Apparatus and methods for including codes in audio signals and decoding

• US 5,764,763 A
• Filed: 03/24/1995
• Issued: 06/09/1998
• Est. Priority Date: 03/31/1994
• Status: Expired due to Term

• Current Assignee: The Nielsen Company LLC (MOOD Media Corporation)
• Original Assignee: Arbitron Inc. (MOOD Media Corporation)
• Inventors: Graybill, Robert B., Lynch, Wendell D., Jensen, James M., Perelshteyn, Michael M., Sabin, Wayne, Hassan, Sayed
• Primary Examiner(s): Barron, Jr., Gilberto
• Application Number:
  US08/408,010
• Time in Patent Office: 1,173 Days
• Field of Search: 380/6, 455/2, 348/1
• 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

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 with an audio signal having a plurality of audio signal frequency components, the 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 code frequency components, comprising:

means for producing the code frequency component sets, 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;

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 code frequency component sets with the audio signal.

2. 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, the first masking evaluation means being 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 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;

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.

3. A method for including a code with an audio signal having a plurality of audio signal frequency components, the 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 code frequency components, comprising the steps of:

producing the code frequency component sets, 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;

evaluating a masking ability of a first set of the plurality of audio signal frequency components to mask 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 code frequency component sets with the audio signal.

4. 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, by 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 factors;

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.

5. An apparatus for including a code with an audio signal having a plurality of audio signal frequency components, the 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 code frequency components, comprising:

a digital processor having an input for receiving the audio signal, the digital processor being programmed to produce the code frequency components such that said components form 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, the digital processor being further 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 processor 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 code frequency component sets with the audio signal.

6. 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 processor having an input for receiving the audio signal, the digital processor 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 processor being operative to evaluate the masking ability of the first set by detecting signal power of audio signal frequency components of the first set within a specified frequency range, detecting 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, the digital processor 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.

7. 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 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 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:

means for producing the 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;

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.

8. 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, the first masking evaluation means being operative to detect signal power 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;

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.

9. 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 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 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:

producing the 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;

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 marking 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 marking 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 marking evaluation; and

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

10. 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, by 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;

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 the code frequency components with the audio signal.

11. 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:

a digital processor having an input for receiving the audio signal, the digital processor 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 processor being further 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;

the digital processor 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.

12. 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 processor having an input for receiving the audio signal, the digital processor being programmed to produce a first respective masking evaluation by 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, wherein the digital processor 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, determining 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, 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 based on the selected masking factors;

the digital processor being further 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 second frequency to human hearing to produce a second respective masking evaluation;

the digital processor 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.

13. An apparatus for including a code with an audio signal having a plurality of audio signal frequency components, 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 comprising:

means for producing the code frequency component sets, 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;

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 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 code frequency component sets with the audio signal.

14. 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 signal power of a first substantially single one of the plurality of the audio signal frequency components within a specified frequency range;

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, the masking evaluation means being operative to determine first and second masking factors on the conditions that the signal power represented by the first tonal signal 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;

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.

15. 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, 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.

16. An apparatus for including a code with an audio signal having a plurality of audio signal frequency components, wherein said code includes a plurality of code 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 based on a number of the code frequency components within a critical band of the at least one code frequency component; and

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

17. 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 and a second tonal signal representing a second 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;

said masking evaluation means being 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;

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

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

18. The apparatus of claim 17, 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.

19. A method for including a code with an audio signal having a plurality of audio signal frequency components, 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, comprising the steps of:

producing the code frequency component sets, 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;

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 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.

20. 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 signal power of a first substantially single one of the plurality of audio signal frequency components within a specified frequency range;

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, by determining first and second masking factors on the conditions that the signal power represented by the first tonal signal 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;

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.

21. 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, 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.

22. A method for including a code with an audio signal having a plurality of audio signal frequency components, wherein said code includes a plurality of code 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 based on a number of the code frequency components within a critical band of the at least one code frequency component; and

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

23. 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 and a second tonal signal representing a second 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;

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;

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

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

24. The method of claim 23, 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.

25. An apparatus for including a code with an audio signal having a plurality of audio signal frequency components, comprising:

a digital processor having an input for receiving the audio signal, the digital processor being programmed to produce the code as a plurality of code frequency component sets, each of the code frequency component set representing a respectively different code symbol and including a plurality of respectively different code frequency components, the code frequency components of the code frequency components, the code frequency component cluster spaced from one another within the frequency domain, each of the component cluster 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 cluster;

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

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

26. 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 processor having an input for receiving the audio signal, the digital processor being programmed to produce a first tonal signal representing signal power of a first substantially single one of the plurality of the audio signal frequency components within a specified frequency range, the digital processor being further programmed 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, by determining first and second masking factors on the conditions that the signal power represented by the first tonal signal 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 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;

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

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

27. 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 processor having an input for receiving the audio signal, the digital processor 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 wherein the digital processor 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, the digital processor 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.

28. An apparatus for including a code with an audio signal having a plurality of audio signal frequency components, wherein said code includes a plurality of code frequency components, comprising:

a digital processor having an input for receiving the audio signal, the digital processor 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, said digital processor being further programmed to assign an amplitude to the at least one code frequency component based on the first masking evaluation and based on a number of the code frequency components within a critical band of the at least one code frequency component; and

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

29. 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 processor having an input for receiving the audio signal, the digital processor being programmed to produce a first tonal signal representing a first substantially single one of the plurality of audio signal frequency components and to produce a second tonal signal representing a second substantially single one of the plurality of audio signal frequency components;

the digital processor being further programmed 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 and 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;

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

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

30. The apparatus of claim 29, 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.

31. 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.

32. 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.

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

a digital processor having an input for receiving the audio signal, the digital processor 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.

34. A method for including a code having a plurality of code frequency components with an audio signal, comprising the steps of:

producing a first code frequency component;

producing a second code frequency component separately from the first code frequency component;

evaluating a first ability of the audio signal to mask the first code frequency component to produce a first masking evaluation;

evaluating a second ability of the audio signal to mask the second code frequency component to produce a second masking evaluation;

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

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

including the first and second code frequency components with the audio signal.

35. The method of claim 34, wherein each of the first and second code frequency components is initially generated so that its amplitude is selected for masking by the audio signal.

36. The method of claim 34, wherein the respective amplitudes are assigned to the first and second code frequency components after the first and second frequency components are generated.

37. The method of claim 34, wherein the first and second frequency components are produced in response to data representing one symbol.

38. An apparatus for including a code having a plurality of code frequency components with an audio signal, comprising:

means for producing a first code frequency component;

means for producing a second code frequency component separately from the first code frequency component;

means for evaluating a first ability of the audio signal to mask the first code frequency component to produce a first masking evaluation;

means for evaluating a second ability of the audio signal to mask the second code frequency component to produce a second masking evaluation;

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

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

means for including the first and second code frequency components with the audio signal.

39. The apparatus of claim 38, wherein the means for producing the first and second frequency components are operative to produce the first and second frequency components in response to data representing one symbol.

40. An apparatus for including a code having a plurality of code frequency components with an audio signal, comprising:

a digital processor having an input for receiving the audio signal, the digital processor being programmed to produce a first code frequency component, to produce a second code frequency component separately from the first code frequency component, to evaluate a first ability of the audio signal to mask the first code frequency component to produce a first masking evaluation, to evaluate a second ability of the audio signal to mask the second code frequency component to produce a second masking evaluation, to assign a first amplitude to the first code frequency component based on the first masking evaluation, and to assign a second amplitude to the second code frequency component based on the second masking evaluation; and

means for including the first and second code frequency components with the audio signal.

41. The apparatus of claim 40, wherein the digital processor is programmed to produce the first and second code frequency components in response to data representing one symbol.