# Questions tagged [time-frequency]

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1 vote
62 views

### The Discrete Fourier Transform (DFT) Pair of Rectangular / Indicator Function

I'm trying to properly understand the fft and tired to recover the sinc function from its Fourier transform, i.e. an indicator ...
• 59
68 views

### Can Autocorrelation be used to Differentiate Signal Quality (High, Medium, Low, Very Low) for Periodic Signals?

I'm working on a project to classify the quality of periodic signals into four categories: high, medium, low, and very low (noisy). I was initially exploring autocorrelation as a potential feature for ...
32 views

### Frequency decomposition of forecast error variance

I think my question concerns statistical signal processing. I was referred to this site by a user at Cross Validated. I want to do a frequency-domain decomposition of generalized forecast error ...
17 views

### Comparison channel impulse in DD and TF domains

How can I plot a similar comparison plot in Matlab? My attempt I have tried to create a random function like/ Matlab: rand(M, N) and then take SFFT of it ...
• 23
78 views

### Frequency Modulation - Demodulation - Distorted frequency shape

I am interested in the effect frequency modulation has on the signal. I am using an acousto-optic deflector to steer a laser beam. The deflector receives a Radio-frequency (RF) signal (~100 MHz, sine-...
• 101
41 views

### Specific de-trending method for damped oscillation?

Say I have a set signals consisting of damped harmonic oscillations, that I want to extract the characteristics of with the prony method. In the datasets I'm working with, it is possible for these ...
• 133
1 vote
94 views

### A filter that decays proportionately to the wavelength of each freq? So for each wavelength at each freq, that freq's amplitude is attenuated by (*c)?

I am trying to design a filter that decays amplitude of signal passed through it proportional to the number of wavelengths that pass at that frequency in a given time. In other words, where for every ...
• 533
1 vote
78 views

### How to find time-varying impulse responses?

Given is a system that can be described as $y(t) = x(t)\cdot \sigma(t)$ with $\sigma(t) = \left\{\begin{array}{ll} 1, & t \geq 0 \\ 0, & t<0\end{array}\right. .$ The output of a ...
• 13
60 views

### jumps in spectrogram of frequency ramping

I create spectrogram of a sine wave that changes its frequency from 60 MHz to 70 MHz over a period of 1 millisecond. can someone help me understand why I see those jumps? how can I make it smoother? <...
• 25
192 views

### How to extract the oscillation frequency from the following signals?

Signals contain both transient and stabilizing processes. In the transient process, the signal exhibits oscillatory behavior with damping. Is there some efficient algorithms to extract the frequency? ...
241 views

### Anonymize / Obfuscate speech when doing audio classification

Let me preface that I am new to audio processing and audio analysis ;) (I asked the same question on reddit, I wanted to increase it's reach)) I am trying to classify specific events (like a gong or ...
1 vote
99 views

### How to find median position of a contour that represents a peak?

I was reading some papers on time-frequency methods of signal analysis and I am confused about one concept. The idea in these works is to plot a power spectrum in time-frequency plane and then to ...
498 views

### The uncertainty principle - Why does it imply that we can't localise

The uncertainty principle states that if you have a signal which is very concentrated in time, then its Fourier transform will be rather outspread and vice versa. However, I don't really understand ...
• 129
1 vote
181 views

### STFT needs circular shift or not?

In some textbooks and websites, circular shift operation is done before doing FFT of windowed data, in the explaination, circular shift is to ensure zero-phase. But in other textbooks and websites(I ...
• 51
1 vote
392 views

### Increasing STFT resolution by repeating the window? Ways to improve STFT resolution?

In theory of FT(Fourier transform) and STFT(Short Time Fourier Transform) it is said that "A narrower window gives good ...
• 135
56 views

### Wavelet signal analysis approach for multi-mode, noisy signal

I have a signal that I am trying to analyze via Matlab's CWT functions. The signal has two distinct oscillating components and I would like to extract the decay factor from each of them. Here is what ...
217 views

### Ambiguity function volume

I find myself confused how two properties of the ambiguity function relate to one another. The properties in question are (presented here from wikipedia, but similar formulas can be found in books by ...
• 21
184 views

### Inverse of wavelet transform modulus gives poor results

I just want to understand, why is the result of my wavelet(?) transform so bad. For $0\le i< k$, where I set $k$ to $10$, I split the signal in blocks of length $s_i:=2^{i+2}$, overlapping by $s/2$...
• 151
711 views

### Equivalence between "windowed Fourier transform" and STFT as convolutions/filtering

I've heard, that "windowed Fourier transform" is but one perspective on STFT, and that STFT is fundamentally convolutions of windowed complex sinusoids with the input, i.e. bandpass ...
• 9,004
1 vote
239 views

### What do computed CWT frequencies and color values correspond to?

I wanted to make wavelet transform and represent the frequencies as function of time instead of the scale of the wavelet as function of time. This example that uses ...
• 55