Questions tagged [fourier]
The fourier tag has no usage guidance.
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Eigenvalue of integral operator with weak polar kernel
There is linear integral operator $A\phi=\mu \int_\Omega |x-y|^{-1}\phi(y)dy$, $x,y \in R^3$, $diam(\Omega)<R_\Omega=const$. What are system of eigenvalues ($\lambda_k=1/\mu_k$) and eigenfunctions $...
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How do you interpret the sign (positive, negative or zero) of the phase spectrum?
How do you interpret the sign (positive, negative or zero) of the phase spectrum of:
1)a digital filter (the phase spectrum of its frequency response aka phase response of the filter).
2)a signal in ...
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Morlet wavelet convolution
I use a simple formula (without normalization) from Mike Cohen's "Analzying neural time series data" book.
\begin{align}
\psi \left( t \right) &= e^{-\frac{t^2}{2 s^2}} \cdot e^{2 \...
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How does the shape of a frequency domain function (Fourier Transformed time domain function) change when a time shift is applied in the time domain?
When there is a time shift (or delay) in the time domain on a function, the Fourier transform gets multiplied by an exponential which corresponds to a phase shift on the original frequency domain ...
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Are integer multiples of a frequency in an FFT necessarily in phase?
I performed a FFT on a signal and the most prominent frequency at about 0.5 cycles/time only makes up about 6% of the total frequency distribution, which is pretty low for my purposes, so I was ...
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Excel FFT of Two Sine Waves Not Giving Expected Results
I did an FFT in Excel on a 440 Hz time domain sine wave, $y_1(t) = \sin(2\pi\cdot440\cdot t)$, and got the expected output in the frequency domain: a single-spike distribution with 100% of the signal ...
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FFT2 to RFFT2 Fourier plane and similarities
I'm trying to understand how Python's fft2 is different from irfft2. Basically, I have some continuous Fourier 2D samples that I need to put in a (n,n) grid (this can be done by a simply count-in-cell ...
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Peak FFT Frequency Off By One Bin
I used Excel's FFT feature to compute an FFT of a 440Hz sine wave that I also generated with Excel. The peak FFT value should occur at 440 Hz. Instead, it occurred one bin later at 528 Hz, so I'm ...
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Comparing custom Welch periodogram with Julia's Welch periodogram
I wrote my own PSD struct in Julia for practice purposes. It involves two type of constructors: a "direct" PSD and a <...
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Ignoring Negative Frequencies from FFT on Real Time Series Seems Inconsistent With Time Series
I ran an FFT on real financial monthly time series data. If I plot the FFT frequency domain output on the interval $[0, f_s)$, the dominant frequency pair peaks occur at $f_{A1}$ $\approx$ $0.02 \ ...
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Binning and Frequency for FFT on Financial Time Series Data
I'm trying to analyze financial market time series data, so are there any particular concerns in using FFT for that kind of data? The data seems to be relatively covariance stationary.
My sampling ...
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Fourier transform processing of iq data
I want to perform fourier transform on the iq data that is taken from spectrum analyzer. The purpose is to estimate phase noise from iq data.
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Minimum amount of data needed for low pass filter on real time sensor data
I need to apply a low pass filter up to a period of 10 hours to my data. My sensor has a sampling rate of 1 sample every 5 minutes. I need to know how much data I at least need to have to be allowed ...
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Result of complex exponential fourier series approximation and trignometric fourier series approximation are not exactly same in MATLAB?
I have a signal and i am trying to observe its approximations using complex exponential fourier series and trignometric fourier series but i am not getting exactly same result(graph of trignometirc ...
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what will be the DC component of this function? [closed]
My answer is that the signal can be splitted into 2 regions, and cancel out the negative and positive areas under the integral, based on the definition
Needed some validation on this analysis
Thanks.....
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