Data embedding system

Abstract

A data hiding system is described for hiding data within an audio signal. The system can be used for watermarking, data communications, audience surveying etc. The system hides data in an audio signal by adding artificial echoes whose polarity varies with the data to be hidden. In one embodiment, each data value is represented by a positive and a negative echo having different delays. A receiver can then remove the effects of natural echoes and/or periodicities in the audio signal by differencing measurements obtained at the different delays.

1 - 48 . (canceled) 
     
     
         49 . A method of embedding a plurality of data values in an audio signal, the method comprising:
 receiving the audio signal;   generating an echo of at least a portion of the received audio signal; and   embedding the plurality of data values in the audio signal by combining the received audio signal with multiple versions of the generated echo at different delays, wherein each delay is associated with a respective data value.   
     
     
         50 . A method according to  claim 49 , wherein each data value is represented by first and second echoes having different delays and opposite polarities and wherein each data value is represented by third and fourth echoes, the third echo having the same polarity, when combined with said audio signal, as said second echo and the fourth echo having the same polarity, when combined with said audio signal, as said first echo, wherein the first and second echoes are generated by repeating substantially a first portion of the received audio signal and wherein the third and fourth echoes are generated by repeating substantially a second portion of the audio signal which is different to the first portion repeated by the first and second echoes. 
     
     
         51 . A method according to  claim 50 , wherein said second portion is adjacent the first portion. 
     
     
         52 . A method according to  claim 51 , wherein said first echo is combined with said audio signal at a first delay relative to said first portion of the audio signal; said second echo is combined with the audio signal at a second delay relative to said first echo; said third echo is combined with said audio signal at a third delay relative to said second portion of the audio signal; and said fourth echo is combined with the audio signal at a fourth delay relative to said third echo and preferably wherein said first delay is equal to said third delay and/or said second delay is equal to said fourth delay. 
     
     
         53 . A method according to  claim 49 , wherein said delays are between 0.5 ms and 100 ms. 
     
     
         54 . A method according to  claim 49 , wherein said echo of at least a portion of the audio signal has a duration of between 20 ms and 500 ms. 
     
     
         55 . A method according to  claim 49 , wherein the polarity of an echo at a given delay is modulated in dependence upon the data value associated with the delay. 
     
     
         56 . A method according to  claim 49 , wherein said audio signal is received as a stream of samples and wherein each echo is generated by passing the stream of audio samples through a respective delay line. 
     
     
         57 . A method according to  claim 49 , wherein said combining step combines the or each echo with the audio signal by adding and/or subtracting each echo to/from the audio signal in dependence upon the data value. 
     
     
         58 . A method according to  claim 49 , wherein the or each echo associated with each data value is faded in and out at different times within a symbol period so that different echoes reach their peak values at different times within the symbol period. 
     
     
         59 . A computer executable instructions product comprising computer implementable instructions for causing a programmable computer device to carry out the method of  claim 49 . 
     
     
         60 . An apparatus for embedding a plurality of data values in an audio signal, the apparatus comprising:
 an input for receiving the audio signal;   an echo generator for generating an echo of at least a portion of the received audio signal; and   a combiner for embedding the plurality of data values in the audio signal by combining the received audio signal with multiple versions of the generated echo at different delays, wherein each delay is associated with a respective data value.   
     
     
         61 . A method of recovering a plurality of data values embedded in an audio signal, the method comprising:
 receiving an input signal having the audio signal and multiple versions of an echo of at least a portion of the audio signal at different delays, wherein each delay is associated with a respective data value;   processing the received input signal to detect said echoes at the delays; and   recovering the plurality of data values from the detected echoes.   
     
     
         62 . A method according to  claim 61 , wherein each data value is represented by first and second echoes having different delays and opposite polarities, wherein each data value is represented by third and fourth echoes, the third echo having the same polarity as said second echo and the fourth echo having the same polarity as said first echo, wherein the first and second echoes are a repeat of substantially a first portion of the received audio signal, wherein the third and fourth echoes are a repeat of substantially a second portion of the audio signal which is different to the first portion repeated by the first and second echoes and wherein said processing processes the received input signal to detect the echoes representing each data value. 
     
     
         63 . A method according to  claim 62 , wherein said second portion is adjacent the first portion. 
     
     
         64 . A method according to  claim 62 , wherein said first echo is at a first delay relative to said first portion of the audio signal; said second echo is at a second delay relative to said first echo; said third echo is at a third delay relative to said second portion of the audio signal; and said fourth echo is at a fourth delay relative to said third echo and preferably wherein said first delay is equal to said third delay and/or said second delay is equal to said fourth delay. 
     
     
         65 . A method according to  claim 61 , wherein said delays are between 0.5 ms and 100 ms. 
     
     
         66 . A method according to  claim 61 , wherein each echo has a duration of between 20 ms and 500 ms. 
     
     
         67 . A method according to  claim 61 , wherein the polarity of an echo at a given delay depends upon the data value associated with the delay and wherein said processing detects the polarity of the echoes and determines said plurality of data values from the detected echo polarities. 
     
     
         68 . A method according to  claim 61 , wherein the or each echo associated with each data value is faded in and out at different times within a symbol period so that different echoes reach their peak values at different times within the symbol period and wherein the processing detects the echoes at a timing when an echo is expected to be at its peak amplitude. 
     
     
         69 . A computer executable instructions product comprising computer implementable instructions for causing a programmable computer device to carry out the method of  claim 61 . 
     
     
         70 . An apparatus for recovering a plurality of data values embedded in an audio signal, the apparatus comprising:
 an input for receiving an input signal having the audio signal and multiple versions of an echo of at least a portion of the audio signal at different delays, wherein each delay is associated with a respective data value; and   a processor for processing the received input signal to detect said echoes at the delays and for recovering the plurality of data values from the detected echoes.