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.
517
questions
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1answer
23 views
Difference between Gabor filtering and Discrete Wavelet Transform
Both Gabor filtering and discrete wavelet transform (DWT) analyze the image in both spatial and frequency domains, unlike Fourier transform which analyzes the image only in the frequency domain. What ...
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1answer
36 views
How do I implement a footstep recognition algorithm? One that recognizes the start and end points of each footstep?
I have some time series data captured from a person's footsteps/strides (specifically, a person on rollerblades). It came from an IMU sensor placed on a person's boot. Each data point captures ...
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11 views
Wavelet, scaling, detail, and smooth/approximation coefficients
I was reading through the documentation for the R wavelets package and doing a little experimentation and noticed that the modwt ...
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22 views
PyWavelets SWT versus MODWT
I'm just learning about wavelets and the PyWavelets package. I saw a reference to MODWT, which led me to the SO post here and then to this Python package: https://github.com/pistonly/modwtpy
What ...
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1answer
24 views
wavelet_transform
I have a signal
$$Y=f(t),$$
which I want to show the anomalies, using the wavelets transform.
I don't know if I use the CWT or the DWT and which mother wavelet could I use?
2
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1answer
60 views
Scalograms in python
I am reading this paper to learning basic concepts of dsp and I want to reproduce the following scalogram of a test signal (fig 4.2 of the paper):
It has been produced from the discretization of the ...
1
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1answer
30 views
3D (time, scale, amplitude) plot in Continuous Wavelet Transform
I will be extremely grateful if someone could please answer this basic question.
How can one plot a 3D (translation, scale, amplitude) plot from the Continuous wavelet transform (CWT) coefficients?
...
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1answer
25 views
How does signal scaling affects stationary wavelet?
I'm currently working on some signals recorded with different sensors with different adc resolutions. I wonder how this different resolutions affect signal's stationary wavelet. Does it just changes ...
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1answer
52 views
Are the Daubechies 4 wavelet function and scaling function dimensionless?
If the dimension of the independent variable $x$ of $f(x)$ is length, i.e. $[x]=L$, then what is the dimension of Daubechies 4 (hereafter D4) wavelet and scaling function?
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42 views
Regarding custom wavelets and their validity
I've recently started working with wavelets, and want to focus primarily on Discrete Wavelet Transform. For experimental purposes, I use the PyWavelets library in Python. In one of my tests, I tried ...
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0answers
13 views
Stockwell S-Transform and multitapering
I want to estimate just the spectral amplitudes at different time points using S-transform given a noisy signal. Would I benefit (in terms of noise reduction) from an approach used in multi taper ...
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0answers
25 views
Pros/Cons to using Spectral and Diffusive Graph Wavelets
As I understand, there are two major methods of constructing wavelets on graphs. Spectral wavelets, from David K Hammond et. al, and diffusive wavelets from Coifman and Maggioni. I can't quite parse ...
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32 views
Check vanishing moment property of db4 wavelets
I am reading the book "a primer on wavelets and their scientific applications" by James S. Walker. In chapter 3, Property I on page 46 says that if a signal $f$ is linear, then the $k$-level ...
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41 views
energy normalization across different scales in case of discrete wavelet transform
In case of continuous wavelet transform (CWT), the wavelets are generated from the mother wavelet by scaling and translation. To achieve energy normalization and to ensure that all wavelets have the ...
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25 views
Why the inverse discrete fourier transform of the Ricker pulse isn't the same as the Ricker pulse in time domain?
Question
I'm trying to use Python's scipy library to compute the IDFT of the Ricker wavelet function and compare it with the analytical time-domain version of the same function. When I compare the ...
1
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1answer
41 views
Why discrete wavelet transforms use sampling rate 2 and need signal length to be a power of 2?
I know Fourier transforms but new to wavelet transforms. I can understand Haar transform needs signal length a power of 2, since the filters have 2 taps and down-sampling and up-sampling in the ...
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16 views
Plot frequency tiling wavelets/curvelets
Is there a convinient way to plot the frequency tiling of for wavelets/curvelets? For example the input would be the number of scales $j$ and the output would be something like this:
Preferably in ...
1
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2answers
188 views
How is wavelet time & frequency resolution computed?
Mallat gives analytic wavelet time & frequency widths/uncertainties as
$$
\begin{align}
\sigma_{ts}^2 &= \int_{-\infty}^{\infty} (t - u)^2 |\psi_{u, s}(t)|^2 dt
= s^2 \sigma_t^...
1
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1answer
67 views
Energy normalization across wavelet subbands
According to the following reference: A Really Friendly Guide to Wavelets, © C. Valens, 1999
Equation 3, the wavelets are generated from the mother wavelet by scaling and translation. S is the scaling ...
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2answers
40 views
Coefficient meaning in DWT
I understand that approximate and detail coefficient represent the different signal bands. But what do the values mean and how are they used?
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16 views
How to compute inner product of Wavelet transform convoluted with signal
I have two datasets $X_1$ and $X_2$ in a sparse wavelet basis, and I have two filters $f_1$ and $f_2$. I’d like to compute the inner product of the convolutions $$\langle X_1 \star f_1, X_2 \star f_2\...
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2answers
74 views
Is there a systematic method for converting an even length FIR filter to odd length?
I'm currently implementing a discrete wavelet transform (DWT) as a cascaded QMF filter bank (pictured below). I've put together a convolution function that attempts to filter an input signal in a non-...
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1answer
82 views
Is it possible to define Fourier or wavelet transforms on DNA sequences?
I am wondering how and if it is possible to define a Fourier transform or Wavelet transform on DNA sequences which are basically arrays with the values $\{T,C,G,A\}$ in them.
I have found a paper ...
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26 views
How to take wavelet transform of sparse input data
I have a sparse dataset indexed by nanoseconds. Storing the dataset in a discrete fashion would take too much memory. I'd like to take a wavelet transform and I'd like it to be relatively fast. The ...
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2answers
872 views
Synchrosqueezing Wavelet Transform explanation?
How does Synchrosqueezing Wavelet Transform work, intuitively? What does the "synchrosqueezed" part do, and how is it different from simply the (continuous) Wavelet Transform?
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1answer
33 views
Does the Fast Wavelet Transform produce the same coefficient as the Discrete Wavelet Transform?
Does the Fast Wavelet Transform(FWT) produce the same coefficients as the Discrete Wavelet Transform(DWT) if configured for the same depths? Or is the the FWT just an approximation of the DWT?
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2answers
51 views
What mother wavelet should be chosen as an alternative to the STFT?
The Short Time Fourier Transform (STFT) is used to identify time localized frequency content of a signal. The STFT operates by chunking an input signal into blocks and performing FFT on the block, and ...
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1answer
44 views
One integral inverse CWT
MATLAB's icwt docs state inversion to be done by a single integral:
$$
f(t) = 2 \Re e\left\{
\frac{1}{C_{\psi, \delta}} \int_0^\infty \left< f(t), \psi(t) \right> \frac{da}{a} \tag{1}
\...
2
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1answer
46 views
What should the time-shift be when implementing a continuous wavelet transform on a computer?
I'm currently researching implementation methods of the Continuous Wavelet Transform(CWT). On paper, the CWT produces infinitely many outputs on a finite signal since the scaling and shifting ...
1
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1answer
53 views
Where is the mother wavelet defined in the Fast Wavelet Transform?
Referring to the Fast Wavelet Transform, this transform is implemented as a QMF filter bank. This algorithm consists of high/low pass filtering and subsampling. However, a wavelet transform is ...
1
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1answer
26 views
Why are the Continuous Wavelet Transforms of the same signal drastically different?
I'm currently studying wavelets and am running into confusion with regards to CWT coefficients. Ideally, I want a CWT algorithm that produces outputs similar to that of a STFT - i.e. produces ...
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0answers
29 views
Reverse biorthogonal 2.2 wavelet inverse DWT implementation
I have some image data that are - supposedly - transformed using the MATLAB’s 5/3 Le Gall integer lifting wavelet transformation. The actual Matlab code that does the inverse DWT calls the following ...
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1answer
52 views
Understanding noise removal method using wavelets
I am trying to understand how wavelet transform can be used to denoise a time series or signal and how to plot the scalogram image. My signal has a lot of fluctuations and as such I am finding it ...
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1answer
70 views
Are Fast Wavelet Transform coefficients constant if the input signal frequency coefficients are constant?
I'm currently studying the Fast Wavelet Transform. As I currently understand, the Fast Wavelet Transform is implemented as a QMF filter bank where the frequency resolution decreases as the signal is ...
0
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1answer
99 views
Inverse Continuous Wavelet Transform derivation?
Wiki writes iCWT as
$$
f(t) = C_{\psi}^{-1} \int_{-\infty}^{\infty} \int_{-\infty}^{\infty} W_f(a,b) \frac{1}{|a|^{1/2}} \tilde\psi \left(\frac{t - b}{a}\right) db \frac{da}{a^2}, \tag{1}
$$
where $\...
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0answers
31 views
Log derivative interpretation
In the origin paper on Synchrosqueezing Wavelet Transform, the phase transform, used to extract the instantaneous frequency of a signal $f(t)$, is defined as
$$
\omega (a, b) = -j[W_\psi f(a, b)]^{-1} ...
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2answers
89 views
Unclear time-to-frequency integration step
From here; $\hat f=\mathcal{F}(f)$, bar = complex conjugate:
Time-shift property: $x(t-b) \Leftrightarrow e^{-j\omega b}{\bf X} (\omega)$, so why is it $+$ (red)?
What at all is happening? Looks like ...
2
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3answers
105 views
Suitable signal processing techniques for frequency response functions?
Good day everyone
I have recorded experimental frequency response functions (frfs) for a loose bolt monitoring project. Please see figure 1 below for an example of the frf.
Figure 1
The purpose of my ...
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2answers
72 views
How is wavelet center frequency computed?
PyWavelets (1) takes index of max DFT magnitude, (2) adds 1 to it, (3) divides by domain, which is the range of input values to the wavelet ("support"). ...
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0answers
135 views
Alternative convolution theorem?
Instead of padding $x_1[n]$ and $x_2[n]$ then taking
$$
\text{iDFT}(\text{DFT}(x_1[n])\cdot\text{DFT}(x_2[n])), \tag{1}
$$
assuming we know $x_1(t)$ and $x_2(t)$, and their FT's, what if we do
$$
\...
1
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2answers
95 views
Multiple peaks in a same signal?
I am working on peak detection in different signals, the signal plot looks like this:
After applying peak detection algorithm and tuning it for each signal, final output looks like this:
As you can ...
1
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1answer
133 views
CWT at low scales: PyWavelets vs Scipy
Low scales are arguably the most challenging to implement due to limitations in discretized representations. Detailed comparison here; the principal difference is in how the two handle wavelets at ...
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0answers
46 views
Wavelet denoising. Simple explanation
I am studying wavelet transform. In the matlab in the "wavemenu" package, I use "SWT denoising 1-D". I loaded my signal, performed a Haar 5 wavelet squelch. I got a good result.
I ...
0
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2answers
75 views
How to test wavelet transforms?
One pertinent attribute is normalization, which measures performance in describing signal spectral amplitude and energy, like here. Others are robustness to noise, time vs frequency resolution. ...
2
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1answer
258 views
PyWavelets CWT: normalization? Vs Scipy?
Related. The equation being implemented normalizes by sqrt(1 / scale):
$$
C_{a, b} = \frac{1}{\sqrt{a}} \sum_k s(k)\left( \int_{-\infty}^{k+1} \overline{\psi \left(\...
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1answer
32 views
PyWavelets CWT: resampling vs recomputing wavelet
Related. The implementation pre-integrates a wavelet once, and resamples it at each scale, finally differencing to implement ...
1
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1answer
195 views
PyWavelets CWT implementation
I seek to understand PyWavelets' implementation of the Continuous Wavelet Transform, and how it compares to the more 'basic' version I've coded and provided here. In particular:
How is integrated ...
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0answers
61 views
Decompose a Morlet wavelet in a sine wave to its gaussian and sine components
I have a sine wave where there is a morlet wavelet inside:
Now, first I'd like to decompose my signal (func) to 2 components which are the sine wave and the wavelet.
After this, I'd like to decompose ...
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0answers
18 views
How can a thresholding method in discrete wavelet transform be adaptive and denoising is performed level independent?
I am a bit confused regarding the thresholding methods and noise estimation options found in Matlab regarding Discrete Wavelet Transform.
Please correct me if I am wrong.
I am understanding that noise ...
0
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0answers
27 views
Is convolving a signal by a wavelet (in time domain) equivalent to wavelet filtering?
I am a noob in signal processing. Please help me understand if the following relation is true or not:
...
