KR101901511B1 - A Method for Controlling a Noise in a Active Feedback Manner for a Headphone or Earphone and A System for Controlling a Noise by the Same - Google Patents

Abstract

The present invention relates to a feedback active noise control method for a headphone or an earphone, and more particularly, to a feedback active noise control method for a headphone or an earphone that enables processing of noise introduced from the outside into a headphone or an earphone in real time, Noise control system. A method for controlling active noise in a headphone or an earphone and an active noise control system therefor, the active noise control method actively controlling a noise signal introduced from the outside, comprising the steps of: -warped) A finite impulse response filter of a low order is approximated by an infinite impulse response method to process the introduced noise signal.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active noise control method for a headphone or an earphone,

Acknowledgments

The present invention is a research result supported by the technology development project of a specialized enterprise having excellent brain capacity of the Ministry of Industry and Commerce (10053203).

The present invention relates to a feedback active noise control method for a headphone or an earphone, and more particularly, to a feedback active noise control method for a headphone or an earphone that enables processing of noise introduced from the outside into a headphone or an earphone in real time, Noise control system.

If the ambient noise is generated in a general headphone / earphone environment, it becomes difficult to hear pleasant music. Sound can be removed physically or passively through means such as sound absorbing materials or ear cups to a certain level. However, in the case of the low-frequency band corresponding to the main attention band, it is difficult to secure a sufficient reduction performance only by such a physical noise control. Therefore, active noise control technology needs to be applied to headphones or earphones to obtain reasonable noise control performance in a low frequency band. Active noise control techniques are technologies that are widely used in automobiles, aircrafts, headphones, earphones, etc., by removing noise by generating and outputting a signal having a phase opposite to that of a noise signal. Active noise control earphones equipped with a digital active noise control algorithm have recently been commercially available.

Patent Publication No. 10-2012-0042218 discloses a noise canceling headphone capable of removing external noise other than a sound generated in front of a wearer of a headphone so that a user can form a listening beam with respect to the front of the user in the viewing direction. Patent Publication No. 10-2015-0076140 discloses an audio input / output device in which no additional power supply is required to supply power to the active noise canceling unit.

Representative digital active noise control schemes disclosed or known in the prior art can roughly be divided into feedforward active noise control, feedback active noise control, and hybrid active noise control scheme combining these two schemes. The feedforward method obtains the reference input signal of the control filter from the outside through the reference microphone to control the noise for the secondary path so that the noise obtained from the error microphone inside the headphone (See reference 1). However, it is difficult to obtain robust performance due to the difficulty in estimating the noise canceling performance depending on the type of the user or the incoming noise in a real environment. The feedback active noise control method regenerates the reference input of the control filter from the error signal obtained by using the error microphone without the reference microphone. Since the reference signal generated in this process is obtained by reflecting the mechanical characteristics of the headphone, relatively strong performance can be secured according to the user. However, when the feedback active noise control is implemented adaptively, it is required to perform secondary path estimation through an additional adaptive filter in addition to the total active noise control system for real - time second - order path estimation for a second - order path that varies with time. The input signal, which is commonly used for this estimation, has the disadvantage that it can increase the residual noise size of the entire system with white noise (Ref. 1). In addition, due to the characteristics of the adaptive feedback method, it is reasonable to remove periodic tonal signals, but there is a disadvantage that sufficient control is not performed on the wideband signals. Constrained optimization techniques can be applied to other feedback active noise control techniques to solve the mentioned problems.

Constraint optimization (Ref. 2) is known as an iterative method of deriving an optimal solution of a designed cost function under various set constraints. Convex optimization, which is a representative technique, can be obtained through sequential quadratic programming techniques (Ref. 3) by using frequency discretization to find the optimal solution of a given objective function in the frequency domain. The feedback control method using the convex optimization is based on the previous research. However, it does not remove only the tonal signal but controls the noise of the whole low frequency band. The noise control function is robust to different secondary paths without generating additional noise. (Cf. 3 and 4).

When designing the control filter of the active noise control system by using the convex optimization, it is possible to prevent the basic problems of the feedback system mentioned in the feedback theory besides the main purpose of the noise control which is basically required. For example, it is possible to set constraints for problem solving, such as preventing system instability problems due to different secondary paths, and preventing waterbed effects (refs 5 and 6) occurring in feedback control schemes. It is also possible to set a desired control band at the design stage of the objective function differently from the conventional adaptive digital feedback method. If the formulas are formulated by designing the objective function while setting various constraints as described above, Equation 1 can be expressed.

Equation 1:

은 주파수 영역에서 필터 계수를 얻기 위해 취해주는 FFT 크기,

는 주파수 빈 색인,

는 Q-파라미터화(Q-parameterization)(참조 4)의 결과로 얻어지는 유한 임펄스 응답 제어 벡터,

는 제어 필터 설계에 사용되는 명목 경로가 되고, 명목 경로는 실제 2차 경로를 모델링하여 얻는다. 또한

는 목적 함수와 제약 조건 설정을 위해 설계되는 가중 함수를 나타낸다. 먼저 목적 함수식에 포함된

는 원하는 제어 대역을 설정해주는 함수로 이에 따라 제어 대역이 결정된다.

는 필터 설계에 사용된 2차 경로 외에 서로 다른 2차 경로들에 대해서도 안정적인 성능을 확보하기 위해 설정하는 함수로 2차 경로들의 응답 특성에 따라 결정된다.

는 물침대 효과로 인한 소음 증폭의 크기를 제한하고자 설정하는 함수로 소음 제어 성능과 증폭 성능의 보상(trade-off)을 고려하여 적절한 값으로 설정될 수 있다. 수학식 1을 통해 얻은 제어 벡터

는 실제 능동 소음 제어 시스템에 적용하기 위해 다음과 같은 식에 따라 최종 필터로 변환된다.In the above,

Is the FFT size taken to obtain the filter coefficients in the frequency domain,

A frequency bin index,

Is a finite impulse response control vector obtained as a result of Q-parameterization (Ref. 4)

Is the nominal path used in the control filter design, and the nominal path is obtained by modeling the actual secondary path. Also

Represents a weighting function designed for objective function and constraint setting. First,

Is a function for setting a desired control band, and the control band is determined accordingly.

Is a function set to secure stable performance for different secondary paths in addition to the secondary paths used in the filter design, and is determined according to the response characteristics of the secondary paths.

Is a function for setting the magnitude of the noise amplification due to the water bed effect and can be set to an appropriate value in consideration of the noise control performance and the trade-off of the amplification performance. The control vector < RTI ID = 0.0 >

Is converted to the final filter according to the following equation for application to the actual active noise control system.

Equation 2:

On the other hand, in the case of a high performance active noise control headphone having a high sampling frequency, generally a high-order control filter is applied to obtain a reasonable noise cancellation performance. However, high-order filters are not suitable for real-time signal processing systems and are generally used in reduced order. In this case, methods such as Balanced Model Truncation (BMT) (Ref. 7) can be used. The BMT technique corresponds to a representative method of approximating a finite impulse response filter with an infinite impulse response filter based on singular value decomposition techniques and constructs a Hankel matrix from the state space equations of a given finite impulse response filter, Can be constructed by reconstructing the reduced state-space space equation by selecting the singular value and the corresponding singular vector (ref. 8).

에 적용하면

에 유사한 무한 임펄스 응답 필터를 얻을 수 있지만, 근사하고자 하는 유한 임펄스 응답 필터의 특성에 따라 정확한 근사가 요구되는 대역에서 부정확한 근사로 인해 관심 대역에서 제어 필터의 성능이 열화가 될 가능성이 있다. 그러므로 이와 같은 문제의 해결을 위한 능동 소음 제어 방식이 개발될 필요가 있다. The BMT technique is simply a control filter obtained through convex optimization

When applied to

It is possible that the performance of the control filter in the band of interest may deteriorate due to an inaccurate approximation in a band requiring accurate approximation depending on the characteristics of the finite impulse response filter to be approximated. Therefore, an active noise control method for solving such a problem needs to be developed.

The present invention has been made to solve the problems of the prior art and has the following purpose.

Prior art 1: Patent No. 10-2012-0042218 (Moon Sung Kyun Moon, May 03, 2012) Active Noise Canceling Headphone with Adaptive Beam Forming Technique Prior Art 2: Patent Publication No. 10-2015-0076140 (published by Cresyn Co., Ltd. on Jul. 06, 2015) Active noise control audio input / output device

SUMMARY OF THE INVENTION It is an object of the present invention to provide a feedback active noise control method for a headphone or an earphone that effectively processes noise signals introduced from the outside on the basis of frequency warping convex optimization, and an active noise control system thereby.

According to a preferred embodiment of the present invention, an active noise control method for actively controlling a noise signal introduced from the outside includes a frequency-warped low-order finite impulse response filter based on constraint optimization of a feedback method The noise signal processed by the approximate impulse response method is processed.

According to another preferred embodiment of the present invention, the frequency warping is frequency warping convex optimization.

According to another preferred embodiment of the present invention, the step of obtaining the low order finite impulse response filter comprises: obtaining a nominal path; Setting a weighting function for optimization; Synthesizing a WFIR filter (Warped Finite Impulse Response Filter) by applying frequency warping to a nominal function and a weight function; Further comprising the step of obtaining a low-order WFIR control filter by frequency warping convex optimization by applying a frequency warping nominal path and a weight function, wherein approximating with the infinite impulse response comprises obtaining BTM from the obtained WFIR control filter Transforming a low order WIIR filter (Warped Infinite Impulse Response Filter) by applying a Blanched Model Truncation technique; Converting the polarity of the converted WIIR filter and the zero point into an IIR filter in a linear frequency domain by frequency despreading; And transforming the transformed IIR filter into a cascaded structure of the second IIR filter.

According to another preferred embodiment of the present invention, a feedback active noise control method for a headphone or an earphone comprises the steps of applying an infinite impulse response approximation technique to a low order finite impulse response filter obtained by applying frequency warping convex optimization to an incoming noise signal And then passed through the IIR filter obtained by applying it to the speaker.

According to another preferred embodiment of the present invention, an active noise reduction filter for a headphone or earphone approximates a low order finite impulse response signal obtained by applying frequency warping convex optimization to an incoming noise signal with an infinite impulse response to obtain an IIR Signal to be acquired.

According to another preferred embodiment of the present invention, an active noise control system for a headphone or an earphone includes an error microphone for acquiring an error signal from an externally supplied noise signal; A second order IIR filter for filtering the obtained error signal; And a speaker outputting the filtered error signal. The second IIR filter generates a signal approximating the low-order finite impulse response signal obtained by applying frequency warping convex optimization to the error signal to an infinite impulse response .

The method according to the invention makes it possible to design a low order IIR filter optimized for active noise control headphone environment. The method according to the present invention ensures that the same performance is ensured while using less orders when compared with a higher order control filter designed in the known linear frequency domain by designing the control filter by applying the optimization technique in the warped frequency domain . The method according to the present invention is characterized in that the obtained WFIR control filter is converted into an IIR filter in a linear frequency domain through frequency demodulation with BMT. In this case, since the degree of the WFIR filter to be approximated is low, a lower order filter can be obtained while having a more precise approximation accuracy in a low frequency band compared with a method of converting from a high order FIR filter to an IIR filter. The deterioration of the noise control performance of the control filter due to the IIR approximation can be minimized. In addition, since the frequency despreading operates in the linear frequency domain, it is possible to prevent problems such as an increase in the amount of computation that may occur when signal processing is performed in the warped frequency domain.

1 is a block diagram illustrating a method of controlling a feedback active noise according to the present invention.
FIG. 2 illustrates an example of a process for designing a low-order IIR control filter by combining a frequency warping convex optimization technique and an IIR approximation technique according to the present invention.
FIG. 3 illustrates an embodiment of an active noise control system operating in an active noise control headphone environment in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the accompanying drawings, but the present invention is not limited thereto. In the following description, components having the same reference numerals in different drawings have similar functions, so that they will not be described repeatedly unless necessary for an understanding of the invention, and the known components will be briefly described or omitted. However, It should not be understood as being excluded from the embodiment of Fig.

1 is a block diagram illustrating a method of controlling a feedback active noise according to the present invention.

The feedback active noise control method according to the present invention is characterized by processing a noise signal introduced by approximating a frequency-warped finite impulse response filter with a infinite impulse response based on constraint optimization of a feedback method . The constraint optimization is also a frequency warping convex optimization.

1, an error signal e (n) is obtained from an externally introduced noise signal d (n), and an error signal e (n) is obtained by a second IIR filter (Infinite Impulse Response Filter ) 11 can be output via the mixer 13 together with the noise signal d (n) flowing from the outside through the secondary path 12. The IIR filter 11 can be a cascaded structure and can be obtained from a low order finite impulse response filter that is frequency warped.

This is explained in detail below.

In order to maintain the maximum noise control performance of a high-order finite impulse response filter in a noise control system such as a high-performance active noise control headphone environment, noise suppression performance deterioration occurs when frequency warping technology (Reference 9) Can be prevented at a certain level. The frequency warping technique can be applied in the field of acoustic signal processing by increasing or decreasing the resolution of a specific frequency band. The frequency warping can be made by converting the unit delay elements of the linear frequency domain into the global pass elements, and can be expressed, for example, by the following equation (3).

Equation (3)

는 전역 통과 요소가 되고,

는 워핑 파라미터로 0과 1 사이의 값이 설정되면 저주파 대역의 분해능이 높아질 수 있다. 이러한 과정이 제어 필터 설계 알고리즘에 적용되면, 컨벡스 최적화를 통해 얻은 유한 임펄스 응답 제어 필터가 그대로 무한 임펄스 응답 필터로 변환되지 않고, 주파수 워핑하여 얻은 워핑된 주파수 영역의 필터에 BMT 기법이 적용되는 것에 의하여 저주파 대역에서 근사 정확도가 향상될 수 있다. 그러나 이러한 과정을 거치는 경우라고 할지라도 목표로 하는 유한 임펄스 응답 필터가 고주파 대역에 지배적인 성분을 가진다면 여전히 성능 열화가 발생하여 원하는 소음 제어 성능이 얻어지지 않을 수 있다. In the above,

≪ / RTI > becomes a global pass element,

Is set to a value between 0 and 1 as a warping parameter, the resolution of the low frequency band can be increased. When this process is applied to the control filter design algorithm, the finite impulse response control filter obtained through the convex optimization is not directly transformed into the infinite impulse response filter, but the BMT technique is applied to the warped frequency domain filter obtained by frequency warping The approximation accuracy can be improved in the low frequency band. However, if the target finite impulse response filter has a dominant component in the high frequency band even if this process is performed, the performance deterioration still occurs and desired noise control performance may not be obtained.

According to the present invention, reasonable noise control performance can be obtained while using a low-order filter. If frequency warping is used after applying the convex optimization technique, there is a problem that performance degradation due to the use of the order reduction technique is inevitable due to the already designed high order filter. Therefore, it is advantageous to apply the frequency-warped convex optimization technique that directly utilizes the frequency warping technique for convex optimization. Accordingly, even if a finite impulse response filter of a low order in the warped frequency domain is obtained and approximated by an infinite impulse response filter, the performance deterioration occurring in the approximation process is minimized, thereby enabling a filter design having a reasonable noise control performance .

A specific embodiment of the active noise control method according to the present invention will be described below.

FIG. 2 illustrates an example of a process for designing a low-order IIR control filter by combining a frequency warping convex optimization technique and an IIR approximation technique according to the present invention.

Referring to FIG. 2, the feedback active noise control method according to the present invention includes: obtaining a nominal path from a secondary path for frequency warping convex optimization; Setting a weighting function for optimization; Synthesizing the nominal path and the weighting functions into a WFIR filter using frequency warping (P21); Designing a low order WFIR control filter through frequency warping convex optimization using the frequency warped nominal path and weighting functions (P22); Converting the obtained WFIR control filter to a low-order WIIR filter through a BMT technique (P23); (P24) from the pole and zero of the WIIR filter to a IIR filter in a linear frequency domain through frequency divergence; And reconstructing the designed IIR filter into a cascaded structure of the secondary IIR filter (P25).

The method according to the present invention is characterized in that it converts an WFIR filter obtained through frequency warping convex optimization to an IIR filter to enable effective noise control with a low order filter in a linear frequency domain without using a global pass element. Frequency warping Convex optimization is similar to constructing the formulation of the known convex optimization, but differs in that the design domain is the warped frequency domain. For the application of the feedback active noise control method, the formulation of frequency warping convex optimization can be expressed as Equation (4) below.

Equation 4:

은 FFT 크기,

는 주파수 빈 색인을 나타낸다.

는 제어 필터 설계에 사용되는 워핑된 명목 경로에 해당하고, FIR 필터 형태로 주어지는 명목 경로

를 주파수 워핑을 하는 것에 의하여 얻어질 수 있다. 가중 함수

또한 공지의 가중 함수

를 주파수 워핑을 하는 것에 의하여 얻어질 수 있다.

는 워핑된 주파수 영역에서 주파수 워핑 컨벡스 최적화를 통해 얻은 WFIR 제어 벡터가 되고 수학식 5와 같은 형태로 본 발명에 따른 최적화 기법의 최종적인 제어 필터를 얻기 위하여 사용될 수 있다. In the above,

FFT size,

Represents a frequency bin index.

Corresponds to the warped nominal path used in the control filter design, and the nominal path given in the form of an FIR filter

Can be obtained by performing frequency warping. Weight function

The known weighting function

Can be obtained by performing frequency warping.

Is a WFIR control vector obtained through frequency warping convex optimization in the warped frequency domain and can be used to obtain the final control filter of the optimization technique according to the present invention in the form of Equation (5).

Equation 5:

는 WFIR 제어 벡터

로부터 얻은 최종적 제어 필터

의 전달함수를 나타낸다. 또한

은 그 자체로 공지의 컨벡스 최적화를 통해 얻을 수 있는 제어 필터

에 비해 훨씬 낮은 차수를 가지지만 이를 그대로 능동 소음 제어 시스템의 필터로 사용하기 위하여 워핑된 주파수 영역에서 신호처리를 수행하기 위한 전역 통과 요소(all-pass element)가 부가적으로 사용되어야 한다. 이는 동일 차수의 FIR 필터를 사용하는 경우 대비 연산량 증가를 발생시킬 수 있다. 본 발명에 따르면, 이러한 문제를 해결하기 위해 전역 통과 요소 없이 소음 제어가 가능하도록 선형 주파수 영역의 필터로 변환하는 알고리즘이 부가적으로 사용된다. 무한 임펄스 응답 근사 기법 BMT를 이용하여 WFIR 제어 필터

를 워핑된 무한 임펄스 응답 (warped IIR, WIIR) 필터

로 변환하고,

의 극점과 영점

을 주파수 디워핑하여 아래의 수학식 6에 따라 선형 주파수 영역의 극점과 영점

을 얻게 된다.In the above,

Is a WFIR control vector

Lt; RTI ID = 0.0 >

. Also

Lt; RTI ID = 0.0 > a < / RTI > control filter

But it is necessary to additionally use an all-pass element for performing signal processing in the warped frequency domain in order to use it as a filter of the active noise control system. This may result in an increase in the amount of contrast computation when an FIR filter of the same order is used. According to the present invention, in order to solve such a problem, an algorithm for converting a linear frequency domain filter is additionally used so that noise control can be performed without using a global pass element. Infinite impulse response approximation technique WFIR control filter using BMT

A warped IIR, WIIR filter,

≪ / RTI >

Pole and zero

And calculates the pole position in the linear frequency domain and the zero point

.

Equation (6)

는 WIIR 필터의 극점과 영점의 개수, 즉 필터 차수를 뜻한다.

로부터 선형 주파수 영역의 IIR 필터

가 합성될 수 있다. 이러한 과정에서 디워핑이 된 영점과 극점

들은 서로 인접할 경우 이로부터 구성되는 IIR 필터의 안정성 문제가 발생될 수 있다. 이러한 문제점을 방지하기 위해 본 발명에 따르면 IIR 필터

는 1차 또는 2차 IIR 필터의 종속 연결 구조로 재구성이 될 수 있다(참조 10). 그리고 최종 제어 필터는 아래의 수학식 7로 표시될 수 있다. In the above,

Means the pole number of the WIIR filter and the number of zero points, i.e., the filter order.

Lt; RTI ID = 0.0 > IIR < / RTI &

Can be synthesized. In this process, the diverted zero and pole

The problems of stability of the IIR filter constituted from these can arise. In order to prevent such a problem, according to the present invention,

Can be reconstructed into a cascade of primary or secondary IIR filters (Ref. 10). And the final control filter can be expressed by Equation (7) below.

Equation (7)

는 수학식 6에서 합성된 IIR 필터

의 전달함수,

은

의 개수,

는

의 이득을 나타낸다.

는

로부터 분해된 1차 또는 2차 IIR 필터의 전달함수에 해당하고, 수학식 6에서 얻은 극점과 영점이 실수인 경우 이들을 1차 IIR 필터의 전달 함수의 분모와 분자의 계수로 구성되고,

과 같은 관계식을 갖게 된다. 실수의 영점과 극점을 제외한 복소수의 극점과 영점들에 대해서는 이들 중 상호 켤레 복소수 관계에 있는 것들을 결합한 후 전개하여 2차 IIR 필터의 전달함수의 분자와 분모의 계수

가 얻어질 수 있다. 이후 종속 연결 구조가 구성되어 발생하는 출력의 오차가 최소화 되도록 적절한 순서로 정렬되면 본 발명에 따른 종속 연결 구조의 IIR 필터가 얻어질 수 있다. In the above,

Lt; RTI ID = 0.0 > IIR < / RTI &

Transfer function,

silver

≪ / RTI >

The

.

The

And the poles and zeros obtained from the equation (6) are real numbers, these are denominators of the transfer function of the first order IIR filter and the coefficients of the molecules,

And so on. For the poles and zeros of the complex number except for the zero and pole of the real number, we combine those in the mutual conjugate complex relationship and develop them so that the numerator and denominator of the transfer function of the second IIR filter

Can be obtained. The IIR filter of the cascade connection structure according to the present invention can be obtained if the cascade connection structure is constructed and arranged in an appropriate order so that the output error generated is minimized.

The active noise control method according to the present invention can be applied to a headphone or a noise environment or a similar noise environment.

FIG. 3 illustrates an embodiment of an active noise control system operating in an active noise control headphone environment in accordance with the present invention.

Referring to FIG. 3, an active noise control system for a headphone or an earphone includes an error microphone 31 for obtaining an error signal from a noise signal d (n) input from the outside; A second order IIR filter 32 for filtering the obtained error signal; And a speaker (33) for outputting a filtered error signal, wherein the second IIR filter (32) applies a low order finite impulse response signal obtained by applying frequency warping convex optimization to the error signal in an infinite impulse response And generates an approximate signal.

을 최소화하기 위하여 헤드폰 내부에 위치한 오차 마이크(31)로부터 취득한 오차 신호가 최소가 되도록 능동 소음 제어 시스템이 작동된다. 설계된 2차의 IIR 필터

(32)은 종속 연결 구조로 연결되어 제어 필터의 입력 신호인 오차 신호

을 필터링한 후, 출력 신호

을 스피커(33)를 통해 출력하여 유입된 소음을 최소화하는 기능을 가질 수 있다. 이에 의하여 소음이 제거된 소리 신호가 사용자의 귀(34)로 전달될 수 있다. Noise signal from the outside

The active noise control system is operated so that the error signal obtained from the error microphone 31 located inside the headphone is minimized. Designed second order IIR filter

(32) are connected in a cascade connection structure, and an error signal

The output signal < RTI ID = 0.0 >

May be output through the speaker 33 to minimize the noise introduced. Thus, the noise-canceled sound signal can be transmitted to the user's ear 34.

The method according to the invention makes it possible to design a low order IIR filter optimized for active noise control headphone environment. The method according to the present invention ensures that the same performance is ensured while using less orders when compared with a higher order control filter designed in the known linear frequency domain by designing the control filter by applying the optimization technique in the warped frequency domain . The method according to the present invention is characterized in that the obtained WFIR control filter is converted into an IIR filter in a linear frequency domain through frequency demodulation with BMT. In this case, since the degree of the WFIR filter to be approximated is low, a lower order filter can be obtained while having a more precise approximation accuracy in a low frequency band compared with a method of converting from a high order FIR filter to an IIR filter. The deterioration of the noise control performance of the control filter due to the IIR approximation can be minimized. In addition, since the frequency despreading operates in the linear frequency domain, it is possible to prevent problems such as an increase in the amount of computation that may occur when signal processing is performed in the warped frequency domain.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention . The invention is not limited by these variations and modifications, but is limited only by the claims appended hereto.

: References

Reference 1: SM Kuo and DR Morgan, " Active noise control: a tutorial review, " in Proceedings of the IEEE , vol. 87, no. 6, pp. 943-973, Jun 1999

Reference 2: PE Gill, W. Murray, and MH Wright, Practical Optimization . New York: Academic, 1981.

Reference 3: B. Rafaely and S. J. Elloitt, " H2 / H∞ output feedback design for active control, " ISVR, Univ. Southhampton, U.K., Tech. Memo 800, July 1996.

Reference 4: Rafaely, Boaz, and Stephen J. Elliott. "H 2 / H ∞ active control of sound in a headrest: design and implementation." IEEE Transactions on control systems technology 7.1 (1999): 79-84.

Reference 5: B. Rafaely, " Active noise reducing headset-an overview, " Proceedings of the Internoise 2001 Conference, August 2001, The Hague, Holland, pp.589-598 (2001)

Reference 6: J. C. Doyle, B. A. Francis, and A. R. Tannenbaum, Feedback Control Theory. New York: MacMillanl, 1992.

Reference 7: J. Mackenzie, J. Huopaniemi, V. Valimaki, and I. Kale, "Low-order Modeling of Head-Related Transfer Functions Using Balanced Model Truncation," IEEE Signal Processing Lett ., Vol. 4, pp. 39-41, Feb. 1997

Reference 8: Ahfir, Maamar, Izzet Kale, and Daoud Berkani. "An Alternative Approach to the Balanced Model Truncation Algorithm for Acoustic Minimum-Phase Inverse Filters Order Reduction." ISRN Signal Processing 2011 (2011)

IEEE 9th International Conference on ASSP Workshop on New Paltz, NY, 1997. [9] M. Karjalainen, A. Harma, UK Laine and J. Huopaniemi, "Warped filters and their audio applications," Applications of Signal Processing to Audio and Acoustics, , pp. 4 pp.-

Reference 10: Alan V. Oppenheim, Ronald W. Schafer, with John R. Buck, " Discrete-time Signal Processing, " Prentice Hall, 1989.

11: IIR filter 12: secondary path
13: mixer 31: error microphone
32: Secondary IIR filter 33: Speaker
34: Ear

Claims (6)

1. A feedback active noise control method for actively controlling a noise signal introduced from the outside,
And processing the introduced noise signal by approximating a frequency-warped low-order finite impulse response filter based on an infinite impulse response scheme based on a feedback-based constraint optimization technique,
Wherein the constrained optimization technique is a convex optimization technique, the step of obtaining the low order finite impulse response filter comprises: obtaining a nominal path; Setting a weighting function for optimization; Synthesizing a WFIR filter (Warped Finite Impulse Response Filter) by applying frequency warping to a nominal function and a weight function; Further comprising the step of obtaining a low-order WFIR control filter by frequency warping convex optimization by applying a frequency warping nominal path and a weight function, wherein approximating with the infinite impulse response comprises obtaining a BMT from the obtained WFIR control filter Transforming a low order WIIR filter (Warped Infinite Impulse Response Filter) by applying a Blanched Model Truncation technique; Converting the polarity of the converted WIIR filter and the zero point into an IIR filter in a linear frequency domain by frequency despreading; And transforming the transformed IIR filter into a cascaded structure of a second order IIR filter. delete delete A method of controlling a feedback active noise for either a headphone or an earphone,
Order low-order finite impulse response filter obtained by applying a frequency warping convolution optimization technique to an incoming noise signal is transmitted to an loudspeaker through an IIR filter obtained by applying an infinite impulse response approximation technique, Obtaining the filter includes obtaining a nominal path; Setting a weighting function for optimization; Synthesizing a WFIR filter (Warped Finite Impulse Response Filter) by applying frequency warping to a nominal function and a weight function; Further comprising the step of obtaining a low-order WFIR control filter by frequency warping convex optimization by applying a frequency warping nominal path and a weight function, wherein approximating with the infinite impulse response comprises obtaining a BMT from the obtained WFIR control filter Transforming a low order WIIR filter (Warped Infinite Impulse Response Filter) by applying a Blanched Model Truncation technique; Converting the polarity of the converted WIIR filter and the zero point into an IIR filter in a linear frequency domain by frequency despreading; And transforming the transformed IIR filter into a cascaded structure of a second order IIR filter. delete 1. An active noise control system for either a headphone or an earphone,
An error microphone for obtaining an error signal from a noise signal d (n) flowing from the outside;
A second order IIR filter for filtering the obtained error signal; And
And a speaker for outputting a filtered error signal,
The second IIR filter generates a signal approximating a low-order finite impulse response signal obtained by applying a frequency warping convex optimization technique to an error signal with an infinite impulse response,
Wherein the step of obtaining the low order finite impulse response filter comprises obtaining a nominal path; Setting a weighting function for optimization; Synthesizing a WFIR filter (Warped Finite Impulse Response Filter) by applying frequency warping to a nominal function and a weight function; Further comprising the step of obtaining a low-order WFIR control filter by frequency warping convex optimization by applying a frequency warping nominal path and a weight function, wherein approximating with the infinite impulse response comprises obtaining a BMT from the obtained WFIR control filter Transforming a low order WIIR filter (Warped Infinite Impulse Response Filter) by applying a Blanched Model Truncation technique; Converting the polarity of the converted WIIR filter and the zero point into an IIR filter in a linear frequency domain by frequency despreading; And converting the converted IIR filter into a cascaded structure of the second IIR filter. The active noise control system as claimed in claim 1,

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