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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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IBM ESSL: DFT - Real to complex & Complex to real - Final array bigger than initial one

I have a real 2D double precision array. I want to perform a FFT on it, some operations on the result, and an inverse FFT. I am using IBM ESSL library on Blue Gene Q. The function DRCFT2 is doing the real to complex transform…
user1824346
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Make Python FFT code faster

Can anyone help me to make my Python code faster? At the moment I reach about 11 meassurements per second. I hope to get this much faster but don't know how to do it. import matplotlib.pyplot as plt import matplotlib.animation as animation import…
manuel
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Masking frequencies in a Fourier Transform

I'm messing around with OpenCV, and am trying to do some of the same stuff signal processing stuff I've done in MatLab. I'm looking to mask out some frequencies, so I have constructed a matrix which will do this. The problem is that there seem to be…
Simonw
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F#/"Accelerator v2" DFT algorithm implementation probably incorrect

I'm trying to experiment with software defined radio concepts. From this article I've tried to implement a GPU-parallelism Discrete Fourier Transform. I'm pretty sure I could pre-calculate 90 degrees of the sin(i) cos(i) and then just flip and…
Jason Kleban
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Android accelerometer frequency domain analysis FFT

I want to create an android app for vibrations analysis using embedded accelerometer, would you suggest an easy solution/library to get a frequency spectrum out of the x,y,z accelerations?
avafab
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Why does negative number show up when I do FFT on a Gaussian?

I'm using this fftw library. Currently I'm trying to plot a 2D Gaussian in the form e^(-(x^2+y^2)/a^2). Here is the code: using namespace std; int main(int argc, char** argv ){ fftw_complex *in, *out, *data; fftw_plan p; int i,j; int…
Chao Xu
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How to plot data logarithmically

I have done an FFT on an audio signal and want to plot the results on a logarithmic scale like this http://abletonuniverse.altervista.org/wp-content/uploads/2013/04/Spectrum.jpg but for some reason I can't figure out how to scale the data to fit…
shane
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Convolution of multiple 1D signals in a 2D matrix with multiple 1D kernels in a 2D matrix

I have a randomly defined H matrix of size 600 x 10. Each element in this matrix H can be represented as H(k,t). I obtained a speech spectrogram S which is 600 x 597. I obtained it using Mel features, so it should be 40 x 611 but then I used a…
shubham sharma
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Runtime Warnings on multiplication of NumPy FFT

I am trying to follow this method of comparing .wav files, but am getting the following warnings: valid:call.py:23: RuntimeWarning: overflow encountered in multiply mult = numpy.multiply(fft1, fft2) call.py:23: RuntimeWarning: invalid value…
Will
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Fourier transform and FFT for an arbitrary plot using MATLAB

I have a simple problem but since I have not used MATLAB Fourier Transform tools I need some help. I have a plot obtained from n excel file. The plot is in time domain. Time range for the plot is 0 to 50 ps. And I have data for the y component of…
H.RJ
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DSP - How to apply gain in frequency domain?

I’m a beginner in DSP and I have to make an audio equalizer. I’ve done some research and tried a lot of thing in the past month but in the end, it’s not working and I’m a bit overwhelmed with all those informations (that I certainly don’t interpret…
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FFT Fast Convolution: How To Apply Window to minimize crackling

I am trying to make a fast fft convolution (fft blocksize=1024 samples) of an headpone related impulse response (L=512 samples) with an sine wave audio signal. Here you can see the plot of the impulse response…
scorprulebad
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FFT: find and cut noisy 50Hz in signal

I have noisy data (peaks with period 1.8s, 2048 bins per period) for which I want to calculate frequency and delete 50Hz. I'm pretty sure that frequency what I looking for is 50Hz, cause I find it by use originlab. When I try to do the same in…
Pakpao
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can't catch a tone frequency of 15k with microphone c# naudio

I record some sound with NAudio to float array and after getting the recorded audio I want to convert it back from float array to wav to check it. I wrote a method but I'm not sure about it because: I try to record a 15Khz tone of 5 seconds and…
axcelenator
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FFT using recursive python function

I am trying to use the following code for finding FFT of a given list. After a lot of trials I have found that this code runs only for an input list having 2^m or 2^m+1 elements. Can you please clarify why this is so and whether it can be modified…
Nachiketa Chauhan
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