US Patent 11423079 Detecting media watermarks in magnetic field data

Methods, apparatus, systems and articles of manufacture (e.g., physical storage media) to detect media watermarks in magnetic field data are disclosed herein. Example media monitors disclosed herein include a magnetic field estimator to determine first magnetic field data, the magnetic field estimator in communication with a magnetometer. Disclosed example media monitors also include a correlator to correlate the first magnitude field data with a reference sequence to determine second magnetic field data. Disclosed example media monitors further include a watermark decoder to process the second magnetic field data to detect an audio watermark encoded in an audio signal.