7
votes
Accepted
Why does a signal with constant frequency have spots that changes colors at a specific value of scale (and so frequency) in the scalogram?
Re: real part
There are oscillations because that's what the wavelet transform is - a decomposition into zero-mean, localized oscillations. CWT is convolution (rather, cross-correlation) of signal ...
- 8,805
4
votes
Accepted
PyWavelets CWT: normalization? Vs Scipy?
Let's follow the math from incubation to delivery. It begins with psi, a rescaled morlet2 (as shown previously) at a scale $a=64$...
- 8,805
3
votes
Accepted
How is wavelet center frequency computed?
Short version: DFT's bin indices are input length-dependent; "center frequency" is measured relative to the function generating the wavelet. Generated length can vary, so must be accounted ...
- 8,805
1
vote
Python's equivalent of MATLAB's cwtfilterbank
Avoid PyWavelets and scipy. ssqueezepy's (disclaimer, am author) scales='auto' is motivated similar to MATLAB's cwtfilterbank, ...
- 8,805
1
vote
Accepted
PyWavelets CWT implementation
First see "Naive Breakdown" in a below section. Onto PyWavelets: the algorithm was found on Github to stem from an old MATLAB implementation, but it provides no details on coding the wavelet ...
- 8,805
1
vote
Accepted
Discrete wavelet decomposition over detail coefficients
Indeed, that will be called a wavelet packet.
No, you will split the cD3 band in two equal parts: $[Fs/16,3Fs/32]$ and $[3Fs/32,Fs/8]$ as you mentioned.
Warning though, the frequency bin you ...
- 31.7k
1
vote
Pywavelets applied to time series
For DWT, the original signal is downsampled by a factor of two at each level of decomposition. It's based on filter banks, in which data is downsampled by a factor of 2, i.e., by a low pass filter - ...
- 11
1
vote
How to do appcoef and detcoef using pyWavelets?
From the matlab docs https://www.mathworks.com/help/wavelet/ref/appcoef2.html
the appcoef function does: "If N = NMAX, then a simple extraction is done; otherwise, appcoef2 computes iteratively ...
- 211
1
vote
Accepted
How to plot the shape of a 2D wavelet?
Transform to time domain
Center
Plot real & imag separately, or use complex colormap, or take modulus
Results below.
Minimal code
...
- 8,805
1
vote
PyWavelets SWT versus MODWT
The answer to your question can be found here :
https://github.com/PyWavelets/pywt/issues/600
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