# Questions tagged [butterworth]

Butterworth filters fall into a class of filters with magnitude frequency response that is "maximally flat" magnitude. Butterworth filters have no ripple either in the passband nor in the stopband.

161 questions
Filter by
Sorted by
Tagged with
50 views

### Is there a library to do Butterworth and Savitsky-Golay filtering in PHP?

I am new to signal processing and have a requirement to apply Butterworth and Savitzky-Golay to a PPG signal. I have read that matlab can handle it but I am a PHP guy. Can I run Matlab on my server ...
91 views

### Implementing a Butterworth low-pass filter in Python without knowing the order

I am relatively inexperienced with respect to lowpass filters, but I am trying to replicate parts of this paper, which deals with the processing of 3D accelerometer and 3D gyroscope data, both from ...
61 views

### algorithm for second order butterworth filter

I want to implement an algorithm for a second order butterworth filter on the form $H(s) = \dfrac{Y(s)}{U(s)}= \dfrac{1}{\left(\frac{s}{w_0}\right)^2+2\zeta\frac{s}{w_0}+1}$ I want to get it on the ...
42 views

### How can I calculate how much of my signal at the beginning and end will be affected by the filtering process?

I'm using a Butterworth bandpass filter to process my signal (low-pass + high-pass, I am also applying a notch filter). I would like to calculate how much of my signal at the edges will be affected by ...
36 views

### recreating in matlab Butterworth Filter filter response

There is a manual which presents a filter response. In the video they present a formula and a plot of the response. However when I tried to implement it in MATLAB I get a totally different plot. ...
107 views

### Smoothening Noisy FFT

I've got the following FFT with a sampling frequency of 192 kHz that has around 17.000.000 samples. The signal is a hiss of escaping gas. This looks noisy and i want to determine the characteristic &...
• 131
102 views

### Converting cutoff_frequency_ratio to Cycles/Pixel in Butterworth Filtering with skimage

I am working on my thesis where I'm employing Butterworth filtering on images using the function butterworth from scikit-image's skimage.filters module. The code/formula I'm referring to is available ...
• 123
1 vote
58 views

### Relative loss of power and length of signal

I have EEG signal data from a single channel for 150 similar events (epochs), each spanning 11s which might be accessed from here. I ran the following code block in MATLAB to remove line noise at 60 ...
36 views

### Improving Modeling of Thermal Noise Propagation Through a Signal Chain

Background I recently asked this question over on Electrical Engineering Stack Exchange. On the advice of some commenters there, I've broken off those pieces which are appropriate for asking as ...
98 views

### Getting displacement from the accelerometer data for vertical motion

I have an accelerometer sensor with gyro and need to figure out the vertical displacement from the acceleration data. The device that contains the accelerometer will move up and down in fairly ...
1 vote
132 views

### Several Low pass filters generate offset when applied on an embedded system on C++

I need to implement a real time butterworth low pass filter on some data, I have an already implemented and tested butterworth function, but when filtering data from one specific variable I get an ...
• 11
1 vote
116 views

### Denoising Signal With Butterworth-Filter

im trying to denoise a signal to which i added AWGN. Here is what ive done so far: ...
• 131
106 views

### IIR bandpass filter attenuates frequencies within the pass band

I applied Butterworth filters (order=5) that have different cutoff frequencies to a simple signal composed of four sinusoidal oscillations and computed its PSD. <...
• 25
506 views

### Calculating the filter coefficients for 2nd order bandpass and bandstop Butterworth filter

I want to calculate the filter coefficients for both bandpass and bandstop filter for 2nd order Butterworth filter, like ...
1 vote
660 views

### How to implement a 3rd order Butterworth IIR allpass filter with perfectly flat frequency response?

I'm working on an audio plugin which splits audio into frequency bands for individual processing. The filters must have zero latency, so no linear phase filters. I would like to have perfect ...
426 views

### How to obtain filtered impulse response from frequency response?

I am trying to find the reverberation time of a room using the Schroeder method (i.e., Reverse-time integration method). Therefore, impulse responses should be measured first. There are many ways to ...
• 61
547 views

### Why do we have a negative gain after a certain point in frequency domain for a channel filter?

Why do we have a negative gain(i.e. not negative as in polarity but gain < 1) after a certain point (1500 Hz). What is the reason and purpose for this. Why is that point the same for both DC and AC ...
350 views

### Why odd-order Butterworth filters don't behave the same as even-order in crossovers?

I have noticed that when you create a crossover using even-order Butterworth filters, you need to use two filters instead of one (Linkwitz-Riley) in order to obtain a flat amplitude response (two low-...
• 121
2k views

### filtering EEG data with scipy.signal

I have EEG data recorded with a sampling rate of 256 Hz. Each recording contains 19 EEG channels. Other channels (like ECG data) are ignored. The recordings of 10 patients are 20 minutes long each, ...
163 views

### How to implement the discrete Butterworth

I'm trying to implement the Butterworth filter as a high pass filter inside a function, where every time stip a measurement will be passed (inside this function I do have buffers for storing the data)....
• 9
1 vote
202 views

### Sampling frequency in bilinear transform when designing butterworth filter

I'm trying to design digital Butterworth filter from scratch. First I use butterap to design an analog prototype to get zeros, poles and gain ...
• 527
742 views

### How to design digital Butterworth filter and return its zeros, poles and gain

I'm implementing digital Butterworth filter and encounter some numerical problem when filter order is high using direct form, so I wonder how to design the digital Butterworth filter and return its ...
• 527
1 vote
108 views

### Butterworth Filter at high Frequencies

So I have this signal sampled at 300 Hz to begin with and this is the frequency domain: I apply a second order butterworth filter using scipy with a cutoff frequency of 12.6 Hz and this is the ...
2k views

### Signal processing in Python vs C++ (band-pass filter)

I have implemented Python signal processing code using a butter bandpass filter and order 3. It is working pretty well. I am required to implement the same signal ...
• 131
724 views

### Why don't unit circle poles lead to infinite amplitude response for Butterworth lowpass?

This is probably a very stupid question. In many places (e.g. here), the Butterworth filters, e.g. lowpass, are described as being "allpole" filters, that have all of these poles on the unit ...
• 468
148 views

### Lowpass Filter for Lock-In-Amplifier

I am implementing a Lock-In-Amplifier in Python with scipy for measurements with light with a decimation afterwards. Right now, this is implemented with an average. This works fine, but I am trying to ...
• 103
147 views

### Butterworth filter cutoff attenuation is not exactly 0.707(-3dB)

The documentation of scipy Butterworth filter says its cutoff attenuation is 0.707(-3dB). To validate this, I created a square wave signal, performed FFT and implemented a bandpass filter with a band ...
• 143
300 views

### Formula to compute FIR and IIR Filter coefficients

I am trying to understand filter design. I am trying to implement butterworth filter which would have high,low and bandpass using the difference equation representation for FIR and IIR. Given the low ...
• 41
117 views

### Accounting for phase shift in time-dependent signals

Background: I am using a vibration sensor and arduino to record signals and log them with timestamps, where the signals need to be time accurate so that I can glean information about which frequencies ...
345 views

### Performing STFT after Butterworth Filter Seems Lower in Resolution

I have a signal recorded at 2MHz sampling rate. Before any decimation might be required, I first looked for peaks in my periodic recorded signal using STFT/spectrogram. From here, I can clearly see ...
• 77
73 views

### Questionable results of on-line butterworth bandpass filtering using scipy.signal.lfilter

I have a data_stream that I'm attempting to filter using two on-line butterworth bandpass filters to extract two frequency bands of interest. The original ...
243 views

### Sampling frequency vs Signal frequency

I've started recently working with the ADXL345 accelerometer with the goal of finding the velocity. And so far, I'm getting "okay" results after applying a second-order Butterworth filter to ...
1 vote
249 views

### I do not understand the frequency calculation used in the construction of this IIR digital Butterworth Low pass filter using MATLAB

The question is to design a Low Pass Butterworth IIR Digital filter. The following code below has the specifications with $A_p$ being the passband attenuation, $A_s$ the stop band attenuation, $f_{pb}$...
1 vote
196 views

### How can I reverse engineer the parameters of this butterworth filter?

I am trying to develop an application which will need a bandpass filter. The sampling rate is 30Hz, and the frequency range I'd like the filter to preserve is: 0.5Hz-4Hz. I've used mkfilter to ...
• 135
2k views

### How to apply Butterworth high pass filter in the frequency domain?

I have a time series of measurements which I want to high pass with Butterworth filter. Python scipy package has a built in function for Butterworth filter (signal.butter) and I know how to apply it ...
1 vote
118 views

### I can't hear my sound after filtering

I am studying on a project which my supervisor gave me this semester. It has multiple steps. Basically, I have my own audio. I added AWGN to this sound using awgn() ...
• 111
717 views

### SOS-matrices' order does not correspond to given parameter when designing bandpass with scipy.signal.butter

I do not understand why this scipy operation: ...
28 views

### How to deal with [h] coefficients which are 0 from sos-matrix

Calling scipy.signal.sosfreqz with a sos-matrix describing an ordinary butterworth bandpass returns an array of h coefficients, ...
390 views

### Theory behind the matlab butter function with the parameters n and [Wl, Wh]

I am writing the theoretical background in my thesis but my thesis is more centered on deep learning and the signals that I am using for classification were filtered through the ...
505 views

### BPF Filtering with DSP IIR Realtime C++ filter library

I am working with complex samples, I have a main signal at 630KHz, my Fs is 1.26MHz and BW is 12.6KHz. If I plot a frequency-magntitude spectrum it looks like this: As you can see along with my main ...
• 169
6k views

### Implementing a Butterworth Filter Manually in C/C++ via Second Order Sections

Short background: I want to implement a lowpass butterworth filter in C/C++. The end goal is to use this in a low-latency Python program, for which of course ...
• 163
1 vote
187 views

### What is the warm-up period of a Butterworth filter?

I am not sure if I use the correct term which may be the reason why I was not able to find the answer, but what I mean by the warm-up period is the number of samples required for the filter to produce ...
• 247
374 views

### Butterworth filter poles

Hi, I'm looking at this textbook question and trying to get a better idea of exactly what its asking. For the processing to be real valued each pole would have to have a complex conjugate right? So ...
1k views

### 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 ...
• 52.3k
1 vote
283 views

### Signal values explode when filtering with bandpass and wiener in Python

I have a five second audio (speech with background noise), which I want to process first with bandpass filter and then with wiener filter to reduce noise. Audio is normalized between [-1, 1] and I ...
295 views

### Butterworth Filter Transfer Function

Butterworth Filter frequency response is given as: $$H_a(j\Omega)=\frac{1}{\sqrt{{1+\left(\frac{\Omega}{\Omega_c}\right)^{2N}}}}\quad \text{where N is the order of the filter}$$ and for the transfer ...
• 211
63 views

### Paper replication: Validating the proper way to pass .wav audio breathing data through a bandpass filter

I am working on trying to apply a low and high pass filter to an audio file that contains a set of exhalations over a microphone. The inhalations have been cut out of the file, and the exhalations are ...
305 views

### 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 ...