Questions tagged [time-frequency]

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67 views

Selection of transforms, windows, wavelets for current signal analysis

I am new to this topic but I already read about the propperties of different signal analysis methods. I am stuck with the obvious advantages of FFT, STFT and Wavelet transforms but can't find good ...
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0answers
76 views

How to derivate in the frequency domain

I have two Time Domain functions, $f_1(t)$ and $f_2(t)$. I have both Fourier Transforms, $F_1(\omega)$ and $F_2(\omega)$. Functions $f_1$ and $f_2$ are not independent and, in fact, $f_1$ is also a ...
2
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0answers
138 views

Vibration signal analysis of non-stationary movement

my task is to develop a condition monitoring system of a machine module. For that I am using the vibration sensors placed on the machine housing. I want to focus on only one module of the machine, a ...
2
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2answers
657 views

what is continuous wavelet (cwt) ,wavelet packet (wpt) and stockwell (S-T) computational complexity?

What is computational complexity of continuous wavelet transform cwt ? What is computational complexity of wavelet packet transform ...
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1answer
179 views

Does the instantaneous frequency contradict the uncertainty principle?

The uncertainty principle states that there is a trade off between time and frequency. So, finding frequency components at specific time is impossible. However, the instantaneous frequency measure the ...
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2answers
213 views

Stability of system with poles inside unit circle - conflict with differential equation

I am trying to understand why a system with a single pole inside the unit circle is stable. For example, take a system with one pole at $z=\frac{1}{2}$. The literature says the system is stable. As a ...
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2answers
607 views

Finite and Infinite support in time and frequency domain

It's known that signals with a finite support in time has an infinite support in frequency (talking about Fourier Transforms). A common example that is given for the claim is the triangle function ...
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2answers
6k views

What does it mean to combine signals coherently?

What does the expression 'combine signals coherently' imply?
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1answer
1k views

Time shifts and change in phase

My question here is in regards to implicit information/terminology. Basically, whenever we say that "a shift in time means a change of phase in fourier space", is it implicit that the shift is ...
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1answer
156 views

Introduction to fast algorithms for time–frequency analysis

I had preliminary knowledge of digital signal processing from Oppenheim's Discrete-Time Signal Processing and is studying time-frequency analysis now. May someone suggest introductory reference (...
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4answers
484 views

Introductory book on time-frequency analysis?

I'm looking for an introductory book to time-frequency analysis. The book should be practical in nature and not mathematics heavy. Suggestions?
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1answer
669 views

Time-frequency analysis of non-sinusoidal periodic signals

Given the history of the sum of a time-varying mixture of periodic signals, say square waves, how would you efficiently estimate the number and frequencies of components active at a particular time? ...
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1answer
68 views

Term for integral multiples of fundamental period?

As we know that a signal has fundamental frequency and integral multiples of fundamental frequency are known as harmonics I am curious about the term that will be used for integral multiples of ...
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1answer
195 views

About phase unwrapping

I am not too familiar with phase-related problems so I need some suggestions or corrections in a problem that might be an old but easy one. Here is my problem: given a complex signal: $$y(t) = e^{j\...
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1answer
525 views

Lowpass filter impulse response in frequency domain

A Linear Time-Invariant system with impulse response $h_1[n]$ is an ideal lowpass filter with cutoff frequency $\omega_c =\pi/2$. The frequency response of the system is $H_1\left(e^{j\omega}\right)$. ...
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2answers
246 views

How can I accurately represent an mp3's wave form in respects to time?

I'm trying to programmatically plot a sound wave that I have placed in a 2d array, however, I cannot consistently get the sound wave to reach the end of the window. For example, when you load a sound ...
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2answers
1k views

Compensate for phase shift of Hilbert transform

I'm using Octave and trying to use the "instfreq" function from the time frequency toolbox which requires an analytic signal input. To get this analytic signal I'm using the Octave function "hilbert" ...
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1answer
90 views

Filtering and peak finding

I have an observed signal which is the norm of the sum of two 3-vectors: $$ S(t) = || \mathbf{A}(t) + \mathbf{B}(t) || $$ Now, I have full knowledge of the vector $\mathbf{A}(t)$, $$ \mathbf{A}(t) = \...
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1answer
227 views

Plotting Hilbert Spectrum from Hilbert Huang Transform

Before anyone calls it a repeat post from past posts. I'd like to point out I've read all of those; however, I have questions on making a hard coded version of the hilbert spectrum. I do indeed have ...
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1answer
3k views

scipy.signal.spectrogram

I want to do time-frequency analysis of a signal. So i decided to use spectrogram function from scipy. This function returns, three parameters f,t,Sxx. I am using below arguements: x : my signal fs : ...
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1answer
95 views

How to compute number of samples in 1 cycle of signal?

I have 3 signal sampled at 12 KHz frequency obtained from a motor rotating at constant 2000, 2020, and 2040 rpm. For 1 second signal recording I have 12,000 time samples. Depending on the frequency I ...
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2answers
4k views

How does the Magnitude of an FFT relate back to the Time Series wave it was created from?

Alright, to start out I am a mechanical engineer with very little circuits and digital signal processing background. So please excuse my ignorance as this is far out of my usual territory. When ...
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2answers
83 views

Defining an average in time for a density in time

I'm reading the text book "Time-Frequency Analysis" by Leon Cohen and I've made my way through a decent portion. There is however a conceptual issue I keep coming back to. The book states: If we ...
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0answers
16 views

Bandpass filtering with passband changing with time

Is it possible to implement some sort of filter which adapts as a function of time? Specifically, say I have a "noiseless" model of some signal which has the same frequency components at the same ...
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0answers
61 views

Power spectral density of a pulse

A little background: I am simulating the response of an antenna to a pulse. The pulse has a wide frequency range, but the antenna only responds to a fairly narrow frequency. I can extract voltage and ...
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0answers
64 views

How to sample a transfer function (angular spectrum) in the frequency domain?

I am having this problem in Fourier optics, where I am using the Angular spectrum method (a lti filter) to calculate the electric field at the required plane given ...
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0answers
28 views

For extracting the characteristics of the signal what minimum duration should be considered?

Being non signal processing student I have a limited understanding of concepts. I have a continuous periodic bearing faulty signal of 10 seconds duration sampled at 12 kHz. So I have 120,000 ...
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0answers
129 views

Feature recognition within a single song

I want to write an algorithm in C++ which is capable of identifying specific features within a single song, e. g. the sound of a drum which is played 100 times during 5 min. State of the project So ...
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0answers
136 views

Does MATLAB have a FM discriminator [closed]

I'm wondering if MATLAB communications or DSP toolboxes has a FM discriminator? If so, what is the name of the function/object?
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0answers
40 views

Dividing a signal in channels

I have a signal in time domain, and I have to convert it into frequency domain and divide it into 100 channels, and find the center frequency of each channel. I am not good in "MATLAB" so how to do ...
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1answer
4k views

Spectrogram, time vs frequency localization, and length of signal

So I'm having some trouble conceptually and am hoping somebody can clear something up for me. This is long and I apologize for that but I want to provide as much information as possible so that the ...
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2answers
540 views

What is a 'time-variant' signal?

I have found in the literature a "time-variant signal" term , but I could not understand what that's mean. I know that there is "time-variant systems", but this is the first time, which I see a time-...
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0answers
74 views

Time-frequency analysis

I had this question in the exam without any further explanation. Why the time translation invariance is an important feature for time-frequency distributions? I am writing to ask whether anyone can ...
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0answers
75 views

How can I get frequency information in wavelet?

I am working in image processing. I am confused while getting into wavelet. I applied the fft2() function on Lena image and I got frequency information for the same. But when I applied bior4.4, a ...
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0answers
302 views

Heisenberg boxes image for Matching Pursuit

I'm using the MATLAB algotirhm Matching Pursuit to obtain the Gabor atoms forming a signal. But now I want to graph them in a "Heisenberg boxes" graph. Does someone how if is there a function to graph ...
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1answer
268 views

Variance of the Discrete Gabor Transform for practical implementation

When we design a discrete Gabor filter for a 1D signal, how do we determine the variance of the filter, depending on the time step of the signal? Is there any empirical theorem/result that we should ...
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1answer
359 views

Impossible to make a scalogram of a signal with 262144 samples

I have a signal with 262144 samples and "sampled" with 200Msps. I want to use the cwt (Continuous Wavelet Transform), for making a time-frequency scalogram. Also, I worked in some scripts in python ...
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2answers
310 views

Parameter extraction from DFT results, possibly with leakage effects

Let's start with a simple temporal law, that I want to analyze in the frequency domain : $x(t)=\frac{1}{2}(A+Bcos(2\pi \nu_0 t+\phi_0))$, with : $A=4$ $B=10$ $\nu_0=10^8$ $\phi_0=10^8$ I made a ...
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0answers
521 views

Estimating The Time-delay using the Phase of the Cross- Correlation function

I am relatively new to time delay estimation. I am working on a project where I am estimating the time-delay from the phase of the cross-correlation function (CCF), since it is more reliable in ...
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2answers
113 views

Filtering on a time signal

I am new to DSP, and am mostly self taught. I have a couple of questions, that may be too basic, but I couldn't really find an answer online. I have a signal obtained by plotting the motion of a ...
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1answer
7k views

Python - time frequency spectrogram

I have some 64 channel EEG data sampled at 256Hz and I'm trying to conduct a time frequency analysis for each channel and plot a spectrogram. The data is stored in a numpy 3d array, where one of the ...
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1answer
443 views

Correct way to implement Discrete and Stationary Wavelet Transform?

Can someone please confirm if this is indeed the correct way to compute DWT: ...
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3answers
296 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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2answers
4k views

Fourier series - time and frequency domain confusion

I am computing the fourier series of the following function between $[-0.5, 0.5]$ $$\displaystyle f(t) = \frac{1}{2} - |t|$$ According to the definition of Fourier Series the coefficients are given by ...
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1answer
688 views

Fourier transform of function division in time domain

$F_1(\omega)$ is the Fourier Transform of $f_1(t)$. $F_2(\omega)$ is the Fourier TRansform of $f_2(t)$. Can I obtain the Fourier Transform ($F_3(\omega)$) of $$ f_3(t) = \frac{f_1(t)}{f_2(t)} $$ ...
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1answer
79 views

Confusion with regards to units in Sinc pulse

I am currently reading a section in the Handbook for MRI Pulse Sequence book where it says that the time-bandwidth product for a SINC pulse is given by: $$ T \Delta f = Z $$ where $T$ is the length ...
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1answer
170 views

Time Period of one Cycle is way too large

I am calculating Time period of Sine/Cos Wave with different frequencies while keeping the Sampling Frequency at 1MHz and plotting it, but in some cases the value of time period is too big, have a ...
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1answer
84 views

Some doubts in the matlab code of computing Wigner distribution

I found that a discrete form of the Wigner distribution was $$WD(n,k) = \sum_{m = -N/2}^{N/2}f(n+m)f^*(n-m)e^{-j\frac{2\pi}{N+1}2mk}$$ where $f(n)$ is the signal and time limited within $|n|\le N/2$. ...
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2answers
282 views

compensation for irregular timestep for FFT

I want to run a clustering algorithm (svm, knn) on the ferquency spectrum data of a temperature sensor that published at irregular times. Here is the temperature data to take the FFT: I got the ...
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1answer
169 views

Why are analytic signals so important in Time-frequency analysis?

I am little confused about why we need analytic signals so bad in time-frequency analysis. What might happen if I use non-analytic signals to do time-frequency analysis?