# US 2020/0401618 A1 · 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 2020/0401618 A1 - Document ID: US20200401618A1 - Status: Published application - Kind: A1 - Application number: 17/011,769 - Filed: 2020-09-03 - Published: 2020-12-24 - 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/US20200401618A1 ## 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 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. ## Claims ### Claim 1 A media monitor comprising: a magnetic field estimator to determine first magnetic field data, the magnetic field estimator in communication with a magnetometer; a correlator to correlate the first magnitude field data with a reference sequence to determine second magnetic field data; and a watermark decoder to process the second magnetic field data to detect an audio watermark encoded in an audio signal. ### Claim 2 (depends on 1) The media monitor of claim 1, further including an output indicator to be asserted when the watermark decoder detects the audio watermark. ### Claim 3 (depends on 1) The media monitor of claim 1, wherein the magnetic field estimator is in communication with the magnetometer via an application programming interface of a media device. ### Claim 4 (depends on 1) The media monitor of claim 1, wherein the audio signal is output by audio circuitry of a media device, 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 magnetic field estimator 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 5 (depends on 1) The media monitor of claim 1, wherein the reference sequence is a pseudo-noise sequence. ### Claim 6 (depends on 5) The media monitor of claim 5, wherein the audio signal is a first audio signal, and the audio watermark is encoded in the first audio signal by: modulating the audio watermark with the pseudo-noise sequence to determine a modulated audio watermark; and combining the modulated audio watermark with a second audio signal to produce the first audio signal. ### Claim 7 (depends on 1) The media monitor of claim 1, wherein the watermark decoder is to process the second magnetic field data with a matched filter to detect the audio watermark. ### Claim 8 (depends on 1) The media monitor of claim 1, wherein the first magnetic field data is representative of a magnitude of a magnetic field measured by the magnetometer over time. ### Claim 9 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. ### Claim 10 (depends on 9) The non-transitory computer readable medium of claim 9, wherein the instructions cause the processor to assert an output indicator when the audio watermark is detected. ### Claim 11 (depends on 9) The non-transitory computer readable medium of claim 9, wherein the instructions cause the processor to access the magnetometer via an application programming interface. ### Claim 12 (depends on 9) The non-transitory computer readable medium of claim 9, wherein the audio signal is output by audio circuitry of a media device, 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 instructions cause the processor to process the second magnetic field data to detect variations in the second magnetic field that are induced by an electrical current carried by the speaker leads. ### Claim 13 (depends on 9) The non-transitory computer readable medium of claim 9, wherein the reference sequence is a pseudo-noise sequence. ### Claim 14 (depends on 13) The non-transitory computer readable medium of claim 13, wherein the audio signal is a first audio signal, and the audio watermark is encoded in the first audio signal by: modulating the audio watermark with the pseudo-noise sequence to determine a modulated audio watermark; and combining the modulated audio watermark with a second audio signal to produce the first audio signal. ### Claim 15 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. ### Claim 16 (depends on 15) The media monitoring method of claim 15, further including asserting an output indicator when the audio watermark is detected. ### Claim 17 (depends on 15) The media monitoring method of claim 15, further including accessing the magnetometer via an application programming interface. ### Claim 18 (depends on 15) The media monitoring method of claim 15, wherein the audio signal is output by audio circuitry of a media device, 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 processing of the second magnetic field data includes processing the second magnetic field data to detect variations in the second magnetic field that are induced by an electrical current carried by the speaker leads. ### Claim 19 (depends on 15) The media monitoring method of claim 15, wherein the reference sequence is a pseudo-noise sequence. ### Claim 20 (depends on 19) The media monitoring method of claim 19, wherein the audio signal is a first audio signal, and the audio watermark is encoded in the first audio signal by: modulating the audio watermark with the pseudo-noise sequence to determine a modulated audio watermark; and combining the modulated audio watermark with a second audio signal to produce the first audio signal.