Active noise reduction device and method

Abstract

An active noise cancellation (ANC) device (700) is provided. The ANC device (700) comprises a first microphone (701) configured to generate a first microphone signal in response to a first acoustic noise in a first zone (780) of the ANC device (700), a loudspeaker (705) configured to be driven with a loudspeaker signal, and a second microphone (703) configured to generate a second microphone signal, wherein the second microphone signal comprises a residual noise component based on a second acoustic noise in a second zone (790) of the ANC device (700). Furthermore, the ANC device (700) comprises processing circuitry configured to generate a compensation signal based on the first microphone signal using a first filter (710). The processing circuitry is further configured to generate the loudspeaker signal based on the compensation signal and the second microphone signal using a second filter (720).

Description

Technical Field

[0001] This invention generally relates to sound processing. More specifically, this invention relates to an active noise cancellation (ANC) device and method. Background Technology

[0002] Noise reduction is a common task in various applications. Active noise cancellation (ANC) is a noise reduction technique applied to sound waves and utilizing the destructive interference of sound waves. In ANC devices such as ANC headphones, noise or disturbance is the external sound wave to be eliminated or at least reduced. The goal of an ANC device is to generate compensating sound waves, which achieves destructive interference with noise in the desired attenuation region (often called the quiet zone). Compensating sound waves are also called noise immunity. The performance of an ANC device is typically characterized by the relative level of noise reduction (also called attenuation) and the size of the frequency range, i.e., the size of the bandwidth, where noise reduction is stable. Given that noise reduction is the primary goal, higher attenuation and a wider attenuation bandwidth mean better performance from the ANC device. Summary of the Invention

[0003] One object of the present invention is to provide an improved active noise cancellation device and method.

[0004] The foregoing and other objectives are achieved through the subject matter claimed in the independent claims. Other implementations are apparent from the dependent claims, the specification, and the drawings.

[0005] According to a first aspect, an active noise cancellation (ANC) device is provided. The ANC device includes a first microphone for generating a first microphone signal in response to first external acoustic noise in a first zone of the ANC device (e.g., a zone where the ANC device is exposed to ambient noise). Furthermore, the ANC device includes a noise-canceling speaker for driving with a speaker signal and a second quiet zone microphone for generating a second microphone signal, wherein the second microphone signal includes a residual noise component based on residual second acoustic noise in the second zone of the ANC device (e.g., a quiet zone of the ANC device). The ANC device also includes processing circuitry for generating a compensation signal, i.e., a noise-canceling or noise-reducing signal, based on the first microphone signal using a first filter (also referred to herein as a feedforward ANC filter, i.e., an FF ANC filter). Furthermore, the processing circuitry is also used to generate a speaker signal, i.e., an anti-noise signal, based on the compensation signal and the second microphone signal using a second filter (also referred to herein as a feedback ANC filter, i.e., an FBANC filter).

[0006] Advantageously, the ANC device enhances active noise cancellation by combining FF ANC filters and FB ANC filters in a queue. Advantageously, this guarantees the improved noise immunity stability of the FF ANC filter supported by the FB ANC filter without any unexpected attenuation. The FF ANC filter processes the observed ambient noise and sends it to the quiet zone, and is used to predict noise propagation. The FB ANC filter provides a stable propagation path for the FF ANC filter and reduces residual noise, which is obtained from the difference between the predicted FF ANC noise immunity and the actual noise observed in the quiet zone.

[0007] ANC devices can be headphones, such as over-ear, on-ear, or in-ear headphones. The first zone can be the outer zone of the headphones, also known as the external zone or ambient zone. The second zone can be the inner zone of the headphones, also known as the internal zone, the quiet zone (e.g., in silent mode), or the playback or listening zone (e.g., in playback mode).

[0008] In another possible implementation of the first aspect, the processing circuitry is used to generate a speaker signal based on the difference between the compensation signal and the second microphone signal using a second filter (i.e., an FBANC filter).

[0009] In another possible implementation of the first aspect, the second microphone signal includes a residual noise component based on the residual second acoustic noise in the second zone of the ANC device and a playback signal component. The processing circuitry is used to generate a speaker signal based on the compensation signal, the second microphone signal, and the playback signal using a second filter (i.e., an FB ANC filter). Therefore, advantageously, the ANC device also provides improved active noise cancellation in playback mode.

[0010] In another possible implementation of the first aspect, the processing circuitry is used to generate a speaker signal based on the difference between the sum of the compensation signal and the playback signal and the second microphone signal using a second filter (i.e., an FBANC filter).

[0011] In another possible implementation of the first aspect, the processing circuit is further configured to generate an equalized playback signal based on the playback signal using an equalization filter (also referred to herein as an EQ ANC filter), wherein the processing circuit is configured to generate a speaker signal based on the difference between the sum of the compensation signal and the equalized playback signal and the second microphone signal using a second filter (i.e., an FB ANC filter).

[0012] In another possible implementation of the first aspect, the equalization filter (i.e., the EQ ANC filter) includes at least one of an IIR filter, an FIR filter, and a distorted FIR filter.

[0013] In another possible implementation of the first aspect, the second filter (i.e., the FB ANC filter) includes multiple second filter parameters, wherein processing circuitry is used to adjust (specifically optimize) the multiple second filter parameters to extend the frequency range of the second filter (i.e., the FB ANC filter).

[0014] In another possible implementation of the first aspect, the second filter (i.e., the FB ANC filter) includes at least one of an IIR filter, an FIR filter, and a distorted FIR filter.

[0015] In another possible implementation of the first aspect, the first filter (i.e., the FF ANC filter) includes a plurality of first filter parameters, wherein the processing circuitry is used to adjust (specifically optimize) the plurality of first filter parameters and a plurality of second filter parameters of the second filter (i.e., the FB ANC filter) to extend the frequency range of the second filter and improve the noise reduction performance of the first and second filters.

[0016] In yet another possible implementation of the first aspect, the first filter (i.e., the FF ANC filter) includes at least one of an IIR filter, an FIR filter, and a distorted FIR filter.

[0017] In another possible implementation of the first aspect, the equalization filter includes multiple equalization filter parameters, wherein the processing circuit is used to adjust (specifically optimize) the multiple equalization filter parameters, as well as multiple first filter parameters of the FF ANC filter and multiple second filter parameters of the FB ANC filter, to extend the frequency range of the second filter (i.e., the FB ANC filter), improve the noise reduction performance of the first and second filters, and compensate for the high-frequency attenuation of the second filter using the equalization filter (i.e., the EQ ANC filter).

[0018] According to the second aspect, an active noise reduction (ANC) method is provided. The ANC method includes the following steps:

[0019] In response to a first external acoustic noise in the first zone, a first microphone signal is generated;

[0020] A second microphone signal is generated, wherein the second microphone signal includes a residual noise component based on the residual second acoustic noise in the second region;

[0021] Using the first filter, namely the FF ANC filter, a compensation signal, namely a noise reduction or noise cancellation signal, is generated based on the first microphone signal;

[0022] A second filter, namely the FB ANC filter, is used to generate a speaker signal based on the compensation signal and the second microphone signal;

[0023] The noise-canceling speaker is driven by the speaker signal.

[0024] In another possible implementation of the second aspect, the second microphone signal includes a residual noise component based on the second acoustic noise in the second zone and a playback signal component, wherein the step of generating the speaker signal includes generating the speaker signal based on the compensation signal, the second microphone signal and the playback signal using a second filter (i.e., an FB ANC filter).

[0025] In another possible implementation of the second aspect, the step of generating the speaker signal includes using a second filter (i.e., an FB ANC filter) to generate the speaker signal based on the difference between the sum of the compensation signal and the playback signal and the second microphone signal.

[0026] In another possible implementation of the second aspect, the ANC method according to the second aspect further includes the step of generating an equalized playback signal based on the playback signal using an equalization filter, wherein the step of generating the speaker signal includes generating the speaker signal using a second filter (i.e., an FB ANC filter) based on the difference between the sum of the compensation signal and the equalized playback signal and the second microphone signal.

[0027] The ANC method according to the second aspect of the invention can be executed by the ANC device according to the first aspect of the invention. Therefore, other features of the ANC method according to the second aspect of the invention are directly derived from the functionality of the ANC devices according to the first aspect of the invention and the various implementations of the invention described above and below.

[0028] According to a third aspect, a computer program product is provided, including a non-transitory computer-readable storage medium for storing program code, which, when executed by a computer or processor, causes the computer or processor to perform the ANC method according to the second aspect.

[0029] According to the fourth aspect, a computer program is provided, including program code, which, when executed by a computer or processor, causes the computer or processor to perform the ANC method according to the second aspect.

[0030] The following drawings and description illustrate one or more embodiments in detail. Other features, objects, and advantages will be apparent from the description, drawings, and claims. Attached Figure Description

[0031] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the drawings:

[0032] Figure 1 A schematic diagram illustrating the general architecture of an ANC device;

[0033] Figure 2A diagram illustrating an ANC device in earbud form;

[0034] Figure 3a A schematic diagram illustrating the architecture of an FF ANC device in silent mode;

[0035] Figure 3b To show by Figure 3a A schematic diagram illustrating various aspects of signal processing implemented by the FF ANC device;

[0036] Figure 4a A schematic diagram illustrating the architecture of an FF ANC device in playback mode;

[0037] Figure 4b To show by Figure 4a A schematic diagram illustrating various aspects of signal processing implemented by the FF ANC device;

[0038] Figure 5 The amplitude response of different transfer functions of the FF ANC filter in a hybrid ANC device as a function of frequency is shown;

[0039] Figure 6a This is a schematic diagram illustrating the architecture of an FB ANC device in silent mode;

[0040] Figure 6b To show by Figure 6a A schematic diagram illustrating various aspects of signal processing implemented by the FB ANC device;

[0041] Figure 7a A schematic diagram illustrating the architecture of an FB ANC device in playback mode;

[0042] Figure 7b To show by Figure 7a A schematic diagram illustrating various aspects of signal processing implemented by the FB ANC device;

[0043] Figure 8 The amplitude response of the FB ANC filter of the hybrid ANC device as a function of frequency is shown for different transfer functions;

[0044] Figure 9a A schematic diagram illustrating the architecture of a hybrid ANC device in silent mode;

[0045] Figure 9b To show by Figure 9a A schematic diagram illustrating various aspects of signal processing implemented in a hybrid ANC device;

[0046] Figure 10a A schematic diagram illustrating the architecture of a hybrid ANC device in playback mode;

[0047] Figure 10bTo show by Figure 10a A schematic diagram illustrating various aspects of signal processing implemented in a hybrid ANC device;

[0048] Figure 11 The amplitude response of different noise transfer functions of a hybrid ANC device as a function of frequency is shown;

[0049] Figure 12 A schematic diagram illustrating the feedback input in a hybrid ANC device;

[0050] Figure 13 The amplitude response of the FB ANC filter with different transfer functions as a function of frequency is shown for a hybrid ANC device with secondary transfer path modification.

[0051] Figure 14 The noise immunity attenuation of FF ANC in a hybrid ANC device is shown;

[0052] Figure 15 Playback impairments were shown in hybrid ANC devices;

[0053] Figure 16 A schematic diagram illustrating the general architecture of a feedback control system (FCS);

[0054] Figure 17 A schematic diagram illustrating the hybrid ANC device architecture as an FCS;

[0055] Figure 18 A schematic diagram illustrating the feedback control architecture of an ANC device with a chain-like ANC architecture provided in the embodiment;

[0056] Figure 19a This is a schematic diagram illustrating the architecture of an ANC device with a chain-like ANC architecture provided in the embodiment in silent mode;

[0057] Figure 19b To show by Figure 19a A schematic diagram illustrating various aspects of signal processing implemented by an ANC device;

[0058] Figure 20a This is a schematic diagram illustrating the architecture of an ANC device with a chain-like ANC architecture provided in the embodiment during playback mode;

[0059] Figure 20b To show by Figure 20a A schematic diagram illustrating various aspects of signal processing implemented by an ANC device;

[0060] Figure 21 The embodiments illustrate various aspects of the FF ANC filter design for an ANC device with a chained ANC architecture provided in the embodiments;

[0061] Figure 22 The various aspects of the pass path of the FF ANC filter in the ANC device with a chained ANC architecture provided in the embodiment are illustrated;

[0062] Figure 23 The illustration shows various aspects of the playback response of an ANC device with a chained ANC architecture provided in the embodiment;

[0063] Figure 24 The illustration shows various aspects of the playback equalizer of an ANC device with a chained ANC architecture provided in the embodiment;

[0064] Figure 25 A flowchart illustrating the chained ANC method provided in the embodiment.

[0065] In the following text, the same reference numerals refer to the same or at least functionally equivalent features. Detailed Implementation

[0066] In the following description, reference is made to the accompanying drawings, which form part of this invention, which illustrate by way of description specific aspects of embodiments of the invention or aspects in which embodiments of the invention may be used. It should be understood that embodiments of the invention can be used in other aspects and include structural or logical variations not depicted in the drawings. Therefore, the following detailed description should not be construed as limiting, and the scope of the invention is defined by the appended claims.

[0067] For example, it should be understood that the disclosure relating to the described method can also apply to the corresponding device or system for performing the method, and vice versa. For example, if one or more specific method steps are described, the corresponding device may include one or more units (e.g., functional units) to perform the described one or more method steps (e.g., one unit performs one or more steps, or multiple units perform one or more of multiple steps respectively), even if the one or more units are not explicitly described or illustrated in the drawings. On the other hand, for example, if a specific apparatus is described based on one or more units (e.g., functional units), the corresponding method may include a step to perform the function of one or more units (e.g., one step performs the function of one or more units, or multiple steps perform the function of one or more of multiple units respectively), even if the one or more units are not explicitly described or shown in the drawings. Furthermore, it should be understood that, unless otherwise explicitly stated, features of the various exemplary embodiments and / or aspects described herein can be combined with each other.

[0068] Before describing the different embodiments of the present invention in detail, some terminology and technical background regarding active noise cancellation (ANC) will be introduced below. Figure 1 This is a schematic diagram illustrating the general architecture of an ANC device 100, such as headphones 100, including over-ear, on-ear, or in-ear types (the latter also referred to as earbuds, see...). Figure 2 (Description) Headphones. Typically, the ANC processing circuit 110 of the ANC device 100 considers... Figure 1 One or more of the sound propagation paths shown are the primary path (PP) and secondary path (SP) used to perform ANC. PP causes variations in the amplitude and phase of the disturbance due to headphone material and position, as well as the angle of incidence. PP affects the noise difference between ambient noise 180 detected by FF microphone (FF-MIC) 101 and quiet zone microphone or feedback microphone (FB-MIC) 103. SP depends on the characteristics of the acoustic path between loudspeaker (SPK) 105, FB-MIC 103, and these components. SP can be modeled using the transfer function used for sound waves propagating from SPK 105 to FB-MIC 103.

[0069] As will be understood, Figure 1 The PP shown is essentially a virtual propagation path, meaning it does not characterize the actual sound wave propagation. In reality, the noise wave is radiated from a distant source and arrives at FF-MIC 101 and FB-MIC 103 along separate paths. Therefore, PP essentially characterizes the difference in its arrival locations at FF-MIC 101 and FB-MIC 103.

[0070] Figure 2 A diagram illustrating an exemplary ANC device 100 in the form of an earpiece inserted into the listener's ear. Figure 2 As shown, the FF-MIC 101 is mounted on the outer surface of the earbud housing to capture external noise (outer zone of the ANC device). The FB-MIC 103 is positioned to record the sound pressure level within the cavity defined by the earbud housing and the ear canal (inner zone of the ANC device). The SPK 105 is placed within the cavity to emit sound waves into the ear canal based on the speaker signal provided by the ANC processing circuitry 110. Typically, the FF-MIC 101 is mounted to provide a stable power supply (PP) with minimal dependence on the incident direction of external noise. The FB-MIC 103 is typically positioned near the quiet zone, resulting in a short sound wave propagation time from the SPK 105. The placement and acoustic characteristics of the SPK 105 are typically optimized for a stable power supply (SP) with minimal dependence on specific use cases (e.g., headphone wearing style, earbud leakage, etc.).

[0071] Embodiments of the present invention will provide an audio processing device for ANC (Audio-Censored Noise), which can operate in one or two different modes, namely, a silent mode and / or a playback mode. In silent mode, the primary objective of the ANC device is to reduce any ambient noise to a level comfortable for the listener. In playback mode, the primary objective of the ANC device is to improve the listener's subjective sound perception during music playback, conversations, etc.

[0072] Figure 3a A schematic diagram of an ANC device 300 implementing an FF ANC (FF ANC) scheme in silent mode is shown. The FF ANC device 300 uses an FF microphone (FF-MIC) 301 to capture ambient noise 380 and generates anti-noise in a quiet zone 390 based on preliminary knowledge of noise propagation via the PP and anti-noise propagation via the SP. The FF ANC device 300 has a relatively simple design because it minimizes the difference between the PP and SP using an FF ANC filter 310 provided by the processing circuitry of the FF ANC device 300.

[0073] Figure 3a The signal processing solution implemented by the FF ANC device 300 is as follows: Figure 3b As shown. Noise x(t) travels along the transfer function H PP The main path described by (s)311 passes through, generating the observed disturbance d(t). The noise x(t) is converted into a digital signal x(n), which is processed by an FF ANC digital filter 310 (e.g., IIR, FIR, distorted FIR filter, etc.). The transfer function H of the FF ANC digital filter 310 is... FF (z) Generates an FF noise-resistant digital signal y FF (n). Signal y FF (n) along the transfer function H SP The secondary path SP described in (s)313 passes through, generating a simulated noise-resistant signal y(t), i.e., a noise-compensated signal. The destructive interferences d(t) and y(t) in the quiet zone generate residual noise e(t).

[0074] Figure 4a A schematic diagram of an ANC device 300 implementing an FF ANC scheme in playback mode is shown. As mentioned above, the main objective of playback mode is lossless noise reduction during playback of a useful signal, which can be streamed from a network in any way or sent from internal memory to the speaker, such as... Figure 4a As indicated by reference numeral 307 in the accompanying drawings. As will be understood, FFANC typically does not require any special measures to compensate for the playback signal or consider the generation of noise immunity in the playback signal. FFANC mixes the noise immunity and the playback signal without special processing and sends the resulting signal to speaker 305.

[0075] More specifically, Figure 4a The signal processing solution implemented by the FF ANC device 300 is as follows: Figure 4b As shown. Noise x(t) travels along the transfer function H PP The main path described in (s)311 passes through, generating the observed disturbance d(t). The noise x(t) is converted into a digital signal x(n), which is then processed by a signal with a transfer function H. FF (z) is processed by an FF ANC digital filter 310 (e.g., IIR, FIR, twisted FIR filter, etc.) to generate an FF noise-resistant digital signal y. FF (n). Mixer 309a converts the noise-resistant signal (i.e., the compensation signal y) into a frequency converter. FF The digital output signal y(n) is mixed with the digital playback signal s(n) to generate the digital output signal y(n). The digital output signal y(n) travels along the transfer function H. SP The secondary path described in (s)313 passes through, thereby generating an analog noise-resistant signal y(t). The destructive interferences d(t) and y(t) in the quiet zone generate an analog playback signal s′(t) that is mixed with the residual noise e(t).

[0076] for Figure 3a , 3b The FF ANC device 300 shown in 4a and 4b aims to select (i.e. design) an FF ANC filter whose output is an approximation of the primary path (PP) through the secondary path (SP) FF filter output. A digital model H of PP can be used. PP (z) and SP's digital model H SP (z) is represented as:

[0077] H PP (z)=-H SP (z)*H FF (z)[1]

[0078] After designing the FF filter, the FF ANC noise attenuation can be estimated as follows:

[0079]

[0080] To model the PP, a low-pass filter with a cutoff frequency determined by the geometry of the FF ANC device 300 and the environment can be used, while for the SP, a low-pass filter with a cutoff frequency much higher than that of the PP, defined by acoustic design and the placement of the quiet zone MIC 303, is used. Therefore, the FF ANC filter 310 is typically matched with a low-pass filter having a cutoff frequency and a roll-off rate dependent on the shape of the PP. An exemplary FF ANC filter design (i.e., the amplitude response of the correlation transfer function) for a headset implementing the FF ANC scheme is shown below. Figure 5 As shown.

[0081] Figure 6a A schematic diagram of an ANC device 400 implementing an FB ANC scheme in silent mode is shown. The FB ANC device 400 uses a feedback microphone (FB-MIC) 403 to capture ambient noise 480 observed in a quiet zone 490 and uses it to generate anti-noise through anti-noise propagation along the SP (from speaker 405). Figure 6a The signal processing solution implemented by the FB ANC device 400 is as follows: Figure 6b As shown. The disturbance d(t) is the ambient noise transmitted to the quiet zone 490. The observed disturbance d(t) is interfered with by a simulated noise-resistant signal y(t), thereby generating residual noise e(t). The residual noise is converted into a digital signal e(n). The digital residual noise e(n) is expressed using a signal with transfer function H. FB (z) is processed by an FB ANC digital filter 420 (e.g., IIR, FIR, twisted FIR filter, etc.) to generate a digital noise-resistant signal y. FB (n). Digital noise-resistant signal y FB (n) along the transfer function H SP The secondary path described by (s)413 is passed through, thereby generating an analog noise-resistant signal, namely the compensation signal y(t).

[0082] For FB ANC schemes in playback mode, achieving lossless noise reduction is particularly challenging in the sense of obtaining the playback signal, as it is difficult to distinguish between noise and useful signals. According to one method, a copy of the SP (Spread Signal) can be obtained, and the modeled playback signal propagation can be subtracted from the actual FB-MIC (Bulk-to-Microwave) signal. This method... Figure 7a The FB ANC device 400 shown is implemented in this device and Figure 6a and 6b The FB ANC device 400 shown also includes an SP copy filter 430 (and another mixer 409b).

[0083] Figure 7a The signal processing solution implemented by the FB ANC device 400 is as follows: Figure 7bAs shown. Noise x(t) travels along the transfer function H PP The main path described in (s)411 passes through, thus generating the observed perturbation d(t). The analog output signal y(t) interferes with the perturbation d(t), thereby generating an analog playback signal s that is mixed with the residual noise e(t). P (t). The mixing signal is converted into a digital signal s′(n)+e(n). The playback signal s(n) is processed using the SP model, i.e., using the transfer function. The described copy filter 430 processes the signal to generate a playback signal prediction. Mixer 409b subtracts the playback signal prediction from the mixed signal. This leaves residual noise e(n). The residual noise e(n) is then sent to a device with transfer function H. FB (z) uses an FB ANC digital filter 420 (e.g., IIR, FIR, twisted FIR filter, etc.) to generate a digital noise-resistant signal y. FB (n). Mixer 409a converts the digital noise-resistant signal y FB The digital signal y(n) is mixed with the digital playback signal s(n) to generate the output digital signal y(n). The digital output signal y(n) travels along the transfer function H. SP The secondary path described by (s)413 passes through, thereby generating the analog output signal y(t).

[0084] Selection (i.e., design) Figure 6a , 6b The goal of the filter in the FB ANC device 400 shown in 7a and 7b is to improve (specifically, optimize) the noise sensitivity function to achieve good noise attenuation. The noise sensitivity function characterizes the noise attenuation capability of the FB ANC device 400 and can be expressed as:

[0085]

[0086] An exemplary FB ANC filter design (i.e., the amplitude response of the transfer function) for headphones used to implement a hybrid ANC scheme (also known as a hybrid ANC scheme) is shown below. Figure 8 As shown.

[0087] Figure 9a A schematic diagram of a corresponding ANC device 500 (also known as a hybrid ANC device 500) is shown. This ANC device combines FF ANC and FB ANC schemes in silent mode to achieve good attenuation at low frequencies (FB ANC) while also extending the attenuation bandwidth (FF ANC). The main components of the hybrid ANC device 500 are FF-MIC 501, FB-MIC 503, speaker 505, FF ANC filter 510, and FB ANC filter 520. (The diagram is from...) Figure 9aIt is understood that the hybrid ANC device 500 implements the FF ANC filter 510 and the FB ANC filter 520 in parallel and uses the sum of their outputs (provided by the mixer 509a) as noise immunity.

[0088] More specifically, Figure 9a The signal processing solution implemented by the hybrid ANC device 500 is as follows: Figure 9b As shown. Noise x(t) travels along the transfer function H PP The main path described in (s)511 passes through, thus generating the observed perturbation d(t). An analog noise-resistant signal y(t) interferes with the perturbation d(t), thus generating residual noise e(t). The analog noise signal x(t) is converted into a digital noise signal x(n), which is used as the transfer function H. FF (z) describes the input of an FF ANC filter 510 (e.g., IIR, FIR, twisted FIR filter, etc.) to generate FF ANC digital noise immunity y. FF (n). The analog residual noise signal e(t) is converted into a digital residual noise signal e(n), which is used as the transfer function H. FB (z) describes the input of the FB ANC filter 520 (e.g., IIR, FIR, twisted FIR filter, etc.) to generate the FB ANC digital noise-resistant signal y. FB (n). Digital noise-resistant signal y FE (n) and y FB (n) are added by mixer 509a to generate a mixed ANC digital noise-resistant signal y(n). The digital noise-resistant signal y(n) travels along the transfer function H SP The secondary path described by (s)513 is traversed, thereby generating an analog noise-resistant signal y(t).

[0089] Figure 10a A schematic diagram of a hybrid ANC device 500 combining FF and FB ANC schemes in playback mode is shown. Figure 10a It can be seen that the hybrid ANC device 500, operating in playback mode, achieves lossless noise reduction by combining FB ANC with FF ANC, which reduces the FB ANC adjustments required to achieve good performance. In addition... Figure 9a and 9b In addition to the components of the hybrid ANC device 500 shown, Figure 10a and 10b The hybrid ANC device 500 shown includes an SP copy filter 530 for subtracting the playback signal from the input of the FB-MIC 501 to reduce the damage caused to it by the FB ANC filter 520.

[0090] More specifically, Figure 10a The signal processing solution implemented by the hybrid ANC device 500 is as follows: Figure 10b As shown. Noise x(t) travels along the transfer function H PP The main path described in (s)511 passes through, generating the observed perturbation d(t). The analog signal interference y(t) perturbs d(t), thus generating residual noise s′(t)+e(t) mixed with the playback signal. The analog noise signal x(t) is converted into a digital noise signal x(n), which is used as the transfer function H. FF (z) describes the input of an FF ANC filter 510 (e.g., IIR, FIR, twisted FIR filter, etc.) to generate FF ANC digital noise immunity y. FF (n). Playing digital signal s(n) using the transfer function The described SP copy filter 530 is processed to produce a digital playback output prediction. The analog signal s′(t)+e(t) is converted into a digital signal s′(n)+e(n). Mixer 509b subtracts the playback signal prediction from this digital signal, generating a digital residual noise signal e(n). This digital residual noise signal e(n) is used as the transfer function H. FB (z) describes the input of the FB ANC filter 520 (e.g., IIR, FIR, twisted FIR filter, etc.) to generate the FB ANC digital noise-resistant signal y. FB (n). Mixer 509a converts the digital noise-resistant signal y FF (n) and y FB The digital noise-resistant signal y(n) is added to the playback signal s(n) to generate the mixed output signal y(n). The digital noise-resistant signal y(n) travels along the transfer function H SP The secondary path described by (t)513 is traversed, thereby generating simulated noise-resistant y(t).

[0091] for Figure 9a , 9b The hybrid ANC device 500 shown in 10a and 10b selects (i.e. designs) the filters for the FF ANC processing branches with the goal of approximating the primary path (PP) by the FF filter output along the secondary path (SP). This can be achieved using a digital model H of PP. PP (z) and SP's digital model H SP (z) is represented by the equation [1].

[0092] To model the PP, a low-pass filter with a cutoff frequency determined by the geometry of the hybrid ANC device 500 and the environment can be used, while for the SP, a low-pass filter with a cutoff frequency much higher than that of the PP, defined by the acoustic design and the placement of the FB-MIC 503, is used. Therefore, the FF ANC filter 510 is typically matched with a low-pass filter having a cutoff frequency and roll-off rate that depend on the shape of the PP. An exemplary FF ANC filter design (i.e., the amplitude response of the transfer function) for a headset implementing hybrid ANC is matched with the FF ANC device 300 design, as described above. Figure 5 As shown.

[0093] Selection (i.e., design) Figure 9a , 9b The goal of the filter for the FB ANC processing branch of the hybrid ANC device 500 shown in 10a and 10b is to improve (specifically optimize) the noise sensitivity function to achieve good noise attenuation. The noise sensitivity function characterizes the noise suppression capability of the FB ANC processing branch of the hybrid ANC device 500 and can be expressed as the above equation [3].

[0094] An exemplary FB ANC filter design (i.e., the amplitude response of the transfer function) for a headset used to implement a hybrid ANC scheme matches the corresponding design of the FB ANC device 400, such as... Figure 8 As shown.

[0095] Ideally, for a hybrid ANC device 500 with an active FF ANC filter 510 and an active FB ANC filter 520, the expected noise transfer function from FF-MIC 501 to FB-MIC 503 is given by the following equation:

[0096]

[0097] An exemplary expected mixed-signal ANC device noise transfer function for headphones is as follows: Figure 11 As shown.

[0098] Although the expected performance defined in mathematical equation [4] implies that the FF ANC branch and the FB ANC branch work simultaneously, in fact, the hybrid ANC device 500 works as follows: first, the FB ANC filter branch 520 introduces a negative loopback, changes the SP function and attenuates the disturbance injected at FB-MIC 503, and then the FF ANC filter branch 510 injects noise immunity into the changed SP.

[0099] As will be understood, the negative loopback introduced by the FB ANC processing branch modifies both the FF ANC processing branch and the SP of the playback signal. The SP function modified by the FB ANC loopback can be described as follows:

[0100]

[0101] The PP transfer function of the hybrid ANC device 500 after FB ANC branch attenuation perturbation can be described as follows:

[0102]

[0103] The corresponding changes in the amplitude response of SP and PP are as follows: Figure 13 As shown.

[0104] Once we consider the hybrid ANC device 500 with adjusted SP and PP functions, there are two signal injection points, such as... Figure 12 The diagram is shown. Point 1 is the noise and disturbance input, characterized by the sensitivity transfer function defined in the above equation [3]. Point 2 is the injection point for the playback signal and the FF ANC noise immunity.

[0105] Considering the noise immunity generation of FF ANC in quiet zone 590, it will be understood that for hybrid ANC device 500, due to the modification of the SP function, the expected noise immunity generation function changes from FF-MIC 501 to FB-MIC 503 as follows:

[0106]

[0107] From a mathematical perspective, this change should be acceptable due to the symmetric PP modification and the FF ANC achieved through simplification:

[0108]

[0109] However, from a physical point of view, this simplification may be incorrect. Compare H in the hybrid ANC device 500. SP (z) and The change between these two points will be understood as follows: the output of the FF ANC filter 510 attenuates when sent to the quiet zone 590. In a physical ANC device, this means that the least significant bit of the FF ANC output is lost, and the most significant bit is rendered ineffective. The FF ANC noise immunity is attenuated. The corresponding effect is as follows Figure 14 As shown. It is also worth noting that the design and processing of the FF ANC filter 510 is a challenging task requiring high-precision calculations. Therefore, the loss of output accuracy due to FB ANC attenuation complicates its design and limits its achievable performance.

[0110] Typically, the dynamic range of the FF ANC filter 510 used in the hybrid ANC device 500 is limited by one or more of the following physical properties / parameters: (i) the signal-to-noise ratio (SNR) of the FF-MIC 501, characterizing the minimum applicable noise level; (ii) the dynamic range of the FF ANC digital filter input, coefficients, states, and output; and (iii) the sensitivity of the SPK 505, characterizing the sound pressure level provided to the loudspeaker 505 in response to the input voltage (i.e., the loudspeaker drive signal). Furthermore, as will be understood, in the hybrid ANC device 500, the attenuation of the FF ANC output with modified SP intensifies the requirements for the hardware design of the hybrid ANC device 500 and degrades the performance of the FF ANC filter 510.

[0111] As mentioned above, from the perspective of the playback signal, the main idea of ​​playback signal compensation is to make SP modifications transparent with FB ANC loopback. This is achieved by introducing, as described above... Figure 10a and 10b SP copy transfer function described in the context This is to achieve the desired playback signal output by subtracting it from the input signal of the FB-MIC 503 and generating the playback transfer function.

[0112]

[0113] However, even a slight mismatch between the SP copy transfer function and the actual SP transfer function can lead to noticeable impairment of the playback signal, such as... Figure 15 As shown. From Figure 15 It can be seen that even within the operating frequency range of the FB ANC filter 520, SP(H) SP2 Even minor changes in a playback path attenuation (SP) with 0-2dB attenuation below 300Hz can lead to drastic playback path attenuation. It's worth noting that SP can vary significantly depending on the specific device example or usage environment.

[0114] In the following embodiments of the invention, a more detailed description will be given. As will be seen from... Figure 16 As understood in the present invention and described in more detail below, embodiments of the present invention implement a chained ANC architecture, wherein an FB ANC filter is used as a feedback controller. Figure 16 This is a schematic diagram illustrating the general architecture of a chain-type ANC device as a feedback control system (FCS) provided in an embodiment. Figure 16In the FCS architecture shown, X represents the desired trajectory pre-shaped by the input filter F. The processing circuit, such as the controller C, uses the difference e between the observed output ym of the plant P and the desired trajectory to generate a control signal u, which causes the plant to follow the desired trajectory.

[0115] exist Figure 16 In the illustrated FCS architecture, the following signals are considered disturbances: output noise d, sensor noise b, and control signal disturbance v. Sensor noise b is typically indistinguishable from the input signal and cannot be attenuated. Meanwhile, one of the main goals of FCS design is to enable the FCS to tolerate output noise d and control signal disturbance v.

[0116] Will Figure 17 Comparing the general architecture of the FCS shown with the architecture of the hybrid ANC device 500 described above, it will be understood that for the FB ANC processing branch, both the noise immunity signal generated by the FF ANC filter 510 and the playback signal are considered disturbances. Therefore, their attenuation is an unavoidable characteristic of FB ANC by design. Meanwhile, with the input signal at zero, the goal of the FB ANC processing branch is to reduce output noise so that it can be tracked.

[0117] like Figure 18 As shown, embodiments of the present invention are based on the idea that by utilizing the input signal tracking and stabilizing FCS characteristics, and by enabling it to track the input by reducing noise and stabilizing rather than attenuating the input, the impact of the FB ANC filter 520 on the FF ANC output and playback signal can be reduced. In this case, the FCS design approach can be naturally applied to provide input tracking and noise tolerance without compromising the FF ANC filter and playback signal due to the FB ANC filter.

[0118] Figure 19a A schematic diagram is shown illustrating the operation of an ANC device 700 implementing a chained ANC architecture in silent mode, as provided in the embodiment. As will be explained below... Figure 19bAs described in more detail in the context of the above, the ANC device 700 includes a first microphone in the form of an FF-MIC 701 for generating a first microphone signal x(n), i.e., a noise signal, in response to external first acoustic noise in the first zone 780 of the ANC device 700. The ANC device 700 also includes a noise-canceling speaker SPK 705 for driving with a speaker signal y(n). Furthermore, the ANC device 700 includes a second quiet zone microphone in the form of an FB-MIC 703 for generating a second microphone signal, wherein the second microphone signal includes a residual noise component e(n) based on residual second acoustic noise in the quiet zone 790 of the ANC device 700. Additionally, the ANC device 700 includes processing circuitry for generating a compensation signal, i.e., a noise reduction or noise cancellation signal (FF anti-noise; y′), based on the first microphone signal x(n) using a first filter in the form of an FF ANC filter 710. FF (n)). The processing circuit is also used to use a second filter in the form of an FB ANC filter 720 based on the compensation signal (FF noise immunity) y′. FF The second microphone signal, including residual noise component e(n), generates the speaker signal, i.e., the noise-resistant signal y(n).

[0119] The processing circuitry of the ANC device 700 (or any other embodiments or processing circuitry described herein) may be implemented in or using hardware and / or software. The hardware may include digital circuitry, or both analog and digital circuitry. Digital circuitry may include components such as application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), digital signal processors (DSPs), or general-purpose processors. The ANC device 700 may also include non-transitory memory for storing data and executable program code that, when executed by the processing circuitry of the ANC device 700, enable the ANC device 700 to perform the functions, operations, and methods described herein.

[0120] If possible Figure 19a As can be seen, the chain-like ANC architecture implemented by the embodiments of the present invention uses a queue to combine the FF ANC filter 710 and the FB ANC filter 720, similar to... Figure 16 The queue in the general FCS is shown. Advantageously, this guarantees the improved FF ANC noise immunity stability supported by the FB ANC filter 720 without any unexpected attenuation. Figure 19aIn the illustrated embodiment, the FF ANC filter 710 processes the observed ambient noise 780 and sends it to the quiet zone 790, and is used to predict noise propagation. The FB ANC filter 720 provides a stable propagation path for the FF ANC filter 710 and reduces residual noise, which is obtained based on the difference between the predicted FF ANC noise immunity and the noise actually observed in the quiet zone 790.

[0121] More specifically, Figure 19a The signal processing scheme implemented in the embodiment of the chain-type ANC device 700 is as follows: Figure 19b As shown. Noise x(t) travels along the transfer function H PP The main path described in (s)711 passes through, generating the observed perturbation d(t). The noise x(t) is converted into a digital noise signal x(n), which is then processed by a method with a transfer function H. FF (z) is processed by the FF ANC digital filter 710 (in one embodiment, it can be implemented as an IIR, FIR, twisted FIR filter, etc.) to generate an FF ANC noise-resistant digital signal y. FF (n). The destructive interference of the disturbance d(t) and the disturbance compensation y(t) at the quiet zone 790 of the ANC device 700 generate residual noise e(t). The residual noise e(t) is converted into a digital signal e(n) from the FF ANC anti-noise signal y. FF Subtracting this digital signal from (n) yields a differential signal e′(n) representing the residual distortion after destructive interference at the quiet zone 790. The differential signal e′(n) is then processed using a signal with transfer function H... FB (z) is processed by the FB ANC digital filter 720 (in one embodiment, it can be implemented as an IIR, FIR, twisted FIR filter, etc.) to generate a digital noise-resistant signal y(n). The digital noise-resistant signal y(n) travels along the transfer function H SP The SP propagation path described in (s)713 propagates, thereby generating an analog anti-noise signal y(t) that participates in the destructive interference in the quiet zone 790.

[0122] As will be understood, for those working in silent mode Figure 19a and 19b In the chain-type ANC device 700, the differential signal e′(n) can be considered as the output H. SP (s) is the instantaneous deviation from the desired trajectory, in this case, the deviation is determined by the FF ANC noise immunity y′. FF The decision is made. The FB ANC filter 720 acts as an integrator, accumulating the differential signal and sending it to an output with an inverted sign.

[0123] Figure 20aA schematic diagram of an ANC device 700 implementing a chained ANC architecture, provided in another embodiment, is shown operating in playback mode, wherein the playback signal can be streamed from a cloud server or retrieved from the data storage of the ANC device 700, for example, Figure 20a As shown by reference numeral 707 in the attached figure. (As can be seen from...) Figure 20a What can be seen from it, besides Figure 19a and 19b In addition to the components of the embodiment of the ANC device 700 shown, Figure 20a and 20b The embodiment of the ANC device 700 shown may further include an equalizer (EQ) 740 for equalizing the playback signal to be mixed by mixer 709a with noise-resistant mixing from FF ANC filter 710. The resulting desired signal is provided to FB ANC filter 720 (similar to...). Figure 16 The general-purpose FCS shown prevents playback signal distortion and FF ANC attenuation caused by the FBANC filter 720. Advantageously, the equalizer 740 applied to the playback signal can produce a constant frequency response from the playback input to the speaker output with high frequency attenuation, which differs from the target playback response in most common applications. Furthermore, embodiments of the ANC device 700 implementing a chained ANC architecture operating in playback mode can provide a stable SP for playback without requiring additional compensation.

[0124] Figure 20a The signal processing scheme implemented in the embodiment of the chain-type ANC device 700 is as follows: Figure 20b As shown. Noise x(t) travels along the transfer function H PP The main path described in (s)711 passes through, generating the observed disturbance d(t). The noise x(t) is converted into a digital signal x(n), which is then processed by a signal with a transfer function H. FF (z) is processed by the FF ANC digital filter 710 (in one embodiment, it can be implemented as an IIR, FIR, twisted FIR filter, etc.) to generate an FF ANC noise-resistant digital signal y. FF (n). In Figure 20a and 20b In the embodiment shown, the playback signal s(n) is represented by a signal with a transfer function H. EQ (z) is pre-processed by the pre-shaped equalizer 740 to generate the playback digital input for chained ANC, i.e., signal s. EQ (n). The destructive interference of the disturbance d(t) and the output signal y(t) in the quiet zone 790 generates an analog playback signal s′(t) (i.e., the desired output) mixed with residual noise e(t). The output signal mixture s′(t) + e(t) is converted into a digital signal s′(n) + e(n). From FF ANC noise immunity y FF (n) and playback signal sEQ Subtracting the digital signal s′(n)+e(n) from the sum of (n) yields the differential signal e′(n). The differential signal e′(n) is then processed by the transfer function H. FB (z) describes the FB ANC digital filter 720 (in one embodiment, it can be implemented as an IIR, FIR, distorted FIR filter, etc.) for processing, thereby generating a digital signal y(n). The digital signal y(n) is then processed by the transfer function H SP The SP transmission path described in (s)713 is played, thereby generating an analog anti-noise signal y(t) that participates in the cancellation of interference.

[0125] As will be understood, for those working in playback mode Figure 20a and 20b An embodiment of the chain-type ANC device 700, with differential signal e P (n) can be considered as the output H SP (s) is the instantaneous deviation from the desired trajectory, in this case, the deviation is controlled by the FFANC noise immunity y′. FF and playback signal s EQ The sum determines the result. As mentioned above, the FB ANC filter 720 acts as an integrator, accumulating the differential signal and sending it to an output with an inverted sign.

[0126] Therefore, in summary, in one embodiment, the FB ANC filter 720 of the ANC device 700 functions as an inverting integrator. The FF ANC branching process is a noise prediction digital filter using a stable SP. The playback equalizer 740 is a digital filter that utilizes a stable SP to achieve the desired frequency response of the playback signal, regardless of actual SP deviation and output disturbances. Furthermore, the equalizer 740 of the ANC device 700 can compensate for SP attenuation at higher frequencies that may be caused by the bandwidth limitation of the FB ANC filter 720.

[0127] In one embodiment, Figure 19a , 19b An embodiment of a chain-type ANC device 700 for silent mode operation and Figure 20a , 20b Different filters in embodiments of the chained ANC device 700 for playback mode operation can be designed to approximate PP (more specifically, their respective transfer functions) by an FF ANC filter 710 convolved with SP. In other embodiments of the chained ANC device 700, the design of the FF ANC filter 710 can explicitly account for any variations introduced by the FB ANC filter 720 with respect to SP and PP.

[0128] In one of the following embodiments, the optimized filter design will be described in more detail. In one embodiment, the optimization of the FF ANC filter 710 of the ANC device 700 can be based on the following equation:

[0129] H′ PP (z)=-H′ FF (z)*H′ SP (z)

[10]

[0130] in:

[0131]

[0132] Considering equations

[10] and

[11] , the optimization can be:

[0133]

[0134] Figure 21 Several graphs are shown showing the corresponding magnitude of the transfer function involved in Equation

[12] as a function of the frequency of a chain ANC device 700 in the form of headphones. Compared to the same graphs for the FF ANC device shown above, the FF ANC transfer function design goals can be explicitly achieved through embodiments of the ANC device 700, which allow, for example, adjustments to the sensitivity of the FF-MIC 701 and / or digital filters to accommodate any permissible dynamic range. Another advantage offered by embodiments of the ANC device 700 compared to the hybrid ANC device 500 described above is in H... FB (z) A nearly constant and stable transmission path H′ within the frequency range SP (z), such as Figure 22 As shown. This allows for the consideration of H′ SP (z) is approximately equal to unity gain, which reduces the amount of work required to train (i.e., adjust) the FFANC filter 720.

[0135] As described above, in playback mode, one of the primary objectives of ANC device 700 may be to minimize useful signal distortion caused by variations in SP in the FB ANC filter 720. According to an embodiment, ANC device 700 is used to mix the playback signal with FFANC noise immunity and send the combination to the FB ANC filter 720, which acts as the FCS, instead of subtracting the useful signal prediction from the FB-MIC input as in the hybrid ANC device 500 described above.

[0136] From the perspective of the playback signal, the transmission path from digital input to output (as sound wave) can be determined by the transfer function H′ of the FF ANC filter 710 as defined in the above equation

[11] . SP (z) Description. Due to SP changes in the hybrid ANC device 500 as previously described (e.g.) Figure 15Compared to the playback path problem caused by (as shown), the transfer function H′ used by the ANC device 700 provided in the embodiment is different. SP (z) is more stable and constant, as can be obtained from Figure 23 This was obtained. As will be understood, it can be obtained without a significant H′. SP (z) Compensation for slight SP variance under varying conditions means a stable playback path in the ANC device 700 provided by the embodiment.

[0137] However, it should be understood that the above design can act as a low-pass filter, which may be undesirable for playback mode applications of the ANC device 700. Therefore, as described above, in an embodiment, the ANC device 700 also includes an EQ filter 740 for maintaining the overall playback transfer function equal to the initial SP without ANC. In one embodiment, the EQ filter 740 can be implemented by approximating the following ratio

[13] :

[0138]

[0139] For the example of headphones considered earlier, this desired equilibrium curve is as follows: Figure 24 As shown. As will be understood, the target playback response of ANC can be set to some psychoacoustic determined value to achieve a comfortable listening experience, rather than fitting the original SP. Therefore, embodiments of ANC device 700 allow for handling playback signal distortion problems caused by SP and SP copy mismatch by utilizing the FB ANC filter 720 as FCS and introducing equalization provided by the EQ filter 740 to compensate for any resulting high-frequency attenuation.

[0140] For the hybrid ANC device 500 described above, the main objective of the FB ANC filter 520 design is noise optimization of the sensitivity function defined in equation [2]. The filter parameters, i.e., the coefficients of the sensitivity function of the FB ANC filter 520 of the hybrid ANC device 500 for the operating frequency range Ω, can be adjusted based on the following equation:

[0141]

[0142] Where the weight W att (ω) typically corresponds to the reciprocal of the expected noise spectrum:

[0143]

[0144] Conversely, according to one embodiment, the filter parameters, namely the coefficients of the FB ANC filter 720 of the ANC device 700, are adjusted with the primary objective of achieving a unity-gain (“constant”) frequency response over the maximum frequency range Ω, as described in the following equation:

[0145]

[0146] Therefore, in one embodiment, the processing circuitry of the ANC device 700 is used to adjust (specifically optimize) the filter parameters, namely the filter coefficients of the FB ANC filter 720, so that the frequency range of the FB ANC filter 720 is extended.

[0147] As will be understood, embodiments of hybrid ANC device 500 and ANC device 700 may have the same constraints regarding the filter parameters of the FB ANC filter 720 during optimization, which may be based on the requirement for the stability of the following characteristic polynomial:

[0148] D(jω)=1+H SP (jω)H FB (jω)

[18]

[0149] According to one embodiment, the ANC device 700 can implement one or more available FCS stability criteria, such as the Nyquist stability criterion or the Routh stability criterion. The processing circuitry of the ANC device 700 can be used to select a specific stability criterion based on the SP model used and the implementation method of the FB ANC filter 720. Therefore, in summary, according to the embodiment, the FB ANC filter 720 of the ANC device 700 can be implemented as a digital integrator and an auxiliary filter to adapt to the optimization objective (as described in the above equation

[17] ) and satisfy the stability constraints based on the above equation

[18] .

[0150] In the aforementioned hybrid ANC device 500, the FF ANC filter 510 is considered an independent, i.e., parallel module (i.e., independent of the FB ANC filter 520), with the prediction of PP as the primary optimization objective:

[0151]

[0152] Conversely, according to an embodiment of the ANC device 700 used to adjust (i.e. optimize) the filter parameters, namely the coefficients of the FF ANC filter 710, FB ANC attenuation and SP variation can be taken into account, which yields an optimization objective described by the following equation:

[0153]

[0154] Therefore, the ANC device 700 provided in the embodiment allows for explicit co-optimization of the FB ANC filter 720 and the FF ANC filter 710 based on equations

[17] and

[20] to achieve maximum noise attenuation performance. Considering H′ in the operating frequency range of the FB ANC filter 720 SP(z) tends to be “constant”, and equation

[20] can be simplified as follows:

[0155]

[0156] Among them, Ω FB This represents the stable frequency range achieved by the optimized FB ANC filter 720. As can be understood from equation

[21] , in an embodiment of the ANC device 700, successful adjustment of the FF ANC filter 710 can be simplified to PP identification after maximizing the FBANC bandwidth, which allows for more efficient achievement of the optimization objective compared to the case of a hybrid ANC device 500 with formally independent designs of FF ANC filter 510 and FB ANC filter 520. Therefore, in one embodiment, the processing circuitry of the ANC device 700 is used to adjust (i.e. optimize) the filter parameters of the FF ANC filter 710 and the FB ANC filter 720, thereby expanding the frequency range of the FB ANC filter 720 and improving the noise reduction performance of the FF ANC filter 710 and the FBANC filter 720.

[0157] The embodiment of ANC device 700 allows for operation within a stable frequency range Ω FB The internal signal provides a stable response to the playback signal, which is robust to external noise (output disturbance) and SP self-bias. Considering equation

[14] , in one embodiment, a transfer function H... EQ The EQ filter 740 can be adjusted, i.e. optimized, based on the following equation:

[0158]

[0159] H EQ (z)=H EQ1 (z)+H EQ2 (z)

[24]

[0160] The resulting playback transfer function will repeat the original (desired) SP transfer function H. SP (z) The attenuation of the FB ANC filter 720 due to SP variation is robust. In one embodiment, the processing circuitry of the ANC device 700 can be used to adjust the transfer function H of the EQ filter 740 by taking into account the FB ANC filter 720 through synergistic optimization based on the above equations

[17] ,

[22] and

[23] . EQ(z). Furthermore, the processing circuitry of the ANC device 700 can be used to co-optimize the FB ANC filter 720, FF ANC filter 710, and playback EQ filter 740 using the set of equations

[17] ,

[20] ,

[22] , and

[23] or

[17] ,

[21] ,

[22] , and

[23] (the latter option may be better, providing a balanced solution for robust playback mode support and noise attenuation). Thus, in one embodiment, the processing circuitry of the ANC device 700 is used to co-adjust (i.e., optimize) the filter parameters of the EQ filter 740, as well as the filter parameters of the FF ANC filter 710 and the FB ANC filter 720, thereby expanding the frequency range of the FB ANC filter 720, improving the noise reduction performance of the FF ANC filter 710 and the FB ANC filter 720, and compensating for the high-frequency attenuation of the FB ANC filter 720 with the EQ filter 740. The coordinated adjustment of the filter parameters of the FBANC filter 720, FF ANC filter 710 and playback EQ digital filter 740 of the ANC device 700 can produce a balanced and optimal solution for the ANC device 700.

[0161] Figure 25 A flowchart illustrating a chained ANC method 2500 provided in an embodiment is shown. In one embodiment, the chained ANC method may be... Figure 19a and 19b Examples of ANC devices 700 and / or by Figure 20a and 20b An embodiment of the ANC device 700 is executed.

[0162] ANC method 2500 includes a first step 2501 of generating a first microphone signal in response to first acoustic noise in a first region 780. ANC method 2500 includes a further step 2503 of generating a second microphone signal, wherein the second microphone signal includes a residual noise component based on the second acoustic noise in a second region 790. Furthermore, ANC method 2500 includes a step 2505 of generating a compensation signal based on the first microphone signal using an FF ANC filter 710. ANC method 2500 includes a further step 2507 of generating a speaker signal based on the compensation signal and the second microphone signal using an FB ANC filter 720. Furthermore, ANC method 2500 includes a step 2509 of driving a speaker 705 with the speaker signal.

[0163] As described above, ANC method 2500 can be derived from the above. Figure 19a , 19b and / or Figure 20a , 20bThe ANC device 700 described in the context of this implementation is used. Therefore, as will be readily understood, other embodiments of the ANC method 2500 are directly derived from the functionality of the ANC device 700 and the various embodiments described above.

[0164] Those skilled in the art will understand that “blocks” (“units”) in the various figures (methods and apparatuses) represent or describe the functionality of embodiments of the invention (and are not necessarily independent “units” in hardware or software), thereby equally describing the functionality or features (unit = step) of apparatus embodiments and method embodiments.

[0165] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the described embodiments of the apparatus are merely exemplary. For example, the unit division is only a logical functional division, and other division methods may be used in actual implementation. For example, multiple units or components may be merged or integrated into another system, or some features may be ignored or not performed. In addition, the mutual coupling or direct coupling or communication connection shown or described can be implemented through some interfaces. Direct coupling or communication connection between devices or units can be implemented electronically, mechanically, or otherwise.

[0166] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of the embodiment solution according to actual needs.

[0167] In addition, the functional units in the embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.

Claims

1. An active noise cancellation, ANC, device (100; 700), characterized by, The ANC device comprises: a first microphone (701) for generating a first microphone signal in response to a first acoustic noise in a first zone (780) of the ANC device (700); a loudspeaker (705) for being driven with a loudspeaker signal; a second microphone (703) for generating a second microphone signal, wherein the second microphone signal comprises a residual noise component based on a second acoustic noise in a second zone (790) of the ANC device (700) and a playback signal component; processing circuitry for: generating a compensation signal based on the first microphone signal using a first filter (710), the first filter (710) comprising a plurality of first filter parameters; generating the loudspeaker signal based on an equalized playback signal, the compensation signal and the second microphone signal using a second filter (720), the second filter (720) comprising a plurality of second filter parameters; adjusting a plurality of equalization filter parameters, the plurality of first filter parameters and the plurality of second filter parameters to extend a frequency range of the second filter (720) and to improve noise reduction performance of the first filter (710) and the second filter (720) and to compensate for high frequency attenuation of the second filter (720) with the equalization filter (740); the processing circuitry is further for generating the equalized playback signal based on a playback signal using an equalization filter (740), wherein the equalization filter (740) comprises the plurality of equalization filter parameters.

2. The ANC device (700) according to claim 1, characterized by the processing circuitry is for generating the loudspeaker signal based on a difference between the compensation signal and the second microphone signal using the second filter (720).

3. The ANC device (700) according to claim 1, characterized by the processing circuitry is for generating the loudspeaker signal based on a difference between a sum of the compensation signal and the playback signal and the second microphone signal using the second filter (720).

4. The ANC device (700) according to claim 3, characterized by the processing circuitry is further for generating an equalized playback signal based on the playback signal using an equalization filter (740), wherein the processing circuitry is for generating the loudspeaker signal based on a difference between a sum of the compensation signal and the equalized playback signal and the second microphone signal using the second filter (720).

5. The ANC device (700) according to claim 4, characterized by the equalization filter (740) comprises at least one of an IIR filter, a FIR filter and a warped FIR filter.

6. The ANC device (700) according to any one of claims 1-5, characterized by, the second filter (720) comprises at least one of an IIR filter, a FIR filter and a warped FIR filter.

7. The ANC device (700) according to claim 6, characterized by the first filter (710) comprises at least one of an IIR filter, a FIR filter and a warped FIR filter.

8. An active noise cancellation, ANC, method (2500) characterized by, The method comprises: generating (2501) a first microphone signal in response to a first acoustic noise in a first zone (780); generating (2503) a second microphone signal, wherein the second microphone signal comprises a residual noise component based on a second acoustic noise in a second zone (790) and a playback signal component; generating (2505) a compensation signal based on the first microphone signal using a first filter (710), the first filter (710) comprising a plurality of first filter parameters; generating (2507) a speaker signal based on the equalized playback signal, the compensation signal and the second microphone signal using a second filter (720), the second filter (720) comprising a plurality of second filter parameters; driving (2509) a speaker (705) with the speaker signal; the method further comprising adjusting a plurality of equalization filter parameters, the plurality of first filter parameters and the plurality of second filter parameters to extend a frequency range of the second filter (720) and improve noise reduction performance of the first filter (710) and the second filter (720), and to compensate for high frequency attenuation of the second filter (720) with the equalization filter (740); the method further comprising: generating the equalized playback signal based on a playback signal using an equalization filter (740), wherein the equalization filter (740) comprises the plurality of equalization filter parameters.

9. The ANC method (2500) according to claim 8, wherein, the step of generating (2507) the speaker signal comprises generating the speaker signal based on a difference between a sum of the compensation signal and the playback signal and the second microphone signal using the second filter (720).

10. The ANC method (2500) according to claim 9, wherein, the step of generating (2507) the speaker signal comprises generating the speaker signal based on a difference between a sum of the compensation signal and the equalized playback signal and the second microphone signal using the second filter (720).

11. A computer program product, characterised in that, a non-transitory computer readable storage medium storing program code which, when executed by a computer or processor, causes the computer or processor to perform the method (2500) according to any one of claims 8 to 10. a non-transitory computer readable storage medium storing program code which, when executed by a computer or processor, causes the computer or processor to perform the method (2500) according to any one of claims 8 to 10.

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