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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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32 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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1answer
115 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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77 views

Using a Passive 1st Order RC filter to Extract DC Component

I am trying to extract the DC component out of a PWM signal produced by the MCU using a LPF. I understand that 1st order RC filter is looked upon as being amateurish because the gain in the passband ...
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308 views

Applying Jake's remez exchange algorithm for filter design

I have found C implementation for remez exchange algorithm(https://github.com/janovetz/remez-exchange/blob/master/remez.c) and I want to use this to implement a generic prototype lowpass filter. ...
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0answers
114 views

What is the reason for this 'linear “error”'

Here's MIM (Magnitude Invariance Method) thesis (press the "View PDF" to get the theis with MATLAB code in hands) and here's a plot showing the issue I'm trying to solve: Magnitude responses for one ...
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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 This image was taken with a scanning electron microscope, but because the equipment is outdated there ...
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0answers
6k 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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120 views

How many different filters are needed for in an iterated filter bank?

I'm trying to implement an iterated filter bank as described in the Subband coding chapter of the Really Friendly Guide to Wavelets. However, the text seems to suggest that The advantage of this ...
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1answer
314 views

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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888 views

Lowpass then Inverse filtering in python

I wrote a simple lowpass filter in python to run against lena. Now I'd like to add Gaussian noise to the lowpass filtered data and then run an inverse filter against the lowpass and try to get the ...
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3answers
1k views

When negative frequencies cannot exist in practice, why do we calculate power in negative frequency?

Suppose a signal with two-sided power spectral density $N/2$ is passed through an ideal LPF having cutoff frequncy $B\,\mathrm{Hz}$. The output power is equal to $N/2 \times 2B = NB$ Watts. Why not $...
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4answers
3k views

Effect of low pass filter on the time domain

Consider an ideal (rectangular profile in frequency domain) low-pass filter (LPF) which simply sets to zero all the frequencies beyond a certain cut-off frequency. Let $x$ be a discrete-time signal of ...
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3answers
83 views

Usefulness of Practical filter ouptput

If a practical filter can't remove all unwanted frequency components like ideal filter, does that mean unwanted frequency component are still present after filtering? how can we use such distorted ...
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2answers
85 views

Calculating the 3dB frequency of an nth order low pass filter and nth order high pass filter

I am using the 6th order high pass filter in the C code. And the cut-off frequency selected for it is 150 Hz and the sampling frequency being used is 32000Hz. Now, I want to calculate the 3 dB ...
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1answer
529 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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2answers
1k views

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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1answer
2k views

Low pass signal filtering using FFT or simple infinite impulse response filter

I am currently in need for filtering accelerometer data for an Android application. First of all, I used a simple low-pass filter (simple infinite impulse response filter) as follows: ...
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3answers
825 views

FIR analog low-pass filter?

Is there a way to construct FIR analog low-pass filter? (By this, I believe I am asking for no-pole analog low-pass filter, in terms of Laplace transform.)
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2answers
3k views

Definition of Ideal Low pass filter (Time Continous)

Actually I got confused about definition of frequency response of Ideal low-pass filters because in some books they mention that phase of H(f) should be linear in pass band and it's value is $ -2\pi ...
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2answers
371 views

Filter design for frequencies in range 0-60Mhz

First of all excuse me for asking a seemingly vague question. But i am going nowhere in the problem i am trying to solve. I am working on a powerline communication system where i need to upconvert ...
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2answers
9k views

Does low-pass filtering a square wave cause a 'ringing' to develop in the signal?

Using the figure below as an example, I wonder if it is possible that the small oscillations in the signal at the time of each step shift could be caused solely by the application of a low-pass filter ...
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2answers
103 views

Envelope analyis basic question

I have a vibration signal sampled at 25.6 kHz, and I want to perform Envelope Analysis on it. "Vibration-Based Condition Monitoring of Wind Turbines" by T. Barszcz has the following figure: I ...
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1answer
232 views

Does mixing brown noise and white noise create pink noise?

What happens if you take a white noise generator, run it through a one-pole LPF set to a low cutoff frequency, and then mix the two together? Do you get pink noise? Say you have this code: ...
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2answers
2k views

How to Classify a Kernel as Low Pass Filter (LPF) or High Pass Filter (HPF)? How to Transform an LPF Kernel into HPF Kernel?

The filter impulse response is [1/9 1/9 1/9;1/9 1/9 1/9;1/9 1/9 1/9]. how do i determine whether it is an Low pass filter or a high pass filter. If this is a low pass filter how do i convert it to a ...
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2answers
569 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
2k views

Why use a gaussian low pass filter, when we can convolve with gaussian kernel

Sorry if this question is too simplistic, but I am new to image processing and after successfully writing two programs, a convolution program and a low pass filtering program, I noticed that for ...
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1answer
2k views

Is a DC signal 0 frequency or extremely high?

If I pass a signal with DC component through a Low Pass Filter will the output be without the DC component?
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3answers
56 views

aliasing in image processing

I know that aliasing occurs when a signal is subsampled. If the sampling rate is lower than twice the max frequency in a signal, aliasing occurs. How is it in pictures? as far as I know, a sinc-filter ...
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1answer
41 views

How to remove the bump from the signal using filters?

I want to have only the slope of the signal. How can I do? I have tried to apply some filters but so far I have not been able to hit the nail on the head. I use Matlab.
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2answers
141 views

Using a low pass filter to interpolate signal

In my DSP university textbook, the interpolation process is described as follows: In order to represent a baseband signal $x[k]$ at an increased sampling rate with the same shapes of its time-...
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2answers
177 views

Digital low pass filter vs continuous low pass filter,?

What is difference between both implementations of low pass filter? Discrete/digital implementation and continuous implementation? As far i am able to understand In case of discrete implementation,...
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2answers
109 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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1answer
151 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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1answer
183 views

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 ...
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1answer
3k views

How to filter out those outliers

I'm struggling to filter some data from an accelerometer. I need to do it in python (and not just on the device collecting the data) to fix the data I have, so that I can build some classification ...
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1answer
129 views

Do you recognize this filter?

I'm trying to decipher the uncommented source code of SoundBox which is a little music tracker written in javascript. There is an included synthesizer, which applies a filter on the output samples. I'...
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2answers
831 views

Gaussian pyramid: why needs the image to be downsampled

In the context of a gaussian pyramid, why is the image downsampled separately although the numbers of pixels are decreased through smoothing already? In my understanding, the number of pixels will ...
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1answer
434 views

Why is the lowpass-filter coming right after the local oscillator when mixing an RF?

In the book, instead of having a band- or lowpass-filter before mixing, it's coming right after mixing, which makes sense, considering there's gonna be a high-frequency component, which has to be ...
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1answer
48 views

Calculating the network function of a filter

Given a system, that behaves as a 1st order filter with network function $H(s)$. We input: $$v_1 (t)=1+3\cos(10^4 t)$$ And we obtain as output: $$v_2(t)=1+1.5\cos \left(10^4 t -\dfrac{\pi}{3}\right)$$...
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2answers
132 views

Explanation relevant to the filter response ($\mathrm{sinc}$ interpolation) - Equation $(2)$ in my question

At present, I am learning the theory of operation of resampling for bandlimited periodic discrete signals using $\mathrm{sinc}$ interpolation. I am developing a design flow and having difficulty in ...
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1answer
961 views

Simulation and theory of first-order low pass filter

I am trying to teach myself some signal processing and control theory. I'm currently working through THIS tutorial. I've started an ipython notebook to keep my notes in. Unfortunately, something is ...
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3answers
2k views

Draw a frequency response graph from a simple equation

How is it possible to draw an audio frequency response graph (x-axis : freq from 20 to 20 000hz, y-axis : dB) from a simple equation like y[n] = x[n] - x[n-486] ...
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1answer
1k views

Low-pass filter for cleaning vocal speech before performing onset detection

I am creating a piece of software that detects when speech starts in an audio recording. Before performing onset detection I would like to remove any noise that may cause any false positives. Which ...
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1answer
58 views

number of multiplications per second required by the system

Consider a system implementing a rational sampling rate change by 5/7: for this, we cascade upsampler by 5, a lowpass filter with cutoff frequency π/7 and a downsampler by 7. The lowpass filter is a ...
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2answers
49 views

Coefficient weights of Simple Moving Average (SMA) on SMA

A simple moving average (SMA: arithmetic mean) is a low-pass FIR-filter. When you cascade 2 SMA's with a window of length $n$, so when you apply the second SMA on the output of the first SMA, and you ...
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1answer
54 views

Low pass equivalent of bandpass white noise

Let $$n(t) = Re\{z(t)e^{j2\pi f_ct}\},\ $$ where $z(t)$ is the low pass equivalent of white noise $n(t)$. We know the autocorrelation of $n(t)$ is $$R_n(\tau) = \frac{N_0}{2} \delta(\tau),\ $$ $\delta(...
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1answer
52 views

Are high pass/low pass filters FIR filters?

I am trying to understand the basic categories of DSP filters, and it seems that the two main groups are FIR and IIR, however I'm not sure how to categorize high pass, low pass, band pass, and band ...
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1answer
27 views

Why is the frequency measured in radians in filter design?

This is my first time posting a question, so sorry if my articulation is not proper. I'v just started out with FIR filter design and I see the domain being -$\pi$ to $\pi$. Now I understand that ...
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1answer
69 views

What is the step response curve of a second order low pass filter? And what if it is set for resonance?

I am doing a lot of audio synthesis DSP where I need to use low pass filters to shape the decay of an impulse. I understand that a one pole filter fed a discontinuity, say from a steady state of 1's ...
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1answer
74 views

Problem with 1st order Massberg LPF [duplicate]

I'm trying to implement this filter in title by following the book "Designing Audio Effect Plug-Ins in C++" By Will Pirkle Problem I'm facing is the magnitude response error when comparing against ...

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