What is Filter: Definition and 604 Discussions

A low-pass filter is a filter that passes signals with a frequency lower than a selected cutoff frequency and attenuates signals with frequencies higher than the cutoff frequency. The exact frequency response of the filter depends on the filter design. The filter is sometimes called a high-cut filter, or treble-cut filter in audio applications. A low-pass filter is the complement of a high-pass filter.
In optics, high-pass and low-pass may have different meanings, depending on whether referring to frequency or wavelength of light, since these variables are inversely related. High-pass frequency filters would act as low-pass wavelength filters, and vice versa. For this reason it is a good practice to refer to wavelength filters as short-pass and long-pass to avoid confusion, which would correspond to high-pass and low-pass frequencies.Low-pass filters exist in many different forms, including electronic circuits such as a hiss filter used in audio, anti-aliasing filters for conditioning signals prior to analog-to-digital conversion, digital filters for smoothing sets of data, acoustic barriers, blurring of images, and so on. The moving average operation used in fields such as finance is a particular kind of low-pass filter, and can be analyzed with the same signal processing techniques as are used for other low-pass filters. Low-pass filters provide a smoother form of a signal, removing the short-term fluctuations and leaving the longer-term trend.
Filter designers will often use the low-pass form as a prototype filter. That is, a filter with unity bandwidth and impedance. The desired filter is obtained from the prototype by scaling for the desired bandwidth and impedance and transforming into the desired bandform (that is low-pass, high-pass, band-pass or band-stop).

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  1. T

    Finding whether a filter is low/high/band pass

    Homework Statement Consider the IIR filter yn = xn - yn-2 State whether the filter is low, high, or band pass. Homework Equations The Z-transform: $$H(z) = \frac {1} {1+z^2},$$ Subbing ##z = e^{2πiw}## : $$H(w) = \frac {1} {1+e^{4πiw}},$$ Amplitude response: $$|H(w)| = \sqrt{{(\frac {1} {1...
  2. R

    MATLAB Frequency domain filtering in Matlab

    I am trying to implement several filters in Matlab for Fourier domain filtering. They are the cosine, Shepp-Logan, and Hann/Hamming window filters. These filters are defined as multiplying the ramp filter by the cosine function, sinc function, and Hann/Hamming windows respectively. This is how...
  3. T

    Filter Performance Assessment Using Basic Equipment: A Practical Guide

    Hi, Say I have a design for a filter, is there a method of bench-marking it's attenuation over a variety of loads and types of harmonics? (or even common and differential noises) For instance, say I wanted to compare a filter to an LC filter or a π filter, how does one evaluate how much better...
  4. Steven Ellet

    Create a Cheaper Water Filter: 25nm Cloth

    I am looking for 25 nm "cloth" (I'm using that term loosely) my goal is to create a cheaper water filter similar to "LifeSaver bottle" (https://en.wikipedia.org/wiki/LifeSaver_bottle) which is $139
  5. Kelsi_Jade

    Design a series RLC filter for 10kHz

    Homework Statement Design a series RLC filter for 10kHz using an 0.01mF capacitor. Homework Equations / 3. The Attempt at a Solution how would the circuit actually look if drawn out here? [/B]
  6. Helmholtzerton

    MATLAB Filter out constant of integration?

    Hello, I'm trying to integrate a signal received on an oscilliscope, but I'm afraid using the function cumtrapz is not giving me the correct value. Here is what I'm seeing when testing out sine functions I could apply an FFt to obtain the components and the phases, and then subtract off the...
  7. H

    Second order low pass filter with unity gain

    Homework Statement I need to design a second order filter with unity gain. Homework Equations None - not taking component values into account for now. The Attempt at a Solution Is this a correct method of creating a 2nd order low pass filter with unity gain?
  8. D

    Hepa filter specifications/ blower match

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  9. R

    How does a hollow fiber membrane work to filter water?

    What is the process? And can/cannot it filter out?
  10. G

    Problems with Unscented Kalman Filter

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  11. T

    Calculating the filter capacitor for a power supply

    Trying to build a simple 9V power supply using a 7809 voltage regulator and full wave rectifier. The load current from the regulator is 1A. So I = C*dv/dt, therefore, C = I*t/(delta V) To my understanding t is the time between the two peaks or the time the capacitor supplies the load. So if...
  12. A

    Measurement of grinding wheel waviness

    I have done experiements on a grinding machine and have collected the data of grinding wheel profile (using a laser sensor). The raw data consists of info on grinding wheel profile, waviness and roughness (because of abrasive grains). I would like to process the colelcted raw data. I want to...
  13. M

    Filter water as rolling it in a barrel

    Hi, I need some help to verify whether this is possible or not. I am working on a project that still in early phase of development. The idea is to create a water filter system to in a barrel as rolling it. Basically the barrel will contain 4 panels placed inside the barrel creating a shape of...
  14. C

    B Has anyone tested a polarization filter sending through photon by photon?

    To properly test a filter, I understand we can use a source of vertically polarized light. We send photon by photon say 1000 though a filter at, for example, 45 degrees the count the ones on the other side. We should get roughly 500, depending of the quality of the setup. I was interested in a...
  15. khurram usman

    Upsampled input to an Adaptive filter?

    I will try to explain the issue I am having as clearly as possible without going into my coding or maths. I have my own and a MATLAB Central implementation pf standard LMS in MATLAB. Fixed step size. No normalization or other stuff. I am trying to use it in a system identification setup. I...
  16. F

    Butterworth filter via Cauer topology

    Hi all. I would like to ask some explanation regarding how to obtain L and C values for a butterworth filter using the first Cauer topology. I will consider a normalized low pass filter. (Link added by Mentor) https://en.wikipedia.org/wiki/Butterworth_filter What I don't understand is this...
  17. R

    I Simple suction air filter: items and preventing implosion

    I want to make a simple air filter(for dust and air pollution) but was a bit confused about some stuff. Basically I've decided to use an exhaust fan to create a vacuum in a sealed box and the air to come in through the filters. Box fans aren't available here, so that can't be used. I want to...
  18. D

    Equations explaining pressure drop across an air filter

    Hi all, I'm having a Kaiser compressor producing compressed air for my garage. I've installed a FRL unit at point of use. I understand that the filter medium adsorbs atmospheric dust, moisture and oil particles in compressed air. Gradually the pressure drop across the filter builds up and I need...
  19. T

    What is the design and performance comparison of third order high pass filters?

    Homework Statement Write a report (of approximately 750 words) that discusses and compares the design of each filter in terms of their performance, circuit topology, application and any other relevant characteristics. You may for example attempt to relate the choice of component values to the...
  20. W

    Releasing Electrons with a color filter

    Homework Statement Simple question we have to answer: (Physics) How do I release the electrons from the cathode with a color filter? (The so called Photoelectric effect)Homework Equations none The Attempt at a Solution[/B] Here we have a conflict , the so called wave-particle duality, if...
  21. J

    Fourier transform: signal with filter

    Hi Guys, I'm having trouble with the following: A finite-time signal is the result of a filter G(t) applied to a signal. The filter is simply “on” (1) for t ∈ [0,T] and off (“0”) otherwise. If x(t) is the signal, and x(ω),its Fourier transform, compute the Fourier transform of the filtered signal...
  22. T

    Cascaded low-pass filter followed by a buffer amplifier

    Homework Statement 3. FIGURE 3(a) shows a simple low-pass filter followed by a buffer amplifier. (a) Write down the transfer function for the filter. (b) Determine the 3db frequency (fc) if R = 10 kΩ and C = 10 nF. (c) If four such stages are cascaded as shown in FIGURE 3(b), determine the gain...
  23. G

    Kalman Filter States: What Do They Represent?

    It will sound a little bit stupid, but Ill ask anyways: I have two series systems, the second is an UKF (Uscented Kalman Filter). I was told to reduce the first system in order to that the UKF estimate less states. My question is: What exactly do the states represent? I mean, if I have a...
  24. OrangeYogi

    Optical Bandpass filter specification

    Hello, For optical bandpass filter specification, what do they mean by 0.1nm bandpass filter? What is the equivalent bandpass frequency range of the filter? Thank you.
  25. B

    Filter HCL with limelayers

    Dear Sir/Madam, Im in my final internship for my bachelor mechanical enginering. And i have to design the filter system of a cremation proces. The fluegas is filled with toxic concentrations. Such as mercury, PCDD/PCDF, HCL, NOx The mercury and dioxine i will filter using activated carbon ...
  26. BiGyElLoWhAt

    Optimization Problem with an RC BP filter

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  27. R

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  28. E

    How to graph amplitude vs. frequency for a Low-Pass Filter?

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  29. X

    Designing butterworth filter of Nth order

    I want to design a digital butterworth lowpass filter of nth order, with only freedom of choice to user being order of the filter and the cut off frequency, i already have a 1st order low pass. Code: T = 1/(2*pi*this.fc); this.A = -1/T; this.B = 1/T; this.C =...
  30. F

    Kalman filter and measurements

    Hello, I am using a Kalman filter with a PI controller. The goal is to control a mirror to stabilize the position of a laser spot: I am sending a disturbance on the mirror and the PI sends command to the same mirror so the spot stays fix. With a camera I am recording the image of the laser and...
  31. S

    Any sunlight band pass filter for 400-700nm of EM Spectrum?

    This 400-700nm slice is the Photosynthetically Active Radiation (PAR) required of plants and, for many applications, there is much unwanted UV and IR heat outside of it. Is there any known translucent material or film that will pass a high % of that 400-700nm wavelength from sunlight while also...
  32. E

    State prediction equation for Kalman filter

    I have to filter data with Kalman filter. I know process error covariance Q and measurment error covariance R. Problem is with state transition matrix A, control matrix B and observation matrix H. First of all, data goes through this transfer function: ##W(s) = \frac{4s}{4s+1}## I can't get it...
  33. mfb

    ArXiv crackpot filter developed by accident

    A very interesting blog post (from @hossi). A program that helps sorting arXiv submissions into categories frequently struggles with crackpot submissions - because they do not fit in anywhere. The program was never designed for it, but is helps finding them.
  34. R

    2nd order RC filter with two equal poles

    Is it possible to make a 2nd order CR LPF or HPF where the cut off frequencies for each pole are equal? Here is a calculator for this system which includes the transfer function.http://sim.okawa-denshi.jp/en/CRCRkeisan.htm I figured that I need to try to solve the denominator of the transfer...
  35. sophiecentaur

    B Moon Filter: how much to spend?

    Here's another question for you experts. I screwed in my new Baader Hyperion Zoom in a brief clear period and the Moon looked absolutely blistering. I am so pleased with this lens. It is so much better than the kit lenses that came with the scope. (Dobs 200p). 'Everyone' says that a Moon filter...
  36. MYMLA

    Filter Graphing Help - Calculate & Graph Response

    Homework Statement Calculate and graph the response of the filter: y(n) = ½*x(n) + ½*x(n-1) at the frequencies: i) 0 Hz, ii) sr/4, iii) sr/2 (Nyquist frequency). Homework EquationsThe Attempt at a Solution If I put each of those into the formula as n? But how do i know what sample rate/4...
  37. K

    Zero phase shift Op-Amp bandpass filter design

    Homework Statement "design a band pass circuit having a midband gain of 20 dB with -3 dB frequencies at 20 Hz and 20 KHz the amplifier should not produce any phase shift." does midband gain strictly apply to voltage gain (because that's how i look at it)? I was going to use a common collector...
  38. E

    Low pass filter (uniform/gauss distribution)

    Homework Statement [/B] I have got data x, which is formed like uniform distribution. After using discrete low pass filter I got output data u, which is Gauss distribution. What is explanation, why using that filter, we from uniform distribution can get Gauss distribution? Homework...
  39. R

    MATLAB Fix Filtering Frequencies Code in Matlab w/o Built-In Filters

    I want to write a Matlab code which removes all frequency components from a .wav sound file except those within ##±25 Hz## of ##523 Hz## as well as its harmonics (up to the Nyquist frequency). I want to do this without using any built in filters. Here is my code so far: [s, Fs] =...
  40. D

    Calculating the frequency response of filter with a matrix

    Homework Statement This is actually part 3 of the question. Part one was to form 7 equations to form a 7x7 matrix, part 2 was to solve it, which I've done. This question is to be done with Matlab, by the way. Part 3: Homework Equations Frequency response = Vout / Vin. The Attempt at a...
  41. F

    Gas pressures with (hypothetical) filter

    Imagine I have 2 constant-volume, constant-temperature containers. Container A has a volume of 10 L and one Container B has a volume of 5 L. My hypothetical gases Ideal Gas A and Ideal Gas B have the same properties as each other (temperature, mass, energy, heat capacity, blah blah blah). If I...
  42. K

    What could have caused an EMI Filter Bead shorted by itself?

    Hi, I am a Reliability Engineer. Currently, I am facing difficulties in finding the root cause to a defective EMI filter bead. Resistance measurements across the four leads (vertically, horizontally, diagonally) show that they are all shorted. However, a good ferrite bead should only be...
  43. F

    Engineering Understanding the Gain and Bode Plot of a Low Pass Filter Circuit with C1 > C2

    The question wants to know the gain of the this circuit, as well as a bode plot for the frequency response, and what type of filter this is when C1 is much greater than C2. Could someone double check my answers and assist in the bode plot? My attempt: For the Gain: If C1 is much greater...
  44. K

    Speed of Falling Objects Creating A Filter System

    I'm currently in High School and we have to create an idea to make the world better. Mine is to use the force of gravity and convert it to energy to power a system that will filter air. This is supposed to be used in developing countries where there are large amounts of biomass and harmful...
  45. S

    MATLAB Center Wavelength of Fiber Bragg Grating Filter

    I would like to locate the center wavelength of a FBG notch filter in MATLAB, but I'm having trouble getting an answer within 0.01nm of the correct wavelength. So far I've tried using a quadratic fit with MATLAB, but that is too dependent on the amount of data points to the left and right of...
  46. entropy1

    Does a polarisationfilter do a measurement?

    Consider a measurement of a photon after it has passed a polarisationfilter. Does the photon jump in a (polarisation-)eigenstate by passing the filter? Does the filter do a measurement? Is the filter part of the entire measurement?
  47. entropy1

    Probability of entangled photons passing filter independent?

    Consider two polarisation-entangled photons A and B fired at two polarisationfilters that are at a certain angle α. Are the probability that A is passing its filter and the probability that B is passing its filter indepedent probabilities? I am aware that is probably an incredibly stupid...
  48. I

    Help with my math in this 2nd order audio filter circuit

    I understand how to use the reactance equations (for capacitor, xc=1/(2PiFC), & for inductor xL=2PiFL when the filter circuit is of first order to get the component values I need, but I don't understand how the math works when the circuit is of second order. The man at the electronics store told...
  49. P

    Find how many times blood is filtered in the kidney?

    Homework Statement The blood that circulates in our body is about 1/12 of our mass. If the kidneys filter 7.5 liter of blood a hour, then how many times does it filter in the kidney the whole blood of a person will mass 60kg? Homework Equations 1/12*60=5 liter blood The Attempt at a Solution...
  50. P

    How many times is blood filtered in the kidney?

    The blood that circulates in our body is about 1/12 of our mass. If the kidneys filter 7.5 liter of blood a hour, then how many times does it filter in the kidney the whole blood of a person will mass 60kg? Here's what my teacher did: 1/12*60=5 liter blood 0.55*5=2.75 liter plasma of blood. The...
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