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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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Amplitude demodulation of sinusidal signal in matlab

AM-demodulation task and I was asked to demodulate the signal in MATLAB and the result should contain three pictures. plotting the $fft$ the (frequency spectrum)of the signal i was able to determine ...
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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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111 views

2-d circularly symmetric low-pass filter

For a square pixel grid, the ideal 2-d low-pass filter with a horizontal and a vertical cut-off angular frequency $\omega_c$ in radians has an impulse response (kernel) $h_{\small\square}(x, y)$ that ...
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Filtering on time or frequency domain?

I'm applying an ideal filter on the frequency domain. My code below: ...
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1answer
47 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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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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714 views

Lowpass Lanczos filter

I am new to Lanczos filters and trying to figure out how they can be used to generate a zero-phase lowpass filter with good time-domain properties. This example shows how to implement such a filter in ...
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How do I filter out the specific components at 20MHz, in this figure?

I used the filter builder (lowpass) , to cut off the frequency at 0.5 MHz, and thus used a stopband of 0.1pi, and a passband of 0.0125pi. (Sampling Frequency= 80MHz). However, the output was still ...
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62 views

Fixed-point Exponential Moving Average filter with given cutoff frequency

I want to implement in fixed point arithmetic an exponential moving average filter, with a specific cutoff frequency for a given sampling rate. The formula for the filter is $$ y_n = \alpha x_n + (1 -...
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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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1answer
38 views

Why is Cheby 2 filter uncommon?

I've been reading the Chebyshev filters chapter in The Scientist and Engineer's Guide to Digital Signal Processing and it says "The Chebyshev filters discussed in this chapter are called type 1 ...
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Why do I have to scale filter coefficients during bandlimited sample rate conversion?

I am writing an example for how to perform sample rate conversion using windowed sinc and polyphase filters. Here is the C++ code as a github gist. So far, this works, and I think I have understood ...
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High quality removing gravity from accelerometer data without Sensor Fusion

My smartphone have only accelerometer sensor. I need to get data close to (0,0,0) in hold in my own application. I did use some app from Google Play and data was very close to it (some like 0.1 and ...
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1answer
374 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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Low pass vs band pass filter

I've been reading some EEG papers where the authors use a bandpass filter at, say, 1Hz and 30Hz. I've also seen some accelerometer papers where they bandpass at 0.5Hz and 10Hz What is the difference ...
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371 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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361 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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1answer
5k views

Differences between low-pass, band-pass, notch filters

I'm studying image processing and I know that there are different filters you can apply. I don't understand the difference between the low-pass/bandpass/notch filter (or high-pass/band-reject/notch). ...
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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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0answers
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Frequency warping while creating filter coefficients

If I have an audio signal at 16kHz with frequencies band-limited to 8kHz. I want to low-pass filter this signal such that fc=4000Hz. Meaning when I reconstruct the signal I do not want any content ...
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What is the difference between a range filter and a low-pass filter?

A low-pass filter attenuates the high frequencies, preserving only smooth variations in the provided image. The result of an image which is low-pass filtered is an image with blurred edges (hence ...
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“Improved” MZT/IIM type One pole LPF

Some time ago, while playing with all kind of approximation of common math functions, I came up to this idea to calculate a1 coefficient for a 1st order LPF filter: \begin{array}{l}a1=-(1+x+\frac12x^...
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Why exactly is the Guassian filter a low-pass filter?

In image processing, a Guassian filter is used to blur an image. A low-pass filter is a filter that attenuates the high frequencies, preserving only smooth variations in the provided image. Is a ...
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1answer
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Understading sampling theorem and aliasing

A real-valued analog signal with a flat spectrum between f = 0 Hz, and fmax is sampled at a sampling frequency fs = 24 kHz. The sampled signal is then processed with an ideal lowpass filter with ...
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0answers
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How to implement one dimensional low pass Gaussian filter with zero-phase shift?

I am trying to apply a low pass Gaussian filter on a signal and find the exact location of maximum/minimum in the resulting smoothed signal. I have to do it for a few values of sigma (Gaussian ...
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3k views

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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Detecting Zero Crossing in Image Filtered by Laplacian Operator

This is my first question on this site, complete noob. But here goes. I have a positive Laplacian operator [[0,1,0], [1,-4,1], [0,1,0]] Now this Laplacian ...
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How to low pass very few samples

I'm asking myself what is the best way to low pass a signal which only has a few hundred samples? Or is there a proper way at all? It must not be a sound signal but I used Audacity to display the ...
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2answers
9k views

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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2answers
8k views

Savitzky-Golay filter parameters

I am trying to smooth a series of data in order to obtain a continuous function that could represent that given data set. It came out that the Savitzky-Golay method could be a good way. Now, I don't ...
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1answer
221 views

What type of low-pass filter to use for gyroscope filtering in control application?

I am using a gyroscope to generate a feedback signal that drives a motor to resist rotation, just as in a camera gimbal. The gyroscope is sampling at 32 KHz with a bandwidth of 8 KHz, and my control ...
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0answers
27 views

Determine filter type using recurrence relation

Given the recurrence relation: $y[n] = x[n] + 0.5y[n-1]$ I want to determine the filter type (i.e. LPF, HPF etc.) I try to use Z transform, and get that the the transfer function is $H(z) = \frac{2z}{...
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How to keep low frequencies in DCT

How can I keep a percentage r of the low frequencies of a Nx1 signal x using the Discrete Cosine Transform of it? Is it simply zeroing all but the first rN elements of DCT(x)?
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Low pass filter preserving amplitude

Are there any types of low pass filters that preserve the amplitude and phase? The one that I am aware of, sometimes called an exponentially weighted moving average does neither. First order Low pass ...
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1answer
62 views

how can I design Chebyshev filter with 5th-order polynomial and 0.001%-allowed ripples?

I'm very beginner in signal processing. I need to design a Chebyshev filter with 5th-order polynomial and 0.001%-allowed ripples by using matlab as I found in a paper. I'm filtering pressure data ...
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2answers
264 views

should I apply low-pass filter when calculating central derivative?

Let us say that we have a discrete signal $I_n$, $n=0, 1, 2, ...$. According to Nyquist theorem the maximum frequency for such discretization is $f_{max} = 0.5$. Now imagine that I want to calculate ...
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1answer
586 views

What exactly is Savitzky-Golay differentiation filter?

I could understand Savitzky-Golay filter as being smoothing filter, but then there also seems to be Savitzky-Golay differentiation filter, though for some reason, details do not seem to be clear. So ...
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1answer
76 views

How to filter an OFDM signal? [closed]

Across the channel bandwidth there shoudd be 100 RBs (central 1200 sub carriers in a 2048 bin). Max power normalized to 0dB, the first OOB lobe should be -34dB. This 1st lobe on either side is at 5 ...
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741 views

How to set the frequency cut-off for a low pass RC filter?

How do I set the frequency for a low pass filter illustrated below?
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Constructing a lowpass digital differentiator such that maximum error is $n$ dB for passband

I want to construct a lowpass digital differentiator with uniform-interval samples such that error from ideal differentiator is $n$ dB in magnitude at maximum for the passband up to frequency $\...
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0answers
35 views

Lowpass-filter necessary before DFT?

I'm trying to distinguish eletrical engines by the magnetic field they create. I have no idea whether this is a smart idea, it's possible at all, whatsoever. However it brought me to a basic question ...
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1answer
28 views

Why do cutoff frequencies of a high-pass digital filter differ from the ones i used to transform it from a low-pass analog filter in MATLAB?

I need to transform an elliptic analog low-pass filter to a digital high-pass filter but i'm having a problem because the resulting filter has lower cutoff frequencies than the ones i set. Here is the ...
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1answer
89 views

Using Parks-Mcclellan (or others) for FIR differentiator?

I have never seen the use of Parks-Mcclellan for differentiator - most uses tend to be lowpass filters. Is this because Parks-Mcclellan implementation of FIR differentiator has numerical problems and ...
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3answers
4k views

What is the intuition of “averaging is a low pass filter”?

As I know, the shape of a low pass filter in time and frequency are as follow: But how averaging work like a normal function in time domain? Is there any intuition in it?
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118 views

Why does my low pass filter diverge below 7000 Hz?

I'm trying to create a LPF, using language JAVA. My first aim is to understand how filters design is working and the second one is to create a "home made" equalizer with "home made" filters. To help ...
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1answer
844 views

Single-pole IIR low-pass filter - which is the correct formula for the decay coefficient?

A single-pole IIR low-pass filter can be defined in discrete time as y += a * (x - y), where y is the output sample, ...
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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
57 views

Low pass to low pass transformation coefficient?

I am unable to solve this question, 10.10 from GATE IN 2004 (a previous year question paper for an exam targeted at engineering graduates in India.) So I tried to solve the 10.10 by considering the ...
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1answer
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How does cascading low pass modules affect pass band ripples?

This question 10.21 is taken from GATE IN paper 2015. I don't understand the answer given, I mean why is the frequency response at the pass band frequency considered to be $(1-\delta)$, isn't the ...