Questions tagged [time-frequency]

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A python-based implementation of time-frequency block thresholding for audio signals?

I'm looking for a python implementation of the block-thresholding algorithm introduced in this classic paper. I've been searching a while but I couldn't find it :(. There is of course a Matlab ...
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Energy in frequency and time domain

I know from Parseval's Theorem that, given a signal $x(t)$, with $t$ a variable in the time domain, $$ \int_{-\infty}^{+\infty} |x(t)|^2 dt = \int_{-\infty}^{+\infty}|X(f)|^2 df, $$ where $|X(f)|$ is ...
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Why is automatic modulation classification hard?

There is a huge amount of research into automatic modulation classification (AMC) using machine learning.. Why is AMC a hard/difficult problem that we need to use machine learning or even deep ...
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Is online Continuous Wavelet Transform possible?

I have recently created a real-time STFT with 50% overlap. I wanted to know if this window-based is possible for scalogram, especially continuous wavelet transform. I haven't found anyone ...
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4 answers
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FFT with High Time and Frequency Resolution

Can anyone describe in a bit more detail or provide references to the techniques for simultaneous enhancements to time and frequency resolution described in a high level in this video? Can anyone ...
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Why does using a log scale ruin (warp) my scaleograms?

I'm trying to make a scaleogram of neural data using the continuous wavelet transform (with Morlet wavelets). As a starting point, I use just a simple sine wave built from two frequencies, 50 and 80 ...
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1 answer
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How do I solve for the normalization constant of a discrete time-frequency Gabor atom?

Given the mathematical expression for the discrete Gabor time-frequency atom $$g_{s,u,\omega,\theta}(n) = \frac{K_{s,u,\omega,\theta}}{\sqrt{s}} e^{-\pi(n-u)^2/s^2} \cos[2\pi\omega(n-u)+\theta]$$ ...
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How to interpret ADEV plot?

I want to understand how to interpret ADEV plots. I was of the understanding that if we see a peak at 1sec of TDEV plot there is a 1Hz noise in Time Interval Error(TIE) Capture. To understand the ...
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A case that zero padding increase real resolution and extract more info than naive DFT?

It is widely accepted that zero padding cannot reconstruct more information that is originally present in the sample data, which I think is intuitive, because zero padding adds no more information. ...
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How to set the "widths" parameter for continuous wavelet transform using Morlet wavelets? (scipy.signal.cwt)

I'm trying to use scipy.signal.cwt() to do a time-frequency decomposition of neural data. However, I don't completely understand the "widths" parameter. I ...
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How to restore time domain signal after multiply cosine signal when cosine signal has unknown initial phase?

I use AD9954 as cosine signal generator,then use ad835 to multiply this cosine signal with antenna signal. As ,the antenna signal frequency shifted after ad835,then ...
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difference in the spectral densities of autoregressive sequence by FFT and analytical solution

I want to obtain the power spectral density (PSD) of an autoregressive sequence, AR(1). The analytical solution according to this reference (page 12) is For $X_t = \phi_1X_{t-1}+W_t, W_t \sim N(0,\...
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Is digital necessarily discrete in both amplitude and time?

Is digital necessarily discrete in both amplitude and time? Or rather it is necessarily discrete only in time (but not necessarily in amplitude)?
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Why signal add noise cause signal undiscoverable after `fft` and `ifft`?

As we all know, Fourier transform of the sinc(t) is rect(f). Simple python script to discover signal after fft and ifft with ...
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Methods to increase FFT time resolution without lowering FFT size

It is known that in FFT time and frequency resolution are inversely related if FFT resolution is increased then time resolution will decrease. However is it possible to overcome issues in time ...
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How to make a time/period (1/frequency) plot with CWT

This is a question about producing a time/period (1/frequency) plot from a CWT, instead of the time/scale output. I am trying to use the ssqueezepy python library to perform the CWTs. Then I ...
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The separation condition of a multi-component signal

Suppose a signal is a superposition of multiple intrinsic-mode-type (IMT) functions, say $$f(t) = \sum_{i=1}^n A_i(t)e^{i\varphi_i(t)} $$ Why is the separation condition of $f(t)$ be $$\forall i,j \...
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1 answer
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Impulse response of Time Varying Channel

I have just started studying LTV channels in wireless communication. I know that $y(t) = \int _{-\infty} ^\infty x(t-\tau)h(t,\tau)d\tau$ Is there any way we can calculate the Impulse response $h(t,\...
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overlap and save method) relation zero padding with double size FIR filter coefficient

i'm doing overlap and save method at frequency domain to do this, i added one block back and forth at filter and signal respectly The problem is my filter is bessel function and that is look like this ...
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2 answers
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Misunderstanding of Nyquist sampling theorem and minimum sampling rate

I sample my time-domain (TD) signal using a distance between time-samples of $\delta = (t_{max} - t_{min}) / N_t$, where $N_t$ is the number of samples taken. The sampling rate is $1 / \delta$. I have ...
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Removing Attenuator and Real Mixer influence on the received Baseband signal in Radar IQ Transmitter - De-embedding

Radar IQ Transmitter Measurement Setup: Waveform Generator + IQ Transmitter + Attenuator + Real Downconversion mixer + Oscilloscope + Post-processing (Hilbert Transform) With the above arrangement ...
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Joint Time-Frequency Scattering structure & implementation?

How does JTFS differ from wavelet time scattering in its computation graph, and how does FDTS discriminability work, at a lower level? How is it implemented in practice, and how can one visualize ...
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1 answer
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Joint Time-Frequency Scattering explanation?

How does JTFS work, intuitively? What are its motivations, and how's it differ from the Wavelet (time) Scattering transform? Can it be visualized?
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1 answer
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Inverting a scalogram

A scalogram is said to discard phase information with modulus; is it still possible to recover the signal to some extent? Algorithms like Griffin-Lim can invert within an error, but what's the ...
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5 votes
1 answer
483 views

Wavelet Scattering properties & implementation?

What are the properties of the scattering transform, besides shift invariance and warp stability? How is it implemented in practice, and how can one visualize its computational graph?
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7 votes
1 answer
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Wavelet Scattering explanation?

How does Wavelet Scattering work, intuitively? What are its motivations, and how's it differ from the (continuous) Wavelet Transform? Can it be visualized?
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1 vote
2 answers
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How to objectively measure how "good" a time-frequency representation of music is?

I've been studying the time-frequency uncertainty principle of Dennis Gabor, and the tradeoff of the STFT window size in representing the tonal and transient characteristics of the musical signal ...
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Gabor uncertainty and time-frequency resolution

I have a question about Gabor's uncertainty theorem, and how it relates to time and frequency resolutions. As I understand it, Gabor's uncertainty theorem states that the standard deviations of a ...
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2 answers
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Computable Time-Frequency Distribution without Cross-Terms

Context: I have a single receiver that is receiving multiple signals. Each signal has a few strong harmonics, but I don't know the fundamental frequency. I would like to display them on a spectrogram ...
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3 votes
3 answers
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scipy.signal.spectrogram() - how to handle gaps in the timeseries data

Looking at the magnitude of variable stars - the dataset is from here: https://dogwood.physics.mcmaster.ca/Cepheid/URL/MW/BD-10d4669.html The magnitude plot: ...
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scipy.signal.spectrogram() with noverlap=nperseg-1, what are the possible side-effects?

I'm using a simulated data set which can be downloaded from the link in the fist paragraph on this page (it's an Excel file): https://www.analyticbridge.datasciencecentral.com/forum/topics/challenge-...
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Estimating significance in time-frequency spectrograms

I want to investigate the common input of two EMG signals using a wavelet-based approach. To this end, I chose the continuous wavelet transform to approach my research question. In addition, I would ...
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Time-frequency analysis of a nonlinear system

I have empirically developed a sensor failure detection system which works fine. The system receives inputs from different types of sensors. Because of noise characteristics, I use low pass filters on ...
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What is the advantage of overlapping windows while evaluating Spectrogram?

I've seen many documents that refer to calculate spectrogram through overlapping windows but haven't found clear documents on why this is done and how to calculate the number of points that need to be ...
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1 vote
1 answer
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How to Frequency Modulate an Audio Signal

I've started to learn about FM and I followed this guide to FM a sine wave. I have managed to do it and here is the result: And the code: ...
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Problem with creating wavelet transform

I am trying to create time-frequency representation of my brain signal. I would like to create the data for frequencies from 0hz - 120hz (so it can cover, delta, theta, alpha, beta, low-gamma and high-...
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How does the scale of a wavelet relate to the Fourier frequency (or period) under CWT?

I noticed that there are many ways to relate the scale factor of wavelets to some characteristic frequency, such as the peak frequency, the central instantaneous frequency, and so on(plz see section 2....
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Extracting different frequency bands (alpha, beta, gamma) from MEG source estimated data

I have a dataset that consists of source estimated data of MEG brain signals. I need to extract the different frequency band features (i.e., alpha, beta, gamma, etc) from them. What steps/procedure ...
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Calculating power of brain signals

I have a dataset that contains EEG (or MEG) recordings of brain signals during some cognitive tasks. Each row, shows the source estimates of neurons in a particular region. source estimate contains ...
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filtering large wiggles in signals

I am trying to filter out large wiggles showing in a signal. Those wiggles are happening due to many signal processing layers and a final sine Fourier transform (no phase) Here's the python code i am ...
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2 answers
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unsymmetric fft in matlab

This is the FFT of a 4khz sin signal. I wonder why the negative part and positive part of X axis is not symmetrical? ...
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How to interpret a break in linearity when performing detrended fluctuation analysis?

I have time series with 1048 values and when I perform detrended fluctuation analysis on this time series (using the windows or scales of 2^4 to ...
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1 vote
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Estimating Average HR from PPG sensor

I am reading Smartphone based Blood Pressure Monitoring via the Oscillometric Finger Pressing Method, which is trying to estimate blood pressure from a PPG sensor and a small applied force finger ...
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1 answer
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Understanding the units of wavelet time & frequency resolution

While using a continuous wavelet transform for my research project, I came up with some questions. Having a set of equations for a Morlet wavelet, $\psi(t)=\sqrt{\frac{2}{\pi}}e^{-t^2/2}e^{i6t}$ $\...
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Aliasing Issues in Sub Band Coding

The general structure of Sub-Band Coding (SBC) is shown below: The diagram shows that after each of the analysis filters, decimation is performed by a factor M which corresponds to the number of ...
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A Fast Power Grid Frequency Estimation Approach Using Frequency Shift Filtering

I have read the paper A Fast Power Grid Frequency Estimation Approach Using Frequency Shift Filtering. I want to prove it using a numerical example, I have problem how to calculate the ...
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2 votes
1 answer
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What is the effect of a larger window size on "temporal resolution"?

I guess my question boils down to what "temporal resolution" means? I'm taking a signal processing class right now and we're learning about DFT and windowing at the moment. We've learned ...
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How to accurately compute the Winger-Ville Distribution of an exponential

I am using MATLAB for this question so hopefully you can help me out. I am trying to compute the Wigner-Ville distribution (WVD) of a sinusoidal signal defined as \begin{equation} x(t) = e^{-i\omega_0 ...
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Reconstructing signal from frames

Edit: Please treat code here as python-esque pseudo-code; it would syntactically fall closest to MATLAB or Python+numpy+scipy users. If I have a signal in frames, and I want to put it back together - ...
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Synchrosqueezed STFT phase transform

Synchrosqueezed STFT paper, Synchrosqueezing based Recovery of Instantaneous Frequency from Nonuniform Samples, defines STFT phase transform as: $$ w(u, \xi) = \xi - \frac{\partial_tS_{g}f(u, \xi)}{j2\...
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