Questions tagged [lowpass-filter]

A low-pass filter is an electronic filter that passes low-frequency signals but attenuates signals with frequencies higher than the cutoff frequency.

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Analogue Filters (Picking the right filter!)

I'm new to Analogue and I'm trying to find the Ideal filter for the following specifications: $0.1\ \rm dB$ ripple Cutoff Frequency $F_c = 80\ \rm{kHz}$ An attenuation of $40\ \rm dB$ at the stop-...
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Converting a lowpass filter to a highpass filter. FIR filter-type 1

I was told that in the FIR filter type I, the impulse response of a highpass filter $h_H[n] $can be obtained as follows, $$h_H[n] = \delta[n − m] − h_L[n]$$ where $h_L[n]$ is the impulse response of a ...
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897 views

How to design a lowpass filter using Hamming window and sinc function

I have these three equations and have a noisy voice signal. I have to design a low pass filter of length N=1000 using hamming window technique. I have selected its cutoff frequecny 0.25 (normalized). \...
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Relationship between order of filter and amplitude/phase response

I am learning about digital filters, for example a lowpass butterworth filter. In many languages, the implmentation requires specification of the order of the filter, which I believe is the number ...
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Output of LTI (in time and frequency $\omega$ domain) : when input goes through LPF

I would like to raise a mathematical question : Let's say we are been given : $$x(t) = \begin{cases} \cos(\pi t) & |t| \leq 0.5 \\ 0 & \textrm{otherwise} ...
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FIR Filter 3dB Frequency

I am new to signal processing and I want to calculate the 3 dB - cut off frequency of this FIR filter, which has the following transfer function: For the evaluation i need to replace the z with and ...
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Is it possible to specify number of taps and cutoff frequency independently?

When specifying the properties of a moving average filter, is it possible to specify the number of taps and the cutoff frequency? My guess is no since taps (the number of samples in a moving average ...
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How to interpret frequency response of moving average system in discrete time signal processing?

Excerpt from Discrete Time Signal Processing by Alan Oppenheim: The text says this can be considered as an approximation of a Low Pass Filter. A low pass filter in continuous signal system is ...
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Using oversampling to increase resolution of a DC-signal as input

Currently I'm working on a project which uses oversampling to increase the resolution of a 12 bit ADC to a maximum of 16 bits. My goal is to fully understand the theory behind oversampling and why it ...
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What are the equations for magnitude plots of the common IIR filters? (Are the ones I have so far correct?)

I need equations that describe the magnitude plots of basic IIR filter types. I had looked into this a few years ago and saved some equations but it only covers part of what I need, and I can't recall ...
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What is the decay rate (time constant) of two One-Pole LPF's cascaded in series?

If you have a One-Pole LPF, and set the cutoff frequency to $\frac{1}{2πt}$ where $t$ is the time to $\frac{1}{e}$ amplitude, it will provide an exponential decay in response to a step function (eg. ...
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How can I lowpass filter by only reducing peak data?

I have a 2D image, which I want to lowpass filter, with these constraints / quality metrics: I can not "add" light to the image, so each pixel in the result should be <= the corresponding pixel in ...
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Is there an equation that will graph the shape or predict the maximum amplitude of a single sample impulse fed through a One-Pole LPF?

If you feed a single sample impulse of a given amplitude through a One-Pole LPF you get an envelope that looks like this: The output of the LPF from its peak will settle into an exponential decay ...
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Apply Low Pass (Smoothing) Filter on a Set of Matrices and Reject Outliers

Given a set of a $ 3 $ by $ 3 $ matrices $ {H}_{i} $. Each matrix is an Homography matrix. They are used to stabilize Video Stream. Yet some of them are outliers which creates "Jumps" in the "...
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filter design for ECG

I would like to ask how to design a digital filter to remove $50$ Hz interference on an ECG signal. Do I need to use notch filter? Thanks.
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How should a moving average handle missing data points?

I'm writing a program that averages the user's weight across different days. I'm planning to use a 5-point moving-average (current day, two before and two after). Sometimes, a data point is missing ...
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LPF and HPF filters in ENVI

Since we know about convolution filter in image processing, it is basically a matrix applied to an image and a mathematical operation comprised of integers and it works by determining the value of a ...
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Performance bounds for low-pass filters

Precisely how does the performance of an FIR filter depend on its design criteria? To illustrate, here is a specific question that probably does not have a convenient answer: The Parks-McClellan ...
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Manually creating a lowpass filter from the frequency domain: what phase?

In an attempt to gain a better understanding of DSP, I want to create a very simple (1D) lowpass, or I think more correctly "stop-band" or "band-reject" filter, to filter out a single frequency, e.g., ...
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Average identical sweeps or lowpass filter sweeps first?

There are 5-10 replicate sweeps of measurements that are meant to be averaged. I also typically lowpass filter the signal at 2000Hz. The target signals are in the 0-100Hz range, and have, for lack of ...
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343 views

Low-Pass Filtering of not evenly sampled signal

I have a signal sampled unevenly over 1 million ns. the signal is sampled over 1GHZ clock and the samples are as the following: 0-100 ns - sample every 1 ns. 100-1000 ns - sample every 10 ns. 1000-...
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Frequency conversion in IIR lowpass-to-lowpass transformation

We use $\ z^{-1} \xrightarrow{} \frac{z^{-1}-\alpha}{1-{\alpha}z^{-1}}$ and $ \alpha = \frac{\sin(\omega_c^{'}-\omega_c)/2}{\sin(\omega_c^{'}+\omega_c)/2}$ for a lowpass-to-lowpass frequency ...
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Downsampling after a highpass filter

Question: The following sentence is not clear to me (especially why down-shift occurs). Could someone explain it please? On the other hand, downsampling the output of the highpass filter down-shifts ...
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Difference between the average operation and the application of the equivalent LPF

I would be glad if someone could answer my question. I have a bit stream of data and I want to extract the low frequency component. When post processing the data I can calculate the average value over ...
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Side Lobes in the Magnitude Response of a Low Pass FIR Filter

I have the impulse response (from the filter coefficients) of an FIR filter obtained from MATLAB's "interp" function using the command: [y, b] = interp(x, 5); % where b contains the interpolation ...
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548 views

Discrete algorithm for low pass filter

I am working on a position controller for a marine vessel. I have a measurement signal containing the y-position of the vessel that consists of both low frequency (<.1 rad/s) and high frequency (&...
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413 views

python rewrite lfilter (iir) with for

It's a beginner question, but useful to users from python - signal.lfilter, I was using lfilter from Find reverse one pole ...
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Correct signal analysis flow (Wind Turbine vibration)?

I have vibration data from WT (gearbox) sampled at 25.6 kHz. From a previous post I received a lot of good recommendation. What I am trying to do: Find early stage bearing faults by using an ...
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Derivation of the lowpass to bandpass transformation

I have a basic question. The "well known" lowpass to bandpass transformation is $$ s \longmapsto \frac{\bar{s}^2 + \omega_1\omega_2}{\bar{s}(\omega_1 - \omega_2)}, $$ which gives a bandpass ...
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interpreting the post filter features in a sensor data

I am new to signal processing and I am working on Filtring signals(using basic analog filters, FIR filters, and IRR filters), for Human activity recognition, using sensor data, I Extract the features ...
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153 views

What impact have different types of border-handling on high pass or low pass filtering?

When high or low pass filters are being applied to an (grayscale) image, the borders need to be handled separately. They could be filled with 0's or 255's (b/w), repeat the nearest pixel value, or ...
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AM Modulator Demodulator in Python

I am trying to make a AM modem using Python Numpy and Matplotlib. I am successful in generating the AM Signal but I cannot demodulate it using a lowpass filter function that I made. The demodulation ...
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Low-pass filters not producing smooth output

I'm relatively new to this material, so apologies in advance if I'm missing something obvious. I'm trying to smooth some very noisy signals. What I observe is that if I apply an ewma, even with a ...
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114 views

Calculate input impedance from S-parameters

I wrote this simple matlab code to calculate input impedance of a low pass filter but not sure whether all the steps are correct. * First attempt ...
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How to produce a high-pass filter from a low-pass one?

I already have a low-pass filter and want to remove the DC offset of a signal with a high-pass one. I guess you can subtract a low-pass filtered signal from the original signal and the result is a ...
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Difference Between Equiripple & Least Squares Design for FIR Digital Filters

For an efficient and optimized digital FIR filter design, there are two methods available broadly, Equiripple filter design & Least Squares filter design. A general method for designing a filter ...
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Interpolated FIR filter

I am confused about this Q&A : Interpolation by factor of 2 If my input signal $$ x[n]= x0,x1,x2,x3 $$ then according to the threads explaination my $v[n]$ will be $$ v[n]=x0,0,x1,0,x2,0,x3,0 ...
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Low pass fir filter with non-unity gain

In my filter specs, the passband gain is given as 6.02db. How do I achieve this? Usually all texts give the passband gain as 0db (as well as passband ripples if any).
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How to test the FIR filter in C++?

I am almost done with design and implementation of my first FIR filter using C++. Its a Sinc-Windowed FIR filter designed for a cut off frequency of 100 Hz with sampling rate of 500, with a filter ...
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815 views

Low-pass filter with varying cut-off frequency over time

Is there a novel way to create a low-pass filter (Finite Impulse Response Filter) with varying cut off frequency over time? For example, I have a white noise that is 10 seconds long sampled at 44.1 ...
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Cutoff frequency of a first order recursive filter

I've implemented a very simple first order recursive low pass filter in c using the algorithm: ...
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How to determine the type of a digital filter given its expression?

I'm trying to understand a variant of the filter presented in http://www.stockspotter.com/files/PredictiveIndicators.pdf in the "Code Listing 1.". Its expression is given as follow: $$y_n = ...
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Weird ringing at signal start and end for default Matlab lowpass filter

**FIND UPDATES BELOW THE ORIGINAL QUESTION TEXT: I am trying to lowpass filter electrophysiological data and I see ringing near sharp transients at signal start and end. Ringing at start: Ringing at ...
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Matlab Filter designer not working, how come?

Before reading any further, to give you on some insight on the output level of the oscilloscope picture's the ~340mV green signal is normal. If you know me I posted a question as to why its 340mV but ...
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How to simulate a signal of a particular frequency according to the number of points in a period of the signal?

I have one period data ($n$ points in total) of a signal. I want to generate a periodic signal with a total of $m$ points and corresponding signal frequency of $F$ according to this data. How do I do ...
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Mitigate floating-point numerical errors for very-low corner frequency low-pass filter with DSP

I'm designing a low-pass filter for a digital signal processing application that ideally just passes a very small bandwidth above DC. I'm using an IIR biquad filter for this, where the coefficients ...
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613 views

windowed sinc filter in matlab

Hello i'm designing a low pass filter windowed sinc in matlab ...
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How to draw the magnitude plot of a variable slope low/high pass shelving filter? (eg. as a function of cascaded shelving filters)

I am interested in making a magnitude graph of a variable slope low/high pass filter. I would like to set slope in dB/oct and a cutoff pitch. The y-axis should be amplitude from 0 to 1, and the x-axis ...
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Output of IIR filter not matching the frequency response - Proximity to fs/4

After not having dealt with digital filters for a long time, I have now been playing around with filter design in octave and I am observing a behavior which I do not understand. After designing a low-...
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Design of a low pass filter with Red Pitaya's FPGA

I'm trying to design a low pass filter in Verilog for use on a Red Pitaya's FPGA (Xilinx® Zynq®-7010). All I'm trying to get the low pass filter to do is to obtain the DC component in the signal. The ...

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