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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Extra frequencies after applying low pass filter

I used Python/scipy to create an input data (sinewave with frequencies {600,1200,1800,2400,...,9000}) and sampling at 10000Hz. A lowpass filter is created using butter(10, 4000/(10000/2), 10000, btype=...
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Is there a way to get output in second order sections (SOS) format from Scipy's signal.firwin

I am using Scipy's signal.firwin to implement a lowpass filter. Using the rule of thumb formula(s) to estimate the order of the filter, I am getting a very high number. I looked into this question, ...
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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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177 views

Transform a Continuous Time Differential Equation of a Low Pass Filter to Discrete Time

Assuming I have a linear differential equation of first order low pass filter: $$RC*y(t)'+y(t) = x(t) $$ And Assuming i know now that the input x(t) is being sampled at a rate of $T_s$ how can now ...
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252 views

How to Get Rid of Ripples from a Gradient Image of a Smoothed Image?

I have a gray scale UINT8 image. When I smooth it with a Gaussian filter and then compute the gradient image with a Sobel filter in OpenCV, ripples would appear. ...
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295 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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55 views

Low pass filter output showing instability

I am fairly new to DSP, and I'm trying to implement the Pan Tompkins algorithm for QRS detection of ECG signals in MATLAB. The first stage of the algorithm consists of a second-order low-pass filter. ...
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86 views

Use recursive least square as an “actual” filter?

I am currently studying recursive least square (RLS) and as far as I understand, the setup is (for example) that we are given a process with uncertain parameters/noise and we want to adapt parameters ...
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51 views

Where should I set my anti-aliasing filter corner frequency for this signal?

I have a Fourier transform of an arbitrary digital signal. The transform has For 1024 frequency bins. The magnitude plot of the first 100 is below, with no surprises in the unplotted 924 bins. Now, ...
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Slew Rate Filter With Different Smoothing Factors in Each Direction

I'm smoothing the output of an ADC with a simple first order low pass filter. Of course the smoothing rate is the same whether the signal is rising or falling. Preferably the smoothing rate needs to ...
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2-D low pass filter

I have an ultrasound signal that is 1536x128. I first downsample the signal by a factor of 2x2 in x and t, then I upsample the missing data with zeros, then I do an fft, fftshift, then another fft to ...
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Shading Correction Using Lowpass Filtering

I was taking the course on DIP. The teacher uses Digital Image Processing by Rafael C. Gonzalez and Richard E. Woods as textbook. In the part about lowpass filter, there's this example. We found that ...
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137 views

windowed sinc filter in matlab

Hello i'm designing a low pass filter windowed sinc in matlab ...
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32 views

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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Does separation of variables of a transfer function followed by a z-domain transform work?

I tried taking a low pass filter transfer function in the form $A/(s^2+Bs+C)$ and separating it into multiple fractions over each root $(D/(s+r1))+(E/(s+r2))$. Then I substituted $s =((2/T)*((z-1)/(z+...
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209 views

Filtering on time or frequency domain?

I'm applying an ideal filter on the frequency domain. My code below: ...
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75 views

IIR Direct FormII Filter second order in VHDL, false output

I am trying to implement an IIR second order in Direct FormII in VHDL. To make it easier to understand for me and to avoid former timing issues, I implemented the operations sequentially. In my ...
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LP to BP transformation steps

Considering the following problem, What i know to convert from LP signal to BP signal is to: Draw the FD of the LP equation From it I can draw the FD for BP From this graph I can deduce the equation ...
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First order low pass filter

I am trying to better understand the first-order low pass filter: Summary: Per wikipedia, a first order low pass filter yields the following in discrete time: $$ \frac{Y(s)}{U(s)}= \frac{\omega_{c}}...
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195 views

Low-Pass Filtering on Small Chunks of Audio

I've got a script (Python) that chops 44.1 kHz realtime audio into 10 ms chunks, processes each chunk, and stitches the chunks back together with no added artifacts. I'm trying to create a low-pass ...
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How to design a filter with smoothness regularisation?

I am rather new to the DSP topic. However, I would like to filter a signal with lowest error and highest smoothness. Until now, I was using tikhonov regularisation inside batch regression with some ...
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59 views

Stability of the Low pass filter after Spectral Transformation

Using a spectral transformation a filter $G(z^{cap})$ is designed to be a low pass filter from an existing lowpass filter $G_{lp}(z)$ via $G(z^{cap}) = G(z)z=H(z^{cap})$ . Which property should H(z) ...
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Can Kaiser's formula be used to estimate the filter length of an FIR filter for all windowing methods?

I came across this problem while designing a FIR filter for given $\omega_p = 0.4\pi$ and $\omega_s = 0.6\pi$ along with the minimum stop-band attenuation $\delta_s$. I have worked out some examples ...
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How Butterworth low-pass filter can be applied on a digital signal (i.e. discrete representation of a signal)?

I would like to know how to apply a low pass filter (Butterworth) to a digital signal. So, I have some values of the signal, let's say $S(t)$. Those values are equally spaced in time. I have read the ...
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Understanding audio downsampling code (JavaScript) and adapting to a different ratio

I inherited responsibility for some audio downsampling code that I don't fully understand: ...
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25 views

Closed loop detection system

I am trying to design a detector of the DC component of a signal (low pass filter). I found the following topology (called Closed Loop Detection System) in an article (https://ieeexplore.ieee.org/...
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69 views

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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35 views

Design of low pass filter

I'm designing a low pass filter to identify the DC content of a signal. The most important aspects of my application are the accuracy and the speed of the identification. I would like to know if the ...
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1answer
99 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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43 views

Why does sampling frequency affect the filter results?

I have a big issue, basically my goal is to create a low-pass butterworth filter around 0-35Hz with a sampling frequency of 5000Hz. My Matlab code is ...
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497 views

Consider an ideal low pass filter $H(\omega)$, and the input to this filter is the periodic square wave $x(t)$. Find the output $y(t)$

The solution to the problem is $$y(t) = 5 + \frac{20}{\pi} \sin(\pi t) + \frac{20}{3\pi} \sin(3 \pi t) $$ and to get that the solution says to find the Fourier series expansion of $x(t)$ and I am ...
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Unable to low pass filter the signal

I am trying to use a basic example of a low pass filter as shown in the example: https://de.mathworks.com/help/signal/ref/lowpass.html However, I change the frequency: ...
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92 views

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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69 views

Polyphase resampling delay

I want to implement polyphase resampling. For this, I wrote a script in matlab. The script performs the following sequence of actions: ...
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115 views

Reverse engineering a digital filter

I have 2 simultaneous signals that both are designed to measure eye movements. They are sampled at 250 Hz. We have 12 subject recordings. For 3 stable periods in each subject, we choose 256 points and ...
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609 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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382 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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97 views

Old style signal processing?

I am wondering if "an array of overlapping band-pass filters" it is 'mostly' equivalent to a Short-Time Fourier transform. See this (figure down), where $s(t)$ is the signal; LPF a second-order low-...
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What is the name of this digital low pass filter?

I found this digital filter in code I am working on. It is a low pass filter. In the code it is called an "alpha filter", but it is not the same as the alpha filter mentioned here. I post the ...
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Apply Low pass Butterworth filter in Python

I want to use a low pass Butterworth filter on my data but on applying the filter I don't get the intended signal. Here is the dummy code: Signal A: ...
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1answer
60 views

analog-to-discrete-to-analog system sampling problem

This is not a homework problem, I am solving practice problems for my exam. Consider the analog-to-discrete-to-analog system shown in figure 1. The CT signal $x_a(t)$ is sampled at a frequency of $...
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low-pass filter and the sharp cut-off filter

are the low-pass filter and the sharp cut-off filter the same thing?? Here there is the definition of sharp cut-off filter https://en.wikipedia.org/wiki/Filter_(large_eddy_simulation) . I tried to ...
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53 views

Low-Pass FIR that keeps all values positive

Let's say, that I want to low-pass the norm (hence positive values) of an analytic signal (related to Hilbert transform). This allows me to perform experiments with the envelope of audio. For low-...
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1answer
29 views

Filtered signal does not follow my cut off frequency

I filtered my signal with low pass filter butterworth forth order with cutoff frequency of 50 hz. However when I compare the filtered signal with original one in frequency domain, it seems that the ...
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81 views

Quadrature demodulator. Relationship of sampling rate and error

Task: to estimate the frequency of the power grid signal. I use a quadrature demodulator. I get the I / Q components. I calculate the angle (phi = atan(Q / I)). I differentiate the angle and get the ...
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10k views

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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How to Actually Use FFT to Implement Low Pass Filter

have searched high and low for a practical guide to implement a simple 50Hz low pass filter on a signal.I understand the theory but its the practical but that's missing. If I was using MATLAB it would ...
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What Techniques Are Used for Signal / Image Denoising (Example Image Provided)?

I have an image that looks like this (it might appear low res in a browser because it is 16 MB). This image was taken with a scanning electron microscope, but because the equipment is outdated there ...