# Questions tagged [butterworth]

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### Filter design by distributing poles and zeros on parametric curves

An $N$th order Butterworth low-pass filter of cutoff frequency $\omega_c$ can be designed by distributing $N$ poles uniformly with respect to parameter $0 < \alpha <1$ on an s-plane parametric ...
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### Mapping of Classic Filters for Digital Filter Design

Of the four classic analog filter types: Butterworth, Chebyshev, Elliptic and Bessel- are any of these relegated to obsolescence for purposes of digital filter design in comparison to optimized ...
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### 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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### DC component in accelerometer data - filter before or after XYZ Euclidean sum

I'm working on filtering accelerometer XYZ data. The aim is gait-pattern recognition via finding characteristic frequency points and feeding these to a artificial neural network. The trouble is, and ...
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### 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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### Simple (Arduino) digital butterworth filter : why do I see oscillations?

I want to filter deviations from an ADC over time (low pass), not very critical. So I first tried exponential averaging, something like y= (7*y+x)/8. That gave useful results, but there is an obvious ...
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### Higher-order (Butterworth) filters

This is a general question, I am just trying to understand the concept. Why should we use higher-order filters, other than a 1st order (of any type for that matter, but we can keep the discussion to ...
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### What is the $Q$ of successive Second-Order Sections of an $N$th-order Butterworth low-pass filter?

What if you had an $N$th-order Butterworth lowpass filter filter with -3 dB frequency of $\Omega_0$? $$\Big| H(j\Omega) \Big|^2 = \frac{1}{1 + \left(\frac{\Omega}{\Omega_0}\right)^{2N}}$$ The number ...
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### LPF in the stage of IQ demodulator is it a analgor filter or digital filter?

I recently designed the LPF of the IQ demodulator using the Butterworth LPF refering to https://dspillustrations.com/pages/posts/misc/baseband-up-and-downconversion-and-iq-modulation.html. But I have ...
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### 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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### MATLAB $\tt butter$ function

I suspect I have a very basic misconception so I'm trying to clarify that here: A signal should be filtered before it is sampled, correct? That is, I always sample an analogue signal at some sampling ...
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### why does butterworth IIR filter for a square pulse show ripple on edges in time domain but not the same for sine wave

I am using butterworth filter for both square pulse and sine wave. In case of square pulse, butterworth produces some sharp ripple of edges of square pulse in time domain for varying butterworth order ...
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### Offset after Butterworth bandpass filtering

guess I'm stuck with this filtering problem and I'm thinking it has something to do with my raw data but I'm not so sure. So the problem is the following, please refer to the figures below, basically, ...
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### 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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### 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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### Calculating cutoff frequency for Butterworth filter

I have a problem while calculating cutoff frequency, suppose we have these specs. Firstly, I calculated the order of the filter and got $N=5.8858$ and round it up to get $N=6$. Now I'm supposed to ...
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### Butterworth lowpass filter

In order to understand the behaviour of the butterworth (lowpass) filter I generated a "spectrum" consisting of 1's. I then went to time domain (ifft), applied the ...
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### Unexpected behaviour when using lfilter with initial filter delay multiple times

I want to filter a very long signal in smaller parts, therefor I am currently using scipys lfilter with an initial filter delay doing multiple iterations of: <...
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### Butterworth filter's gain formula does not agree with R's signal package

I'm trying to calculate the Butterworth filter gain. If I use the formula mentioned on Wikipedia: $$G^2(\omega) = \frac{G_0^2} {1+\left(\frac{j\omega}{j\omega_c}\right)^{2n}}$$ I don't get a ...
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### How to practically correct for group delay imposed by a digital filter (Python)

I'm using Python to filter a signal using a Butterworth filter (scipy.signal.butter) and subsequently passing this through a forward-backward filter with cascaded second order sections (scipy.signal....
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### Ripple in a SciPy Butterworth SOS Filter

I have a script using SciPy for checking the RMS of various Butterworth Bandpass Filters of varying orders. I would expect the RMS values to increase and decrease linearly and consistently as you get ...
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### 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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### 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 ...