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Questions tagged [fft]

FFT is short for fast Fourier transform, any of a set of algorithms for quickly computing the discrete Fourier transform (DFT).

The FFT finds a lot of application in data analysis, particularly time-series and image data, and particularly when the data has a periodic nature, or at least a periodic component. The FFT also finds application in digital filtering. There are many FFT algorithms; they all calculate the Discrete Fourier Transform in O(n log n) operations, while the naive DFT implementation is O(n^2).

Mathematically, the Fourier Transform fits a set of sinusoids to the input data - revealing relative strengths of periodic components of the signal. The fit is optimal in a least-squared error sense. In the case of the Discrete Fourier Transform, the sinusoids are periodically related.

Related topics include DFT, signal processing, convolution, and window functions.

More information on FFT can be found in the Wikipedia article on FFT.

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Smoothing FFT graph in Python

I would like to smooth my FFT graphs that are obtained at 200Hz (I capture 500 points at the moment) so that the representative peaks would be shown close to THIS. This is my code: N = 500 T = 5/1000 y1 = np.array(data_Ax) yf1 =…
mcluka
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Not getting the desired FFT for sigma-delta modulator

I have a second order sigma delta modulator in simulink matlab. it's working fine i applied a sinusoidal waveform to the input with Vp - p = 1V and i have the same waveform(with a little delay), after low-pass filtering in the output : I get this…
Fateme
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Error in running KissFFT on Beaglebone black

I am trying to use KissFFT on BeagleBone Black, running Debian 7.5 with 3.8 kernel. The program gets compiled yet when I try to run it, It shows error Real FFT optimization must be even . The same program run properly on Ubuntu laptop. I also…
rathin2j
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What are the differences between DFT and FFT that make FFT so fast?

I'm trying to understand FFTs, here's what I have so far: In order to find the magnitude of frequencies in a waveform, one must probe for them by multiplying the wave by the frequency they are searching for, in two different phases (sin and cos) and…
Seph Reed
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MATLAB FFT -> Equalizer -> iFFT

I’m trying to implement a 32 point FFT - Equalizer - iFFT On a step by step basis. I input a Time domain signal to a FFT block and then used iFFT to obtain the original data back. Naturally after FFT, I get 32 points of symmetrical real and…
Big Head
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FFT of 50 hz signal

I have to take the FFT of a sin wave of 50 Hz and measure up to the 16 harmonics. My sampling frequency is as per Nyquist criteria: fs = 16*50*2 = 1600 Hz = 1600 samples/sec i.e in one period of 50Hz corresponds to 20 msec or 32 samples. As shown in…
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how to decompose an image into magnitude and phase and reconstruct it again using Matlab?

How can I decompose an image (e.g. Lena) into magnitude image and phase image and reconstruct it again from those two images using Matlab? Here is the code I have written in Matlab but I dont know why the reconstructed image is too dark or too…
MJay
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compute derivative fourier coefficient Julia

I am trying to calculate the derivative of a function from the fourier coefficients of this function with IJulia. for that, i there is a link between the fourier coefficient of the function and the fourier coefficient of the derivative , being…
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Recovering time function from its single-sided spectrum + its Hermitian

I am trying to get a real wavelet, w, which is a column vector, from its single-sided Discrete Fourier Transform. According to the theory, the negative frequency side is complex-conjugate of the positive frequency side, but in implementing it in…
Turhan Tisinli
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C# MathNet FFT Definition

I have some problem when testing FFT from MathNet: The idea is that if I apply FFT to the characteristic function of a gaussian variable I should find the gaussian density function. When I plot VectorFFT the figure does seems a density function but…
plccrl
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How to create a guitar tuner in javascript?

i would like to create a guitar tuner in javascript but i don't know to to do it... Once I recorded a 2 sec fragment audio file from the microphone, I would like for example what frequency is the note played in the recorded wav file !. How to do it…
ErrorMan
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Need explanation how specgram function work in python (matplotlib - MATLAB compatible functions)

I'm working on converting my code from python to objective c. Inside matplotlib.mlab.specgram function I see 3 important functions before fft : result = stride_windows(x, NFFT, noverlap, axis=0) result = detrend(result, detrend_func, axis=0) …
hoangpx
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Fourier transform visualization in javascript

I use this library to do an fft on an audio file, after this I want to visualize the result with canvasjs, but I do not know how to do this. I am not sure what should I use as x and y axes. If it is frequency and amplitude, how to do it? The max x…
Hexiler
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Frequency domain phase shift, amplitude, hope size and non-linearity

I am trying to implement a frequency domain phase shift but there are few points on which I am not sure. 1- I am able to get a perfect reconstruction from a sine or sweep signal using a hanning window with a hop size of 50%. Nevertheless, how…
papaya
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Computing wrapped 2D correlation with fftconvolve

I have a set of of 2D arrays that I have to compute the 2D correlation of. I have been trying many different things (even programming it in Fortran), but I think the fastest way will be calculating it using FFT. Based on my tests and on this answer…
TomCho
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