Questions tagged [scipy]
The scipy tag has no usage guidance.
0
votes
1answer
8 views
How to pad a array representing music to pad the stft of this array?
I have an array named samples of size (2, 1321967) representing an audio file. When I pass it to scipy stft with
...
0
votes
2answers
47 views
Delay in Savitzky-Golay filtering
I am applying a Savitzky-Golay filter to a signal, using the scipy function.
I need to calculate the lag of the filtered signal, and how much is it behind the original signal.
Could someone shed ...
0
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0answers
14 views
Scipy Deconvolve help
I was playing with the deconvolve method in scipy and I can't seem to get it working properly (I am still really new to DSP/deconvolution). I convolved a gaussian with a fwhm of 2.0e-9 with a ...
0
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0answers
33 views
Filtering out different narrow-band frequencies at once
I have asked a closely related question on SO at https://stackoverflow.com/questions/55168460/python-implementation-for-filtering-out-multiple-distinct-narrow-band-frequencie
but I am still unclear ...
0
votes
1answer
53 views
Third octave bandpass filter with python
I am very new to signal processing and coding which is why my questions might be really basic. I have a signal of the acoustic pressure p'(t) and I would like to use a third octave bandpass filter in ...
1
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2answers
48 views
Checking Parseval's Theorem for Gaussian Signal by Using Scipy
I'm trying to check Parseval's theorm for Gaussian signal. It's well known that fourier transform of $\exp(-t^2)$ is $\sqrt{\pi}\exp(-\pi^2 k^2)$. So I implement it by using quad and simps. I think ...
0
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0answers
18 views
Scipy Welch's gives different first element
I've re-implemented Welch's method and want to compare it to scipy.signal.welch. However, the first two and last elements of the resulting array are different.
My ...
2
votes
2answers
105 views
Why does a higher sampling frequency mess up my bandpass filter?
I was designing a bandpass filter in python using some of the scipy.signal modules.
I am plotting the frequency response of my filter to verify that my desired frequency is in the passband. However, ...
0
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2answers
106 views
How to calculate the PSD from the complex calculated STFT?
I have calculated the STFT with scipy python library:
...
0
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0answers
37 views
How to know the time of my window to calculate the STFT with python knowing only the length?
I am trying to implement a work presented in an IEEE paper where they have mentioned that the STFT was performed on the signal measurements to obtain a spectrogram with no overlap window of 3 min :
I ...
0
votes
0answers
36 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 (...
0
votes
1answer
1k views
Write a 440 Hz Sine Wave to .wav-File using Python and SciPy [closed]
This is my first post on DSP.SE! I'm a student in Computer Sciences and am just getting started with Signals and Systems, thus getting in touch with discrete signals and analyzing them.
I wanted to ...
3
votes
1answer
317 views
Scipy resample, “fourier method” explanation
I am seeking explanation of what "Fourier method" is that is described for resampling in documentation of resample() method. I want to downsample an array. I know what decimation is and how it works, ...
1
vote
0answers
209 views
real refractive index from Kramers Kronig relation
I have a measurement of the complex part of the refractive index $k$ (where the refractive index is $m = n + i\,k$) measured at a nonlinear grid of wavelengths or frequencies that span several orders ...
1
vote
1answer
500 views
How to filter out those outliers
I'm struggling to filter some data from an accelerometer. I need to do it in python (and not just on the device collecting the data) to fix the data I have, so that I can build some classification ...
1
vote
1answer
609 views
Amplitude of frequency bin in FFT doesn't match time-domain amplitude
I have a sinusoidal current that I am sampling at about 357k SPS. The current signal is about 3A pk-pk @ 750hz (top figure). I am wondering why when I take the fft using numpy/scipy's fft function, ...
0
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0answers
487 views
How does the Scipy implementation of CWT actually work?
I'm trying to use the SciPy implementation of the Continuous Wavelet Transform to analyze EEG data.
I am using The problem is that I have no idea what the width parameter should be. It says that it's ...
0
votes
1answer
326 views
How to Apply Gaussian Filter to Raw Audio Files in Python?
I am recording raw files in python to later break them into phonemes, but the noise in the surrounding environment is hampering the result. So, there is a need to apply a filter to the recorded raw ...
2
votes
3answers
138 views
Decreasing Sample Rate in DFT (FFT) for Audio Analysis
I'm working with audio data analysis through FFT algorithm.
My example audio is a sine wave at 440 Hz and 44100 Hz sampling rate.
FFT methods in programming, like ...
0
votes
0answers
445 views
Understanding scipy.ndimage.filters.convolve function
So I am using scipy.ndimage.filters.convolve function. I understood how it works for 2D matrices from the documentation. But when I apply this to 3D matrices it is ...
5
votes
1answer
146 views
Morphing between two FFTs
I'm a musician and I'm making a script that takes a wave file and snaps each of its frequencies from the fourier transforms to the nearest musical harmonic. Thanks to help from another question I ...
0
votes
1answer
50 views
Unexpected peaks in power density following downsampling and filtering
I first applied a 100 Hz lowpass filter to my data, which was recorded at 30000 Hz:
...
0
votes
1answer
181 views
Should scipy.signal.coherence be 1 for single input and output signals?
I am trying to calculate the coherence between input and output signals. I thought I could work with a single input and a single output time series and calculate the coherence $\gamma^2$ between them. ...
1
vote
1answer
48 views
Help generating coefficients for basic FIR LPF
I'm trying to generate coefficients for a FIR low pass filter to be used in an FPGA. I'm using python (scipy.signal) to attempt to do this, but am having trouble getting coefficients in a usable form....
0
votes
1answer
193 views
Outlier Detection after Detrending a Time Series With Missing Values or NaN
Goal
Substitute outliers in a time series by most recent valid data
Problem
The time series (end-of-day stock prices) has several 'uncomfortable' properties:
It is non-stationary and can have ...
5
votes
1answer
771 views
How to generate random samples of Gaussian distribution directly in the frequency domain?
One can easily draw (pseudo-)random samples from a normal (Gaussian) distribution by using, say, NumPy:
...
-1
votes
0answers
90 views
Extract Db and Hz from the results of FFT from scipy.fftpack [duplicate]
I got the FFT results of a short slice of human speech using scipy.fftpack. I know that this is a list of complex numbers. What should I do to extract Decibels vs Hz from the result?
Eventually I ...
0
votes
2answers
80 views
Can I combine an IIR (an EWMA) with a maximum?
I'd like to have a exponentially weighted moving average (EWMA) which is raised to the value of the input signal whenever this is higher than the filter output. This taking of the maximum shall take ...
0
votes
2answers
4k views
Avoiding “RuntimeWarning: invalid value encountered in log10” when converting FFT data to dBFS
I've attached some code below that I'm having some issues with. Basically, I need to write a function to get the dBFS value of a signal at a specified Hz value, at a given channel in a .wav file. ...
3
votes
3answers
3k views
Why is Scipy implementation of Hilbert() function different from Matlab implementation of the function?
I am trying to fit Hilbert envelop to a high frequency ultrasonic signal of frequency 250 KHZ and sampling rate 12000000. Raw signal looks like below: .
I used hilbert() function from scipy.signal ...
1
vote
1answer
428 views
Trying to implement MATLAB $\tt pwelch$ in Python
I'm implementing an existing MATLAB script in Python and noticing some differences in the behaviour of MATLAB's pwelch function compared to ...
0
votes
1answer
171 views
Delay filters in Python using for loop and $\tt lfilter$
I have these two filters as given in recursive form:
\begin{align}
y_1[i] &= y[i] - y[i-d] + 1.2y_1[i-d] - 0.8y_1[i-2d]\\
y_2[i] &= y[i] - 2y[i-d] + y[i-2d]
\end{align}
where $d$ is an ...
2
votes
1answer
1k views
How to compute the power bands of an eeg signal using python?
so I have an eeg signal (edf format) that has 25 channels and 248832 entries, sampling frequency of 512Hz. I have to compute the frequency bands:
– Delta: 0.1-4Hz
– Theta: 4-8Hz
– Alpha: 8-12Hz
– ...
3
votes
0answers
4k views
Downsampling and upsampling of a signal in Python
If I want to downsample a signal in Python, is it better to use method resample from SciPy Signal Processing module or method decimate from the same module? What is the difference between these two ...
0
votes
1answer
495 views
Welch spectrogram
I have been using scipy's spectrogram function (STFT) to compute a PSD spectrogram for a non-stationary signal. I provide X length window (with nperseg = X/10) each ...
1
vote
0answers
155 views
Understanding why spectral flatness cannot be computed
I have a real signal recorded 512Hz for 1s. After resampling the signal at 256Hz, I would like to compute its spectral flatness. To do so, I start by taking its discrete Fourier transform with ...
0
votes
1answer
22k views
Convert RGB Image to Grayscale and Display It (Python + Matplotlib) [closed]
I just started learning image processing and I was trying to read a RGB image then convert it to grayscale. I was hoping for something like this:
However, what I get was:
I tried using both scipy ...
2
votes
1answer
153 views
consecutive filtered blocks with filtfilt
I'm doing basic signal processing in Python. I'm filtering consecutive blocks of a signal with scipy's filtfilt (to get zero phase). I would like to concatenate several blocks after filtering, however,...
3
votes
1answer
732 views
Python different autocorrelation with FFT and non-FFT
Im trying to calculate the autocorrelation of soundwaves when I noticed that I get different results with scipys FFT based and with numpys methods.
The 4 functions Im using:
...
-1
votes
1answer
430 views
Forward Backward filter Scipy - $\tt signal.filtfilt$ changes the amplitude when $\tt signal.butter$ is used with $\tt btype='high'$
In the plot below the blue wave is the original signal. The orange wave is after the low pass filter. The green wave is after the high pass filter.
I have a noisy ECG signal stored in the ...
1
vote
1answer
121 views
Issue with the time vector returned by $\tt signal.spectrogram$ function
I'm puzzled by some very simple concept with building up a spectrogram.
Here is a toy example of the issue:
...
2
votes
1answer
1k views
How to implement bandpass filter on complex valued signal?
I am using Scipy to implement bandpass filter but it assumes that positive normalized frequency is passed but I & Q samples range from [Fc-Fs/2,Fc+Fs/2] where Fs is sampling frequency & Fc is ...
0
votes
1answer
981 views
How to design bandpass filter in python when centre frequency is greater than sampling frequency?
I implemented basic bandpass filter using Scipy resource. But how to implement the same when signal is centred at non-zero centre frequency with centre frequency > sampling frequency.
I trying to ...
1
vote
1answer
3k views
How to normalize output of $\tt scipy.signal.correlate$
I have 2 different signals and I'm trying to cross-correlate then using Python 2.7 and scipy.signal.correlate. How do I normalize my results (such that the max ...
4
votes
2answers
534 views
Do DCT results contain phase spectrum?
I've been working much with numpy.fft lately where just like the documentation says:
When the input a is a time-domain signal and ...
4
votes
3answers
14k views
Calculating values of frequency bins in Python
I have to use FFT to determine the period of waves inside a signal, after applying the FFT on a window of 10000 point from a signal I get something like this:
What I don't understand is that FFT is ...
2
votes
2answers
2k views
Python butter filter: choosing between analog and digital filter types
I have a system that performs wireless sampling of data about every 7.5ms (133Hz). Due to it being wireless, I get occasional data drop out. I want to construct a LP butter filter with cut-off ...
1
vote
2answers
160 views
problem with decimate in scipy 0.18
I use scipy.signal.decimate to downsample a large spectroscopic data-set.
This has worked superbly so far.
...
1
vote
2answers
811 views
Why does python's scipy.signal.dimpulse introduce delay in impulse response?
Consider a simple linear, time invariant system of the form:
$y_k = cy_{k-1} + (1-c)x_k$
The impulse response of this system can be computed by either dimpulse or by applying lfilter to a vector ...
1
vote
2answers
207 views
Need of $\tt abs()$ method when plotting a power spectral density for a given dataset
I am a newbie in signal processing and would like to know the significance of using the abs() function and squaring the values received as an output of ...
