# US 12,002,447 B2 · Noise cancellation system and signal processing method for an ear-mountable playback device > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,002,447 B2 - Document ID: US12002447B2 - Status: Granted - Kind: B2 - Application number: 17/780,733 - Filed: 2020-11-18 - Published: 2022-12-29 - Granted: 2024-06-04 - Earliest claimed: 2019-11-28 - Assignees: Ams AG - Applicants: ams AG - Inventors: Peter McCutcheon - Web page: https://patentgrep.com/patent/US12002447B2 ## CPC - G10K 11/17854: {the filter being an adaptive filter} - G10K 11/17879: {using both a reference signal and an error signal} - G10K 11/17881: {the reference signal being an acoustic signal, e.g. recorded with a microphone} - H04R 1/1083: {Reduction of ambient noise (active noise reduction per se G10K11/175; protective devices for the ear, e.g. providing acoustic protection A61F11/06)} - H04R 3/005: {for combining the signals of two or more microphones (specially adapted for hearing aids H04R25/407)} - H04R 2460/01: Hearing devices using active noise cancellation - H04R 2499/11: Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's - G10K: SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR - H04R: LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS (producing sounds with frequency not determined by supply frequency G10K) ## Abstract A noise cancellation system for an ear-mountable playback device having a speaker, a feedforward microphone and an error microphone comprises a filter chain for coupling the feedforward microphone to the speaker, the filter chain comprising a series connection or parallel connection of a coarse filter and a fine filter, and a noise control processor. The fine filter is formed of a set of sub-filters having a predefined frequency range, wherein the predefined frequency range of each of the sub-filters together forms an effective overall frequency range of the fine filter. The noise control processor is configured to calculate an error signal based on a first noise signal sensed by the feedforward microphone and on a second noise signal sensed by the error microphone, to perform an adaptation of coarse filter parameters of the coarse filter based on the error signal, and to perform a limited adaptation of fine filter parameters of each of the sub-filters based on the error signal, wherein limits of the limited adaptation comprise the predefined frequency ranges of the sub-filters and at least one of a gain limit and a Q factor limit. ## Claims ### Claim 1 A noise cancellation system for an ear-mountable playback device having a speaker, a feedforward microphone configured to predominantly sense ambient sound and an error microphone configured to sense ambient sound and sound being output from the speaker, the noise cancellation system comprising a filter chain for coupling the feedforward microphone to the speaker, the filter chain comprising a series connection or parallel connection of a coarse filter and a fine filter; and a noise control processor; wherein the fine filter is formed of a set of sub-filters; each of the sub-filters has a predefined frequency range; the predefined frequency range of each of the sub-filters together forms an effective overall frequency range of the fine filter; and the noise control processor is configured to calculate an error signal based on a first noise signal sensed by the feedforward microphone and on a second noise signal sensed by the error microphone; perform an adaptation of coarse filter parameters of the coarse filter based on the error signal; and perform a limited adaptation of fine filter parameters of each of the sub-filters based on the error signal, wherein limits of the limited adaptation comprise the predefined frequency ranges of the sub-filters and at least one of a gain limit and a Q factor limit. ### Claim 2 (depends on 1) The noise cancellation system according to claim 1, wherein the predefined frequency range of each of the sub-filters is adjacent to or at least partially overlap with the predefined frequency range of at least one other sub-filter of the set of sub-filters. ### Claim 3 (depends on 1) The noise cancellation system according to claim 1, wherein the set of sub-filters comprises between 6 and 12 sub-filters, in particular between 8 and 10 sub-filters. ### Claim 4 (depends on 1) The noise cancellation system according to claim 1, wherein the effective overall frequency range of the fine filter is from 80 Hz to 2000 Hz, in particular from 80 Hz to 1000 Hz. ### Claim 5 (depends on 1) The noise cancellation system according to claim 1, wherein each sub-filter is one of a peak filter and a notch filter. ### Claim 6 (depends on 1) The noise cancellation system according to claim 1, wherein each sub-filter is a minimum-phase filter. ### Claim 7 (depends on 1) The noise cancellation system according to claim 1, wherein the limited adaptation of the sub-filters is based on an error minimization algorithm, in particular a least-mean-squares, LMS, algorithm. ### Claim 8 (depends on 1) The noise cancellation system according to claim 1, wherein the limited adaptation of the sub-filters comprises an adaptation of a gain, a center frequency and a Q factor of at least one of the sub-filters. ### Claim 9 (depends on 1) The noise cancellation system according to claim 1, wherein the limited adaptation of the sub-filters comprises directly adapting the fine filter parameters of at least one of the sub-filters and checking the limits of the limited adaptation for the adapted fine filter parameters. ### Claim 10 (depends on 1) The noise cancellation system according to claim 1, wherein the noise control processor is configured to perform the coarse adaptation in advance of or at a different adaptation rate to the limited adaptation. ### Claim 11 (depends on 1) The noise cancellation system according to claim 1, wherein the noise control processor is configured to perform the coarse adaptation by adapting a gain factor and/or a cut-off frequency of the coarse filter. ### Claim 12 (depends on 1) The noise cancellation system according to claim 1, further comprising a feedback noise filter coupling the error microphone to the speaker. ### Claim 13 (depends on 1) An ear-mountable playback device, in particular headphone (HP) or handset, comprising a noise cancellation system according to claim 1, the speaker, the feedforward microphone and the error microphone located in proximity to the speaker. ### Claim 14 (depends on 1) An audio player comprising a noise cancellation system according to claim 1. ### Claim 15 (depends on 1) The noise cancellation system according to claim 1, wherein the gain limit limits a gain range of the respective sub-filter, and the Q factor limit limits a Q factor range of the respective sub-filter. ### Claim 16 A signal processing method for an ear-mountable playback device having a speaker, a feedforward microphone configured to predominantly sense ambient sound and an error microphone configured to sense ambient sound and sound being output from the speaker, wherein the feedforward microphone is coupled to the speaker via a filter chain, the filter chain comprising a series connection or parallel connection of a coarse filter and a fine filter, wherein the fine filter is formed of a set of sub-filters, each of the sub-filters has a predefined frequency range, and the predefined frequency range of each of the sub-filters together forms an effective overall frequency range of the fine filter, the method comprising calculating an error signal based on a first noise signal sensed by the feedforward microphone and on a second noise signal sensed by the error microphone; performing an adaptation of coarse filter parameters of the coarse filter based on the error signal; and performing a limited adaptation of fine filter parameters of each of the sub-filters based on the error signal, wherein limits of the limited adaptation comprise the predefined frequency ranges of the sub-filters and at least one of a gain limit and a Q factor limit. ### Claim 17 (depends on 16) The method according to claim 16, wherein the gain limit limits a gain range of the respective sub-filter, and the Q factor limit limits a Q factor range of the respective sub-filter.