Encoding and decoding of information in audio signals

Abstract

Systems and methods are provided for decoding a message symbol in an audio signal. This message symbol is represented by first and second code symbols displaced in time. Values representing the code signals are accumulated and the accumulated values are examined to detect the message symbol.

1. A system for decoding a predetermined message symbol of a plurality of message symbols embedded in an audio signal, comprising:
 means for receiving an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being contained within a predetermined message as a plurality of code symbols, the predetermined message symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols; 
 means for accumulating a first signal value of the first code symbol representing the predetermined message symbol and a second signal value of the second code symbol representing the predetermined message symbol; and 
 means for examining the accumulated first and second signal values to detect the predetermined message symbol represented by the first and second code symbols. 
 
     
     
       2. The system of  claim 1 , wherein the accumulating means is operative to produce a third signal value derived from the first and second signal values and the examining means is operative to detect the predetermined message symbol based on the third signal value. 
     
     
       3. The system of  claim 2 , wherein the accumulating means is operative to produce the third signal value by linearly combining the first and second signal values. 
     
     
       4. The system of  claim 2 , wherein the accumulating means is operative to produce the third signal value as a non-linear function of the first and second signal values. 
     
     
       5. The system of  claim 1 , wherein the accumulating means is operative to store the first and second signal values, and the examining means is operative to detect the predetermined message symbol by examining both of the first and second signal values. 
     
     
       6. The system of  claim 1 , wherein the receiving means comprises an acoustic transducer for transducing an acoustic audio signal to an electrical signal, the acoustic audio signal having a plurality of code symbols representing a plurality of message symbols comprising source data for the acoustic audio signal, and further comprising a memory for storing indications of detected message symbols. 
     
     
       7. The system of  claim 5 , further comprising a housing for the system adapted to be carried on the person of an audience member and means for transmitting the stored data for use in producing audience estimates. 
     
     
       8. A method for decoding a predetermined message symbol of a plurality of message symbols incorporated in an audio signal, comprising:
 receiving an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being contained within a predetermined message as a plurality of code symbols, the predetermined message symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols; 
 accumulating a first signal value of the first code symbol representing the predetermined message symbol and a second signal value of the second code symbol representing the predetermined message symbol; and 
 examining the accumulated first and second signal values to detect the predetermined message symbol. 
 
     
     
       9. The method of  claim 8 , further comprising receiving the first and second code symbols by transducing an acoustic audio signal to an electrical signal, the acoustic audio signal having a plurality of message symbols comprising source data for the acoustic audio signal, and storing data representing indications of detected message symbols. 
     
     
       10. The method of  claim 9 , further comprising transmitting the stored data for use in producing audience estimates. 
     
     
       11. A system for decoding a predetermined message symbol of a plurality of message symbols incorporated in an audio signal, comprising:
 an input device for an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being contained within a predetermined message as a plurality of code symbols, the predetermined message symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols; and 
 a digital processor in communication with the input device to receive the audio signal therefrom, the digital processor being programmed to accumulate a first signal value representing the first code symbol and a second signal value representing the second code symbol, the digital processor being further programmed to examine the accumulated first and second signal values to detect the predetermined message symbol. 
 
     
     
       12. The system of  claim 11 , wherein the input device comprises an acoustic transducer for transducing an acoustic signal to an electrical signal, the acoustic audio signal having a plurality of code symbols representing a plurality of message symbols comprising source data for the acoustic audio signal, the digital processor having a memory for storing data representing indications of detected message symbols. 
     
     
       13. The system of  claim 12 , further comprising a housing for the system adapted to be carried on the person of an audience member and means for transmitting the stored data for use in producing audience estimates. 
     
     
       14. A system for decoding a predetermined message symbol of a plurality of message symbols embedded in an audio signal, comprising:
 means for receiving an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being contained within a predetermined message as a plurality of code symbols, the predetermined message symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols, the first and second code symbols each comprising a predetermined number of frequency components; 
 means for producing first and second sets of component values, each set corresponding to a respective one of the first and second code symbols and each component value of each set representing a characteristic of a respective frequency component of the corresponding symbol; 
 means for accumulating a first signal value of the first code symbol representing the predetermined message symbol based on the first set of component values and a second signal value of the second code symbol representing the predetermined message symbol based on the second set of component values; and 
 means for examining the accumulated first and second signal values to detect the predetermined message symbol represented by the first and second code symbols. 
 
     
     
       15. A method for decoding a predetermined message symbol of a plurality of message symbols incorporated in an audio signal, comprising:
 receiving an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being contained within a predetermined message as a plurality of code symbols, the predetermined message symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols, the first and second code symbols each comprising a predetermined number of frequency components; 
 producing first and second sets of component values, each set corresponding to a respective one of the first and second code symbols and each component value of each set representing a characteristic of a respective frequency component of the corresponding symbol; 
 accumulating a first signal value of the first code symbol representing the predetermined message symbol based on the first set of component values and a second signal value of the second code symbol representing the predetermined message symbol based on the second set of component values; and examining the accumulated first and second signal values to detect the predetermined message symbol. 
 
     
     
       16. A system for decoding a predetermined message symbol of a plurality of message symbols incorporated in an audio signal, comprising:
 an input device for an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being contained within a predetermined message as a plurality of code symbols, the predetermined message symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols, the first and second code symbols each comprising a predetermined number of frequency components; and 
 a digital processor in communication with the input device to receive the audio signal therefrom, the digital processor being programmed to produce first and second sets of component values, each set corresponding to a respective one of the first and second code symbols and each component value of each set representing a characteristic of a respective frequency component of the corresponding symbol the digital processor being further programmed to produce a first signal value based on the first set of component values and a second signal value based on the second set of component values and to accumulate a first signal value representing the first code symbol and a second signal value representing the second code symbol, the digital processor being further programmed to examine the accumulated first and second signal values to detect the predetermined message symbol. 
 
     
     
       17. A system for decoding predetermined message symbols of a plurality of message symbols embedded in an audio signal, comprising:
 means for receiving an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being represented by plural sets of first and second code symbols, each set representing a respective one of the plurality of message symbols, the plural sets of first and second code symbols being arranged as a message having a predetermined sequence including at least one marker symbol and at least one data symbol, at least one of the marker symbol and the data symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols; 
 means for accumulating sets of first and second signal values, each signal value set corresponding to a respective one of the sets of first and second code symbols and including a first signal value representing the first code symbol of the respective code symbol set and a second signal value representing the second code symbol thereof; and 
 means for examining the accumulated sets of first and second signal values to detect the presence of the at least one marker symbol based on its signal value set and to detect the at least one data symbol based on the detected presence of the at least one marker symbol and the corresponding signal value set of the at least one data symbol. 
 
     
     
       18. A method for decoding predetermined message symbols of a plurality of message symbols incorporated in an audio signal, comprising:
 receiving an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being represented by plural sets of first and second code symbols, each set representing a respective one of the plurality of message symbols, the plural sets of first and second code symbols being arranged as a message having a predetermined sequence including at least one marker symbol and at least one data symbol, at least one of the marker symbol and the data symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols; 
 accumulating sets of first and second signal values, each signal value set corresponding to a respective one of the sets of first and second code symbols and including a first signal value representing the first code symbol of the respective code symbol set and a second signal value representing the second code symbol thereof; and 
 examining the accumulated sets of first and second signal values to detect the presence of the marker symbol based on its signal value set and to detect at least one data symbol based on the detected presence of the marker symbol and the corresponding signal value set of the at least one data symbol. 
 
     
     
       19. A system for decoding predetermined message symbols of a plurality of message symbols incorporated in an audio signal, comprising:
 an input device for an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being represented by plural sets of first and second code symbols, each set representing a respective one of the plurality of message symbols, the plural sets of first and second code symbols being arranged as a message having a predetermined sequence including at least one marker symbol and at least one data symbol, at least one of the marker symbol and the data symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols; and 
 a digital processor in communication with the input device to receive the audio signal therefrom, the digital processor being programmed to accumulate sets of first and second signal values, each signal value set corresponding to a respective one of the sets of first and second code symbols and including a first signal value representing the first code symbol of the respective code symbol set and a second signal value representing the second code symbol thereof, the digital processor being further programmed to examine the accumulated sets of first and second signal values to detect the presence of the marker symbol based on its signal value set and to detect at least one data symbol based on the detected presence of the marker symbol and the corresponding signal value set of the at least one data symbol. 
 
     
     
       20. A system for decoding a predetermined message symbol of a plurality of message symbols embedded in an audio signal, comprising:
 means for receiving an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being contained within a predetermined message as a plurality of code symbols, the predetermined message symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols; 
 means for accumulating a first signal value of the first code symbol representing the predetermined message symbol and a second signal value of the second code symbol representing the predetermined message symbol, wherein the accumulating means is operative to produce the first and second signal values based on multiple other signal values; and 
 means for examining the accumulated first and second signal values to detect the predetermined message symbol represented by the first and second code symbols. 
 
     
     
       21. A method for decoding a predetermined message symbol of a plurality of message symbols incorporated in an audio signal, comprising:
 receiving an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being contained within a predetermined message as a plurality of code symbols, the predetermined message symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols; 
 accumulating a first signal value of the first code symbol representing the predetermined message symbol and a second signal value of the second code symbol representing the predetermined message symbol based on multiple other signal values; and 
 examining the accumulated first and second signal values to detect the predetermined message symbol. 
 
     
     
       22. A system for decoding a predetermined message symbol of a plurality of message symbols incorporated in an audio signal, comprising:
 an input device for an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being contained within a predetermined message as a plurality of code symbols, the predetermined message symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio sign al and positioned in time between the first and second code symbols; and 
 a digital processor in communication with the input device to receive the audio signal therefrom, the digital processor being programmed to accumulate a first signal value representing the first code symbol and a second signal value representing the second code symbol based on multiple other signal values, the digital processor being further programmed to examine the accumulated first and second signal values to detect the predetermined message symbol. 
 
     
     
       23. A system for decoding a predetermined message symbol of a plurality of message symbols embedded in an audio signal, comprising:
 means for receiving an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being contained within a predetermined message as a plurality of code symbols, the predetermined message symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols; 
 means for accumulating a first signal value of the first code symbol representing the predetermined message symbol and a second signal value of the second code symbol representing the predetermined message symbol, wherein the first and second signal values are produced from respective sets of time displaced signal values, each of the time displaced signal values representing a value of a respective one of the first and second code symbols during a corresponding time period thereof; and 
 means for examining the accumulated first and second signal values to detect the predetermined message symbol represented by the first and second code symbols. 
 
     
     
       24. A method for decoding a predetermined message symbol of a plurality of message symbols incorporated in an audio signal, comprising:
 receiving an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being contained within a predetermined message as a plurality of code symbols, the predetermined message symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols; 
 accumulating a first signal value of the first code symbol representing the predetermined message symbol and a second signal value of the second code symbol representing the predetermined message symbol, wherein the first and second signal values are produced from respective sets of time displaced signal values, each of the time displaced signal values representing a value of a respective one of the first and second code symbols during a corresponding time period thereof; and 
 examining the accumulated first and second signal values to detect the predetermined message symbol. 
 
     
     
       25. A system for decoding a predetermined message symbol of a plurality of message symbols incorporated in an audio signal, comprising:
 an input device for an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being contained within a predetermined message as a plurality of code symbols, the predetermined message symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols; and 
 a digital processor in communication with the input device to receive the audio signal therefrom, the digital processor being programmed to accumulate a first signal value representing the first code symbol and a second signal value representing the second code symbol, wherein the first and second signal values are produced from respective sets of time displaced signal values, each of the time displaced signal values representing a value of a respective one of the first and second code symbols during a corresponding time period thereof, the digital processor being further programmed to examine the accumulated first and second signal values to detect the predetermined message symbol. 
 
     
     
       26. A system for decoding a predetermined message symbol of a plurality of message symbols embedded in an audio signal, comprising:
 means for receiving an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being contained within a predetermined message as a plurality of code symbols, the predetermined message symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols, the first and second code symbols each comprising a predetermined number of frequency components; 
 means for producing first and second sets of component values, each set corresponding to a respective one of the first and second code symbols and each component value of each set representing a characteristic of a respective frequency component of the corresponding symbol; 
 means for accumulating a first signal value of the first code symbol representing the predetermined message symbol based on the first set of component values and a second signal value of the second code symbol representing the predetermined message symbol based on the second set of component values, and for producing a third signal value derived from the first and second signal values; and 
 means for detecting the predetermined message symbol represented by the first and second code symbols based on the third signal value. 
 
     
     
       27. A system for decoding a message represented by a plurality of message symbols embedded in an audio signal, comprising:
 means for receiving an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being represented by plural sets of first and second code symbols, each set representing a respective one of the plurality of message symbols, the plural sets of first and second code symbols being arranged as a message having a predetermined sequence including at least one marker symbol and at least one data symbol, at least one of the marker symbol and the data symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols; 
 means for accumulating sets of first and second signal values, each signal value set corresponding to a respective one of the sets of first and second code symbols and including a first signal value representing the first code symbol of the respective code symbol set and a second signal value representing the second code symbol thereof and for producing a third signal value derived from the first and second signal values; and 
 means for detecting a respective one of the plurality of message symbols represented by the first and second code symbols based on the third signal value and for detecting the message by detecting the presence of the marker symbol based on its signal value set and detecting at least one data symbol based on the detected presence of the marker symbol and the corresponding signal value set of the at least one data symbol. 
 
     
     
       28. A system for decoding a predetermined message symbol of a plurality of message symbols embedded in an audio signal, comprising:
 means for receiving an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being contained within a predetermined message as a plurality of code symbols, the predetermined message symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols; 
 means for accumulating a first signal value of the first code symbol representing the predetermined message symbol and a second signal value of the second code symbol representing the predetermined message symbol, wherein the accumulating means is operative to produce the first and second signal values based on multiple other signal values and wherein the accumulating means is operative to store the first and second signal values; and 
 means for examining both of the accumulated first and second signal values to detect the predetermined message symbol represented by the first and second code symbols. 
 
     
     
       29. The system of  claim 28 , wherein the first and second signal values are produced from respective sets of time displaced signal values, each of the time displaced signal values representing a value of a respective one of the first and second code symbols during a corresponding time period thereof. 
     
     
       30. The system of  claim 28 , wherein the first and second code symbols each comprise a predetermined number of frequency components, and further comprising means for producing first and second sets of component values, each set corresponding to a respective one of the first and second code symbols and each component value of each set representing a characteristic of a respective frequency component of the corresponding symbol, and means for producing the first signal value based on the first set of component values and producing the second signal value based on the second set of component values. 
     
     
       31. A method for decoding a predetermined message symbol of a plurality of message symbols embedded in an audio signal, comprising:
 receiving an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being contained within a predetermined message as a plurality of code symbols, the predetermined message symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols, the first and second code symbols each comprising a predetermined number of frequency components; 
 producing first and second sets of component values, each set corresponding to a respective one of the first and second code symbols and each component value of each set representing a characteristic of a respective frequency component of the corresponding symbol; 
 accumulating a first signal value of the first code symbol representing the predetermined message symbol based on the first set of component values and a second signal value of the second code symbol representing the predetermined message symbol based on the second set of component values, and for producing a third signal value derived from the first and second signal values; and 
 detecting the predetermined message symbol represented by the first and second code symbols based on the third signal value. 
 
     
     
       32. A method for decoding a message represented by a plurality of message symbols embedded in an audio signal, comprising:
 receiving an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being represented by plural sets of first and second code symbols, each set representing a respective one of the plurality of message symbols, the plural sets of first and second code symbols being arranged as a message having a predetermined sequence including at least one marker symbol and at least one data symbol, at least one of the marker symbol and the data symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols; 
 accumulating sets of first and second signal values, each signal value set corresponding to a respective one of the sets of first and second code symbols and including a first signal value representing the first code symbol of the respective code symbol set and a second signal value representing the second code symbol thereof; 
 producing a third signal value derived from the first and second signal values; 
 detecting a respective one of the plurality of message symbols represented by the first and second code symbols based on the third signal value; and 
 detecting the message by detecting the presence of the marker symbol based on its signal value set and detecting at least one data symbol based on the detected presence of the marker symbol and the corresponding signal value set of the at least one data symbol. 
 
     
     
       33. A method for decoding a predetermined message symbol of a plurality of message symbols embedded in an audio signal, comprising:
 receiving an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being contained within a predetermined message as a plurality of code symbols, the predetermined message symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols; 
 accumulating a first signal value of the first code symbol representing the predetermined message symbol and a second signal value of the second code symbol representing the predetermined message symbol based on multiple other signal values; 
 storing the first and second signal values; and 
 examining both of the accumulated first and second signal values to detect the predetermined message symbol represented by the first and second code symbols. 
 
     
     
       34. The method of  claim 33 , wherein the first and second signal values are produced from respective sets of time displaced signal values, each of the time displaced signal values representing a value of a respective one of the first and second code symbols during a corresponding time period thereof. 
     
     
       35. The method of  claim 33 , wherein the first and second code symbols each comprise a predetermined number of frequency components, and further comprising producing first and second sets of component values, each set corresponding to a respective one of the first and second code symbols and each component value of each set representing a characteristic of a respective frequency component of the corresponding symbol, and producing the first signal value based on the first set of component values and producing the second signal value based on the second set of component values. 
     
     
       36. A system for decoding a predetermined message symbol of a plurality of message symbols embedded in an audio signal, comprising:
 an input device for an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being contained within a predetermined message as a plurality of code symbols, the predetermined message symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols, the first and second code symbols each comprising a predetermined number of frequency components; 
 a digital processor in communication with the input device to receive the audio signal therefrom, the digital processor being programmed to produce first and second sets of component values, each set corresponding to a respective one of the first and second code symbols and each component value of each set representing a characteristic of a respective frequency component of the corresponding symbol, the digital processor being further programmed to accumulate a first signal value of the first code symbol representing the predetermined message symbol based on the first set of component values and a second signal value of the second code symbol representing the predetermined message symbol based on the second set of component values, to produce a third signal value derived from the first and second signal values, and to detect the predetermined message symbol represented by the first and second code symbols based on the third signal value. 
 
     
     
       37. A system for decoding a message represented by a plurality of message symbols embedded in an audio signal, comprising:
 an input device for an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being represented by plural sets of first and second code symbols, each set representing a respective one of the plurality of message symbols, the plural sets of first and second code symbols being arranged as a message having a predetermined sequence including at least one marker symbol and at least one data symbol, at least one of the marker symbol and the data symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols; and 
 a digital processor in communication with the input device to receive the audio signal therefrom, the digital processor being programmed to accumulate sets of first and second signal values, each signal value set corresponding to a respective one of the sets of first and second code symbols and including a first signal value representing the first code symbol of the respective code symbol set and a second signal value representing the second code symbol thereof, the digital processor being further programmed to produce a third signal value derived from the first and second signal values, to detect a respective one of the plurality of message symbols represented by the first and second code symbols based on the third signal value, and to detect the message by detecting the presence of the marker symbol based on its signal value set and detecting at least one data symbol based on the detected presence of the marker symbol and the corresponding signal value set of the at least one data symbol. 
 
     
     
       38. A system for decoding a predetermined message symbol of a plurality of message symbols embedded in an audio signal, comprising:
 an input device for an audio signal in which a plurality of message symbols have been incorporated so that the message symbols are inaudible when the audio signal is reproduced audibly, the plurality of message symbols being contained within a predetermined message as a plurality of code symbols, the predetermined message symbol being represented by first and second code symbols incorporated in and displaced in time in the audio signal with at least one code symbol representing a different one of the message symbols being incorporated in the audio signal and positioned in time between the first and second code symbols; and 
 a digital processor in communication with the input device to receive the audio signal therefrom, the digital processor being programmed to accumulate a first signal value of the first code symbol representing the predetermined message symbol and a second signal value of the second code symbol representing the predetermined message symbol based on multiple other signal values, to store the first and second signal values, and to examine both of the accumulated first and second signal values to detect the predetermined message symbol represented by the first and second code symbols. 
 
     
     
       39. The system of  claim 38 , wherein the first and second signal values are produced from respective sets of time displaced signal values, each of the time displaced signal values representing a value of a respective one of the first and second code symbols during a corresponding time period thereof. 
     
     
       40. The system of  claim 38 , wherein the first and second code symbols each comprise a predetermined number of frequency components, and wherein the digital processor is programmed to produce first and second sets of component values, each set corresponding to a respective one of the first and second code symbols and each component value of each set representing a characteristic of a respective frequency component of the corresponding symbol, and the digital processor is further programmed to produce the first signal value based on the first set of component values and to produce the second signal value based on the second set of component values. 
     
     
       41. A method of encoding a predetermined message in an audio signal using a processing device, comprising:
 encoding the audio signal using the processing device with a first encoded sequence of code symbols representing the predetermined message; and   encoding the audio signal using the processing device with a second encoded sequence of code symbols representing the predetermined message, such that the second encoded sequence of code symbols differs from the first encoded sequence of code symbols and the second encoded sequence of code symbols is displaced in time in the audio signal with respect to the first encoded sequence of code symbols;   wherein each of the code symbols in the first encoded sequence of code symbols comprises a first plurality of single frequency components and each of the code symbols in the second encoded sequence of code symbols comprises a second plurality of single frequency components, and wherein the first encoded sequence of code symbols has a frequency content which differs at least in part from a frequency content of the second encoded sequence of code symbols.   
     
     
       42. A method according to claim 41, wherein each code symbol in the first encoded sequence of code symbols corresponds to a respective code symbol in the second encoded sequence of code symbols, and wherein each code symbol in the first encoded sequence of code symbols has a frequency content which differs at least in part from a frequency content of the respective code symbol in the second encoded sequence of code symbols. 
     
     
       43. A method according to claim 41, wherein the code symbols in the first and second encoded sequences of code symbols are selected from a predetermined set of code symbols in which the code symbols are arranged in a predetermined order, and wherein each code symbol of the second encoded sequence of code symbols corresponds to a respective code symbol of the first encoded sequence of code symbols and is selected based on the order of the respective code symbol of the first encoded sequence of code symbols. 
     
     
       44. A method according to claim 43, wherein each code symbol of the second encoded sequence of code symbols is selected from the predetermined set of code symbols based on a predetermined offset in the predetermined order from the respective code symbol of the first encoded sequence of code symbols. 
     
     
       45. A method according to claim 44, wherein the predetermined offset is the same for all code symbols of the second encoded sequence of code symbols. 
     
     
       46. A method according to claim 41, wherein the code symbols of the first and second encoded sequences of code symbols are selected from a predetermined set of code symbols and wherein each code symbol in the predetermined set of code symbols comprises a combination of single-frequency code components unique among all combinations of single frequency code components of the code symbols within the predetermined set of code symbols. 
     
     
       47. A method according to claim 41, wherein the processing device is a record device storing a recorded audio signal encoded with a predetermined message. 
     
     
       48. A method according to claim 47, wherein each code symbol in the first encoded sequence of code symbols corresponds to a respective code symbol in the second encoded sequence of code symbols. 
     
     
       49. A method according to claim 47, wherein the code symbols in the first and second encoded sequences of code symbols are selected from a predetermined set of code symbols in which the code symbols are arranged in a predetermined order, and wherein each code symbol of the second encoded sequence of code symbols corresponds to a respective code symbol of the first encoded sequence of code symbols and is selected based on the order of the respective code symbol of the first encoded sequence of code symbols. 
     
     
       50. A method according to claim 49, wherein each code symbol of the second encoded sequence of code symbols is selected from the predetermined set of code symbols based on a predetermined offset in the predetermined order from the respective code symbol of the first encoded sequence of code symbols. 
     
     
       51. A method according to claim 50, wherein the predetermined offset is the same for all code symbols of the second encoded sequence of code symbols. 
     
     
       52. A method according to claim 47, wherein the code symbols of the first and second encoded sequences of code symbols are selected from a predetermined set of code symbols and wherein each code symbol in the predetermined set of code symbols comprises a combination of single-frequency code components unique among all combinations of single frequency code components of the code symbols within the predetermined set of code symbols. 
     
     
       53. A method for encoding information in an audio signal using a processing device, comprising the steps of:
 translating an information signal using the processing device into a first set of code symbols representing the information signal and a second set of code symbols representing the information signal, such that each of the code symbols in the first and second sets of code symbols comprises a corresponding plurality of single-frequency code components, at least some of the single-frequency code components of the code symbols in the first set of code symbols differing from the single-frequency code components of the code symbols in the second set of code symbols;   and, using the processing device, combining the single-frequency code components of the first and second sets of code symbols with the audio signal to produce an encoded audio signal, such that the single-frequency code components of the code symbols in the first set of code symbols are time-displaced from the single-frequency code components of the code symbols in the second set of code symbols in the audio signal.   
     
     
       54. A method according to claim 53, wherein the processing device is a record device storing a recorded audio signal encoded with a predetermined message. 
     
     
       55. A method of encoding a predetermined message in an audio signal using a processing device, comprising:
 encoding the audio signal using the processing device with a first encoded sequence of code symbols representing the predetermined message; and   encoding the audio signal with a second encoded sequence of code symbols representing the predetermined message, such that the second encoded sequence of code symbols differs from the first encoded sequence of code symbols and the second encoded sequence of code symbols is displaced in time in the audio signal with respect to the first encoded sequence of code symbols;   wherein the first encoded sequence of code symbols has a frequency content which differs at least in part from a frequency content of the second encoded sequence of code symbols.   
     
     
       56. A method according to claim 55, wherein each code symbol in the first encoded sequence of code symbols corresponds to a respective code symbol in the second encoded sequence of code symbols, and wherein each code symbol in the first encoded sequence of code symbols has a frequency content which differs at least in part from a frequency content of its respective code symbol in the second encoded sequence of code symbols. 
     
     
       57. A method according to claim 55, wherein the code symbols in the first and second encoded sequences of code symbols are selected from a predetermined set of code symbols in which the code symbols are arranged in a predetermined order, and wherein each code symbol of the second encoded sequence of code symbols corresponds to a respective code symbol of the first encoded sequence of code symbols and is selected based on the order of the respective code symbol of the first encoded sequence of code symbols. 
     
     
       58. A method according to claim 57, wherein each code symbol of the second encoded sequence of code symbols is selected from the predetermined set of code symbols based on a predetermined offset in the predetermined order from the respective code symbol of the first encoded sequence of code symbols. 
     
     
       59. A method according to claim 58, wherein the predetermined offset is the same for all code symbols of the second encoded sequence of code symbols. 
     
     
       60. A method according to claim 55, wherein the code symbols of the first and second encoded sequences of code symbols are selected from a predetermined set of code symbols and wherein each code symbol in the predetermined set of code symbols comprises a combination of single-frequency code components unique among all combinations of single frequency code components of the code symbols within the predetermined set of code signals. 
     
     
       61. A method according to claim 55, wherein the processing device is a record device storing a recorded audio signal encoded with a predetermined message. 
     
     
       62. A method according to claim 61, wherein each code symbol in the first encoded sequence of code symbols corresponds to a respective code symbol in the second encoded sequence of code symbols, and wherein each code symbol in the first encoded sequence of code symbols has a frequency content which differs at least in part from a frequency content of the respective code symbol in the second encoded sequence of code symbols. 
     
     
       63. A method according to claim 61, wherein the code symbols of the first and second encoded sequences of code symbols are selected from a predetermined set of code symbols and wherein each code symbol in the predetermined set of code symbols comprises a combination of single-frequency code components unique among all combinations of single frequency code components of the code symbols within the predetermined set of code symbols. 
     
     
       64. A method according to claim 61, wherein the code symbols in the first and second encoded sequences of code symbols are selected from a predetermined set of code symbols in which the code symbols are arranged in a predetermined order, and wherein each code symbol of the second encoded sequence of code symbols corresponds to a respective code symbol of the first encoded sequence of code symbols and is selected based on the order of the respective code symbol of the first encoded sequence of code symbols. 
     
     
       65. A method according to claim 64, wherein each code symbol of the second encoded sequence of code symbols is selected from the predetermined set of code symbols based on a predetermined offset in the predetermined order from the respective code symbol of the first encoded sequence of code symbols. 
     
     
       66. A method according to claim 65, wherein the predetermined offset is the same for all code symbols of the second encoded sequence of code symbols. 
     
     
       67. A method of encoding a predetermined message in an audio signal using a processing device, comprising:
 encoding the audio signal using the processing device with a first encoded sequence of code symbols representing the predetermined message; and   encoding the audio signal using the processing device with a second encoded sequence of code symbols representing the predetermined message, such that the second encoded sequence of code symbols differs from the first encoded sequence of code symbols and the second encoded sequence of code symbols is displaced in time in the audio signal with respect to the first encoded sequence of code symbols;   wherein each code symbol in the second encoded sequence of code symbols corresponds to a respective code symbol in the first encoded sequence of code symbols, and wherein each code symbol in the second encoded sequence of code symbols has a frequency content which differs at least in part from a frequency content of the corresponding code symbol in the first encoded sequence of code symbols.   
     
     
       68. A method according to claim 67, wherein the code symbols in the first and second encoded sequences of code symbols are selected from a predetermined set of code symbols in which the code symbols are arranged in a predetermined order, and wherein each code symbol of the second encoded sequence of code symbols is selected based on the predetermined order of the corresponding code symbol of the first encoded sequence of code symbols. 
     
     
       69. A method according to claim 68, wherein each code symbol of the second encoded sequence of code symbols is selected from the predetermined set of code symbols based on a predetermined offset in the predetermined order from the corresponding code symbol of the first encoded sequence of code symbols. 
     
     
       70. A method according to claim 69, wherein the predetermined offset is the same for all code symbols of the second encoded sequence of code symbols. 
     
     
       71. A method according to claim 67, wherein the processing device is a record device storing a recorded audio signal encoded with a predetermined message. 
     
     
       72. A method according to claim 71, wherein the code symbols in the first and second encoded sequences of code symbols are selected from a predetermined set of code symbols in which the code symbols are arranged in a predetermined order, and wherein each code symbol of the second encoded sequence of code symbols is selected based on the predetermined order of the corresponding code symbol of the first encoded sequence of code symbols. 
     
     
       73. A method according to claim 72, wherein each code symbol of the second encoded sequence of code symbols is selected from the predetermined set of code symbols based on a predetermined offset in the predetermined order from the corresponding code symbol of the first encoded sequence of code symbols. 
     
     
       74. A method according to claim 73, wherein the predetermined offset is the same for all code symbols of the second encoded sequence of code symbols. 
     
     
       75. A method of encoding a predetermined message in an audio signal using a processing device, comprising:
 encoding the audio signal using the processing device with a first encoded sequence of code symbols representing the predetermined message; and   encoding the audio signal using the processing device with a second encoded sequence of code symbols representing the predetermined message, such that the second encoded sequence of code symbols differs from the first encoded sequence of code symbols and the second encoded sequence of code symbols is displaced in time in the audio signal with respect to the first encoded sequence of code symbols, wherein the first and second encoded sequences of code symbols are inaudible when the audio signal is reproduced audibly;   wherein the code symbols of the first and second encoded sequences of code symbols are selected from a predetermined set of code symbols in which the code symbols are arranged in a predetermined order, and wherein each code symbol of the second encoded sequence of code symbols corresponds to a respective code symbol of the first encoded sequence of code symbols and is selected based on the order of the respective code symbol of the first encoded sequence of code symbols,   and wherein the first encoded sequence of code symbols has a frequency content which differs at least in part from a frequency content of the second encoded sequence of code symbols.   
     
     
       76. A method according to claim 75, wherein each code symbol of the second encoded sequence of code symbols is selected from the predetermined set of code symbols based on a predetermined offset in the predetermined order from its respective code symbol of the first encoded sequence of code symbols. 
     
     
       77. A method according to claim 76, wherein the predetermined offset is the same for all code symbols of the second encoded sequence of code symbols. 
     
     
       78. A method according to claim 75, wherein the processing device comprises a record device storing a recorded audio signal encoded with a predetermined message. 
     
     
       79. A method according to claim 78, wherein each code symbol of the second encoded sequence of code symbols is selected from the predetermined set of code symbols based on a predetermined offset in the predetermined order from the respective code symbol of the first encoded sequence of code symbols. 
     
     
       80. A method according to claim 79, wherein the predetermined offset is the same for all code symbols of the second encoded sequence of code symbols. 
     
     
       81. A method of encoding a predetermined message in an audio signal using a processing device, comprising:
 encoding the audio signal using the processing device with a first encoded sequence of code symbols representing the predetermined message;   encoding the audio signal using the processing device with a second encoded sequence of code symbols representing the predetermined message, such that the second encoded sequence of code symbols differs from the first encoded sequence of code symbols and the second encoded sequence of code symbols is displaced in time in the audio signal with respect to the first encoded sequence of code symbols; and   wherein the code symbols of the first and second encoded sequences of code symbols are selected from a predetermined set of code symbols and each code symbol of the predetermined set of code symbols comprises a combination of single-frequency code components unique among all combinations of single-frequency code components of the code symbols within the predetermined set of code symbols,   and wherein the first encoded sequence of code symbols has a frequency content which differs at least in part from a frequency content of the second encoded sequence of code symbols.   
     
     
       82. A method according to claim 81, wherein the processing device comprises a record device storing a recorded audio signal encoded with a predetermined message. 
     
     
       83. A method of encoding a predetermined message in an audio signal in a processing device, comprising:
 encoding the audio signal using the processing device with a first encoded sequence of code symbols representing the predetermined message, each of the first encoded code symbols comprising a first plurality of single frequency components; and   encoding the audio signal using the processing device with a second encoded sequence of code symbols representing the predetermined message, each of the second encoded code symbols comprising a second plurality of single frequency components, such that the second encoded sequence of code symbols differs from the first encoded sequence of code symbols and the second encoded sequence of code symbols is displaced in time in the audio signal with respect to the first encoded sequence of code symbols,   and wherein the first encoded sequence of code symbols has a frequency content which differs at least in part from a frequency content of the second encoded sequence of code symbols.   
     
     
       84. A method according to claim 83, further comprising:
 encoding the audio signal with a marker symbol positioned in time adjacent at least one of the first encoded sequence of code symbols and the second encoded sequence of code symbols.   
     
     
       85. A method according to claim 83, further comprising:
 encoding the audio signal with a first marker symbol adjacent the first encoded sequence of code symbols and a second marker symbol adjacent the second encoded sequence of code symbols.   
     
     
       86. A method according to claim 83, wherein the processing device comprises a record device storing a recorded audio signal encoded with a predetermined message. 
     
     
       87. A method according to claim 86, further comprising:
 encoding the audio signal with a marker symbol positioned in time adjacent at least one of the first encoded sequence of code symbols and the second encoded sequence of code symbols.   
     
     
       88. A method according to claim 86, further comprising:
 encoding the audio signal with a marker symbol adjacent the first encoded sequence of code symbols and adjacent the second encoded sequence of code symbols.   
     
     
       89. An apparatus for encoding a predetermined message in an audio signal, comprising:
 a memory   an encoder, operatively coupled to the memory, that encodes the audio signal with a first encoded sequence of code symbols representing the predetermined message and a second encoded sequence of code symbols representing the predetermined message, such that the second encoded sequence of code symbols differs from the first encoded sequence of code symbols and the second encoded sequence of code symbols is displaced in time in the audio signal with respect to the first encoded sequence of code symbols;   wherein each of the code symbols in the first encoded sequence of code symbols comprises a first plurality of single frequency components and each of the code symbols in the second encoded sequence of code symbols comprises a second plurality of single frequency components,   and wherein the first encoded sequence of code symbols has a frequency content which differs at least in part from a frequency content of the second encoded sequence of code symbols.   
     
     
       90. An apparatus according to claim 89, wherein each code symbol in the first encoded sequence of code symbols corresponds to a respective code symbol in the second encoded sequence of code symbols. 
     
     
       91. An apparatus according to claim 89, wherein the code symbols in the first and second encoded sequences of code symbols are selected from a predetermined set of code symbols in which the code symbols are arranged in a predetermined order, and wherein each code symbol of the second encoded sequence of code symbols corresponds to a respective code symbol of the first encoded sequence of code symbols and is selected based on the order of the respective code symbol of the first encoded sequence of code symbols. 
     
     
       92. An apparatus according to claim 91, wherein each code symbol of the second encoded sequence of code symbols is selected from the predetermined set of code symbols based on a predetermined offset in the predetermined order from the respective code symbol of the first encoded sequence of code symbols. 
     
     
       93. An apparatus according to claim 92, wherein the predetermined offset is the same for all code symbols of the second encoded sequence of code symbols. 
     
     
       94. An apparatus according to claim 89, wherein the code symbols of the first and second encoded sequences of code symbols are selected from a predetermined set of code symbols and wherein each code symbol in the predetermined set of code symbols comprises a combination of single-frequency code components unique among all combinations of single frequency code components of the code symbols within the predetermined set of code symbols. 
     
     
       95. An apparatus for encoding information in an audio signal, comprising:
 a translator that translates an information signal into a first set of code symbols representing the information signal and a second set of code symbols representing the information signal, each of the code symbols in the first and second sets of code symbols having a corresponding plurality of single-frequency code components, such that at least some of the single-frequency code components of the code symbols in the first set of code symbols differ from the single-frequency code components of code symbols in the second set of code symbols; and   an encoder that combines the single-frequency code components of the first and second sets of code symbols with the audio signal to produce an encoded audio signal, such that the single-frequency code components of the code symbols in the first set of code symbols are time-displaced from the single-frequency code components of the code symbols in the second set of code symbols in the audio signal.   
     
     
       96. An apparatus for encoding a predetermined message in an audio signal, comprising:
 a memory;   an encoder, operatively coupled to the memory, that encodes the audio signal with a first encoded sequence of code symbols representing the predetermined message and a second encoded sequence of code symbols representing the predetermined message, such that the second encoded sequence of code symbols differs from the first encoded sequence of code symbols and the second encoded sequence of code symbols is displaced in time in the audio signal with respect to the first encoded sequence of code symbols; and   wherein the first encoded sequence of code symbols has a frequency content which differs at least in part from a frequency content of the second encoded sequence of code symbols.   
     
     
       97. An apparatus according to claim 96, wherein each code symbol in the first encoded sequence of code symbols corresponds to a respective code symbol in the second encoded sequence of code symbols, and wherein each code symbol in the first encoded sequence of code symbols has a frequency content which differs at least in part from a frequency content of the respective code symbol in the second encoded sequence of code symbols. 
     
     
       98. An apparatus according to claim 96, wherein the code symbols in the first and second encoded sequences of code symbols are selected from a predetermined set of code symbols in which the code symbols are arranged in a predetermined order, and wherein each code symbol of the second encoded sequence of code symbols corresponds to a respective code symbol of the first encoded sequence of code symbols and is selected based on the order of the respective code symbol of the first encoded sequence of code symbols. 
     
     
       99. An apparatus according to claim 98, wherein each code symbol of the second encoded sequence of code symbols is selected from the predetermined set of code symbols based on a predetermined offset in the predetermined order from the respective code symbol of the first encoded sequence of code symbols. 
     
     
       100. An apparatus according to claim 99, wherein the predetermined offset is the same for all code symbols of the second encoded sequence of code symbols. 
     
     
       101. An apparatus according to claim 96, wherein the code symbols of the first and second encoded sequences of code symbols are selected from a predetermined set of code symbols and wherein each code symbol in the predetermined set of code symbols comprises a combination of single-frequency code components unique among all combinations of single frequency code components of the code symbols within the predetermined set of code symbols. 
     
     
       102. An apparatus for encoding a predetermined message in an audio signal, comprising:
 a memory;   an encoder, operatively coupled to the memory, that encodes the audio signal with a first encoded sequence of code symbols representing the predetermined message and a second encoded sequence of code symbols representing the predetermined message, such that the second encoded sequence of code symbols differs from the first encoded sequence of code symbols and the second encoded sequence of code symbols is displaced in time in the audio signal with respect to the first encoded sequence of code symbols; and   wherein each code symbol in the second encoded sequence of code symbols corresponds to a respective code symbol in the first encoded sequence of code symbols, and wherein each code symbol in the second encoded sequence of code symbols has a frequency content which differs at least in part from a frequency content of the corresponding code symbol in the first encoded sequence of code symbols.   
     
     
       103. An apparatus according to claim 102, wherein the code symbols in the first and second encoded sequences of code symbols are selected from a predetermined set of code symbols in which the code symbols are arranged in a predetermined order, and wherein each code symbol of the second encoded sequence of code symbols is selected based on the predetermined order of the corresponding code symbol of the first encoded sequence of code symbols. 
     
     
       104. An apparatus according to claim 103, wherein each code symbol of the second encoded sequence of code symbols is selected from the predetermined set of code symbols based on a predetermined offset in the predetermined order from the corresponding code symbol of the first encoded sequence of code symbols. 
     
     
       105. An apparatus according to claim 104, wherein the predetermined offset is the same for all code symbols of the second encoded sequence of code symbols. 
     
     
       106. An apparatus for encoding a predetermined message in an audio signal, comprising:
 a memory; and   an encoder, operatively coupled to the memory, that encodes the audio signal with a first encoded sequence of code symbols representing the predetermined message and a second encoded sequence of code symbols representing the predetermined message, such that the second encoded sequence of code symbols differs from the first encoded sequence of code symbols and the second encoded sequence of code symbols is displaced in time in the audio signal with respect to the first encoded sequence of code symbols, wherein the first and second encoded sequences of code symbols are inaudible when the audio signal is reproduced audibly;   and wherein the code symbols of the first and second encoded sequences of code symbols are selected from a predetermined set of code symbols in which the code symbols are arranged in a predetermined order, and wherein each code symbol of the second encoded sequence of code symbols corresponds to a respective code symbol of the first encoded sequence of code symbols and is selected based on the order of the respective code symbol of the first encoded sequence of code symbols,   and wherein the first encoded sequence of code symbols has a frequency content which differs at least in part from a frequency content of the second encoded sequence of code symbols.   
     
     
       107. An apparatus according to claim 106, wherein each code symbol of the second encoded sequence of code symbols is selected from the predetermined set of code symbols based on a predetermined offset in the predetermined order from the respective code symbol of the first encoded sequence of code symbols. 
     
     
       108. An apparatus according to claim 107, wherein the predetermined offset is the same for all code symbols of the second encoded sequence of code symbols. 
     
     
       109. An apparatus for encoding a predetermined message in an audio signal, comprising:
 a memory;   an encoder that encodes the audio signal with a first encoded sequence of code symbols representing the predetermined message and a second encoded sequence of code symbols representing the predetermined message, such that the second encoded sequence of code symbols differs from the first encoded sequence of code symbols and the second encoded sequence of code symbols is displaced in time in the audio signal with respect to the first encoded sequence of code symbols; and   wherein the code symbols of the first and second encoded sequences of code symbols are selected from a predetermined set of code symbols and each code symbol of the predetermined set of code symbols comprises a combination of single-frequency code components unique among all combinations of single-frequency code components of the code symbols within the predetermined set of code symbols,   and wherein the first encoded sequence of code symbols has a frequency content which differs at least in part from a frequency content of the second encoded sequence of code symbols.   
     
     
       110. An apparatus for encoding a predetermined message in an audio signal, comprising:
 a memory; and   an encoder that encodes the audio signal with a first encoded sequence of code symbols representing the predetermined message and a second encoded sequence of code symbols representing the predetermined message, such that the second encoded sequence of code symbols differs from the first encoded sequence of code symbols and the second encoded sequence of code symbols is displaced in time in the audio signal with respect to the first encoded sequence of code symbols,   wherein each of the code symbols in the first encoded sequence of code symbols comprises a first set of single frequency components and each of the code symbols in the second encoded sequence of code symbols comprises a second set of single frequency components, and wherein the first encoded sequence of code symbols has a frequency content which differs at least in part from a frequency content of the second encoded sequence of code symbols.   
     
     
       111. An apparatus according to claim 110, wherein the audio signal is further encoded with a marker symbol positioned in time adjacent at least one of the first encoded sequence of code symbols and the second encoded sequence of code symbols. 
     
     
       112. An apparatus according to claim 110, wherein the audio signal is further encoded with a first marker symbol adjacent the first encoded sequence of code symbols and a second marker symbol adjacent the second encoded sequence of code symbols.