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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What is the name of these simple filter algorithms?

I found some snippets of code on the internet that are really simple signal filters. Unfortunately there wasn't much info to back it up. Using Google I've found similar code, but none of it backed up ...
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476 views

How to implement a time-varying filter?

I'm working on a 10-second sound, sampled at 44.1 khz. I want to do filtering, and have a desired EQ (equalization) curve that varies over time, as suggested here (here $f0=250\ Hz$) How to ...
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332 views

OFDM Transmitter knowledge

I have some questions regarding some concepts used in designing the OFDM transmitter which i got from different literature reviews but i got mixed up with these concepts. • The N-Ifft points and ...
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1answer
264 views

Low-pass filtering bounces when signal doesn't start at 0

Say I have an array representing a signal, going from 30 to -30 in 1000 increments, with a little bit of noise on those values. If I apply any king of low pass filtering (Besset, Butterworth, Savitsky-...
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97 views

How to interpret these filter coefficients?

I am trying to make sense of the filter coefficients. The author claims that they are running a 3rd order lowpass Butterworth filter and were willing to give their design. They are not the most ...
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3k views

How to convert a low-pass Gaussian filter to a high pass filter

I have the following code for a applying a Gaussian filter to an image. From what I understand this is a low pass filter. Now I have to convert this into a high-pass filter, and from what we were told ...
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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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629 views

Is it normal that a DAC outputs spikes?

I'm using a Raspberry Pi 2 and an AD/DA Board, with no extra circuit. Reading on the internet though, I found that DACs need a low pass filter in their output, and I don't understand if the behaviour ...
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363 views

Effect of window function on audio output

If I have a low pass filter, does the choice of window function I use have any effect on the quality of the audio input? What would be the effective difference between using a rectangular window and a ...
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132 views

$Q$ factor refers to what on a lowpass filter? (EE kind of definition)

For what I'm learning, the bandwidth (of a BPF, for example) refers to the $\Delta$ between $f_L$ and $f_H$ at (usually) $-3\textrm{ db}$ from the $f_0$ (from wiki). For a peaking filter instead, $f_L$...
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Why analog anti aliasing filter is used before analog to digital converter when there is already a digital filter after ADC?

Normal data acquisition consist of: Analog anti aliasing filter( Sampling frequency : $5\textrm{ kHz}$) ADC - Digital Filter - (Sampling : 200K samples /sec) Digital low pass filters Filters DAC ...
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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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Velocity estimation from distance sensor

I know it is a generic question but I did not find a specific answer to it online. My question is: I have a range sensor based on the time of flight (Infrared Sensor. Transmitter-Reflector-Receiver)....
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167 views

Two way Audio crossover MATLAB code using Bessel

Could MATLAB's besself function be used in designing an Audio crossover (Tweeter and Woofer) with highpass and lowpass filters? Most likely the same with this ...
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405 views

How to design and implement a low-pass AR1 filter in Matlab?

I have a data series y(n) that I want to filter using a low-pass AR1 filter. I found that this filter has a transfer function ...
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1answer
1k views

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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1answer
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Cutoff frequency of a first order recursive filter

I've implemented a very simple first order recursive low pass filter in c using the algorithm: ...
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1k views

Resampling an audio signal

I am trying to resample an audio signal in my application. It will be between 48kHz and 96kHz audio (both upsampling and downsampling). Looking at the Wikipedia page for resampling I see there are ...
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3answers
587 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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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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1answer
215 views

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
406 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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1k views

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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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
199 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. The first image is what happens when ...
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354 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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248 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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142 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
690 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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5k views

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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574 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
5k views

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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395 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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15k views

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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602 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
132 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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980 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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495 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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734 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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454 views

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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1answer
57 views

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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128 views

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
84 views

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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1answer
253 views

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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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
2k views

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.