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Detecting media watermarks in magnetic field data

  • US 9,679,053 B2
  • Filed: 12/18/2013
  • Issued: 06/13/2017
  • Est. Priority Date: 05/20/2013
  • Status: Active Grant
First Claim
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1. A method to detect media watermarks, the method comprising:

  • accessing, by executing an instruction with a processor in communication with a magnetometer, multidimensional magnetic field data determined by the magnetometer, the multidimensional magnetic field data representative of values of a magnetic field measured by the magnetometer, the multidimensional magnetic field data including a plurality of directional components; and

    processing, by executing an instruction with the processor, the multidimensional magnetic field data determined by the magnetometer to detect a watermark included in an audio signal output by audio circuitry of a media device, the audio signal corresponding to media presented by the media device, wherein the watermark modulates a first frequency of the audio signal, the multidimensional magnetic field data is accessed at a first sampling rate that is less than twice the first frequency, and the processing includes;

    processing the directional components to determine magnitude values representative of a magnitude of the magnetic field over time;

    transforming the magnitude values into a frequency domain to determine transformed magnetic field data; and

    evaluating the transformed magnetic field data at a second frequency different from the first frequency to detect the watermark, the second frequency selected to compensate for aliasing caused by accessing the multidimensional magnetic field data at the first sampling rate.

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