Questions tagged [scipy]
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126
questions
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1answer
21 views
Getting error while performing upsampling of an audio signal processing using low pass filter in python
I want to perform upsampling of an audio signal introducing zeros between samples to create a longer signal with factor of N=2. The sampling rate is 44100Hz, time = 5sec.
...
0
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1answer
49 views
Apply FFT to positive spiky signal
I have a signal that looks like this
It has regularly occurring peaks 50 units apart, and offset from 0 by approximately 20. I thought I could apply the DTFT to this signal and extract the period (...
1
vote
1answer
52 views
Compare two Fourier transforms of two signals by calculating the coherence
My overall aim is to compare the edges of two images by comparing their Fourier Transforms (FFT) and to calculate one number as a key performance indicator that describes how much they are similar to ...
0
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1answer
26 views
Problem wih (diverging?) digital IIR filter for an online acquisition system
I am trying to plot windows of acquired data from an LSL-compatible system. For the example below, let's consider 1-second window of a 64 channel EEG system. In practice, I use shorter 0.2-window, but ...
0
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1answer
27 views
How to correctly set the zi parameter (initial condition) for a scipy IIR filter
Let's take as an example an IIR filter using the 'sos' output, as this is what I use the most. To apply a bandpass filter, you can do:
...
1
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1answer
29 views
Difference between MATLAB zp2sos and python zpk2sos functions
I am trying to port some code from MATLAB to python. The goal is to use Butterworth filter (4th order, bandpass) API and convert it to second-order sections. I get the same output between MATLAB and ...
0
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1answer
41 views
Obtaining real numbers from FFT with same length as original signal
In this article the real valued time domain signal is transformed to the frequency domain to extract some features like mean or variance.
But after transform to the frequency domain I calculate ...
0
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0answers
25 views
Trying to implement matlab pwelch function in python using scipy welch
I am trying to port the statistics toolbox function pwelch from matlab into python, but when I am trying to implement it using scipy.signals.welch, it does not return the same results as it does in ...
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0answers
27 views
Periodogram/PSD from FFT amplitude
I have performed a STFT for signals and obtained the amplitude through
...
0
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0answers
66 views
Boundary effects with scipy.fftconvolve after convolution
I am having some numerical error in my code that propagates continuously, and has to do with the implementation of convolutions in Python; this is kind of struggling my progress and I would really ...
0
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0answers
17 views
Using Scipy.correlate2d output matrix to determine best image match
I'm struggling to wrap my head around how I can use the output of a correlation matrix to determine if my image is present.
If I am trying to match characters, how can I compare the outputs of these ...
2
votes
1answer
107 views
Scalograms in python
I am reading this paper to learning basic concepts of dsp and I want to reproduce the following scalogram of a test signal (fig 4.2 of the paper):
It has been produced from the discretization of the ...
0
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2answers
49 views
Designing digital low pass filter with low pass-band group delay
I'm interested in specifying a digital low pass filter with low (and near constant) pass band group delay. I tried python's spicy.signal.minimum_phase to transform ...
1
vote
1answer
78 views
Memory efficient filtering with scipy.signal in Python
I have several EEG channels that need filtering, and one channel may reach a recording length of 12 hours or potentially even more. This results in billions of data points stored which, when loaded, ...
0
votes
1answer
32 views
Is there an a method to fit a wave created from two wave?
I need to get the frequency and amplitude for a wave that consists of multiple function.
for example, if I have a sine curve (created from two sine waves), How can I extract the parameters for this ...
0
votes
1answer
19 views
What is the function of init in Active Contour Model
In practice of image processing using scikit-image, I didn't understand the role of constructing init numpy array in Active Contour Model example. Is it the red section drawn in the example astronaut ...
1
vote
2answers
181 views
How to apply an anti-aliasing filter before downsampling
I have an eeg signal with two channels (f3m2 and f4m1) which is divided into epochs. I want to augment the data by taking every 5th sample. I can re-use the discarded samples to create 5 versions of ...
0
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0answers
67 views
Find corresponding wavenumber from FFT - Python
I have a set of data taken from a high speed camera. I've done some image processing which results in getting a pixel location at each frame. This oscillates with time and so I have performed an FFT ...
0
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1answer
44 views
Why use both a high pass and a low pass filter in a Butterworth implementation for noise reduction?
I am a new to audio processing . I want to develop an application that reduces audio noise using a Butterworth filter. I found some existing code doing this, but I still do not understand the use of ...
2
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1answer
103 views
Compute minimum phase version of a FIR
I am working with HRIR filters, in particular I am trying to interpolate them.
One commod method in the literature to perform interpolation of HRIR is to use the minimum-phase decomposition and ...
0
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0answers
13 views
refractive index KK relation
I make Kramers Kroing relation(KK relation) with scipy.integrate.quad to change $\kappa(w)$ into $n(w)$.
Their KK relation is $n(w) = 1 + \frac{1}{\pi}\int_{-\infty}^{\infty} \frac{\kappa(w^{\prime})}...
0
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0answers
34 views
Interpreting scipy spectrum from audio signal
I have recorded some audio and would like to obtain a spectrum from it. As the audio is a real valued signal, I figure that I could perform a FFT with some window and obtain a spectrum for that period....
4
votes
2answers
48 views
Why is FFT-based convolution efficient only for signals of large size?
According to the documentation of scipy.signal.fftconvolve
This is generally much faster than convolve for large arrays (n >
~500), but can be slower when only ...
0
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0answers
63 views
The difference between tensorflow stft and scipy stft
I'm trying to wrap my head around stft, and checking the docs, tf.signal.stft and ...
1
vote
1answer
55 views
trying to reproduce the behavior of initial conditions for the filter delays of scipy lfilter with R
I'm trying to reproduce the behavior of lfilter and lfilter_zi (from scipy) in R (using signal package if possible).
This is the example provided by ...
0
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1answer
39 views
Filter design for an unusual EEG experiment
I'm designing a quite unusual (in terms of signal analysis) EEG experiment, which forces me to design my own filter. I have never done this before, so kindly please check my work and suggest ...
1
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2answers
110 views
Scipy butter filter - remove DC offset w/ high sample rate
I am having a hard time figuring out how to employ a high pass filter to remove the DC offset of my data signal with the "scipy butter" function because my sample rate is quite high. The ...
0
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0answers
29 views
Why the inverse discrete fourier transform of the Ricker pulse isn't the same as the Ricker pulse in time domain?
Question
I'm trying to use Python's scipy library to compute the IDFT of the Ricker wavelet function and compare it with the analytical time-domain version of the same function. When I compare the ...
1
vote
1answer
165 views
Dynamic filter in real time audio
Following my previous question: Removing cracking in real time audio, I'm trying to implement a dynamic filter in real time audio.
What I want to do is to create a filter where I can change the cut-...
0
votes
1answer
52 views
Strange behavior from frequency to angular frequency in FFT
I have written a code to compute the Fast Fourier Transform of a simple complex exponential with frequency $f=50.0$, using scipy.fft. The code is written below:
...
1
vote
2answers
472 views
Difference between librosa.stft and scipy.signal.stft
I read the source code of librosa.stft and sicpy.signal.stft, and notice that the calculation results of STFT(short-time fourier transform) in these two libraries are quite different:
In scipy.signal....
0
votes
2answers
125 views
Scipy Butterworth highpass filter results in distortion and bloated output
Trying to use Scipy Butterworth filter to filter frequencies below 54 Hz from audio files. Audio files are stored as WAVs. Sample rate is 44100.
When I try using this filter the result is distorted (...
0
votes
2answers
207 views
Scipy fourier transform zero frequency spike (from DC offset) - de-meaning and hanning window have no effect
I am trying to plot the FFT of essentially a random signal that has a non-zero mean shown below.
The FFT of the signal is peaked over the zero frequency which usually indicates a DC offset. Although ...
1
vote
3answers
277 views
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....
1
vote
1answer
90 views
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 ...
1
vote
1answer
198 views
CWT at low scales: PyWavelets vs Scipy
Low scales are arguably the most challenging to implement due to limitations in discretized representations. Detailed comparison here; the principal difference is in how the two handle wavelets at ...
0
votes
1answer
55 views
How to calculate PSD if i have power vs freq spectrum?
i have a signal something like this
how to calculate PSD?
i have freq from 191000200 to 196500000
time gap or delta t = 1 or 2 sec, (what i mean is [tn] - [tn-1])
i will be computing in python any ...
0
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0answers
26 views
Python, Is there a way to find the properties of a subregion within a larger image region?
The goal: I have images with particles that I need to find the area of. Each particle also has four to five sub-regions that I need to know the area of. Think of a bunch of stripped shirts in a ...
3
votes
2answers
606 views
Are IIR filters (and specifically Butterworth filter) causal?
I am new to signal processing. I am learning now about filtering and I am trying to implement high pass filter (HPF),and later band-pass filter (BPF). I implement the filters in ...
2
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0answers
72 views
Filtering a square signal with a median filtering to preserve the edges
If needed, you can find my first post for this problem here.
I am trying to clean the following signal:
As proposed in the comment, I tried to use this post proposing 2 methods: median filtering and ...
1
vote
1answer
81 views
How do I set window length and shift length for computing STFT on Scipy?
Does nperseg=32, noverlap=16 mean the window length is 32mS with a shift of 16mS?
Refer here for more details
0
votes
1answer
55 views
Showing specific values in an STFT plot
I have a short term fourier transform plot that I plot using matplotlib's pcolormesh() function:
If I zoom in the plot, I see this:
Now, I want the plot to just ...
0
votes
2answers
248 views
Complex Samples (IQ) - Baseband Filtering
We are currently analyzing a large set of IQ samples in a desktop application and we are interested in implementing many different bandpass filters dynamically.
We realized, that working with scipy ...
3
votes
0answers
30 views
Are there any tools for generating fixed point filter implementations?
It's very easy to make a filter in Scipy or many other tools, but implementing this filter in fixed point in C or VHDL/Verilog is always a chore. I mean, in theory it's just a matter of adequately ...
0
votes
1answer
192 views
Difference between freqz vs freqresp in scipy?
I'm always confused that scipy has
scipy.signal.freqz, but also
scipy.signal.lti.freqresp / ...
1
vote
2answers
215 views
Hilbert transform with scipy.signal
I'm coding with python and I just started to use the Hilbert transform from scipy.signal. Consequently, to check the result I got I tried to verify a property of ...
0
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0answers
52 views
Why is there a difference in the spectrum of an audio file between Sonic Visualizer and my Python script?
I am working on a script which is creating a spectrum analysis from an audio file using SciPy and NumPy. Before I started, I analyzed the file using Sonic Visualizer, which got me the following result:...
0
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0answers
63 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, ...
0
votes
1answer
68 views
How to Save FFT output for fast read-in?
For a project, I'm reading in hundreds of short (4 sec) wavefiles and giving them to scipy fft for the frequency information for further processing/experimenting in various ways. Problem is, I want to ...
1
vote
1answer
502 views
Why is the number of frequencies decomposed in scipy.signal.stft() equal to the hop size?
I asked this over on StackOverflow first but figured you fine people might know more about signal processing (duh).
I'm trying to calculate the spectrogram of an audio file in python. There's a nice ...
