Detecting media watermarks in magnetic field data

A non-transitory computer readable medium comprising computer readable instructions that, when executed, cause a processor to at least:

• determine first magnetic field data representative of a magnitude of a magnetic field measured by a magnetometer over time;
• correlate the first magnitude field data with a reference sequence to determine second magnetic field data;
• and
• process the second magnetic field data to detect an audio watermark encoded in an audio signal.

A media monitoring method comprising:

• determining, by executing an instruction with a processor, first magnetic field data representative of a magnitude of a magnetic field measured by a magnetometer over time;
• correlating, by executing an instruction with the processor, the first magnitude field data with a reference sequence to determine second magnetic field data;
• and
• processing, by executing an instruction with the processor, the second magnetic field data to detect an audio watermark encoded in an audio signal.