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Questions tagged [wavelet]

A wavelet is a wave-like oscillation with an amplitude that starts out at zero, increases, and then decreases back to zero.

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What is "modified frequency slice wavelet transform"?

What is "modified frequency slice wavelet transform"? It was written in an article but It's not been described on the web.
mohammad rezza's user avatar
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Question about the derive of a theory of the scaling function in the wavelet analysis

Page 5 in link: For the scaling function, it holds: $\int \phi(x)dx = 1 $ or, equivalently: $\Phi(0) = 1$ How is this derived?
WilliamW's user avatar
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Question about the definition of wavelet

From the definition, we will use wavelet for expanding signals the same way Fourier series use sinusoids: $$f(t) = \sum a_{l}ψ_l(t)$$ The definition then defines that if $ψ_l(t)$ form an orthonormal ...
WilliamW's user avatar
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Discrete Wavelet Transform With Overlaps

Maybe this is a trivial question, but I couldn't find an answer yet. Is there some discrete wavelet transformation which works with overlapping wavelets (half on half)? In other words, is there some ...
fweth's user avatar
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How to get frequency axsis from pythnon CWT

I did the cwt on a chirp signal : ...
Fearless_Wolf's user avatar
2 votes
3 answers
190 views

Algorithm to detect down-up-down pattern in time series

I'm trying to write an online algorithm in Python to detect this below Down-Up-Down pattern in time-series. It's not hard to do roughly if I calculate 3 contiguous non-overlapping moving averages, and ...
Jase's user avatar
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2 votes
1 answer
1k views

Wavelet transformation to analyse time series

I am new to wavelet transformation. I am learning it as a tool for signal processing. I have a time series that I want to analyze. I tried to learn wavelet transformation by applying it to a periodic ...
The Wanderer's user avatar
1 vote
1 answer
200 views

Weird Noise arises on the small scales: one question about the fast CWT algorithm implemented in real space

Background: I am learning an interesting Fast CWT algorithm(PPCWT) by reading this paper published in 2019. The algorithm is summarized as below. The continuous wavelet transform of a signal can be ...
Wang Yun's user avatar
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268 views

Estimate Power spectral density using Discrete wavelet transform form pycwt

I want to estimate the Power spectral density using Discrete wavelet transform and a Morlet Wavelet. Bellow you can find the function I am using. Any comments or suggestions on wether or not the ...
Jokerp's user avatar
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1 answer
484 views

How to calculate FIR filter coefficients?

I have EEG signal data (19 channels) sampled at 128Hz. I am trying to retrieve the coefficients that are mentioned in a research paper included below. To decompose an EEG signal, a digital FIR filter ...
M.V.Ramprakash's user avatar
2 votes
1 answer
84 views

Do wavelets at a given scale $2^j$ sum up to 0 when summing over all discrete translations of size $n$?

suppose I have a wavelet $\psi:\mathbb{R}\to\mathbb{R}$ satisfying $\int \psi(t)dt=0$. Do we also have that for all $j\in\mathbb{Z}$ $$ \langle f\,,\sum_{n\in\mathbb{Z}} \psi_{j,n}(t) \rangle = 0 $$ ...
StefanKolek Martinez de Azagra's user avatar
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1 answer
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Practical applications of wavelets

I know wavelets were all the rage a few years ago, but I missed that boat and am wondering if it is worth putting significant effort into learning about them. My impression is that they were a little ...
Gillespie's user avatar
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What is the purpose of wavelet extraction from the seismic trace?

I did a basic google search but, I wasn't really satisfied with the output info. I would love to know what exactly we can do with the extracted wavelet. What kind of information extracted wavelet can ...
Fearless_Wolf's user avatar
1 vote
2 answers
126 views

Questions about the paper titled "Rapid computation of the continuous wavelet transform by oblique projections"

This paper introduced a fast method for computing the real CWT and achieved $O(N)$ complexity per scale. However, in the context of this article, I'm not sure what the definition of oblique projection ...
Wang Yun's user avatar
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What is the most likely imaging processing step associated with the term 'Riesz' in clinical MRI?

I understand that it is an odd question, and this is arguably not the ideal forum, but I am at a loss. Some of you may be familiar with DICOM as a consensus or standard format for medical image ...
Antoni Parellada's user avatar
2 votes
2 answers
418 views

Interpretation of wavelet trasformation (synchrosqueezing)

I'm working on a dataset of spectroscopies and i'm classifying them by transforming the 1D signal into a 2D one by the ssqueezepy library. For instance, consider to ...
PiEmmeC's user avatar
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3 votes
1 answer
244 views

Inverse continuous wavelet transform output has significant error in magnitude and phase

For the inverse continuous wavelet transform, I am using a for-loop which runs through each frequency. At each frequency, I convolve the corresponding morlet wavelet with the signal at that frequency, ...
user63598's user avatar
1 vote
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Meaning of "standard deviation noises of wavelet coefficients"

I am currently working on a research project based on the paper titled A deep learning approach for anomaly detection based on SAE and LSTM in mechanical equipment. The paper uses data in the acoustic ...
frostblue's user avatar
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1 answer
439 views

Not showing the right frequency in ssqueezepy CWT plot

I am following the ssqueezepy simple example. The plot should show f=12 but it shows around 33. Is this a bug or have I scaled the y-axis wrong? Also the plot is not a straight plot as it waves at ...
Eddy Piedad's user avatar
2 votes
1 answer
85 views

what are the advantages of higher-order Generalized Morse Wavelets?

What are the advantages of the higher-order Generalized Morse Wavelets in comparison with the first-order ones? Are they also more computationally expensive?
Eddy Piedad's user avatar
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1 answer
486 views

Is online Continuous Wavelet Transform possible?

I have recently created a real-time STFT with 50% overlap. I wanted to know if this window-based is possible for scalogram, especially continuous wavelet transform. I haven't found anyone ...
Eddy Piedad's user avatar
3 votes
1 answer
546 views

Does Fast Continuous Wavelet Transform (fCWT) have theory-supported novelty or just simply a computation optimization?

A recent publication, The fast Continuous Wavelet Transform (fCWT), enables real-time, wide-band, and high-quality, wavelet-based time–frequency analysis on non-stationary noisy signals. I'm a ...
Eddy Piedad's user avatar
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0 answers
21 views

Is it possible to update wavelet packet from fixed-sized window of data without repeating the whole process?

Assume that a scalogram is generated from performing wavelet packet in a fixed size window of data. Then, is it possible to update the scalogram with the incoming and outgoing data points without ...
Eddy Piedad's user avatar
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163 views

Standard method of smoothing (amplitude envelope) of continuous wavelet transform

My basic question is, "What is the standard way to post-process/smooth a continuous wavelet transform result to measure the wavelet's activation at a specific frequency?" When using wavelets ...
Sam Lapp's user avatar
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232 views

Down-sampling a signal after convolution

I was trying to understand more about image compression using the Wavelet transform and I got quite confused about the down-sampling step. I took a picture from here for reference: At each step a ...
user avatar
3 votes
2 answers
333 views

Calculating signal power from Continuous Wavelet Transform in MATLAB

I would like to ask a question about the calculation of the signal power using CWT in Matlab. Assume a signal of length N points with sampling frequency $f_{s}$. Using conventional approach, the power ...
M-S's user avatar
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76 views

Discrete wavelet transform - DWT (beginner)

I recently stumbled upon this article: A wavelet-based multivariate multi scale approach for forecasting (PDF) In the paper they use DWT and I am having trouble understanding how to construct them. ...
minattosama's user avatar
2 votes
0 answers
85 views

Estimation of scaling exponent in the wavelet leaders multi-fractal formalism

I am trying to extract multi-fractal features from time-series data by estimating the singularity spectrum using the wavelet leaders multi-fractal formalism (WLMF) method. Specifically, I want to be ...
Kevin's user avatar
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58 views

Output of pywt.dwt

I am using 'dwt' function and I can't understand what the values in the approximation and detail lists actually represent. I have read that in each level the function uses high pass filters and low ...
yba's user avatar
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1 answer
336 views

How to achieve a periodized Mexican hat wavelet with period L by using Python?

Now I have a scaled Mexican hat wavelet, i.e. $$ \psi(a,x)=\frac{1}{\sqrt{a}}…\left(1-\frac{x^2}{a^2}\right)e^{-x^2/(2a^2)}, $$ which decays quickly along the x-axis. Here I want to define a ...
Wang Yun's user avatar
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Adjust Wavelet output to CNN

I want to extract features from the signal using DWT and then feed the results into CNN, after calling the 'dwt' library function I got a runtime error. ...
yba's user avatar
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1 vote
0 answers
85 views

Why some implementation of Wavelet transform use reconstruction filter instead of decomposition filter?

I'm using MODWT (Maximal Overlap DWT) to extract features from a signal. Matlab implementation is using reconstruction filter instead of decomposition filter. In the first level of modwt decomposition,...
Rafael Santos's user avatar
-1 votes
1 answer
91 views

How to inject a 2D plane sine wave to the array of seismic sensors?

I've several sensors positioned at various points in the $X$,$Y$-Cartesian coordinate system, and I've experienced a problem to inject a planar Sine wave to the spatially positioned sensors, the ...
Alan22's user avatar
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1 answer
247 views

Calculating instantaneous power of a frequency band in a 1-d signal

I am trying to calculate the instantaneous power of a 1-d signal within a particular frequency band in an on-line, real-time, streaming application. I have tried using sliding window FFTs but these ...
BeginnersMindTruly's user avatar
1 vote
1 answer
255 views

Classification of Signals using Features Extracted from Wavelet Scattering Coefficients

I have a set of RF signal samples of 2s length each recorded at 2MHz sampling rate, such as this IQ file: https://www.dropbox.com/s/dd6fr4va4alpazj/move_x_movedist_1_speed_25k_sample_6.wav?dl=0 I can ...
rshah's user avatar
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0 answers
400 views

Difference between Discrete Wavelet Transform and convolution

Sorry in advance if my question is too dumb. I'm going through the book of Mallat, and from what I understand, the approximation/wavelet coefficients $a_j[n] = <f, \phi_{j,n}>$ and $d_j[n] = <...
Elenie's user avatar
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2 votes
1 answer
60 views

When is a continuous wavelet in the Schwartz space?

I was thinking if the continuous wavelet transform can be in the Schwartz space or not? If someone knows can help me and tell me what are the conditions on the mother wavelet or the signal so that the ...
cywar hkimi's user avatar
-1 votes
1 answer
281 views

Why does using a log scale ruin (warp) my scaleograms?

I'm trying to make a scaleogram of neural data using the continuous wavelet transform (with Morlet wavelets). As a starting point, I use just a simple sine wave built from two frequencies, 50 and 80 ...
neverreally's user avatar
0 votes
1 answer
2k views

How to set the "widths" parameter for continuous wavelet transform using Morlet wavelets? (scipy.signal.cwt)

I'm trying to use scipy.signal.cwt() to do a time-frequency decomposition of neural data. However, I don't completely understand the "widths" parameter. I ...
neverreally's user avatar
0 votes
1 answer
143 views

Wavelet Scattering (Kymatio) Zero Divison Error

I'm attempting to make use of wavelet scattering to analyse my signal samples. The example IQ Wav file I am using is as follows: https://www.dropbox.com/s/dd6fr4va4alpazj/...
rshah's user avatar
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1 vote
0 answers
149 views

Function reconstruction after a DWT

I'm new to this field, my apologies if my question sounds too naive. From what I understood, a function can be decomposed using the scaling function at a given scale $\{\phi_{J, k}\}_{k \in \mathbb{Z}}...
Carline's user avatar
  • 11
1 vote
1 answer
747 views

Pywavelets applied to time series

I'm new on this field. I am applying a discrete wavelet decomposition to a timeseries and the decomposition yields subsets of the data, specifically the half. Nothing wrong with that since that is the ...
Sherwood's user avatar
-1 votes
1 answer
119 views

Why NMSE is the same as output SNR but with an opposite sign?

I am doing denoising on signal, and as performance measures Normalized Mean Squared Error (NMSE) and output-SNR between original/clean and denoised signals are used. However, for several cases the ...
Fktime's user avatar
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Detecting whether the signal is increasing intensity or decreasing intensity

I am trying to determine whether the signal is increasing intensity, decreasing intensity, fade-in, fade-out or peak using an audio file. The graph has an x-axis with time and a y-axis with the data. ...
user61749's user avatar
1 vote
1 answer
839 views

How to make a time/period (1/frequency) plot with CWT

This is a question about producing a time/period (1/frequency) plot from a CWT, instead of the time/scale output. I am trying to use the ssqueezepy python library to perform the CWTs. Then I ...
vibe's user avatar
  • 290
-1 votes
1 answer
282 views

How can the detail coefficients in discrete wavelet transform (DWT) be downsampled?

This question is asked with reference to this paragraph For the high-pass filter, the frequency content lies in the range $\frac{F_s}{4} \rightarrow \frac{F_s}{2}$. There is no content in the range $...
Jk Er's user avatar
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4 votes
1 answer
75 views

custom raw compression

I'm planning to acquire between 50k and 200k image per day with a 50MPixels (or 68MPixels or 130MPixels) sensor; I'll be acquiring the raw data (10 or 12 or 14 bits) from the sensor through SLVS-EC ...
Soleil's user avatar
  • 139
2 votes
0 answers
35 views

Implementation boundary-corrected wavelets on the unit interval

I was wondering if there is a 'ready-to-use' implementation available of the (boundary-corrected) wavelets constructed in Cohen, Albert, Ingrid Daubechies, and Pierre Vial. "Wavelets on the ...
Brazilian Cérebro's user avatar
1 vote
0 answers
68 views

Near Real Time Algorithm For Approximating Fundamental Frequency

I'd like to analyse the notes being played on a cello C2(65.4Hz) to C6(1046.5Hz) recorded on a PC and thus a likely sampling rate of 44.1kHz. If I can get that to behave then I'd like to be able to ...
TJA's user avatar
  • 113
2 votes
1 answer
112 views

Choosing a good low pass filter in the wavelet scattering transform

What's the impact of a specific filter $\phi$ when building the wavelet scattering transform? I mean, if I compute the MFCC choosing different windows, (Hamming, Blackman, etc.), the behaviour ...
dac's user avatar
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