Noise control system and noise control device and applicable method thereof

Abstract

A noise control system and a noise control device and an applicable method thereof, wherein the noise control system comprises a pre-feedback module, a feedback module, an error pre-processing module and an integrated signal module. The pre-feedback module receives a reference signal and outputs a pre-feedback noise reduction signal after subjecting the reference signal to a pre-feedback process. The feedback module receives an error signal and outputs a feedback noise reduction signal after subjecting the error signal to a feedback process. The error pre-processing module receives the error signal and outputs a first pre-processing signal to the pre-feedback module and a second pre-processing signal to the feedback module. The integrated signal module integrates the pre-feedback noise reduction signal and the feedback noise reduction signal and outputs a noise reduction output signal. The first pre-processing signal corresponds to a first part of the error signal belonging to a first frequency range, and the second pre-processing signal corresponds to a second part of the error signal belonging to a second frequency range.

Description

Technical Field

[0001] The present invention relates to a noise control system and a noise control device and an applicable method thereof, and in particular to a noise control system and a noise control device with an error pre-processing module and an applicable method thereof. Background Art

[0002] Modern people pursue a higher quality of life, and therefore also seek quieter and more comfortable environments. For example, when riding or driving a vehicle or using audio-visual equipment such as headphones, the demand for noise reduction is increasing. Furthermore, in applications susceptible to noise, such as medical equipment, reducing noise levels can also improve detection quality.

[0003] Common noise reduction methods can be categorized as passive and active. Passive methods, for example, utilize sound-absorbing or sound-isolating materials to reduce sound transmission. However, passive noise reduction also has its limitations, such as the specific environment and the applicable noise frequency range. Therefore, active noise reduction is often used to enhance noise reduction effectiveness.

[0004] Active noise reduction, for example, cancels out noise by generating a cancelling sound with a similar amplitude but opposite phase (180° phase difference). However, generating a cancelling sound based on the noise requires significant hardware or software processing speed. Furthermore, the cancelling sound typically requires repeated calculations to converge for optimal noise reduction. If the convergence time is too long, the noise reduction effect will be affected. Therefore, improving the convergence speed of noise control systems is a crucial issue in this field. Summary of the Invention

[0005] The present invention provides a noise control system, comprising a pre-feedback module, a feedback module, an error pre-processing module and an integrated signal module. The pre-feedback module receives a reference signal and outputs a pre-feedback noise reduction signal after subjecting the reference signal to a pre-feedback process. The feedback module receives an error signal and outputs a feedback noise reduction signal after subjecting the error signal to a feedback process. The error pre-processing module receives the error signal and outputs a first pre-processing signal to the pre-feedback module and a second pre-processing signal to the feedback module. The integrated signal module integrates the pre-feedback noise reduction signal and the feedback noise reduction signal and outputs a noise reduction output signal. The first pre-processing signal corresponds to a first part of the error signal belonging to a first frequency range, and the second pre-processing signal corresponds to a second part of the error signal belonging to a second frequency range.

[0006] In one embodiment, the error pre-processing module includes: a noise bandwidth detection element for receiving the error signal; a first pre-filter element coupled to the noise bandwidth detection element for outputting the first pre-processed signal; and a second pre-filter element coupled to the noise bandwidth detection element for outputting the second pre-processed signal.

[0007] In one embodiment, the first pre-filter element is a low-pass filter element, and the second pre-filter element is a band-pass filter element.

[0008] In one embodiment, the first pre-filter element and the second pre-filter element are infinite impulse response filter elements.

[0009] In one embodiment, when the error signal has a signal segment that appears periodically, the noise bandwidth detection element adjusts the range of the second frequency interval according to the frequency of the signal segment.

[0010] In one embodiment, the noise bandwidth detection element calculates a frequency distribution of the error signal and adjusts the filtering ranges of the first pre-filter element and the second pre-filter element according to the frequency distribution.

[0011] In one embodiment, the first frequency range is at least partially lower than the second frequency range.

[0012] In one embodiment, the pre-processing module adjusts the parameters of the pre-processing process according to the first pre-processing signal; and the feedback module adjusts the parameters of the feedback process according to the second pre-processing signal.

[0013] The present invention provides a noise control device comprising the aforementioned noise control system, a first sound receiving element, a second sound receiving element, and a sound generating element. The first sound receiving element is configured to sample a target sound and output a reference signal. The sound generating element is configured to receive the noise reduction output signal and output a canceling sound. The second sound receiving element is configured to sample the noise reduction sound and output an error signal. The noise reduction sound is the sum of the target sound and the canceling sound.

[0014] The present invention provides a noise control method, comprising: receiving an error signal and outputting a first pre-processed signal and a second pre-processed signal; wherein the first pre-processed signal corresponds to a first portion of the error signal belonging to a first frequency range, and the second pre-processed signal corresponds to a second portion of the error signal belonging to a second frequency range; receiving a reference signal and performing a pre-processing operation on the reference signal to output a pre-processing noise reduction signal; performing a feedback operation on the error signal to output a feedback noise reduction signal; and integrating the pre-processing noise reduction signal and the feedback noise reduction signal to output a noise reduction output signal.

[0015] In one embodiment, when the error signal has a signal segment that appears periodically, the range of the second frequency interval is adjusted according to the frequency of the signal segment.

[0016] In one embodiment, the first frequency range is at least partially lower than the second frequency range.

[0017] In one embodiment, when the error signal is received and the first pre-processed signal and the second pre-processed signal are output, a frequency distribution of the error signal is calculated, and the ranges of the first frequency range and the second frequency range are adjusted according to the frequency distribution.

[0018] In one embodiment, the parameters of the pre-processing are adjusted according to the first pre-processing signal; wherein the parameters of the feedback processing are adjusted according to the second pre-processing signal.

[0019] As described above, the error pre-processing module generates different pre-processing signals based on the error signal in different frequency ranges and provides them to the pre-feedback module and the feedback module accordingly. This allows the pre-feedback module and the feedback module to improve their computational efficiency based on the pre-processing signals, thereby accelerating the convergence speed of the noise control system. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1A FIG. 1 is a schematic diagram of a noise control device processing a target sound according to an embodiment of the present invention.

[0021] Figure 1B Schematic diagram of the application and configuration of a noise control device according to an embodiment of the present invention.

[0022] Figure 2 FIG. 1 is a simplified block diagram of a noise control system according to an embodiment of the present invention.

[0023] Figure 3 Schematic diagram of an error pre-processing module in one embodiment of the present invention.

[0024] Figure 4 FIG. 4 is a schematic diagram of a noise control system and the operations between various modules in one embodiment of the present invention.

[0025] Figure 5 FIG. 4 is a flow chart of a noise control method according to an embodiment of the present invention.

[0026] Description of main component symbols:

[0027] 10 Noise control device

[0028] 12 Noise Control System

[0029] 14,16 radio components

[0030] 18 sound elements

[0031] 20 earphone housing

[0032] TS, RS, DS sound

[0033] A vocal cavity

[0034] E concha

[0035] U User

[0036] FF pre-teaching module

[0037] FB feedback module

[0038] EP error pre-processing module

[0039] IM Integrated Signal Module

[0040] e(n),x(n),y(n),yff(n),yfb(n),ps1,ps2 signal

[0041] PF1, PF2 pre-filter elements

[0042] LMS1, LMS2 signal processing components

[0043] W(z) forward processing element

[0044] M(z) feedback processing element DETAILED DESCRIPTION

[0045] The following drawings and detailed descriptions clearly illustrate the spirit of the present invention. After understanding the embodiments of the present invention, any person skilled in the art can change and modify the technology described in the present invention without departing from the spirit and scope of the present invention.

[0046] The terms "first," "second," etc., as used herein, do not specifically indicate an order or sequence, nor are they intended to limit the present invention; they are merely used to distinguish between elements or operations described by the same technical term. The terms "including," "comprising," "having," "containing," etc., as used herein, are open-ended terms, meaning including but not limited to.

[0047] The terms used herein generally have their ordinary meanings in the art, in the context of this disclosure, and in the specific context, unless otherwise noted. Certain terms used to describe the present disclosure are discussed below or elsewhere in this specification to provide additional guidance to those skilled in the art in describing the present disclosure.

[0048] In the accompanying drawings, the thickness of layers, plates, areas or spaces, etc., is exaggerated for clarity. Throughout the specification, the same reference numerals represent the same elements. It should be understood that when an element such as a layer, plate, area or space is referred to as being "on" or "connected to" another element, it can be interpreted as being directly on or connected to another element, or it can be interpreted as having or having an intermediate element between the element and the other element. As used herein, "connection" or "coupling" can refer to physical and / or electrical connection. Furthermore, in order to simplify the drawings and highlight the content to be presented in the drawings, the existing structures or elements in the drawings may be drawn in a simple schematic manner or presented in an omitted manner.

[0049] like Figure 1A As shown, the present invention provides a noise control device 10 comprising a noise control system 12, a first sound receiving element 14, a second sound receiving element 16, and a sound generating element 18. The first sound receiving element 14 is configured to sample a target sound TS and output a reference signal x(n). The sound generating element 18 is configured to receive a noise reduction output signal y(n) and output a canceling sound RS. The second sound receiving element 16 is configured to sample a noise reduction sound DS and output an error signal e(n). The noise reduction sound DS is the sum of the target sound TS and the canceling sound RS. Specifically, the first sound receiving element 14 and the second sound receiving element 16 may be, for example but not limited to, microphones, piezoelectric materials, or sensors that sample mechanical energy (vibration). The sound generating element 18 may be, for example but not limited to, speakers, piezoelectric materials, or other elements that output mechanical energy (vibration). The reference signal x(n) and the error signal e(n) may be, for example, digital or analog signals generated by sampling with a microphone. The noise reduction output signal y(n) is generated by computation by the noise control system 12 and transmitted to the sound generating element 18. The noise reduction output signal y(n) can be an analog signal or a digital signal. The sound-generating element 18 converts the noise reduction output signal y(n) into mechanical energy and outputs a cancellation sound RS. Preferably, the amplitude of the cancellation sound RS and the target sound TS are substantially the same or close, but the phases are opposite, so that a noise reduction sound DS can be generated. It should be noted that the opposite phases of the cancellation sound RS and the target sound TS are only a basic concept, and the amplitude and phase relationship between the cancellation sound RS and the target sound TS is also affected by the angle between the cancellation sound RS and the target sound TS or the transmission medium. In addition, Figure 1A The directions of the target sound TS, the canceling sound RS, and the noise reduction sound DS are merely illustrative and are not intended to limit the sound transmission directions of the noise control device 10 of the present invention.

[0050] In one embodiment, the noise control device 10 can be disposed in an electronic device such as, but not limited to, headphones. Figure 1BTaking the illustrated earphone as an example, the first sound receiving element 14 of the noise control device 10 is preferably disposed outside the earphone housing 20, while the second sound receiving element 16 is preferably disposed inside the earphone housing 20. More specifically, the earphone housing 20 and the concha E of the user U form an acoustic cavity A. The first sound receiving element 14 is disposed outside the acoustic cavity A, while the second sound receiving element 16 is disposed inside the acoustic cavity A. In other words, the first sound receiving element 14 is preferably disposed at a location on the electronic device where external noise is received, while the second sound receiving element 16 is preferably disposed at a location on the user U or a receiver where noise reduction is desired. The first sound receiving element 14 can receive the target sound TS outside the earphone housing 20 and output a reference signal x(n) to the noise control system 12. The second sound receiving element 16 can receive the noise reduction sound DS inside the earphone housing 20 and output an error signal e(n) to the noise control system 12. The sound generating element 18 can be, but is not limited to, disposed inside the earphone housing 20 and provide a cancellation sound RS along the transmission path to the target sound TS for summation with the target sound TS. It should be noted that the noise reduction sound DS can be the sum of the target sound TS and the cancellation sound RS, and then the noise reduction sound is reduced by a passive noise reduction element (such as but not limited to the earphone housing 20 or other sound-absorbing materials in the transmission path). The second sound receiving element 16 can be used to detect the noise reduction effect of the noise control device 10, and provide an error signal e(n) to the noise control system 12 for correction and then output an updated noise reduction output signal y(n) to minimize the error signal e(n). In other words, the user U cannot feel the target sound TS. However, Figure 1B The purpose of this description is merely to illustrate the positions and relative relationships of the first sound receiving element 14, the second sound receiving element 16, and the sound emitting element 18 and / or their possible integration with electronic devices. This description is not intended to limit the scope of application of the noise control device 10 of the present invention. Any noise control device that is applied to the noise control system 12 of the present invention shall fall within the scope of the present invention.

[0051] like Figure 2As shown, the present invention provides a noise control system 12, comprising a feedforward module FF, a feedback module FB, an error pre-processing module EP, and a signal integration module IM. The feedforward module FF receives a reference signal x(n), subjects the reference signal x(n) to feedforward processing W(z), and outputs a feedforward noise-reduced signal yff(n). The feedback module FB receives an error signal e(n), subjects the error signal e(n) to feedback processing M(z), and outputs a feedback noise-reduced signal yfb(n). The error pre-processing module EP receives the error signal e(n) and outputs a first pre-processed signal ps1 to the feedforward module FF and a second pre-processed signal ps2 to the feedback module FB. The signal integration module IM integrates the feedforward noise-reduced signal yff(n) and the feedback noise-reduced signal yfb(n) to output a noise-reduced output signal y(n). In other words, the noise-reduced output signal y(n) is the integration result of the feedforward noise-reduced signal yff(n) and the feedback noise-reduced signal yfb(n) after summing or other operations. The first pre-processed signal ps1 corresponds to the first portion of the error signal e(n) belonging to the first frequency range, and the second pre-processed signal ps2 corresponds to the second portion of the error signal e(n) belonging to the second frequency range. In a preferred embodiment, the first frequency range is the range below 2 kHz, and the second frequency range is between 2 kHz and 5 kHz. It should be noted that the present invention is not limited to the frequency range perceptible to the human ear (20 Hz to 20 kHz), and in this embodiment, the first and second portions are distinguished by the frequency ranges to which they belong. The present invention does not limit the signal properties of the first and second portions.

[0052] In one embodiment, the error signal e(n) may have a non-periodic first portion ent(n) and a periodic second portion et(n). Preferably, the non-periodic portion ent(n) mostly occurs in the low-frequency range, and the feedforward module FF primarily processes low-frequency signals. If only the first portion ent(n) of the error signal e(n) is provided to the feedforward module FF, the convergence speed of the feedforward module FF can be improved by avoiding the influence of high-frequency noise. On the other hand, the second portion et(n) at least partially has a higher frequency than the first portion ent(n), and the feedback module FB primarily processes periodic signals. If only the second portion et(n) of the error signal e(n) is provided to the feedback module FB, the convergence speed of the feedback module FB can be improved by avoiding low-frequency or irregular noise. In a preferred embodiment, the error signal e(n) can be provided to artificial intelligence (AI) or big data related technologies for training and inference, thereby achieving a better convergence effect. Furthermore, the first pre-processed signal ps1 corresponds to the first portion ent(n) of the error signal e(n) that belongs to the first frequency range. Therefore, outputting the first pre-processed signal ps1 to the feedback module FF may be directly outputting the first portion ent(n) of the error signal e(n) to the feedback module FF, or may be amplifying or subjecting the first portion ent(n) of the error signal e(n) to other signal processing means before outputting it to the feedback module FF. Similarly, the second pre-processed signal ps2 corresponds to the second portion et(n) of the error signal e(n) that belongs to the second frequency range. Therefore, outputting the second pre-processed signal ps2 to the feedback module FB may be directly outputting the second portion et(n) of the error signal e(n) to the feedback module FB, or may be amplifying or subjecting the second portion et(n) of the error signal e(n) to other signal processing means before outputting it to the feedback module FB.

[0053] In a preferred embodiment, the forward module FF adjusts the parameters of the forward processing W(z) according to the first forward processing signal ps1; the feedback module FB adjusts the parameters of the feedback processing M(z) according to the second forward processing signal ps2. Specifically, the method for calculating the parameters of the forward processing W(z) and the feedback processing M(z) is, for example but not limited to, the least mean square (LMS) method, the least square method, or any other existing error minimization method. The forward module FF can adjust the parameters of the forward processing W(z) according to the first forward processing signal ps1, thereby improving the convergence speed of the forward module FF; the feedback module FB can adjust the parameters of the feedback processing M(z) according to the second forward processing signal ps2, thereby improving the convergence speed of the forward feedback module FB.

[0054] like Figure 3As shown, in a preferred embodiment, the error pre-processing module EP includes a noise bandwidth detection element NBD, a first pre-filter element PF1, and a second pre-filter element PF2. The noise bandwidth detection element NBD is used to receive the error signal e(n) and calculate the frequency distribution of the error signal e(n). Specifically, the noise bandwidth detection element NBD can be a microprocessor (MCU), a field-programmable gate array (FPGA), or other device with computing capabilities. The method for calculating the frequency distribution of the error signal e(n) is, for example, but not limited to, discrete Fourier transform, discrete fast Fourier transform, or other frequency domain estimation methods. The first pre-filter element PF1 is coupled to the noise bandwidth detection element NBD to output a first pre-processed signal ps1. The second pre-filter element PF2 is coupled to the noise bandwidth detection element NBD to output a second pre-processed signal ps2. Preferably, the first pre-filter element PF1 is a low-pass filter, and the second pre-filter element PF2 is a band-pass filter. It should be noted that the second pre-filter element PF2 can also achieve the effect of a bandpass filter by connecting a low-pass filter element and a high-pass filter element in series. In a preferred embodiment, the first pre-filter element PF1 and the second pre-filter element PF2 are infinite impulse response (IIR) filter elements.

[0055] In one embodiment, the noise bandwidth detection element NBD can set the filtering ranges of the first pre-filter element PF1 and the second pre-filter element PF2. In other words, the noise bandwidth detection element NBD can calculate the frequency distribution of the error signal e(n) and adjust the filtering ranges of the first pre-filter element PF1 and the second pre-filter element PF2 based on the frequency distribution. Specifically, the first pre-filter element PF1 is a low-pass filter element. Therefore, the noise bandwidth detection element NBD can set the threshold of the first pre-filter element PF1 (for example, but not limited to, below 2 kHz) to determine the frequency range of the signal that can pass through the first pre-filter element PF1. The second pre-filter element PF2 is a bandpass or high-pass filter. When the error signal e(n) has periodic signal segments, the noise bandwidth detection element NBD adjusts the range of the second frequency range (for example, but not limited to, 2 kHz to 5 kHz) based on the frequency of the signal segments.

[0056] In one embodiment, the noise bandwidth detection element NBD can optimize the filtering ranges of the first pre-filter element PF1 and the second pre-filter element PF2 using methods such as machine learning, deep learning, or neural network analysis. For example, when no noise is received or the noise control system 12 is not fully operational, the noise bandwidth detection element NBD can be trained using background error signals received from the surrounding environment to establish, for example, but not limited to, a database. When the noise control system 12 is fully activated or a target sound TS is received, the noise bandwidth detection element NBD can use the parameters in the database to improve the response speed of the noise control system 12.

[0057] like Figure 4 As shown, Figure 4 This is a preferred embodiment of the noise control system 12 of the present invention. The first pre-filter element PF1 comprises N infinite impulse response filters FF-IIR1 through FF-IIRN, and the second pre-filter element PF2 comprises N infinite impulse response filters FB-IIR1 through FB-IIRN. The pre-feedback module FF includes a pre-feedback processing element W(z) and a first signal processing element LMS1. The feedback module FB includes a feedback processing element M(z) and a second signal processing element LMS2. It should be noted that in this embodiment, the attenuation function of the transmission line is omitted for simplicity. The noise bandwidth detection element NBD can adjust the parameters of each infinite impulse response filter element FF-IIR1 through FF-IIRN and FB-IIR1 through FB-IIRN in the first pre-filter element PF1 and the second pre-filter element PF2 based on the frequency distribution of the error signal e(n). The first pre-processed signal ps1 and the second pre-processed signal ps2 are output to the first signal processing element LMS1 and the second signal processing element LMS2, respectively. The first signal processing element LMS1 and the second signal processing element LMS2 can adjust parameters of the forward processing element W(z) and the feedback processing element M(z) according to the first pre-processed signal ps1 and the second pre-processed signal ps2.

[0058] like Figure 5The present invention provides a noise control method, comprising: step S1 receiving an error signal and outputting a first pre-processing signal and a second pre-processing signal. The first pre-processing signal corresponds to the first part of the error signal belonging to the first frequency range, and the second pre-processing signal corresponds to the second part of the error signal belonging to the second frequency range. Step S2 receiving a reference signal and performing pre-processing to output a pre-feedback noise reduction signal, wherein the parameters of the pre-feedback processing are adjusted according to the first pre-processing signal; step S3 performing feedback processing on the error signal and outputting a feedback noise reduction signal. The parameters of the feedback processing are adjusted according to the second pre-processing signal. And step S4 integrating the pre-feedback noise reduction signal and the feedback noise reduction signal and outputting a noise reduction output signal. It should be noted that after step S4 outputs the noise reduction output signal, the error signal will be received again to determine whether the noise reduction output signal needs to be adjusted, for example, whether the error signal is still too large or does not meet the expected noise reduction effect, and then entering step S1 again.

[0059] The present invention has been described with reference to the above embodiments. However, the above embodiments are merely exemplary embodiments of the present invention. It should be noted that the disclosed embodiments do not limit the scope of the present invention. On the contrary, modifications and equivalents within the spirit and scope of the claims are intended to be within the scope of the present invention.

Claims

1. A noise control system, characterized in that: Include: A pre-processing module receives a reference signal and outputs a pre-processing noise-reduced signal after processing the reference signal; a feedback module that receives an error signal, processes the error signal through feedback, and outputs a feedback noise reduction signal; an error pre-processing module, receiving the error signal and outputting a first pre-processing signal to the pre-feedback module and a second pre-processing signal to the feedback module; and a signal integration module, integrating the forward noise reduction signal and the feedback noise reduction signal and outputting a noise reduction output signal; The first pre-processed signal corresponds to a low-frequency non-periodic portion of the error signal belonging to a first frequency interval, and the second pre-processed signal corresponds to a high-frequency periodic portion of the error signal belonging to a second frequency interval; The error pre-processing module includes: a noise bandwidth detection element for receiving the error signal; a first pre-filter element, coupled to the noise bandwidth detection element, for outputting the first pre-processed signal; and a second pre-filter element, coupled to the noise bandwidth detection element, for outputting the second pre-processed signal; When the error signal has a signal segment that appears periodically, the noise bandwidth detection element adjusts the range of the second frequency interval according to the frequency of the signal segment.

2. The noise control system according to claim 1, wherein: The first front-filter element is a low-pass filter element, and the second front-filter element is a band-pass filter element.

3. The noise control system according to claim 1, wherein: The first pre-filter element and the second pre-filter element are infinite impulse response filter elements.

4. The noise control system according to claim 1, wherein: The noise bandwidth detection element calculates a frequency distribution of the error signal and adjusts the filtering ranges of the first pre-filter element and the second pre-filter element according to the frequency distribution.

5. The noise control system according to claim 1, wherein: The first frequency range is at least partially lower than the second frequency range.

6. The noise control system according to claim 1, wherein: The pre-processing module adjusts the parameters of the pre-processing process according to the first pre-processing signal; and the feedback module adjusts the parameters of the feedback process according to the second pre-processing signal.

7. A noise control device, characterized in that: Include: The noise control system according to any one of claims 1 to 6; a first sound receiving element for sampling a target sound and outputting the reference signal; a sound-generating element for receiving the noise reduction output signal and outputting a canceling sound; as well as a second sound receiving element for sampling a noise-reduced sound and outputting the error signal; The noise reduction sound is the sum of the target sound and the cancellation sound.

8. A noise control method, characterized in that: Include: Receive an error signal and output a first pre-processed signal and a second pre-processed signal; wherein the first pre-processed signal corresponds to a low-frequency non-periodic portion of the error signal belonging to a first frequency range, and the second pre-processed signal corresponds to a high-frequency periodic portion of the error signal belonging to a second frequency range; receiving a reference signal and performing a pre-processing and then outputting a pre-processing noise reduction signal; Performing feedback processing on the error signal and then outputting a feedback noise reduction signal; and Integrating the forward noise reduction signal and the feedback noise reduction signal to output a noise reduction output signal; When the error signal has a signal segment that appears periodically, the range of the second frequency interval is adjusted according to the frequency of the signal segment.

9. The noise control method according to claim 8, wherein: The first frequency range is at least partially lower than the second frequency range. 10 . The noise control method of claim 8 , further comprising: calculating a frequency distribution of the error signal when receiving the error signal and outputting the first pre-processed signal and the second pre-processed signal, and adjusting the ranges of the first frequency range and the second frequency range according to the frequency distribution.

11. The noise control method according to claim 8, wherein: The parameters of the pre-processing are adjusted according to the first pre-processing signal; wherein the parameters of the feedback processing are adjusted according to the second pre-processing signal.

Images