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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1answer
44 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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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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1answer
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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1answer
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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1answer
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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16 views
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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27 views
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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1answer
137 views
windowed sinc filter in matlab
Hello i'm designing a low pass filter windowed sinc in matlab
...
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1answer
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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34 views
First Order Butterworth filter has low frequency noise and only cuts off about 13db/decade
I designed a low pass Butterworth filter like so
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How to filter out noise in high frequency signal?
I am trying to filter this signal (download-zip):
...
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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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2answers
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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1answer
71 views
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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3answers
10k views
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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3answers
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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1answer
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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60 views
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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2answers
69 views
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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1answer
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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38 views
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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1answer
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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3answers
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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1answer
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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1answer
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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2answers
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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3answers
621 views
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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3answers
24k views
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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81 views
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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1answer
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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2answers
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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2answers
4k views
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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0answers
57 views
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 ...
