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. elou

    B How to build a simple polarization filter

    For that we will need a laser pen and two square pieces of opaque, non reflecting material. In both these squares a slit will be cut, wide enough to let a beam of the laser pass through without any refraction effects. First, after the laser has been turned on, one of the squares is placed in...
  2. P

    Finding R and C values for an active second-order bandpass filter

    I have been assigned the task to design an active bandpass filter with a passband of 0.1 to 10 Hz. At these two frequencies, there should be an attenuation of -6dB or more. So far I have selected my circuit layout which can be seen below I found my transfer function so that I could calculate...
  3. kolleamm

    Could we filter out diseases with a process similar to dialysis?

    I was wondering if it would be possible to remove diseases such as cancer from the blood with a mechanical device similar to the one used for dialysis. When the blood passes through the device certain cells would bind to the walls that have just the right binding sites so that they get stuck...
  4. A

    Engineering Is it possible for a low pass filter to have such a transfer function?

    Hello! Consider this filter,and that I have to find the transfer function U2/U1 with the norm Ω= ωRC (also double fractions are not allowed) Now I can see that that the resistor and capacitor left as well as right are parallel to each other. So simplifying that ## Z_1 = \frac{R}{jωRC +1}...
  5. PhysicsTest

    Can LCL Filter Convert AC to DC for Half Bridge Section?

    I am trying to simulate the active converter, I have seen in you tube video the output of the grid 3 phase voltage is given to LCL filter, the output of the LCL filter is then given to the half bridge section. I assume that the output of the LCL filter is a DC instead of the sine wave, as it is...
  6. mohamed_a

    I Polarizing filter synthesis and dynamics

    I have found a fair amount of sources for studying polarized light but I haven't found sources discussing synthesis of polarizers in detail along with mechanistic discussion.
  7. S

    Some coffees clog the coffee filter -- Why or how?

    The summary describes the situation. Most coffee ground beans let the hot water go through the filter paper more or less slowly maybe taking a few minutes to brew a serving of coffee through the coffee filter paper. Some other beans, usually of African origin, take much longer to brew. The...
  8. T

    Is it possible to run a pond filter using a solar panel?

    Hey is it possible to run a normal pond filter of a solar panel my pond is placed at the top of my garden and there's lots of sun around the pond i already have solar panel water fountain in there running with solar lighting to. The pond is to far away from the house to run cables down and I am...
  9. ARoyC

    High Pass Filter Working Principle

    A few days ago, I learned to make an AC to DC converter. One question is troubling my mind. How does a High Pass Filter Capacitor work? Going through some websites I got a sketchy idea. As the current after passing through the bridge rectifier comes to capacitor, the capacitor starts charging...
  10. The Bill

    Why/how does filter paper block/trap coffee oils?

    What mechanism or mechanisms cause filter paper to block coffee oils? As I understand it, these "oils" are mostly cafestol and kahweol, which are both functionalized polycyclic molecules with a molar mass around 315. Cloth filters do not prevent these oils from getting into the brewed coffee...
  11. B

    Finding the output V of a filter

    Hi everyone, I've been having trouble on how to answer this question This is my attempt at it below, but I am not sure what values of t to sub in for evaluating the integral. Any help would be appreciated! Thanks
  12. R

    Design a linear phase low pass filter

    Design a linear phase low pass filter whose specification is:1) Maximum tolerance in the passband equal to 0.01% (linear) in the passband;2) Cutoff frequency at ω_c = 0.3π and transition band at 0.05π;3) Minimum reduction of the 0.95 rejection band.
  13. Paige_Turner

    B Need to Check GR Beliefs? Integrity Filter Here!

    Being mistaken gives me the creeps because, to the extent that truth matters, it's my only tool, shield, and weapon. So I'm always looking over my shoulder, worrying that I might believe something that's not true. Are any of these NOT true? The spacetime interval is "absolute distance,"...
  14. J

    Engineering Calculating the DC value of the output voltage for a full wave rectifier

    I need help with part (a)... I know that the root-mean-square voltage is the dc-equivalent voltage for an AC waveform and what my book labels "##V_{dc}## is actually the average voltage. Hence I am assuming the question is asking me to find ##V_{rms}## ... Is my assumption that the...
  15. M

    Engineering Image Processing: what is the correct form of the Laplacian Filter

    Hi, I just have a quick question regarding image processing. What is the correct form of the Laplacian for image processing? I have seen different versions online and don't understand which one is meant to be the conventional one. I know that: \nabla^2 f(x, y) = \frac{\partial^2 f}{\partial...
  16. brainbaby

    LT spice result analysis, Capacitance Multiplier vs RC filter circuit

    Hi friends, I have simulated two circuits, one is an RC filter and other is a Capacitance multiplier. My aim of experiment is to validate a decrease in Iout (load current) of CM circuit as compared to load current in RC filter circuit. Theoretically, Iout (CM circuit) < Iout (RC filter) Vp-p...
  17. MisterH

    A Fitness function for window length of filter

    Fitness function for window length of filter On a sinusoidal signal with amplitude 1, and period P, an exponential moving average (EMA) (with alpha = 1/n), and a linear weighted moving average (LWMA) (with window length n) are calculated; when you subtract the EMA from the LWMA, it can be seen...
  18. snatchingthepi

    Engineering Bandwidth Filtering: Get Help Solving Last Problem

    Hi everyone I am finishing the last problem for a DSP problem set and just frankly have no idea where to start this one. I'm thinking I could compute the magnitude of each filter and then compare, but again am not sure. Can anyone point me in the right direction? Thanks
  19. I

    Engineering Bandpass filter Maths help please

    Hello ,am posting this thread because i need help with 1Q , i was told by my tutor to measure Vo and Vi over the range of frequencies 1khz to 100khz , but i have no idea how to do that ,am not very good at maths and that's why i been really struggling to do it , i have tried doing it but am 100%...
  20. M

    Two-port network: transformation of low-pass to band-stop filter

    Hi, Context: I was looking through some circuits material in the topic of filter synthesis for two port networks. For simplicity, these networks have been synthesized for normalized conditions: 1 rad/s cut-off frequency and a termination resistor of 1 ## \Omega ##. An example filter is shown...
  21. A

    I How can one see the noise in the Fourier Domain (Nyquist Frequency)?

    Say we have a transform of a line profile that extends out to the Nyquist frequency such that you cannot see the noise level, what could you change in your spectrograph arrangement that would allow you to see the noise level in the Fourier domain? My thought is that we can apply a filter, P(s)...
  22. Ntip

    How Do I Design an EMI Filter for a Converter with Only Voltage and Power Specs?

    I am starting the input filter design for a converter and only have the voltage and power specs. It will be the input filter to other converters on a parallel bus, so I could look at the datasheets for those and get some specs there. I do not have any information from the input converter to this...
  23. M

    Engineering Extended Kalman Filter Jacobians

    Hi, I have a question about calculating the Jacobian matrices for the Extended Kalman filter. Question: If we have a system of the form: \begin{align*} x_{k+1} =f_k (x_k , u_k) + w_k \\ y_k = h_k (x_k , u_k ) +v_k \end{align*} where the state x_k comprises of the three variables p_1 ...
  24. M

    Engineering Filter Linear Phase Property for non-integer time delays

    Hi, I just have a quick question regarding the linear phase property of filters. It might be easier to provide some context before getting to the question, but feel free to skip to the bottom. Consider a system input as a discrete sequence obtained by sampling at t = 0, T, . . . , kT from an...
  25. M

    Engineering Recursive implementation of an FIR Filter

    Hi, I have a question related to filter structures. Question: An FIR filter can also be implemented using a recursive structure. Can you find such an example? I don't really know how to proceed here. Method: FIR filter is a 'finite impulse response', which means that the response doesn't last...
  26. mfb

    The Significance Filter: How selective publishing biases results

    On arXiv: The Significance Filter, the Winner's Curse and the Need to Shrink It's well known that it is difficult to publish null results in various fields. The authors try to quantify that by analyzing over a million z-scores from Medline, a database for medical publications. A very striking...
  27. K

    Comp Sci Kalman filter in one dimension to track a moving object

    Below is the whole code. I can't change the whole code, I can only change the "Kalman class". The Kalman class in the code below is my attempt to solve the problem. But the code doesn't work well. I have written these 5 equations in the Kalman-filter algorithm: State Extrapolation Equation...
  28. T

    I IRAS Filter Profile: Computing ##\lambda_{mean}##

    I am looking at the following IRAS filter profile IRAS Filter Profile and I am wondering how they computed ##\lambda_{mean}##? They provided the following equation below but what is ##T(\lambda)## and ##\lambda##?
  29. T

    Apparatus for a polarization filter rotator dial

    Wondering where I can purchase the polarization filter rotator dial equipment? I tried searching online and couldn't find it. I will like to rotate the polarization filter sheets and measure the angle of the rotation but I can't find that equipment online. I have attached the image below:
  30. R

    Ladder-like bandpass filter theoretical analysis problem

    I consider the band-pass filter of the following configuration (the ##u_m## is a voltage controlled voltage source): The transfer function is $$K_1(p)=\hat{U}_o(p) = \frac{p}{RC(p+1/RC)^2} = \frac{\omega_c p}{(p+\omega_c)^2}, \quad \omega_c=\frac{1}{RC}.\qquad (1)$$ Now I connect ##n## such...
  31. N

    Air Filter Sizing: Calculate Required Surface Area

    I have two filter materials and I have manufacturer-supplied pressure drops across the filters at given flow rates. I know the desired flow rate and the negative pressure "sucking" on the downstream side of the filter, and I want to calculate the required filter surface area for each filter...
  32. S

    Medical Effect of Melt-Blown (MB) filter fibers of facial masks on lung tissues

    I came up with a curiosity whether having a facial mask on face to breathe can actually be safe to lungs in the following aspect. I remember when I was young, Asbestos was so popularly used in construction. and now, people wear Hazmat suits to remove any remaining Asbestos since it is...
  33. F

    Line filter, proper LTspice simulation

    Dear forumers, I have two high performance AC feedthrough capacitors (47nF, 100A, class Y2, DC-60Hz) which I want to either combine with a general purpose EMC line filter, or build a custom one to filter the mains from of about 100khz to as high as possible (for shielding purposes). I can see...
  34. N

    I Selective filter based on angle of incidence?

    I am a using a mirror to reflect an image at an angle of incidence of 10 degrees. The mirror is also at an angle of incidence of approximately 30 degrees from the viewer and it creates undesired reflections when looking at the mirror. Here is a diagram illustrating the situation. I am looking...
  35. DaveC426913

    Gas filter mask on Mars - sci fi

    In the early parts of the books, Mars' ambient atmo pressure (and temperature) was increased, including not just CO2, but oxygen as well. It rose to the point where they only needed masks that let through oxygen but not CO2. In my amateur view, I would expect that this would not work very...
  36. sophiecentaur

    B Learning to use a Solar Scope with an H alpha filter

    I just bought a Coronado and, typically, there are no sunspots to look at. If there were, then I could compare what I see in that dim dark red image with what my basic Baader shiny filter delivers. I understand that there's a learning process involved and I imagine all first-time users have had...
  37. Remedyworld

    Stargazing DIY Hydrogen Alpha Solar Filter

    I'm interested in doing more detailed photos of the Sun using my solar filter and a 1.25" Hydrogen Alpha (Ha) filter. Is this possible to do or is it best to purchase a Coronado telescope?
  38. D

    Confusion on: High Pass Filter at Op Amp Input

    Hello, I am simulating the input impedance of a high-pass filter with the output voltage of the filter input to the non-inverting pin of an op amp. I'm confused as to why the input impedance can possibly dip below the resistance of the high-pass filter resistor. Please see the following circuit...
  39. Arman777

    Comp Sci Low Pass Filter, plotting a graph

    I wrote this code, but I am not sure its ture or not from numpy import arange from math import floor from pylab import plot, show Vout = 0 #inital condition t_i = 0 #initial time t_f = 10 #final time N = 100000 h = (t_f - t_i) / N RC_values = [0.01, 0.1, 1] def f(Vout, t): if floor(2 *...
  40. qnach

    The history of the home water filter

    Now home water filter is ubiquitous using almost every family. I am wondering who designed such systems (and become its standard form used today) ? I think after second world war the New York water is pretty dirty hence the development of such filter. But I am not sure whether it is correct or not.
  41. paulmdrdo

    Engineering Finding the center frequency and bandwidth of a Pass-band filter

    I tried solving this problem and got it correctly until the part A of the question. My solution is the same as the one given in the solutions manual until the part I put in the red box. I don't understand what is the logic behind the calculation of the bandwidth and center frequency there...
  42. C

    A How does a polarising filter work?

    Being an old school Newtonian engineering type, I have a model of a polarising filter that generally works for day to day stuff like taking photos, explaining sun glasses etc.. But it is clearly wrong. Given that opening remark, the 'A' index, and the forum subject area, I trust you will...
  43. X

    Computing AC voltage in a complex filter

    Problem Statement: Computing AC voltage Relevant Equations: cut off frequency, ac voltage. Hey guys, Amazing to be in this group ! Please find attached the diagram of the problem. E = 10kV at 60Hz, C1 = 60pF and R1 = 1k. I have to compute the ac voltage in reference to ground at point [1]...
  44. D

    I What optical filter to use for Raman spectroscopy?

    Raman spectroscopy involves Illuminating a target with a laser Beam. This produces Raleigh scattering. Does The releigh scattering have the same frequency as the laser beam? So use an optical filter to block the same frequency as the laser?
  45. Spinnor

    Plumbing Stainless steel house water filter, leaks past o-ring

    Bought a stainless steel whole house water filter for a very good price ($100), turns out too good. On inspection I suspected it would leak so rather then installing it into the house water system I pressure tested it. There was a small leak that stopped after a minute or so. Relieve the...
  46. Andy Resnick

    New Optics Toy: A 'Varicolor' filter

    Spike Walker, whom I semi-regularly consult with about my Ultraphot III, recently told me about a really cool optical device: a 'Varicolor' filter, manufactured (and discontinued) by Cokin. I found one for $10 on eBay, received it yesterday, and I can't put it down. Here's a set of images of...
  47. J

    Water pressure question involving pipe, flexible hose and a filter

    Summary: water pressure issues what happens when you take water from a 3/4 inch pipe copper to 1/2 inch flexible braided hose through a filter for a 3/4 pipe back through a flexible braided hose 1/2 inch tube to 3/4 inch copper pipe?
  48. theycallmevirgo

    Analog (mechanical) pressure gauge for a single cylinder filter

    https://www.flairespresso.com/product-page/flair-signature made a manual espresso machine and specify using 30 lb of pressure in the manual. In order to determine the correct pressure, they literally tell the user to push down on a kitchen scale. I'm considering a competing product, and that...