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Low-pass filter

About: Low-pass filter is a(n) research topic. Over the lifetime, 24290 publication(s) have been published within this topic receiving 249367 citation(s). The topic is also known as: LPF & low-pass filter:LPF.

More filters
Journal ArticleDOI
TL;DR: Modifications to the fitting procedure are described which allow more accurate derivations of filter shapes derived from data where the notch is always placed symmetrically about the signal frequency and when the underlying filter is markedly asymmetric.
Abstract: A well established method for estimating the shape of the auditory filter is based on the measurement of the threshold of a sinusoidal signal in a notched-noise masker, as a function of notch width. To measure the asymmetry of the filter, the notch has to be placed both symmetrically and asymmetrically about the signal frequency. In previous work several simplifying assumptions and approximations were made in deriving auditory filter shapes from the data. In this paper we describe modifications to the fitting procedure which allow more accurate derivations. These include: 1) taking into account changes in filter bandwidth with centre frequency when allowing for the effects of off-frequency listening; 2) correcting for the non-flat frequency response of the earphone; 3) correcting for the transmission characteristics of the outer and middle ear; 4) limiting the amount by which the centre frequency of the filter can shift in order to maximise the signal-to-masker ratio. In many cases, these modifications result in only small changes to the derived filter shape. However, at very high and very low centre frequencies and for hearing-impaired subjects the differences can be substantial. It is also shown that filter shapes derived from data where the notch is always placed symmetrically about the signal frequency can be seriously in error when the underlying filter is markedly asymmetric. New formulae are suggested describing the variation of the auditory filter with frequency and level. The implications of the results for the calculation of excitation patterns are discussed and a modified procedure is proposed. The appendix lists FORTRAN computer programs for deriving auditory filter shapes from notched-noise data and for calculating excitation patterns. The first program can readily be modified so as to derive auditory filter shapes from data obtained with other types of maskers, such as rippled noise.

2,317 citations

Journal ArticleDOI
Abstract: A simple filter for controlling high-frequency computational and physical modes arising in time integrations is proposed. A linear analysis of the filter with leapfrog, implicit, and semi-implicit, differences is made. The filter very quickly removes the computational mode and is also very useful in damping high-frequency physical waves. The stability of the leapfrog scheme is adversely affected when a large filter parameter is used, but the analysis shows that the use of centered differences with frequency filter is still more advantageous than the use of the Euler-backward method. An example of the use of the filter in an actual forecast with the meteorological equations is shown.

782 citations

Journal ArticleDOI
TL;DR: An efficient procedure for the design of finite-length impulse response filters with linear phase is presented, which obtains the optimum Chebyshev approximation on separate intervals corresponding to passbands and/or stopbands.
Abstract: An efficient procedure for the design of finite-length impulse response filters with linear phase is presented. The algorithm obtains the optimum Chebyshev approximation on separate intervals corresponding to passbands and/or stopbands, and is capable of designing very long filters. This approach allows the exact specification of arbitrary band-edge frequencies as opposed to previous algorithms which could not directly control pass- and stopband locations and could only obtain (N - 1)/2 different band-edge locations for a length N low-pass filter, for fixed \delta_{1} and \delta_{2} . As an aid in practical application of the algorithm, several graphs are included to show relations among the parameters of filter length, transition width, band-edge frequencies, passband ripple, and stopband attenuation.

772 citations

15 Jan 1967
Abstract: CHAPTER 1 FILTERS IN ELECTRONICS 11 Types of Filters 12 Filter Applications 13 All-Pass Filters 14 Properties of Lattice Filters 15 Filter Building Blocks 16 Higher Order Filters 17 Coil-Saving Bandpass Filters 18 Frequency Range of Applications 19 Physical Elements of the Filter 110 Active Bandpass Filters 111 RC Passive and Active Filters 112 Microwave Filters 113 Parametric Filters CHAPTER 2 THEORY OF EFFECTIVE PARAMETERS 21 Power Balance 22 Types of General Network Equations 23 Effective Attenuation 24 Reflective (Echo) Attenuation 25 Transmission Function as a Function of Frequency Parameter, s 26 Polynomials of Transmission and Filtering Functions 27 Filter Networks 28 Voltage and Current Sources 29 The Function D (s) As An Approximation Function 210 Example of Transmission Function Approximation 211 Simplest Polynomial Filters in Algebraic Form 212 Introduction to Image=Parameter Theory 213 Bridge Networks 214 Examples of Realization in the Bridge Form 215 Hurwitz Polynomial 216 The Smallest Realizabel Networks, 217 Fourth-Order Networks 218 Fifth-Order Networks CHAPTER 3 FILTER CHARACTERISTICS IN THE FREQUENCY DOMAIN 31 Amplitude Responses 32 Phase-and Group-Delay Responses 33 Group Delay of an Idealized Filter 34 Group Delay-Attenuation Relationship 35 The Chebyshev Family of Response Characteristics 36 Gaussian Family of Response Characteristics 37 A Filter with Transitional Magnitude Characteristics 38 Legendre Filters 39 Minimum-Loss Characteristics 310 Synchronously Tuned Filters 311 Arithmetically Symmetrical Bandpass Filters 312 Attenuation Characteristics of Image Parameter Filters 313 Other Types of Filter Characteristics 314 Plots of the Attenuation and Group Delay Characteristics CHAPTER 4 ELLIPTIC FUNCTION AND ELEMENTS OF REALIZATION 41 Double Periodic Elliptic Functions 42 Mapping of s-Plane into u-Plane 43 First Basic Transformation of Elliptic Functions 44 Filtering Function in z-Plane 45 Graphical Representation of Parameters 46 Characteristic Value of D(s) 47 An Example of Filter Design 48 Consideration of Losses 49 Introduction of Losses by Frequency Transformation 410 Highpass Filters with Losses 411 Transmission Functions with Losses 412 Conclusions on Consideration of Losses 413 Realization Process 414 Bandpass Filter with a Minimum Number of Inductors 415 The Elements of a Coil-Saving Network 416 Consideration of Losses in Zig-Zag Filters 417 Realization Procedure 418 Numerical Example of Realization 419 Full and Partial Removal for a Fifth-Order Filter CHAPTER 5 THE CATALOG OF NORMALIZED LOWPASS FILTERS 51 Introduction to the Catalog 52 Real Part of the Driving Point Impedance 53 Lowpass Filter Design 54 Design of Highpass Filters 55 Design of LC Bandpass Filters 56 Design of Narrowband Crystal Filters 57 Design of Bandstop Filters 58 Catalog of Normalized Lowpass Models CHAPTER 6 DESIGN TECHNIQUES FOR POLYNOMIAL FILTERS 61 Introduction to Tables of Normalized Element Values 62 Lowpass Design Examples 63 Bandpass Filter Design 64 Concept of Coupling 65 Coupled Resonators 66 Second-Order Bandpass Filter 67 Design with Tables of Predistorted k and q Parameters 68 Design Examples using Tables of k and q Values 69 Tables of Lowpass Element Values 610 Tables of 3-dB Down k and q Values CHAPTER 7 FILTER CHARACTERISTICS IN THE TIME DOMAIN 71 Introduction to Transient Characteristics 72 Time and Frequency Domains 73 Information Contained in the Impulse Response 74 Step Response 75 Impulse Response of an Ideal Gaussian Filter 76 Residue Determination 77 Numerical Example 78 Practical Steps on the Inverse Transformation 79 Inverse Transform of Rational Spectral Functions 710 Numerical Example 711 Estimation Theory 712 Transient Response in Highpass and Bandpass Filters 713 The Exact Calculation of Transient Phenomena for Highpass Systems 714 Estimate of Transient Responses in Narrowband Filters 715 The Exact Transient Calculation in Narrowband Systems 716 Group Delay Versus Transient Response 717 Computer Determination of Filter Impulse Response 718 Transient Response Curves CHAPTER 8 CRYSTAL FILTERS 81 Introduction 82 Crystal Structure 83 Theory of Piezoelectricity 84 Properties of Piezoelectric Quartz Crystals 85 Classification of Crystal Filters 86 Bridge Filters 87 Limitation of Bridge Crystal Filters 88 Spurious Response 89 Circuit Analysis of a Simple Filter 810 Element Values in Image-Parameter Formulation 811 Ladder Filters 812 Effective Attenuation of Simple Filters 813 Effective Attenuation of Ladder Networks 814 Ladder Versus Bridge Filters 815 Practical Differential Transformer for Crystal Filters 816 Design of Narrowband Filters with the Aid or Lowpass Model 817 Synthesis of Ladder Single Sideband Filters 818 The Synthesis of Intermediate Bandpass Filters 819 Example of Band-Reject Filter 820 Ladder Filters with Large Bandwidth CHAPTER 9 HELICAL FILTERS 91 Introduction 92 Helical Resonators 93 Filter with Helical Resonators 94 Alignment of Helical Filters 95 Examples of Helical Filtering CHAPTER 10 NETWORK TRANSFORMATIONS 10 1 Two-Terminal Network Transformations 102 Delta-Star Transformation 103 Use of Transformer in Filter Realization 104 Norton's Transformation 105 Applications of Mutual Inductive Coupling 106 The Realization of LC Filters with Crystal Resonators 107 Negative and Positive Capacitor Tranformation 108 Bartlett's Bisection Theorem 109 Cauer's Equivalence 1010 Canonic Bandpass Structures 1011 Bandpass Ladder Filters Having a Cononical Number of Inductors without Mutual Coupling 1012 Impedance and Admittance Inverters 1013 Source and Load Transformation Bibliography Index

769 citations

Proceedings ArticleDOI
James D. Johnston1
09 Apr 1980
TL;DR: This paper discusses a family of filters that have been designed for Quadrature Mirror Filter (QMF) Banks that provide a significant improvement over conventional optimal equiripple and window designs when used in QMF banks.
Abstract: This paper discusses a family of filters that have been designed for Quadrature Mirror Filter (QMF) Banks. These filters provide a significant improvement over conventional optimal equiripple and window designs when used in QMF banks. The performance criterion for these filters differ from those usually used for filter design in a way which makes the usual filter design techniques difficult to apply. Two filters are actually designed simultaneously, with constraints on the stop band rejection, transition band width, and pass and transition band performance of the QMF filter structure made from those filters. Unlike most filter design problems, the behavior of the transition band is constrained, which places unusual requirements on the design algorithm. The requirement that the overall passband behavior of the QMF bank be constrained (which is a function of the passband and stop band behavior of the filter) also places very unusual requirements on the filter design. The filters were designed using a Hooke and Jeaves optimization routine with a Hanning window prototype. Theoretical results suggest that exactly flat frequency designs cannot be created for filter lengths greater than 2, however, using the discussed procedure, one can obtain QMF banks with as little as ±.0015dB ripple in their frequency response. Due to the nature of QMF filter applications, a small set of filters can be derived which will fit most applications.

722 citations

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