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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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Fast Fourier Transform and Clustering of Time Series

I'm making a project connected with identifying dynamic of sales. That's how the piece of my database looks like: There are free columns: Product - present the group of product Week - time since ...
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2k views

use wavelet transform to extract frequencies from given signal

let us suppose that we have following signal values,which consists by deterministic components and random noise(white noise) ...
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149 views

Algorithms for removing oscillations?

I am interested in removing oscillations from a signal to capture the lower-frequency variations, similar to the objective of this problem. The oscillations vary in frequency in the time domain, so ...
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370 views

Causal Wavelet Decomposition

I've seen the use of a Causal wavelet mentioned a few times but have never seen any examples of them in use with Matlab. Is it possible to to perform a Wavelet Decomposition using a causal wavelet i....
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Difference between a wavelet transform and a wavelet decomposition

I'm confused about the difference between a wavelet transform and a wavelet decomposition is. For example ...
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396 views

Need to learn wavelet, suggest steps and resources [closed]

I am looking for a good introduction to wavelets and wavelet transforms. that covers the following: Vector Spaces – Properties– Dot Product – Basis – Dimension, Orthogonality and Orthonormality – ...
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155 views

Derive Maximum of zero phase rotated wavelet from rotated wavelet

I have one question concerning phase rotation of signals and I am not sure wether it works or not: Let's assume we have a zero-phase wavelet x(t) i.e. Ricker wavelet. Unfortunately, in our ...
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Daubechies Wavelet and Matlab

I want to use waverec to evaluate a linear combination of the scaled and shifted wavelet of the form $$ \sum_{i=1}^n\sum_{j=0}^{2^n-1}d_{nj} 2^{-n}\psi_{ij} (\...
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148 views

Suggestions for FFT based tools to analyze music - Preferably MATLAB/free software packages [closed]

I am interested in analyzing full length songs for general features of the track which are not otherwise apparent. For e.g., I want to look at various parts of the song with time-frequency plots/...
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Why does a narrower window in a Fourier transform or STFT give poor frequency resolution?

In theory of FT(Fourier transform) and STFT(Short Time Fourier Transform) it is said that "A wide window gives better frequency resolution but poor time resolution. A narrower window gives good time ...
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Why does the high frequency component of an image contain more noise?

I am working with wavelet transforms. When we apply a discrete wavelet transform to an image, it decomposes into four components named the approximation component, thevertical component, the ...
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168 views

mean of wavelet for image processing

For many papers which talks about using wavelet transforms for feature detection in image processing, it is stated that it is advantageous for the wavelet to have zero mean? Why is this so? Thanks in ...
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what is proper setting for Fb,Fc in Complex morlet wavelet (cmor)?

I am using Cmor-Fb-FC wavelet transform in matlab environment. Fb is bandwidth and Fc is center frequency parameters. with trail and error procedure I select Fb-Fc as 5-1, and I've got rational output....
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157 views

how can i call the input data in wavelet transform and generate code for gabor wavelet manually? [closed]

I am an ECE student, and i am doing my project I want to generate a code for gabor wavelet transform. I have no idea could you help me with a sample program I have DNA as input sequences and how ...
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512 views

Shifting of Shift-Invariant Wavelet Transforms

Main Question: Why would iterative wavelet/inverse-wavelet transforms cause a shift along the x-axis for undecimated (shift-invariant) wavelet transforms? I am attempting to remove backgrounds from ...
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104 views

Are all isotropic bandpass filter kernels, wavelets?

Are all isotropic bandpass filter kernels, wavelets? Are there any properties that the radial frequency profile has to meet to be considered a wavelet?
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177 views

How do I implement the CDF wavelet inverse?

I understand and have implemented a 2D discrete wavelet transform that uses a Haar wavelet to process images. Now I would like to implement a 2D Cohen-Daubechies-Feauveau wavelet transform, but I am ...
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496 views

gabor wavelet and gabor transform

I was reading a paper 'A Flexible Framework for Local Phase Coherence Computation' (paper URL) on using wavelets for local phase coherence. I just want to be sure. Is the gabor wavelet the same as the ...
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343 views

Relationship between windowed fourier transform and wavelet transform

I was reading on windowed fourier transform and wavelet transform, and i was thinking that the windowed fourier transform is a subset of wavelet transform. Is that true?
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166 views

How to undecimate and make shift invariant a Dual-tree Complex Discrete Wavelet Transform in R

I have the following vector and wavelet transform (from R waveslim package) ...
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1answer
928 views

Denoise EEG signal by using Daubechies function

I have an EEG signal and it contains eye blink artifacts. I read some references and know that it is possible to detect eye blinks and remove them by using wavelet transforms, but I don't know that ...
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interpret wavelet scalogram

My knowledge of wavelets is less than epsilon. Bear with me. If I have a signal of two well separated sinusoids (15 and 48 Hz) plus some random noise, I can clearly make out the two in a spectrogram (...
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1answer
253 views

How can a zero-padded length n signal be truncated to n coefficients from which a signal can be reconstructed?

A wavelet transform is defined for infinite length signals. Finite length signals must be extended in some way before they can be transformed. I know that periodic replication and zero padding are ...
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138 views

DWT edge/indexing problem

I'm implementing a very basic forward and inverse DWT, based on Mallat's book. Nothing fancy, simple inefficient matlab code (proof-of-concept more than runtime necessary, so I'm not focusing on ...
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1answer
93 views

Get spectral picture from a wavelet transform

According to my previous question, I have changed the generate command to: y=generate1(100,1000,1); and got the following picture: Now I want to test a wavelet ...
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1answer
411 views

Wavelet signal analysis for ultrasound echo

I am new to the wavelet field, and I am working with ultrasound signal. For my study, I needed to measure material using the pulse echo reflection method. Basically, when the transducer transmits ...
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Discretized CWT vs. DWT vs. FWT vs. MRA

By reading some books about wavelets, it seems that Discretized CWT is not the same thing as DWT. Can we give a classification of Discretized CWT vs DWT vs FWT etc. ? A few remarks : All I read ...
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Any idea how can I optimize morlet wavelet parameters by Heisenberg uncertainty principal and Shannon entropy?

Based on a paper in here, they have proposed a method to optimize morlet function parameter. I have tried to implement their technique, but I can't get rational results. any idea? In here you can see ...
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540 views

Wavelet transform wavdec returns matrix of the wrong size

I have a question regarding the wavdecand dwt functions in MATLAB. I am using ...
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145 views

Differences observed on the complex wavelet transform applied on the same signal

I have applied a complex wavelet transform on two signals : a first one a second one that is a concatenation of the first signal and another one For the 4th coefficient (as an example, i've got the ...
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722 views

what is Shannon entropy?

I was reading a paper about finding optimal morlet wavelet function for CWT, and they were minimizing Shannon entropy. what is Shannon entropy and it uses? (specially on continuous wavelet transform)
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Nonlinear wavelets transform?

Is wavelet a Nonlinear transform, or Not? specifically, continuous wavelet transform with morlet function. I am studying behavior of a dynamic system, and it has nonlinear behaviour. can I employ ...
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Need to understand how wavelet is applied on Image matrix?

i want to understand ,how to find out Discrete wavelet transform of image 4 by 4 size using Haar wavelet on paper ?
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inquiries for writing continuous wavelet transform codes manually

I want to write continuous wavelet transform codes manually by matlab. And I want to use complex morlet function. Here are some background: Continuous wavelet transform definition: $C(S,T;f(t),\psi (...
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218 views

DWT with more precise scale

With a signal x of length $2^{16}$, the DWT (computed for example with pyWavelet's wavedec) has only 16 or 17 rows (the wavelet ...
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580 views

Reconstruct DWT for each cD1,cD2,cD3 and cA3 signals

This question must be basic for this forum, but I'm only start working with DWT recently, and I was working with CWT before. I ...
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693 views

Examples of Causal and Complex Wavelets?

I'm looking for wavelets that are both: causal (a wavelet coefficient $W(j,k)$, where $j$ is scale and $k$ is translation, does not use data from $t > k$ to be estimated). complex (such as the ...
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discrete Haar wavelet transform, fast and efficient method?

I'm working on my own implementation of the discrete Haar wavelet transform, I understand the wavelet theory and how to construct the Haar matrix of size N to perform the transform, but obviously ...
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Hints and helps to implement an accurate wavelet packet transfrom

I want to implement a Time-Freqency analysis by wavelet packets. I don't know what level and sampling rate should I use. I've tried different value for level(3,4,5,6,). but I couldn't get an accurate ...
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868 views

Spectrogram from Complex Morlet wavelet ( recreating article result from data)

I am trying to recreate the following results: ...from the following data: Dropbox Link (FS40.dat) The time is in milliseconds (frequency is 40000 Hz) The article state that they used Complex ...
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What's the similarities and differences between Wigner transform and wavelet transform?

Wigner transform and continuous wavelet transform are both some kind of time-frequency representation of a signal. What are the similarities and differences between them? Could you give some ...
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363 views

Creating a matrix of Gaussian wavelets at dyadic scales

I need to create a diagonal matrix containing the Fourier coefficients of the Gaussian wavelet function, but I'm unsure of what to do. Currently, I'm using function ...
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What is the definition of a noiselet?

I am reading about different integral transforms. Fourier transform being a subject I will soon take a class on. Looking at the wavelet transform there is one term that I do not understand, that is ...
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1answer
841 views

Heisenberg Uncertainly Principle and wavelet transform

I am using CMOR(complex morlet) wavelet in Fourier space in order to reconstruct my signal and also estimate damping and frequencies of the embedded modes. there are two main parameters in cmor. the ...
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1answer
923 views

Wavelet time extraction

I am trying to understand one simple thing in wavelets and I searched a lot, but did not get any idea. I need to perform Multilevel 1-D wavelet decomposition on my signal. I have arrays ...
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161 views

understanding discrete wavelets

I was reading section 4.3.3 from chapter 4 of "A Wavelet Tour of Signal Processing", "...Let $\bar{f}(t)$ be a continuous time signal defined over $[0,1]$. Let $f[n]$ be the discrete signal obtained ...
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Plotting wavelet co-efficients

I need to take the wavelet transform of an image (for reference, I will be using Debauchies wavelets, and the test image will either be Lenna or matlabs default woman image),and plot the coefficients ...
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inverse continuous wavelet transform and [Parm] in cwtft

what is 'parm' means when you set the name of wavelet function in cwtft or icwtft. ...
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1answer
179 views

What's the physical meanning and principle of applying anisotropic diffusion in transform domain?

I am reading several papers applying anisotropic diffusion in the transform domain like Shearlet, curvelet. All of them have got excellent results. The physical meaning and principle of applying ...
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190 views

Can I run a GA to optimize wavelet transform?

I am running a wavelet transform (cmor) to estimate damping and frequencies that exists in a signal.cmor has 2 parameters that I can change them to get more accurate results. center frequency(Fc) and ...