# Questions tagged [time-frequency]

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### 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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
6k views

### What does it mean to combine signals coherently?

What does the expression 'combine signals coherently' imply?
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 ...
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 (...
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?
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? ...
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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### 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 ...
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 : ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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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### 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 ...
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 ...
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-...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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: ...
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?
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 ...
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 $$f_3(t) = \frac{f_1(t)}{f_2(t)}$$ ...
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 ...
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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### 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 $|n|\le N/2$. ...