EP4356622A1 - Système de classification pour contrôle actif du bruit - Google Patents

Système de classification pour contrôle actif du bruit

Info

Publication number
EP4356622A1
EP4356622A1 EP23776664.7A EP23776664A EP4356622A1 EP 4356622 A1 EP4356622 A1 EP 4356622A1 EP 23776664 A EP23776664 A EP 23776664A EP 4356622 A1 EP4356622 A1 EP 4356622A1
Authority
EP
European Patent Office
Prior art keywords
filter
filters
feedforward
feedback
microphone
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP23776664.7A
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German (de)
English (en)
Inventor
Erfindernennung liegt noch nicht vor Die
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Austrian Audio GmbH
Original Assignee
Austrian Audio GmbH
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Filing date
Publication date
Application filed by Austrian Audio GmbH filed Critical Austrian Audio GmbH
Publication of EP4356622A1 publication Critical patent/EP4356622A1/fr
Pending legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/10—Earpieces; Attachments therefor ; Earphones; Monophonic headphones
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • 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
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1781—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions
    • G10K11/17813—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions characterised by the analysis of the acoustic paths, e.g. estimating, calibrating or testing of transfer functions or cross-terms
    • G10K11/17815—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions characterised by the analysis of the acoustic paths, e.g. estimating, calibrating or testing of transfer functions or cross-terms between the reference signals and the error signals, i.e. primary path
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • 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
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1781—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions
    • G10K11/17813—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions characterised by the analysis of the acoustic paths, e.g. estimating, calibrating or testing of transfer functions or cross-terms
    • G10K11/17817—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase characterised by the analysis of input or output signals, e.g. frequency range, modes, transfer functions characterised by the analysis of the acoustic paths, e.g. estimating, calibrating or testing of transfer functions or cross-terms between the output signals and the error signals, i.e. secondary path
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • 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
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1783—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase handling or detecting of non-standard events or conditions, e.g. changing operating modes under specific operating conditions
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • 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
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1785—Methods, e.g. algorithms; Devices
    • G10K11/17853—Methods, e.g. algorithms; Devices of the filter
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • 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
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1787—General system configurations
    • G10K11/17879—General system configurations using both a reference signal and an error signal
    • G10K11/17881—General system configurations using both a reference signal and an error signal the reference signal being an acoustic signal, e.g. recorded with a microphone
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • 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
    • G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/16—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
    • G10K11/175—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound
    • G10K11/178—Methods or devices for protecting against, or for damping, noise or other acoustic waves in general using interference effects; Masking sound by electro-acoustically regenerating the original acoustic waves in anti-phase
    • G10K11/1787—General system configurations
    • G10K11/17885—General system configurations additionally using a desired external signal, e.g. pass-through audio such as music or speech
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • 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
    • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/10—Applications
    • G10K2210/108—Communication systems, e.g. where useful sound is kept and noise is cancelled
    • G10K2210/1081—Earphones, e.g. for telephones, ear protectors or headsets
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • 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
    • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/30—Means
    • G10K2210/301—Computational
    • G10K2210/3038—Neural networks
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • 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
    • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/30—Means
    • G10K2210/301—Computational
    • G10K2210/3041—Offline
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • 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
    • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/30—Means
    • G10K2210/301—Computational
    • G10K2210/3048—Pretraining, e.g. to identify transfer functions
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • 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
    • G10K2210/00—Details of active noise control [ANC] covered by G10K11/178 but not provided for in any of its subgroups
    • G10K2210/30—Means
    • G10K2210/301—Computational
    • G10K2210/3056—Variable gain
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2460/00—Details of hearing devices, i.e. of ear- or headphones covered by H04R1/10 or H04R5/033 but not provided for in any of their subgroups, or of hearing aids covered by H04R25/00 but not provided for in any of its subgroups
    • H04R2460/01—Hearing devices using active noise cancellation
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2460/00—Details of hearing devices, i.e. of ear- or headphones covered by H04R1/10 or H04R5/033 but not provided for in any of their subgroups, or of hearing aids covered by H04R25/00 but not provided for in any of its subgroups
    • H04R2460/15—Determination of the acoustic seal of ear moulds or ear tips of hearing devices

Definitions

  • the invention relates to a method for classifying and using filters for active noise control in hearing systems according to claim 1.
  • Hearing systems of all kinds be they hearing aids or headphones (hereinafter used as a synonym for all types of hearing systems) of the types over-ear, on-ear, in-ear, or ear-buds, with ANC (used in this application as an abbreviation for Active Noise Canceling or Active Noise Control and used synonymously with ANR, i.e. Active Noice Reduction) are affected by the problem of ANC performance depending on the wearing situation. Ears are very different from person to person and every time the headphones are put on or used, the wearing situation changes, which has a major impact on the ANC performance, especially with static, i.e. non-adaptive systems.
  • ANC used in this application as an abbreviation for Active Noise Canceling or Active Noise Control and used synonymously with ANR, i.e. Active Noice Reduction
  • headphones usually do not have the same passive attenuation everywhere and in every wearing situation, which is why the passive attenuation of the headphones varies depending on the direction of incidence, and thus also the ANC performance.
  • a system must evaluate the current wearing situation/interference direction and adapt the filters of the ANC circuit.
  • a typical approach is adaptive filters, with least mean squares (LMS) being the most common.
  • LMS least mean squares
  • an identical sampling rate is usually required for the filter and the LMS algorithm.
  • ICs Integrated Circuits
  • audio processing occurs at high sampling rates (e.g. 384kHz) and control occurs at low sampling rates (e.g.
  • US 9,773,490 B2 discloses a method in which an acoustic leakage between a speaker of a headphone and a fault microphone is measured or estimated and the feedback system is adjusted accordingly in order to avoid instabilities in the ANC system.
  • the basis for this procedure is the presence of a useful signal (source signal) which is measured at the reference microphone.
  • source signal a useful signal
  • US 9,142,205 B2 further discloses a method that measures or estimates the acoustic leakage between the speaker and the error microphone and adjusts the feedback ANC system so that a portion of the playback signal arriving at the reference microphone is not canceled.
  • the disadvantage of this method is that playback performance is only optimized for ideal useful signal.
  • US 9,516,407 B2 shows a method for estimating the transfer function of an ANC system.
  • the disadvantage is, among other things, the complex two-stage filter selection process.
  • a method for the classification and application of ANC systems in headphones which has the method steps specified in claim 1.
  • a method is used that identifies the wearing situation and noise incidence direction of ANC headphones as well as the physical characteristics (e.g. ear shape, jaw/skull shape,...) of the person wearing the headphones and, using a classifying algorithm, from a
  • a variety of filters selects the filter that is best suited to the respective wearing situation and noise environment so that it can be used for the ANC system.
  • a significant advantage of the method is that the ANC system is sampling rate independent of the system that selects the filter to let work. The independent implementation between the filter-selecting system part and the ANC system part enables a more energy-efficient and error-resistant implementation.
  • measurements must be carried out for headphones that use the method according to the invention and the transmission distances for different ears (which are shaped differently for each wearer), wearing situations and directions of interference sound in different environments must be determined.
  • These measurements are carried out in a controlled environment (e.g. acoustic laboratory) on one or more headphones of the same model.
  • a set of filters is determined that covers the different situations (or averages from them). This filter set represents the widest possible range of situations in which noise can occur, from street noise, turbine noise, the background noise of a coffee house to children playing. There are hardly any limits for the technicians due to the controlled environment of the acoustic laboratory.
  • these filters are stored (saved) in a memory located in the headphones.
  • these (stored) filters can be FIR (finite impulse response) or IIR (infinite impulse response) coefficients.
  • FIR finite impulse response
  • IIR infinite impulse response
  • Fig. 2 shows an application example of the method according to Fig. 1 and
  • Fig. 3 is a flowchart of the classifier of a method according to Fig. 1 or Fig. 2.
  • Fig. 1 shows a schematic representation of the method according to the invention, in which a classifying algorithm makes the decision as to which filter, defined by a set of coefficients, currently provides the best ANC performance and applies these filters in the audio chain.
  • the method includes a hearing system with at least one feedforward microphone and at least one feedback microphone, at least one loudspeaker, at least one integrated circuit consisting of a memory and at least one processor unit, at least one feedback path and at least one feedforward path and runs through it several steps: a) receiving an audio signal, referred to as a feedback microphone signal, through the at least one feedback microphone (FB microphone) and an audio signal, referred to as a feedforward microphone signal, through the at least one feedforward microphone (FF microphone).
  • FB microphone feedback microphone
  • FF microphone feedforward microphone
  • Pre-filtering of the audio signal whereby classic high-pass, low-pass, bandpass, etc. filters can be used (see also Fig. 2).
  • the task of the pre-filter is, for example, to limit and/or weight the frequency-related bandwidth range for ANC optimization.
  • FB path Estimation of the transfer function of the feedback path (FB path) based on the comparison of the internal (feedback) microphone signal and the loudspeaker signal (speaker signal), whereby an adaptive algorithm (adaptive algorithms include, for example, all LMS variants including the new PEAK -LMS, RLS, affine projection or algorithms based on cross-correlation) is used to estimate the transfer function, with variants in both the time domain and the frequency domain (subband/frequency domain LMS) being possible.
  • the calculation is carried out using algorithms known to the person skilled in the art. d) Determination of the performance indicator based on the level at the feedback microphone in relation to the feedforward microphone.
  • a classifying algorithm Selection of a set of coefficients by a classifying algorithm, based on the relevant properties of the transfer function determined in c) and the level determined in d), whereby there are two options: Either the classifying algorithm (hereinafter referred to as “classifier”) discretely gives a class to which a set of filters stored in a memory located in the headphones is assigned, or the classifier outputs a one-dimensional function.
  • Suitable classification algorithms include: Decision Tree, Support Vector Machine, Multivariate Gauss or Neural Network. Preferred implementations are decision trees and nonlinear multilayer neural networks. The training of the classification algorithm usually takes place offline, ie in a laboratory environment.
  • the decision for a filter is made by the classifying algorithm, which has been trained to select a filter, selecting a specific filter from the list of stored filters.
  • the classifying algorithm which has been trained to select a filter, selecting a specific filter from the list of stored filters.
  • a quantifier that assigns a filter function to each range of values.
  • each class is assigned a set of filter coefficients that can be taken from the lookup table (LUT).
  • the one-dimensional function is particularly advantageous when using a neural network.
  • a neural network as a classifier has one neuron for each class in the output layer. This means a certain computational effort, which can be reduced if the network is reduced to a single output neuron. In this case, the output neuron goes through the classes (here the LUT).
  • the output of the network is understood as a one-dimensional function, which is assigned to the LUT in a quantized form.
  • f) Application of the coefficient set of the filter selected in e) in the current feedback audio path, ie the coefficients are copied into the current feedback audio path FB(z) (symbolized by the oblique arrows for a variable function block) or a reference to the start address becomes the coefficients are made
  • FB-ANC an estimate of the feedforward path (FF path) is made based on the comparison of the external (feedforward) and internal (feedback) microphone signal determined under a), whereby an adaptive algorithm (LMS or comparable , see also point b) is used to estimate the transfer function of the FF path, with variants both in the time domain and in the frequency domain (subband/frequency domain LMS) being possible.
  • LMS adaptive algorithm
  • h) Calculation of various, not necessarily all but at least one, relevant properties from the transfer function of the feedforward path, analogous to point c). This can be one, several, or all of the following properties: total gain, temporal centroid, average energy, envelope, rise time of the envelope, crest factor, autocorrelation, histogram, spectral flatness measure or even kurtosis. The calculation is carried out using algorithms known to the person skilled in the art.
  • i) Determination of a performance indicator by referencing the feedback microphone signal (FB mic signal) to the feedforward microphone signal (FF mic signal), analogous to point d). This shows the current ANC performance of the system.
  • the referencing is, for example, a division and preferably takes place in the frequency domain, but can also take place in the time domain if necessary.
  • the signals are averaged and rectified before division and then additional smoothing with optional filtering to focus on frequency ranges.
  • smoothing is also useful or possible.
  • their output is used as a performance indicator. In this sense, smoothing represents a form of averaging the results of the division over a defined period of time. The corresponding period of time can be freely defined within limits that make sense for the application.
  • the transfer functions estimated in h) and the performance indicator determined in i) are used as inputs to a classifying algorithm, shown in Fig.
  • the FF filter is always adapted; conversely, the FF filter can be adapted without adapting the FB filter.
  • the FB filter is therefore adjusted at most as often as the FF filter is adjusted.
  • the decision whether only the FF filter is adjusted or whether FF and FB filters have to be adjusted can either be predetermined by a defined scheme, determined by user input, or by an algorithm (e.g. based on the performance indicators, of the sound pressure, or a similarly suitable measure of system quality).
  • the use of the pre-filters from point al) is optional.
  • the FF or FB paths must also be determined for each of the desired combinations. This step is logical for the person skilled in the art with knowledge of the invention and can be carried out without further explanations. In the above process description, the singular number of components was chosen to make the example easier to read.
  • the filter gain can optionally be adjusted either before, in parallel, or after the filter selection. It should be noted that the estimated and applied transfer functions can be different.
  • the filter coefficients assigned to the class are applied in the ANC path.
  • the filter based on the chosen coefficients, can be the right choice in different wearing situations as long as the gain is adjusted correctly. This can result in the situation where, purely mathematically speaking, another filter would be more suitable, but the selected filter has a sufficiently strong effect due to the gain that it does not trigger an adjustment of the filter. There is therefore an interplay of the gain estimator and the classifier in this case.
  • a gain estimator can be a PID controller, LMS (with a coefficient), or cross-correlation.
  • the coefficient set can also contain different coefficients for audio playback.
  • the audio playback path depends not only on the audio source (audio stream source in Fig. 1), but also on the wearing situation and the physical characteristics (e.g. ear shape, jaw/skull shape,...) of those wearing the headphones Person can change and should ideally be adapted.
  • This changeable filter for audio playback (or useful signal playback such as music) is shown in Fig. l as Audio(z).
  • the final playback of the audio chain can take place via various systems such as dynamic speakers, balanced armature drivers, MEMS speakers, bone conduction systems, etc. and is shown as a loudspeaker in Fig.l.
  • the selection of the filter function and the calculation of the gain can be done simultaneously or alternately (ping-pong mode).
  • the term “simultaneous” here means that the processor performing the calculation simultaneously makes the calculation results available to the system at the end of the calculating cycle.
  • the duration of a calculation cycle with alternating selection of the filter function and calculation of the gain (ping-pong mode) can be selected variably.
  • the system can allow the estimate of the transfer function to converge for 100ms, then adjust the gain for 100ms, then estimate the transfer function again, etc. Variations of this scheme are easily understandable and feasible for those skilled in the art with knowledge of the invention.
  • Fig. 2 shows an application example of the method according to Fig. 1, in which the selection of the filter function and the calculation of the gain take place simultaneously.
  • the gain of the filter can optionally be adjusted either before, in parallel, or after the filter selection (see point e) or j) in the description for FIG. 1).
  • This variant of simultaneous gain/filter adaptation uses the gain controller as the main control element, which initiates or forces the change between the filter functions.
  • the process sequence of the example shown in FIG. 2 is therefore analogous to that in FIG. 1, with the following differences:
  • the gain of the filter can be adjusted (shown as Variable Gain).
  • the level on the feedback microphone (point a) in the description of Fig.l) and on the feedforward microphone (point g) in the description of Fig.l) and/or the performance indicator (point i) in the description to Fig.l) are used to to determine the ideal filter gain for the wearing situation (“Gain estimation” function block).
  • a gain estimator from step II can be a PID controller known from control engineering, an LMS algorithm (with a coefficient) or a cross-correlation function (see above)
  • step IV stopping or starting the adaptation
  • a noise floor for each of the different parts of the system, i.e. a lower threshold value which can be given as an absolute limit by the sensor sensitivity, or fixed for the algorithm can be defined. If this is not reached, the adaptation is stopped.
  • An example of this is a quiet environment: Since there is hardly any energy in the acoustic signal, only poor estimates can be made and are not relevant for good ANC performance since the environment is quiet anyway. It is therefore preferable to stop the system, otherwise in the worst case scenario the ANC system itself could cause noise.
  • a typical static filter A default filter is therefore defined for the algorithm, which can be used in such situations in order to achieve this defined state known to the algorithm.
  • the adaptation of the filters is only paused if the performance (indicated by the performance indicator) is sufficiently good or if disruptive events are detected .
  • the threshold values for starting and stopping the adaptation based on the indicator can be static or adaptive as already described and in the latter case change with long-term averaging ANC overall performance.
  • the algorithm tries to achieve a noise minimum.
  • optimal performance cannot always be achieved. Stopping the adaptation is necessary to prevent borderline cases in which the classifier would constantly switch between two states (e.g. two filters).
  • a reference threshold value is set to which the smoothed signal is fed.
  • the decision as to whether an adaptation takes place is made by a threshold switch, which usually has a hysteresis.
  • the performance indicator also prevents you from jumping between filters too often.
  • the classifier pays attention to the current value of the gain estimate: If the value of the gain estimate is at its maximum or minimum over a defined period of time, the classifier can move to the next higher or - Switch to a lower filter class. The reason for this is that, for example, with a constant high gain, a neighboring filter probably delivers better results at medium gain, which was not reflected in the transfer function estimation.
  • the classifier only pays attention to the gain estimate, since in extreme cases the transfer function can only be made dependent on the gain estimate, and switches classes according to this information.
  • Fig. 3 shows the flowchart of the classifier used in the examples of Fig. 1 and Fig. 2 with an optional timer that is used for the ping-pong variants.
  • the timer has a duty cycle, similar to a periodic square wave function, and fulfills the task of switching between gain estimation and classifier.
  • a timer designed analogously can also be used to control the sequence of adaptation runs for FB and FF filters (point 1) in the description of Fig. l).
  • Fig. 4 shows a flowchart that shows the filter selection by the classifying algorithm (classifier), whereby the scheme only applies in the first run from subpoint g) of the process flow. It uses an adaptive algorithm (see points b) or h)) to estimate the transfer functions of the FF path and/or the FB path used and a performance indicator is used, which is determined by referencing the feedback microphone signal to the feedforward microphone signal (see point i)).
  • the transfer functions estimated by the adaptive algorithm and the performance indicator serve as input to the classifying algorithm.
  • the estimated transfer function provides the classifying algorithm with the characteristics of the current wearing situation based on the energy content of the ambient sound, so it “recognizes” the situation and tries to select the right filter based on the transfer function.
  • the performance indicator shows the classifying algorithm whether the selected filter is sufficiently suitable for the situation being analyzed and classified, or whether a better filter needs to be chosen.
  • the classifier processes both parameters together. This is done by the classifying algorithm, such as a neural network, mapping the mismatch between the measurement point (FB microphone) and the target point (eardrum) based on its pre-training. This information is used to identify which mismatch is assigned which suitable filter based on the transfer function estimated by the adaptive algorithm.
  • the determined filter is taken from the lookup table (LUT) stored on the IC.
  • the filter taken from the LUT is subsequently applied in the FF or FB path.
  • the advantage of using such a classifier over adaptive filters is the possibility of carrying out measurements in advance (e.g. in special laboratories by a specialist), which allow different conditions, such as an anechoic room or a diffuse sound field.
  • the filters can be calculated for sampling rates other than the sampling rate of the classifier. It is common for classifiers to work with sampling rates ⁇ 50 kHz, while filters with >300 kHz are applied.
  • Another major advantage of the invention over an adaptive system that calculates the filters in real time is the possibility of determining the filters, for example, using in-situ measurements, i.e. using probe microphones near the eardrum (usually the target point).
  • the LUT is separate from the transfer function estimation and any classification can be carried out.
  • the transfer function to the target point is already inherent in the LUT during the laboratory-based characterization measurements and is not estimated as in the application US 9,516,407 B2 and is applied.
  • the transfer function estimation is limited to its reference points: for example the microphones (feedforward and feedback).
  • the filters in the LUT can be created for any target point, which does not necessarily have to correspond to the microphone points.
  • the classifier is trained to map the difference between the microphone point and the target point.
  • the filters in the LUT are designed for the target point (as close as possible to the drum field point).
  • the transfer function estimation optimized for the feedback microphone point.
  • the classifier is trained in a laboratory environment using in-situ measurements for the target point in reference to the microphone points (feedforward and feedback).
  • the filters are arranged hierarchically by class in a filter matrix depending on shape and gain. This makes sequential jumps possible and allows the algorithm to vary between two filters with slightly different shapes or between slightly different gains in borderline cases.
  • a big advantage of this method over adaptive filters is that only useful filters are stored in the memory.
  • the ANC algorithm therefore does not run the risk of getting stuck on local optima.
  • the system is therefore stable in any case and does not produce any artifacts (e.g. hiss noise).
  • a particularly preferred embodiment of this method uses, instead of just a classic LMS algorithm, a combination of a classic LMS algorithm and a PEAK filter in the sense of the application PCT/EP2022/068392, published as WO2023280752A1 on January 12, 2023. Transmitted in this way The advantages of the cited application apply to the application presented here.
  • an audio playback filter can also be assigned to each class (in addition to feedforward and/or feedback filters). This is intended for playing an audio source (e.g. Bluetooth audio or 3.5mm jack) and has the task of keeping the sound constant when the wearing situation changes.
  • the feedback path is defined as a transmission path, described as a transfer function, between an internal feedback microphone located near the loudspeaker and the loudspeaker.
  • the feedforward path is defined as the calculated transmission distance (transfer function) based on the transfer function of the FF microphone, the internal transfer function of the speakers (headphone speaker frequency response) and the transfer function of the passive damping (mechanical system).
  • the invention relates to a method for classifying and applying acoustic filters for active noise control in hearing systems, the filters being determined in advance and stored in a memory in the headphones. While wearing the headphones, it is possible to quickly and efficiently select and apply a specific filter to improve ANC performance and stability.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Health & Medical Sciences (AREA)
  • Audiology, Speech & Language Pathology (AREA)
  • General Health & Medical Sciences (AREA)
  • Soundproofing, Sound Blocking, And Sound Damping (AREA)

Abstract

L'invention concerne un procédé de classification et d'utilisation de filtres acoustiques pour le contrôle actif du bruit dans des systèmes auditifs, les filtres étant préalablement déterminés et étant stockés dans une mémoire des écouteurs. Il est donc possible de sélectionner et d'utiliser rapidement et efficacement un certain filtre lors du port des écouteurs afin d'améliorer les performances du filtre et la stabilité du filtre.
EP23776664.7A 2022-09-30 2023-09-29 Système de classification pour contrôle actif du bruit Pending EP4356622A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP22198999 2022-09-30
PCT/EP2023/077053 WO2024038216A1 (fr) 2022-09-30 2023-09-29 Système de classification pour contrôle actif du bruit

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EP4356622A1 true EP4356622A1 (fr) 2024-04-24

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Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US9142205B2 (en) 2012-04-26 2015-09-22 Cirrus Logic, Inc. Leakage-modeling adaptive noise canceling for earspeakers
US9123321B2 (en) 2012-05-10 2015-09-01 Cirrus Logic, Inc. Sequenced adaptation of anti-noise generator response and secondary path response in an adaptive noise canceling system
US9516407B2 (en) 2012-08-13 2016-12-06 Apple Inc. Active noise control with compensation for error sensing at the eardrum
US11842717B2 (en) * 2020-09-10 2023-12-12 Maxim Integrated Products, Inc. Robust open-ear ambient sound control with leakage detection
US11303258B1 (en) * 2020-09-16 2022-04-12 Apple Inc. Method and system for adaptive audio filters for different headset cushions
US11468875B2 (en) * 2020-12-15 2022-10-11 Google Llc Ambient detector for dual mode ANC
EP4117306A1 (fr) 2021-07-05 2023-01-11 Austrian Audio GmbH Procédé électro-acoustique utilisant un algorithme lms

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