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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Code for a wavelet based hilbert transform? [closed]

I normally implement the Hilbert transform using the Fourier transform. I have noise related issues I want to solve. Does anybody have an (apodized) implementation of the Hilbert transform handy, ...
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8 views

Is it required to quantize wavelet coefficients before one derives features from?

I am using wavelet coefficients for feature extraction in classification problem. As the wavelet coefficient values are real, positive and negative, is it required to quantize them before feature ...
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21 views

Wavelet transform: How to compute the initial coefficients when only samples are available?

In standard MRA we have that the space of functions at scale J can be expressed as $$V_j = V_0\oplus \left(\bigoplus_{j=0}^{J} W_j\right)$$ where $V_0$ is spanned by the orthonormal system of the ...
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17 views

Example of radial frequency functions that give scale shiftability

Simoncelli's "Shiftable multi-scale transforms" paper talks about shiftability of the parameters of a wavelet transform, in particular translation, rotation and scale. The first two are used in his ...
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9 views

how to use dwt2 function for correct multiresolution decomposition of image using db2 and higher order filters?

I want to perform multilevel decomposition of a image using Daubechies, symlets,coif filters of all order. When i use dwt2 function for order higher than 1 the subband size is not the half of input. I ...
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35 views

Are wavelets for audio spectrograms available as a simple FIR filter?

I have read that "Debauchies Wavelet is simply a short FIR" so i am searching for a single FIR that i can make into a filterbank, a precise "bandpass filter" that detects narrow frequencies, i.e. 1Hz ...
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40 views

Expanding piecewise polynomial using Daubechies wavelet

What is the best Daubechies wavelet (i.e. the number of vanishing moment) to expand a signal $\boldsymbol{x} \in \mathbb{R}^n$? $\boldsymbol{x}$ consists of $m$ pieces of polynomial with $d$ degree. ...
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4 views

Known Rolling computation for fast wavelet packet transform?

Is there a known way to update the wavelet packet coefficients (approximation & detail at all scalings) such that you don't have to recompute the entire wavelet packet transform if you move the ...
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1answer
32 views

How to implement a $j$-level $M$-band wavelet transform of an image?

I want to implement an $M$-band (or multi-band) wavelet transform, to be used for feature extraction on images. Is there a built-in Matlab function available? Do I have to implement is using filter ...
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28 views

Wavelets vs FFT based spectrogram for RF signal identification/analysis

What are the advantages / disadvantages of using a Wavelet based spectrogram vs an FFT based spectrogram (as shown by Baudline, for example) for RF signal analysis / identification ? This paper seems ...
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7 views

Shift invariant in wavelet

I always hear that wavelet transform is not shift invariant, and that there are other types of wavelet, like stationary wavelet and double density dual-tree wavelet transform, that are shift ...
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1answer
16 views

Measures that can be used to truncate linear series of functions

Say we have the following (wavelet) series representation at some location and scale in a signal: $$ f = \sum_{k=1}^{K} c_k \psi_k$$ where $c_k$ is the coefficient, in order of magnitude ($|c_k| ...
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21 views

Is there R package that combines wavelet and GARCH?

I am new to R but I need to solve a problem related to high frequency data. I need a R package which combines Wavelet and Garch. I found similar approach in MATLAB but not in R.
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1answer
53 views

Downsampling in DWT algorithm

I was working on wavelet signal decomposition and got confused with the downsampling part of Discrete Wavelet Transform algorithm. If we consider a signal $\{a_0[0], ... ,a_0[N-1]\}$ of length N and ...
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1answer
66 views

Discrete wavelet transform

I am unable to understand the discrete wavelet transform on images. I followed Robi Polikar's tutorial and got a brief idea about the theory. But I'm unable to understand w.r.t images. Using Matlab's ...
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16 views

Extract the frequency range/mean from time series using Wavelet

I am working with Wavelet for the first time, and I need your help. I have time series of velocity collected for 2 min at 32 Hz: x = [n] where n = 120 (sec)*32 = 3840 counts. I am using Morlet ...
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29 views

questions on the wavelet digital filters

I am new in wavelet transform and digital filters. My knowledge on wavelet transforms was mainly from its applications with the implementation using Matlab or mathematica. So my question might be too ...
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27 views

Wavelet transform of time series(PyWavelets)

I am a newbie in wavelet transform and I would be glad if you help me. I have different time series(ECG with rate = 1000 points in second, length = 100 000 points). I need to classify them in two ...
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35 views

How to find the energy of a single frequency from its time-frequency distribution?

I have a non-stationary time series. I am interested in finding the energy content of a single frequency (actually the ratio of that single frequency over the total energy of the signal). The problem ...
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24 views

Question about vanishing moments in wavelet tranforms

I am reading the book Noise reduction by wavelet thresholding by Maarten Jansen. About vanishing moments, it reads To create a really sparse representation, we try to make coefficients that ...
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3answers
95 views

What are the spike removal techniques in matlab without using filters

output from wavelet filter using daubechies 4 wavelet. Using wavelet filter this is the output obtained. The problem is elimination of the spikes at 0.023,0.043,0.063 and so on. Please note: no ...
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1answer
131 views

Daubechies wavelet transform

i have N samples obtained by sampling a signal with lot of frequency contents. How will i apply daubechies wavelet transform to obtain the frequency and its location? i need to write a program which ...
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8 views

Interpretation of Diagonal detail wavelets

I am a statistics grad student, and I have just begun exploring the topic of wavelet regression (specifically, Haar wavelets for discrete functions). I understand the generalization from a one ...
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45 views

Undecimated discrete wavelet transform in Python and Matlab

Loosely based on the above figure: I need to make an array like this: array = [(image),(1,ll),(1,lh),(1,hl),(2,ll),(2,lh),(2,hl)] Here, image is a numpy 2D ...
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28 views

Cohen-Daubechies-Fauraue 7/9 wavelet in Matlab

I just want to ask what the wavelet filter name used for Cohen-Daubechies-Fauraue 7/9. what name should I used in 'wname' when I want to use this type of wavelet in Matlab. some say that it is ...
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1answer
20 views

Compression Ratio in ECG compression using Wavelet Decomposition

I have compressed and reconstructed an ECG signal using Wavelet Coefficient. In compressing part, many of Wavelet Coefficient have set to zero. for example, if in original ECG, 5000 wavelet ...
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1answer
77 views

How to do edge detection using Curvelet transform?

I wanted to use Curvelet thresholding for edge detection, that is first take discrete curvelet transform then choose coefficient which are for curve and then reconstruct back to get an edge map. ...
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193 views

Is R suitable for digital signal processing

While asking a question about representing large time series in R I was discouraged from using R for digital signal processing. I understand that R is geared towards statistics. However, a signal is ...
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83 views

Optimized 2D wavelet transform using FFT

I'm currenty aiming to optimize my fast wavelet transform (FWT) algorithm for 2D signals (images). It works as follows: one iteration of 1D FWT does convolution of 1D input data with a selected 1D ...
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1answer
71 views

Implementing wavelet transform for finding transients in the power supply

I am new to the concept of wavelet transforms. Can somebody please help me in understanding this ? and also how to implement it in c. Is Short term Fourier transform more efficient than Wavelet ...
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23 views

How to choose a wavelet order

I'd like to perform the DWT on a signal in order to find the time-frequency information. I've read from a textbook that the coiflet performs best on this type of signal (ECG), I guess due to the shape ...
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40 views

This is an expression for the computation of kurtosis.

However, I don't understand what the subscript '4x' or the parameter (0,0) stand for. Could anyone explain ?
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86 views

stationary vs. undecimated wavelet transform

I have a little bit confused on the difference between stationary wavelet transform and un-decimated wavelet transform. So, can anyone tell me, if there is a difference between them?
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36 views

Getting frequency content at different times from discrete wavelet transform coeffs

After being away from DSP for a long time, I am trying to familiarize myself with wavelet transform. Here is what I (think) have understood so far: Wavelet transform provides you high time ...
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36 views

Plotting the log- log plot of scalogram of Continuous wavelet transform

I'm new to DSP stack exchange also I'm posting a question for the first time. now I have written the following code to find the Wavelet transform coefficients using the standard cwt function of the ...
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1answer
32 views

change the central frequency of a wavelet

I am using the discrete meyer wavelet in MATLAB for time series decomposition. I would like to change the central frequency of this wavelet but I do not know if this is possible or if I would need to ...
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16 views

Finding the original signal from the CWT Scalogram?

I have a Time-Frequency Representation (TFR) of a signal using Complex Wavelet transform with a half wavelet length of 6, I was wondering if there is a way to calculate the original time-domain data ! ...
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31 views

Is this a valid thresholding approach?

I am using a wavelet transform and am testing the following approach to thresholding: All coeffients (whatever their value) after the first N are set to 0 So if my timeseries window is 128 ...
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1answer
65 views

Wavelet decomposition

For the following code, X=[2 2 3 100 4 0 98 100 90 2 3 67 98 0 6 6 89 9 21 78] [C,L]=wavedec(X,N,'db1'); where N is the ...
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48 views

relationship between number of wavelet decomposition level and noise level

I am studying wavelet theory by myself and hope to use wavelet to denoise images. I write one matlab program to watch denoised image. ...
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1answer
33 views

2D DWT Image Issue

In the literature, I see that a 2D signal can be transformed by first doing a 1D transformation on each row of the matrix followed by the same procedure on each column. It seems that $k^{th}$ level ...
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159 views

Plotting Discrete Wavelet Transform in Python

I'm using Pywavelets to perform a discrete wavelet transform on a signal, which returns the approximation and detail coefficients as a list of float64 1d arrays with increasing size. I was wondering ...
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287 views

Why is a wavelet transform implemented as a filter bank?

The mother wavelet function $\psi(t)$ must satisfy the following: $$\int\limits_{-\infty}^{+\infty} \frac{|\psi(\omega)|^2}{\omega} d \omega < +\infty,$$ $$\psi ( \omega ) \bigg|_{ \omega =0} ...
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16 views

How to properly explain that computing wavelet at fine scale reveal localized high frequency component

I wonder if it is fair enough if I try to follow "Wavelet Tour of signal processing" which apply the Parseval formula: $$ Wf(u,s) = \langle f,\psi^{u,s}\rangle = \int f(t) \bar{\psi}^{u,s}(t)dt = ...
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1answer
56 views

Time-Frquency Resolution issues

While Im studying wavelet transform, I have this questions in my mind which can't find it's answer: I understand that when we take longer time windows and take the fourier transform we would suffer ...
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15 views

How accurate is Wavelet packet decomposition for emg signals with frequencies from 10 to 40 Hz?

I have an electromyographic signal sampled at a frequency between 10 and 40 Hz in a time window of 300ms. Is wavelet packet decomposition adequate in order to perform features extraction for ...
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230 views

How to use wavelet decomposition for feature extraction (of fMRI images)?

I have a dataset consisting of fMRI images (from mice) which are divided into 4 groups (different drug dose levels applied). Each fMRI image is 4D, that means each voxel is a time series. For each ...
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1answer
61 views

Opposite of wavelet transform?

Wavelet transform gives good time resolution for high-frequency events and good frequency resolution for low-frequency events. => I want to have complete opposite of wavelet transform, where I get ...
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91 views

Generating Wavelet family matrixes

We have unnormalized Haar matrix which, is for example, H4=[1 1 1 1;1 1 -1 -1;1 -1 0 0;0 0 1 -1] After normalizing it, we use for haar transform. I know how to ...
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50 views

Singularity Detection from 2D Wavelet Modulus Plot

I was wondering if I could get some tips/resources on how to pick out the singularity from my 2D Continuous Wavelet Transform Coefficient Plot (scalogram) using the Gaussian Derivative as the ...