# Questions tagged [scipy]

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### Welch method implementation not smooth

I have been trying to recreate the welch method implemented in scipy.signal by hand but my results don't look close enough in my opinion. How come the scipy.signal.welch method is displaying much ...
2k views

### Help on audio filter with FFT on python

I need to take a .wav audio file that's noisy and filter out some noise. I have to do it using Fourier Transform. After some days researching and experimenting, I finally made a working function, the ...
386 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 ...
1 vote
80 views

### reproduce Scipy's stft

I failed to reproduce Scipy's stft. When I have tried to remove all the possible modifications and go the minimal example, I converge to the following: ...
72 views

### Numerical issues in scipy's Savitzky Golay filter coefficients for large polynomial order

Consider the design of a Savitzky-Golay filter of window length 101 and (high) polynomial order 20. Using scipy version 1.10.1, the filter coefficients can be obtained in python as: ...
727 views

### (Python - Scipy - Wave files) Can a float signal be written with values higher than 1?

While developing an application, I noticed strange behaviour while using scipy.io.wavfile to write audio files. The documentation says that floating-point data is written within a range between -1 and ...
1 vote
162 views

### How to construct a bandpass filter with minimal loss in amplitude/power near the lower and upper frequency limit in Python?

I am analyzing functional MRI data with a sampling rate of 1 second (1 Hz). The frequency band that I am interested in is 0.01-0.2 Hz. Regarding measurements, I am interested in computing (1) the ...
517 views

### Why doesn't the convolution of the impulse response match the system's output?

If you define an LTI system sys in scipy, you may conveniently feed an input x to it to get ...
3k 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 in these two libraries are quite different: In scipy.signal.stft, the stft result is ...
1 vote
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1 vote
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### Scipy and Matlab Spectrogram not matching

I am trying to replicate a spectrogram from MATLAB in Python. I've read other posts but they either don't use complex data or the data doesn't match between languages. I've defined my FFT length (<...
1 vote
203 views

### Filtering with scipy sosfiltfilt generates flat edge artifact

I need to filter some array of data before differentiating it, I do this so I don't drown the signal in noise. It's also important that no delay is applied to the signal, that's why I decided to use a ...
90 views

### Initial conditions of backward filter for forward-backward filtering on chunked real data in python

I have to apply a downsampling filter on a realtime data stream (signal) and I want to do it in python. The data is sampled at 16 kHz and loaded in a loop in chunks of 1 second. I have to downsample ...
690 views

### Amplitude extraction using STFT

I'm trying to recover amplitude/magnitude from an audio stream. I'm using FFT to go from time domain to frequency. If I feed in a signal of known amplitude, the results I get from either windowing or ...
460 views

### Why does changing the format of an audio file from int16 to float produce jitter?

I read an audio file (an instrumental music file that is mono and 16000) with wav.read (read function from scipy.io.wavfile.) This function gives me a data file in int16 format. When I change the type ...
385 views

### Scipy filter analog vs. digital

It would be greatly appreciated if the usage of the python package scipy's filter (e.g. butter) analog=True argument could be explained. I don't understand what is meant by this (any signal being ...
158 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:...
1 vote
135 views

### using scipy.signal.sosfilt to filter a stereo signal with zi, zf

I'm stuck trying to filter a two-channel signal using sosfilt() with the zi initial state. I need to use the zi parameter so I can carry the filter state over ...
319 views

### python how to demodulate iq fm signal that was moved to 0 frequency

I am struggling with implementing FM demodulation for IQ samples that has 0 center frequency from RTL-SDR ... I have found the following algorithm for FM demodulation, see FM demodulation: ...
15 views

### Extract PVC feature from singal to train the ML model with PVC characteristics

I have ML model which is trained on Afib, Normal, Other - 3 class. Currently when I am testing the model with unseen database, sometimes it identify PVC singals as Afib class. For example - enter ...
1 vote
138 views

### Possible error when finding group/phase delay in scipy

After designing a "least square optimal" FIR filter I wanted to find the group/phase delay, defined as: $P(\omega) \triangleq - \frac{\Theta(\omega)}{\omega}$ (Depending on the literature ...
10k views

### downsample signal to a specific number of samples in Python

The Python Scipy library provides several functions to downsample signals, but they all have limitations: The resample function is based on Fourier method, which means it assumes periodic signals. ...
206 views

### find out ideal window size for coherence analysis - python

Is there a general formula I could use to calculate the ideal window for the window argument in the function ...
337 views

### Signal Reconstruction Using Scipy.signal.cwt

Can someone explain to me how I can reconstruct a signal using the scipy.signal.morlet2? The codes in the link only allows one to do a fourier transform using the morlet wavelet, but there is no such ...
1 vote
38 views

### Convert MUSIC algorithm to EV

I write some code, but result looks very strange: ...
1 vote
93 views

### Prony method doesn't work

I have used the code from: https://github.com/quantumlib/OpenFermion/blob/v1.5.1/src/openfermion/linalg/wave_fitting.py#L41-L76 try using with my signal: ...
63 views

### Why is DFT magnitude less than expected?

Code for signal: ...
225 views

### scipy convolve and fftconvolve return different output [closed]

I'm writing an autocorrelation function using and I noticed a difference between fftconvolve and convolve that should use fft if it's faster. This is my function with convolve: ...
256 views

### Vectorizing a biquad filter (python / numpy)

I'm having a lot of fun writing signal processing code in Python / numpy, and I'm resisting the urge to pre-optimize the code. But my biquad implementation is slower than I want. Here's the inner ...
1 vote
9k 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 ...
298 views

### Jerk detection in accelerometer data

I want to detect jerk from accelerator data i.e. values beyond 1.57 m/s^2, but due to the high frequency nature of the sensor (400 values per second), it gives multiple jerks instead of one. How can I ...
524 views

### How to convert between 2d convolution and 2d cross-correlation?

I am using cross-correlation for the purposes of image stabilisation. The images which I'm processing can sometimes be rather large. The contents of the image are often repeating patterns. For these ...
1k 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 ...
1 vote
435 views

### detrend a signal with break point but without jumps

Yesterday I asked a question and got the answer to detrend my time series which I think is really better than applying a highpass filter. So I read the description of scipy.signal.detrend and there I ...
1k 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, ...
378 views

### How to get scipy remez to give matlab firpm answer?

If I run this in matlab: h = firpm(100,[0 0.1 0.2 1],[0 0 1 1]) and this in scipy: h = remez(100,[0, 0.05, 0.1, 0.5],[0, 1]) I ...
1 vote
156 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 ...
1 vote
407 views

### Constraints on number of taps in a FIR filter vs. FFT length

I want to implement a FIR highpass filter for acoustic signals. I generate the FIR using Python's SciPy code: ...
410 views

### Why does Python welch give me a different answer from MATLAB's pwelch?

I am trying to implement the following line of MATLAB code: [pxx, f] = pwelch(data,[],[],4096,F_S) in Python. Knowing that MATLAB using a Hamming window type that ...
572 views

### How does SciPy's Welch function change the shape of the data?

I am working with some time series data with a shape of 8064. The data is actually the popular EEG data called DEAP. It basically is a 3D array of size (40, 40, 8064) and here is the link to the ...
83 views

### Decimate a signal whose values are calculated, not stored

tl;dr I'm looking for something like Scipy's decimate function, but one that takes in a generator, rather than a Numpy array. I am turning on and off a light using ...
289 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. ...
129 views

### Understanding FFT bins interpretability

I am familiar with the continuous Fourier transform yet the more I try to understand FFT, the more I'm confused. If we've got a discrete N sample signal, FFT is a faster way to calculate DFT. If ...
223 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 ...