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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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84 views

Optimizing Two Parallel IIR Filter Sweeps

Got an audio related question here; So I have two IIR low pass filters that work in parallel to do a filter sweep. Basically: ...
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Beginner's question on LPF, Need for Sinc and windowing [duplicate]

As a student who has never constructed any real world DSP application, I am inclined to ask the following. Convolution in time domain is multiplication in frequency domain. For low pass filtering, ...
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2k views

Cancel Drift after numerical integration

I am trying to integrate angular acceleration obtained from a set of accelerometers positioned specifically at opposite corners of a cube, based on the paper EcoIMU: A Dual Triaxial-Accelerometer ...
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1answer
453 views

Kalman filter after lowpass filter: bad idea?

I am new to Kalman filter and am enjoying playing with it. However, I generated some random velocities and acceleration and Kalman filter (with the covariance matrices I have chosen) is comparable ...
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1answer
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Interpolation filter gain

If somebody could clarify why everywhere is written that the interpolation filter should have gain $L$ where $L$ is upsampling factor. What this gain actually means? Does it compensates for the ...
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1answer
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Does lowpass filtering and decimating improve SNR?

I did not manage to find clear answers to this question: does decimation after an appropriate lowpass filter improve the signal to noise ratio? To investigate this question, I considered data ...
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1answer
250 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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400 views

Sampling the impulse response

Given two IIR filters (one Low-Pass and one High-Pass) designed using Butterworth, how can I know if they can be obtained using sampling the impulse response?
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1answer
260 views

Making a low pass filter for irregular samples

We are interested in reconstructing the red channel of a scene. The red channel is slowly varying. Unfortunately the camera does not have a Bayer sensor, and the red samples are irregularly spaced ...
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1answer
153 views

Output of lowpass filter with damped sine wave input

The random process $$Y(t)=\cos(\omega_0t)\cos(\omega_0t+\pi N(t))$$where $N(t)$ is a Poisson process of parameter $\lambda$ enters a lowpass filter with transfer function $$H(j\omega) = \left\{ \...
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1answer
754 views

Low-pass elliptic filter design: equation for calculating required minimum order

In this paper on page 4 (or in slide page, 23), it describes the equation for calculating the minimum required order for elliptic filter for design specification. However, it says it is only the ...
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Bandwidth of lowpass filter?

This article here on the Window method for FIR filter design speaks of the total normalized bandwidth of the lowpass filter in $\textrm{Hz}$ (counting both negative and positive frequencies) What ...
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Can you turn a square wave into a sine wave using a low pass filter?

And if it could, would it make the sound of the square wave thinner than before because of losing its harmonics?
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674 views

Fast Integer 8 Hz 2nd Order LP for Microcontroller

I need an 8 Hz 2nd order LP filter. It does not have to be terribly accurate but it should be 2nd order-ish. Performance is much more important. My sample rate at the moment is ~9.5 kHz. The filter ...
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1answer
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How can I construct a Band-pass filter from a low and a high-pass filter?

Suppose, I need to construct a Band-pass filter in OpenCV. But, I know, there are no functions in OpenCV for Band-pass filters. Now, what I need to do is to have a low-pass filter and a high-pass ...
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453 views

Upsampling with FIR filter causing discontinuity at start of new buffer [closed]

I have implemented an oversampling algorithm for an audio signal in C++ which is producing a distortion of the signal at the start of a buffer. The algorithm is wrapped in a class with methods for up ...
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2answers
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Transfer function of second order notch filter

Can anyone mention the transfer function of second order notch filter to remove the line frequency of 50 Hz, in terms of frequency and sampling rate. Just like for Low pass Butterworth filter as, $$ ...
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1answer
648 views

Filtering/Analyzing Complex Data stream

I receive complex I and Q data from an USRP. I want to do a Hamming window LP filter on the data. However, I don't get the grasp of how I use the complex data. It is unusual because most of the time ...
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1answer
185 views

2D Digital Signal Processing - Applying High Pass on and Image

I have been doing my research on 2D digital signal processing. What I am doing is about noise removal of digital image: Type of noise that I want to remove from an images is like the Gaussian noise ...
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Translating Bessel filter from python to C - odd behavior past the cutoff frequency

I recently translated the code from scipy.signal.bessel to C in order to implement a bessel filter in a piece of analysis ...
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2answers
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Formula for Bessel low-pass filter coefficients

When I am filtering a signal in python, it has a built in function to generate bessel filter coefficients given a cutoff ratio and a filter order (number of poles). I am trying to translate this to C ...
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558 views

Continuous low-pass filter (LPF) on a periodic signal

I have a continuous-time signal $x(t)$ that has the following properties: It is periodic, with a periodicity of 1 (sec). It has no discontinuities or infinite values at any time. I want to come up ...
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764 views

Slope of 2nd order low pass vs band pass Butterworth filters

I have noticed that some manufacturers of audio processing products label a 2nd order Butterworth low pass as having a slope of 12dB per octave, but then also label a 2nd order Butterworth band pass ...
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When input data into a low pass filter, are the first several data unusable?

For example, I want to feed a DC into a low pass filter. The the filter's first several output will not have the same DC value I want. Does it mean that I need to dispose first several results? How ...
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extending windowing function to higher dimensions

I was looking at this particular thread that discusses extending windowing functions for singling function to higher dimension. There is one bit in the accepted answer that I could not get my head ...
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graph of lowpass filter

Check the equation 4.8-1 $H(u,v)=1$ if $D(u,v)\le D_0$ my question is the high frequency is at center. $D(u,v)$ is smaller if it is close to center. why $H(u,v)=1$ in that case. Thanks
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Which method to choose to get linear phase response zero group delay low-pass filter?

Background: I do time-dependent simulations of physical systems. Like this: http://journals.aps.org/prb/abstract/10.1103/PhysRevB.91.115431 During the simulation, observables are recorded and later ...
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1answer
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Short lowpass filter that also extrapolates lines

I'm looking for a short lowpass filter that also extrapolates lines, [0 1 2 3] --> 4, so I need (correct me) $H([\ 0\ \ 0.25\ \ 0.5\ ]) \approx [ 1\ \ 2\ \ 0 ]$ . How close can one get to this with 2 ...
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MATLAB fvtool: Setting the passband ripple below 0dB for a FIR Filter

I'm new to using filter tools in MATLAB and I'm having a bit of difficulty. I'm designing a lowpass FIR filter and I'm trying to keep the passband ripple below 0dB in the magnitude response. So far, ...
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2answers
6k views

How do I find the phase response of a filter from the filter equation?

I am new to this forum. I have been teaching myself DSP for the last two years, so my experience and knowledge has a long way to go. I am trying to find the phase response of a specific filter that I ...
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1answer
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Is there a set formula for calculating FIR coefficients (for a LPF ir 96 taps)?

I need to calculate a series of coefficients for several FIR filters having 96 taps is there a standard or set formula for calculating these, it is a low pass filter.
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how to design LPH and HPF from APF

I came across a concept that says we can design LPH and HPF from APF when the transfer function of the two APFs given as $$\begin{align}A_0(z)&=1\\ A_1(z)&=\frac{-a+z^{-1}}{1-az^{-1}}\\\\ H_{...
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1answer
189 views

Low Pass Filter - pixel correlation

I am trying to understand low pass filters for image processing, I came across an article that stated that low pass filters effect noise more than the real data due to that the image Noise always ...
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1answer
4k views

Why Butterworth filter always starts my signal from from zero mark (amplitude)?

I am trying to filter my force signal using Butterworth low pass filter. so this is the signal, I have to filter (noise frequency is around 33 Hz). So when I use Butterworth filter with following ...
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How do I smooth this noisy signal?

I have a numerical solution to a problem in mechanics. I am computing the force applied to an object as a function of its deformation and in the problem, there is an instability, due to which the ...
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1answer
898 views

Choosing minimum sampling frequency of a filtered signal

I have a time series of acceleration sampled at 1000Hz to capture random impacts on a structure. The ringing of the structure (not of interest) produces noise which a 50Hz filter seems to eliminate ...
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101 views

Transform one-pole cascaded system into a biquadratic section

I have two cascaded one-pole sections with the same coefficient b for both sections. $$ y_A[n]=x_A[n]+b\cdot(y_A[n−1]−x_A[n])\\ y_B[n]=y_A[n]+b\cdot(y_B[n−1]−y_A[n]) $$ The final output of the system ...
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1answer
253 views

Cascaded one-pole sections and relationship to time constant

I have implemented a typical one-pole lowpass filter to smooth out some control signals. The form of the filter is: $$ y1 = x0 + b1\centerdot(y1 - x0) $$ x0 is the current input sample. y1 is the past ...
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1answer
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calculating the stop-band edge frequency of a low-pass FIR

I have three information about a low-pass FIR filter. pass-band edge frequency pass-band ripple stop-band ripple I want to get the stop-band edge frequency I've been googling for the last hour ...
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Integration of square wave

trying to program an integrator. My input is a square wave and my expected output should be a triangle wave. However, whenever I pass it through my low pass filter algorithm (just a 2nd order ...
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1answer
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Why is the output of the LPF half that of the real/imaginary part of the complex envelope?

The passband signal $\ u_p(t) = I_{[−1,1]}(t) \cos 400πt $ is passed through an LPF as $\ u_p(t) \cos(401\pi t).$ The question is to find the output. The example does the following: If we let $\ u_1 =...
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1answer
696 views

Relation between poles and cut off frequency of a filter

I noticed that for a low pass Butterworth filter, as the cut off frequency reduces, the poles get closer to the unit circle. Is it applicable to all filters and why is this so? As the normalized cut ...
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1answer
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Smoothed Square Wave

new here and probably pretty unexperienced compared to the rest of you. This should be simple enough but just wanted some clarification. I'm trying to model an analog square wave oscillator with C. ...
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2answers
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Interpolation based on sinc function

I implemented an interpolation method in C++ based on this equation ...
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2answers
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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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0answers
5k views

Digital low pass filter vs Kalman filter

I have experience with the design of FIR, IIR digital filters. I also know about the Kalman filter, but I am not skilled at using them. Consider the case of a low frequency signal from discrete ...
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2answers
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Complex low pass filters

I am searching for documentation on the behaviour of complex low pass filters, and their application in telecommunications. Thank you
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what is magnitude responce at ω = π/2M for freqz function [duplicate]

what is magnitude responce at ω = π/2M.Code Given is ...
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1answer
56 views

Find Magnitude Responce at $\omega=\dfrac{\pi}{2M}$ where $M$ is the number of channel in QMF

I have frequency response of low pass filter ...
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265 views

Frequency response of a rolling linear regression

I am looking for a way to characterise the frequency response of the slope from a linear regression. We are exploring the effect of window length of the regression to the magnitude of the slope of the ...