# US 9,437,182 B2 · Active noise reduction method using perceptual masking > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,437,182 B2 - Document ID: US9437182B2 - Status: Granted - Kind: B2 - Application number: 12/846,677 - Filed: 2010-07-29 - Published: 2011-02-03 - Granted: 2016-09-06 - Earliest claimed: 2009-07-30 - Assignees: NXP B.V. - Applicants: Simon Doclo - Inventors: Simon Doclo - Web page: https://patentgrep.com/patent/US9437182B2 ## CPC - 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)} - G10K 11/17817: {between the output signals and the error signals, i.e. secondary path} - G10K 11/17827: {Desired external signals, e.g. pass-through audio such as music or speech} - G10K 11/17854: {the filter being an adaptive filter} - G10K 11/17857: {Geometric disposition, e.g. placement of microphones} - G10K 11/17881: {the reference signal being an acoustic signal, e.g. recorded with a microphone} - G10K 11/17885: {additionally using a desired external signal, e.g. pass-through audio such as music or speech} - G10K 2210/1053: Hi-fi, i.e. anything involving music, radios or loudspeakers - G10K 2210/108: Communication systems, e.g. where useful sound is kept and noise is cancelled - H04R 2460/01: Hearing devices using active noise cancellation - 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) - 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 ## Abstract A method of active noise reduction is described which comprises receiving an audio signal (132) to be played, receiving a noise signal (105, 107, 116, 118, 126), indicative of ambient noise (111), from at least one microphone (104, 106), and generating a noise cancellation signal (114) depending on both, said audio signal (132) and said noise signal (105, 107, 116, 118, 126). ## Claims ### Claim 1 A method of active noise reduction, the method comprising: receiving an audio signal to be played; receiving at least one noise signal from at least one microphone, said at least one noise signal being indicative of an ambient noise; and generating a noise cancellation signal depending on both said audio signal and said at least one noise signal, wherein the noise cancellation signal reduces an intensity of the ambient noise in frequency regions where the ambient noise is not masked by the audio signal. ### Claim 2 (depends on 1) The method according to claim 1, wherein generating said noise cancellation signal comprises: providing an active noise reduction filter having a plurality of filter parameters which define filter characteristics of the active noise reduction filter; providing optimized values for said plurality of filter parameters of said active noise reduction filter depending on said audio signal and at least one said noise signal; and filtering said at least one noise signal with said active noise reduction filter by using said optimized values for said plurality of filter parameters. ### Claim 3 (depends on 2) The method according to claim 2, further comprising: determining said optimized values for said plurality of filter parameters in an optimization procedure, said optimization procedure using spectro-temporal characteristics of said audio signal and spectro-temporal characteristics of said at least one noise signal to improve masking of a perception of residual noise by said audio signal. ### Claim 4 (depends on 2) The method according to claim 2, the method further comprising: determining a frequency masking threshold from the audio signal; determining a desired active performance indicating how much the ambient noise must be suppressed such that it is masked by the audio signal; and optimizing said plurality of filter parameters so as to decrease a difference between an actual active performance and the desired active performance. ### Claim 5 (depends on 4) The method according to claim 4, further comprising: determining said desired active performance from a difference between the frequency masking threshold and a power spectral density of said at least one noise signal. ### Claim 6 (depends on 1) The method according to claim 1, wherein said at least one noise signal is a feedforward signal obtained by receiving a reference microphone signal from a reference microphone which is configured for receiving said ambient noise and for generating in response thereto said reference microphone signal. ### Claim 7 (depends on 1) The method according to claim 1, wherein said at least one noise signal is a feedback signal obtained by receiving an error microphone signal from an error microphone which is configured for receiving said ambient noise, and a secondary path filters the noise cancellation signal between a loudspeaker and said error microphone, filters said audio signal filtered by said secondary path, and generates in response hereto said error microphone signal. ### Claim 8 (depends on 1) The method according to claim 1, wherein said at least one noise signal is an ambient noise estimation signal, obtained by subtracting an estimate of a secondary path signal from an error microphone signal, the secondary path signal is a signal received by the error microphone which corresponds to a sum of said audio signal and said noise cancellation signal, and said error microphone signal is generated by the error microphone which is configured for receiving said ambient noise, said noise cancellation signal and said audio signal, and for generating in response thereto said error microphone signal. ### Claim 9 (depends on 1) The method according to claim 1, further comprising: considering simultaneous masking effects in a frequency domain. ### Claim 10 (depends on 1) The method according to claim 1, further comprising: considering temporal masking effects in a time domain. ### Claim 11 A cancellation signal generator comprising: a first input configured to receive an audio signal to be played; and a second input configured to receive, from at least one microphone, at least one noise signal indicative of an ambient noise, wherein said cancellation signal generator is configured for generating a noise cancellation signal depending on both said audio signal and said at least one noise signal, wherein the noise cancellation signal reduces an intensity of the ambient noise in frequency regions where the ambient noise is not masked by the audio signal. ### Claim 12 (depends on 11) The cancellation signal generator according to claim 11, further comprising: a power spectrum unit configured to provide, based on said at least one noise signal, an ambient noise power spectrum density corresponding to said ambient noise; a psychoacoustic masking model unit configured to generate, based on said audio signal, a frequency masking threshold, said frequency masking threshold indicating a power below which a residual noise is masked by the audio signal; and a subtraction unit configured to calculate, as a desired active performance, a difference of said ambient noise power spectrum density and said frequency masking threshold. ### Claim 13 (depends on 11) The cancellation signal generator according to claim 11, further comprising: an active noise reduction filter having filter characteristics depending on both said audio signal and said at least one noise signal, wherein said active noise reduction filter is configured to filter said at least one noise signal to thereby generate said noise cancellation signal. ### Claim 14 (depends on 13) The cancellation signal generator according to claim 13, further comprising: said active noise reduction filter having a plurality of filter parameters which define said filter characteristics of the active noise reduction filter, and a filter optimization unit configured for providing optimized values for said filter parameters of said active noise reduction filter depending on said audio signal and said at least one noise signal. ### Claim 15 (depends on 11) An active noise reduction audio system comprising: the cancellation signal generator according to claim 11; a loudspeaker for playing said audio signal; and said at least one microphone for providing said at least one noise signal.