Questions tagged [butterworth]

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29 views

Filtering artefacts and filtering short signals

I have a signal from EEG sensors and I try to denoise it from AC frequencies. For that reason, I estimated PSD of my signal and found that 50 Hz and 100 Hz are likely to represent noise. I constructed ...
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1answer
40 views

How to derive 2nd order Butterworth condition for the damping coefficient mathematically?

The magnitude of 2nd order low pass filter is given as $$|H(\omega)|^2= \frac{1}{(1-(\frac{\omega}{\omega_o})^2)^2+(\frac{2\zeta\omega}{\omega_o})^2}$$ Now in order to achieve maximally flat within ...
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1answer
59 views

Pole locations of Butterworth filter

I am reading Proakis book "DSP using Matlab", 3rd edition. I am reading chapter 8, section 8.3, p. 402, and I am confused regarding the equation of poles (roots of denominator of system ...
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2answers
25 views

Design and a notch filter using two Butterworth filters in parallel (MATLAB)

I am doing a project to filter out a 1kHz noise inserted to a 30sec .wav audio file. To filter out the 1kHz noise, I am required to design using two Butterworth filters connected in parallel where ...
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2answers
44 views

Relationship between order of filter and amplitude/phase response

I am learning about digital filters, for example a lowpass butterworth filter. In many languages, the implmentation requires specification of the order of the filter, which I believe is the number ...
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1answer
32 views

What is absolute ripple specification and how does it arrive in low pass prototype for Butterworth?

Digital Signal Processing by John G. Proakis, Dimitris G. Manolakis(4th Edition) gives the prototype function for Butterworth low pass filter in an analog system which is fine till the point where the ...
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49 views

Lowpass Butterworth filter equation

I am using a 5th order lowpass Butterworth filter with a varying cutoff frequency, $f_c$, to smoothen some data coming from a spectrometer. An example of a spectrum, plotted with the filtered data, ...
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0answers
30 views

Difference in results between iirj and mkfilter with Butterworth filter in BandPass

When I generate a filter on www-users.cs.york.ac.uk/~fisher/mkfilter/trad.html and another iirj (github.com/berndporr/iirj) these are not the same results. Configuration (mkfilter): Type : ...
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34 views

removing noise using Scipy.signal.butter:

I am going to remove the noise from a brain recorded signal. It was a continuous recording and with sample rate=30kHz, it was digitized. So now it is a digital signal. I have written the code here ...
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3answers
643 views

Butterworth filter transfer function in time domain

Preliminaries I need to know the response of Butterworth filter in time domain of the following input (at least numerically): $$ x(t) = \theta(t)(1-\exp\{-at\})\exp\{-bt\}, \quad a,b>0,\quad a\gg b ...
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1answer
140 views

How is the formula of the cutoff frequency of a 2nd order Butterworth low-pass filter derived?

According to articles and notes, the cutoff frequency of a 2nd order Butterworth lowpass filter: is expressed by the formula: $\omega _c = {1\over\sqrt{R_1R_2C_1C_2}}$ and since $\omega _c = 2 \pi ...
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34 views

Converting a simple analog Butterworth filter into a digital filter

I was just studying an old circuit analysis textbook that was describing how to design a Butterworth filter, and that seemed easy enough.. then, I started to wonder if I can take this analog filter ...
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0answers
48 views

Apply a butterworth filter to columns of a large dataframe

I have a large dataframe (7200, 132) and each column is a signal. I want to apply a butterworth filter to each signal, however, I'm not sure how to do this in Python. When I do it in matlab I can ...
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2answers
95 views

Why is my signal attenuated after applying a HighPass-filter?

I am new to DSP, but I've been attempting apply a butterworth high-pass filter on a 1D array (Values peeking at 300~) to eliminate any noise, yet when applying a high pass filter, I'm ending up with ...
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1answer
35 views

Cut-off frequency in Fourier-Spectrum of a noise message

I have a problem involving cut-off frequency. I have a voice message in an audio file .mat which have an eletromagnetic noise. I am trying to recover the original message by applying digital ...
2
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1answer
162 views

Large spike at beginning of signal after applying Bandpass filter

Foreword: I am a PhD student and fairly unexperienced with many signal processing and engineering concepts, please be gentle. I am attempting to filter out a frequency range of 1Hz to 2Hz from a 2....
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1answer
89 views

Applying a 2D band pass filter (Butterworth ?) to an array with NaNs

I am trying to filter out the low frequencies of an array looking like this : For now, I am taking transects of this array and applying a 1D - butterworth band pass filter : ...
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1answer
78 views

Plotting curved peaks on PSD graph

I am a PhD student with little engineering experience, currently attempting to recreate the signal processing techniques used in this paper: Monitoring Vital Signs and Postures During Sleep Using WiFi ...
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37 views
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1answer
63 views

Frequency response plot and actual behavior of a digital Butterworth LPF

I have been struggling with a not-too-high (2nd) order digital Butterworth low-pass filter both in SciPy and MatLab (latest of both). The intention is to apply this filter on signals with different ...
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1answer
129 views

Using a Butterworth high-pass filter together with Fast Fourier transform

I have a signal and I'm interested in identifying the dominant frequencies greater than 1/3600 Hz. To do this, I use Fast Fourier Transforms and examine the locations of the peaks in the frequency ...
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2answers
172 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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1answer
91 views

what is the theory behind Butter function?

I want to understand why this code used tan and cos ? ...
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0answers
19 views

What is the meaning of these Fixed Point Properties e.g.CustomSectionInputDataType?

I was trying tom implement a Butterworth filter and i came across a example on Mathworks site which emphasizes to customize various terms related to the filter. Following are some of the terms i could ...
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1answer
677 views

How to choose order and cut-off frequency for low-pass Butterworth filter?

When using IMU data (accelerations and angular velocities), many papers use a 4th order low-pass butterworth filter with a cutoff frequency of 5 Hz. However, none of them really justify why those ...
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1answer
101 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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1answer
94 views

Bandpass filter with very high sampling rate

Consider a bandpass filter with Low Cut 17Hz, High Cut 22 Hz, Fs = 45000 Hz and Order = 6. When I pass a mixture of multiple sinusoidal waves through this filter (with a sine wave of frequency 20 Hz), ...
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1answer
78 views

Analytical design of a bandstop Butterworth filter

I am trying to analytically design a bandstop Butterworth filter. I am trying to use: $$|H(s)|^2 = \frac{1}{1+\big(\frac{s}{j\omega_1}\big)^{2N}}+\frac{1}{1+\big(\frac{s}{j\omega_2}\big)^{-2N}}$$ to ...
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1answer
185 views

Odd-order Butterworth filter gain at cutoff frequency

Wikipedia gives the gain of an n-order Butterworth filter as $$G^2(\omega)=\left |H(j\omega)\right|^2 = \frac {{G_0}^2}{1+\left(\frac{j\omega}{\omega_c}\right)^{2n}}$$ here. If you look at the gain ...
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85 views

how to detrend a carrier phase with butterworth filter?

I am new with detrending techniques, I have a carrier phase measurements and I want to detrend it by 6th order butterworth digital filter. After creating the digital filter I get its numerator (...
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2answers
2k views

FIR butterworth also possible or just IIR?

can we use butterworth and other such filters like chebyshev,elliptic etc with FIR or they can be only used with IIR?
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1answer
73 views

difference between conventional analog butterworth filter and that implemented through IIR

I am confused what is difference between conventional analog butterworth filter and that implemented through digital technique using IIR
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1answer
126 views

“Side Lobes” When Using a Butterworth filter

So I am attempting to filter a signal containing frequencies at 7Hz, 11Hz, and 74Hz. The signal lasts for 30s and looks like this between -1s and 1s: Using a butterworth filter of order 2 with lowcut=...
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1answer
88 views

iir biquad filter not working

I am trying to implement a butterworth bandpass filter My filter requirement is Fs= 500Hz, Fc1=0.4Hz, Fc2=4Hz, Oreder=2. Below is the code which is implemented on 16bit-mcu and is called for every ...
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0answers
90 views

Digital or analogue filtering?

I'm trying to self learn the art of signal processing whilst moving through my third year pure maths degree. Sorry if my terminology is incorrect however I hope I am understandable! I am looking at ...
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1answer
125 views

Time-domain LPF not showing expected behavior

I am trying to implement a simple first-order Butterworth Low-Pass filter in Python. I have some code that makes use of scipy.signal.butter and scipy.signal.filtfilt. It works fine, but I wanted to ...
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2answers
390 views

How to compare many bandpass filters (for their signal propogation delay)?

Let's say we have an audio signal sampled at 96 kHz, and we want to compare several bandpass filters to find the one with the lowest rectangular-envelope-propagation-delay (see graph below). The band ...
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2answers
303 views

Initialize Hi Pass Filter

I want to remove the DC from a ADC, so I designed a two-pole, 1 Hz high-pass Butterworth filter for a signal sampled at 10kHz. The filter coefficients are: ...
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0answers
249 views

How can I manually find the coefficients, poles and zeros of Butterworth low pass filter in MATLAB instead of using the built-in functions?

Actually I need to filter a raw ECG signal using low pass Butterworth filter at 70 hertz. And j need to implement the Butterworth filter first for that. Please any help since I'm very new to this ...
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1answer
366 views

Question of Digital filter; stability and order

Below 1~6 are my question. Shortcomings of IIR filter. Mean of unstable. (Things that will happen when system is unstable.) How to select the best order(n). What happens when I raise order too much. ...
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2answers
2k views

Bandpass butterworth filter in python is not working

I've implemented this bandpass filter in matlab for the audio signals and it's working as expected. Now, I tried to implement the same thing in Python but it doesn't produced expected results, it just ...
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1answer
555 views

How to decompose raw acceleration signals into gravity and dynamic acceleration?

I have a data from $3$-axis $50$ Hz accelerometer, acceleration over each of $3$-axis: $acc_X,\ acc_y,\ acc_z$. I want to decompose acceleration into gravity and movement components. First ...
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1answer
432 views

4th order butterworth filter using frequency response formula

I know this may be a kind of basic question, but I have my head wrapped over it for some time and hadn't found a solution. I want to generate the frequency response of a 4th order butterworth filter ...
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2answers
3k views

How to implement a filter associated to a specific wavelet

I am working on ECG signals, to eventually extract features in order to detect an arrhythmia and classify it. I am using Discrete Wavelet Transform with biorthogonal wavelet bior6.8 During my research,...
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0answers
2k views

Implement a Butterworth Filter in C#

I'm very new to signal processing, but was asked to implement a filter function for Butterworth low pass filter for given order, cutoff frequency and sample rate. After reading some articles I think ...
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1answer
440 views

Butterworth Polynomial from Butterworth Filter

For the butterworth filter, in Matlab command: [B,A]=butter(2,0.5,'low') I find this result: ...
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1answer
1k views

Why is the second-order-section cascade approach giving “worse” results?

It seems that as a general rule, for digital IIR filters of order more than 2, one is encouraged to use a cascade of second order sections, for reasons connected to the poor stability of high-order ...
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1answer
8k views

Apply butterworth filter (lowpass) to a signal

I'm working on a DSP lab and I can't figure out how to apply the filter I've created to a sound. The only thing I found online that did something to my sound was ...
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2answers
1k views

What is the largest “safe” order for the digital Butterworth filter of a given signal?

Say I want to apply a zero-phase Butterworth bandpass filter, implemented in MATLAB using butter and filtfilt. So, for an order-$...
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1answer
452 views

Butterworth low pass filter zeros location after bilinear transformation explanation

I am studying in a text book the transformation of a continuous time Butterworth low pass filter into a discrete time filter by means of bilinear transformation: $$ s = \frac{2}{T_d}*\frac{1-z^{-1}...