# Questions tagged [scipy]

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31 views

### Why are low frequency peaks not sharp in scipy fft?

I am using numpy/scipy to plot graphs of sine waves. frequencies at 15 Hz or higher give nice, sharp peaks, but at lower frequencies, the peaks are smeared and the actual peak frequency can't be seen ...
23 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 ...
19 views

### Can't seem to get welch function in scipy work correctly

I'm trying to learn DSP through using Python's scipy package. I have measure some 200Hz signal from a machine. Now I want to inspect the spectral density of the signal. Here's the signal plotted out: ...
19k views

### Calculating values of frequency bins in Python

I have to use FFT to determine the period of waves inside a signal. After applying FFT on a window of 10000 point from a signal, I get something like this: What I don't understand is that FFT is ...
87 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 ...
5k 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. ...
299 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 ...
8 views

### Logical Steps to segmenting Lung Fissure Structures

I am given the task to do the Lung Major Fissure Segmentation in a CT image to find it's position in an image. This is what a Major Fissue looks like: https://www.med-ed.virginia.edu/courses/rad/cxr/...
81 views

### Python Hilbert does not seem to calculate the envelope

I am following the example from: https://docs.scipy.org/doc/scipy/reference/generated/scipy.signal.hilbert.html And although I can replicate their example, it does not work with my data. This is the ...
79 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), ...
30 views

### Spectrogram using SciPy - bad scaling of the timeline [duplicate]

I have a real value signal which has 197 samples (every 1 second). I made its spectrogram using the SciPy library: ...
48 views

### Negative Exponential Filter SciPy

I'm trying to transform a time series with a recursive filter to model a feedback. I was able to do a simple filter like : ...
160 views

### How to convert a spectrogram back to a signal [duplicate]

I'm converting a signal to a spectrogram, manipulating that (nonlinear stuff), and then want to use the modified audio signal. I can make it so the segments are not overlapping, but am unsure how to ...
39 views

### Losing lowest Frequencies in frequency modulated signal, rest of spectrum is fine

For several reasons I am attempting to re-modulate a de-modulated FM (as in WFM Radio) signal using python. Demodulating the initial signal goes well, it produces the PSD chart below which looks just ...
37 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 ...
113 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 ...
58 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 ...
5k 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 ...
40 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 ...
25k 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 ...
179 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, ...
411 views

### How to calculate the PSD from the complex calculated STFT?

I have calculated the STFT with scipy python library: ...
50 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 (...
74 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 ...
205 views

### Beginner Question: Extracting Features for Image Classification

I'm a Python programmer, but a beginner to image processing :) Apologies if this isn't a suitable question for the forum, happy to rewrite or move. I want to create a supervised classifier to ...
3k 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 ...
824 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, ...
340 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 ...
2k 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 ...
154 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: ...
1k 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, ...
757 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 ...
401 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 ...
276 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 ...
208 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 ...
54 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: ...
332 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. ...
2k 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 – ...
60 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....
971 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: ...
239 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 ...
1k 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 ...
99 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 ...
575 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 ...
234 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 ...
6k 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 ...
657 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 ...
198 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 ...