# US 10,769,206 B2 · Detecting media watermarks in magnetic field data > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 10,769,206 B2 - Document ID: US10769206B2 - Status: Granted - Kind: B2 - Application number: 16/417,131 - Filed: 2019-05-20 - Published: 2019-09-05 - Granted: 2020-09-08 - Earliest claimed: 2013-05-20 - Assignees: The Nielsen Company (US), LLC - Applicants: The Nielsen Company (US), LLC - Inventors: Alexander Topchy; Venugopal Srinivasan - Web page: https://patentgrep.com/patent/US10769206B2 ## CPC - G06F 16/683: using metadata automatically derived from the content - G10L 19/018: Audio watermarking, i.e. embedding inaudible data in the audio signal - G11B 20/00086: {Circuits for prevention of unauthorised reproduction or copying, e.g. piracy (indicating unauthorised use of record carriers in general G11B23/28; scrambling for television signal recording H04N5/913; network architectures or network protocols for network security H04L63/00; cryptographic mechanisms or cryptographic arrangements for secret or secure communication H04L9/00)} - G06F: ELECTRIC DIGITAL DATA PROCESSING (computer systems based on specific computational models G06N) - G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING - G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R) ## Abstract 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 monitoring apparatus disclosed herein include means for transforming magnitude values of magnetic field data to a frequency domain to determine transformed magnetic field data, the magnetic field data associated with a first sampling rate, the magnetic field data obtained from a sensor. Disclosed example media monitoring apparatus also include means for detecting an audio watermark in a portion of the transformed magnetic field data associated with a first frequency, the audio watermark encoded in an audio signal, the audio watermark to have a frequency component associated with a second frequency different from the first frequency, the first frequency to be aliased relative to the second frequency based on the first sampling rate. ## Claims ### Claim 1 A media monitoring apparatus comprising: means for transforming magnitude values of magnetic field data to a frequency domain to determine transformed magnetic field data, the magnetic field data associated with a first sampling rate, the magnetic field data obtained from a sensor; and means for detecting an audio watermark in a portion of the transformed magnetic field data associated with a first frequency, the audio watermark encoded in an audio signal, the audio watermark to have a frequency component associated with a second frequency different from the first frequency, the first frequency to be aliased relative to the second frequency based on the first sampling rate. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the sensor is a magnetometer. ### Claim 3 (depends on 1) The apparatus of claim 1, wherein the first sampling rate is less than twice the second frequency. ### Claim 4 (depends on 1) The apparatus of claim 1, wherein the first frequency is based on a difference between the first sampling rate and the second frequency. ### Claim 5 (depends on 4) The apparatus of claim 4, further including means for selecting the first frequency based on the difference between the first sampling rate and the second frequency. ### Claim 6 (depends on 1) The apparatus of claim 1, further including means for outputting an indicator when the audio watermark is detected. ### Claim 7 (depends on 1) The apparatus of claim 1, wherein the audio signal is output by audio circuitry of a media device, the audio circuitry including speaker leads to electrically couple a speaker to a speaker driver circuit. ### Claim 8 (depends on 7) The apparatus of claim 7, wherein the watermark is included in a first frequency range of the audio signal, the first frequency range below a threshold of audio frequencies capable of reproduction by the speaker, the first frequency range including the second frequency of the audio signal. ### Claim 9 (depends on 1) The apparatus of claim 1, further including means for determining the magnitude values of the magnetic field data from a plurality of directional components included in the magnetic field data obtained from the sensor. ### Claim 10 A media monitoring apparatus comprising: means for transforming magnitude values of a magnetic field measured by a sensor over time into a frequency domain to determine transformed magnetic field data, the magnitude values associated with a first sampling rate; and means for detecting a watermark included in an audio signal based on the transformed magnetic field data, the audio signal output by audio circuitry of a media device, the watermark to modulate a first frequency of the audio signal, the first sampling rate to be less than twice the first frequency, the means for detecting to evaluate 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 the first sampling rate associated with the multidimensional magnetic field data. ### Claim 11 (depends on 10) The apparatus of claim 10, wherein the sensor is a magnetometer. ### Claim 12 (depends on 10) The apparatus of claim 10, further including means for determining the magnitude values from a plurality of directional components included in multidimensional magnetic field data obtained from the sensor, the multidimensional magnetic field data representative of values of the magnetic field measured by the sensor. ### Claim 13 (depends on 10) The apparatus of claim 10, wherein the audio circuitry includes speaker leads to electrically couple a speaker driver circuit to a speaker that is to reproduce the audio signal, the watermark is included in a first frequency range of the audio signal, the first frequency range below a threshold of audio frequencies capable of reproduction by the speaker, the first frequency range including the first frequency of the audio signal. ### Claim 14 (depends on 10) The apparatus of claim 10, further including means for selecting the second frequency based on the first frequency and the first sampling rate. ### Claim 15 (depends on 14) The apparatus of claim 14, wherein the means for selecting is to select the second frequency based on a difference between first frequency and the first sampling rate. ### Claim 16 (depends on 10) The apparatus of claim 10, further including means for outputting an indicator when the audio watermark is detected. ### Claim 17 A media monitoring apparatus comprising: means for determining magnitude values of a magnetic field measured by a sensor over time, the means for determining to determine the magnitude values from a plurality of directional components included in first magnetic field data obtained from the sensor, the first magnetic field data representative of values of the magnetic field measured by the sensor; means for detecting a watermark included in an audio signal based on the magnitude values of the magnetic field, the audio signal output by audio circuitry of a media device, the means for detecting to: correlate the magnitude values with a reference sequence to determine second magnetic field data; and process the second magnetic field data to detect the watermark. ### Claim 18 (depends on 17) The apparatus of claim 17, wherein the sensor is a magnetometer. ### Claim 19 (depends on 17) The apparatus of claim 17, wherein the audio circuitry includes speaker leads to electrically couple a speaker driver circuit to a speaker that is to reproduce the audio signal, and the means for detecting is to process the second magnetic field data to detect variations in the second magnetic field that are induced by an electrical signal carried by the speaker leads. ### Claim 20 (depends on 17) The apparatus of claim 17, further including means for outputting an indicator when the audio watermark is detected.