a first range of audio frequencies including the predetermined audio frequency of the at least one code frequency component;

the processor being further programmed to establish a noise amplitude for the first range of audio frequencies and to detect the presence of the at least one code frequency component in the first range of audio frequencies based on the established noise amplitude thereof and the determined amplitude of the frequency component therein;

the processor being operative to produce a code output signal based on the detected presence of the at least one code frequency component; and

an output terminal coupled with the processor to provide the code signal thereat.