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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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Performing FFT to find fundamental frequencies of a polyphonic audio sample

I am using the Accelerate Framework in Swift to perform FFT on an audio file. I am trying to find the fundamental frequencies of a polyphonic audio file using a Fast Fourier Transform. I have performed a fast fourier transform on the audio file…
user98874
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How to get FFT Data in Swift using EZAudio?

I am working on a fft analysis in swift with ezaudio. My problem is how can i get the all fft data from ezaudio. I would make a algorithm to look is a frequency present when yes how much strong. Example: I looking in the FFT Data is the Frequency…
norbu
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Audio equalizer using FFmpeg

I'm developing audio player using FFmpeg. I want to add audio equaliqer to my app, but I don't know how to do it. I know that FFmpeg has a FFT functions, but I have count of samples that not mutch with any power of 2. I also tried to use other FFT…
Evgeniy Kharchenko
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How to apply frequency filter on fftw output

I get the 2d FFTW output of an image using fftw_plan_dft_2d(). As I understand it, the output represents a 2D array (width x height) of complex numbers. Can someone please explain to me how exactly I should interpret this array? What does each point…
user827329
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How to apply Fourier transform to extract the frequency of only certain edges in an image?

The title may seem a little bit unclear, but I'm going to tell you the whole story and hope to have your comments on it. I'm trying to detect some certain edges, especially those that occurs much more than the others, in a given image. To do this,…
Federico
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EZAudio FFT data - what is the range of output floats?

I'm using the EZAudio project which is located at: https://github.com/syedhali/EZAudio I am trying to create an app that outputs a pattern based on the FFT of the audio source. Basically as the audio plays time is along the x axis and the FFT is…
mikeydelamonde
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proper FFT length for ARM CMSIS DSP fft function

I'm currently trying to use the ARM CMSIS DSP library on my cortex m3 PSoC 5lp chip. I ran into some issues using some of the functions and I have a question about using the functions arm_cfft_q15 (or any of the arm_cfft_*** functions). Say I have …
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Python 2D convolution without forcing periodic boundaries

I'm modeling a disease problem where each individual in a 2D landscape has a transmissibility described by a (radial basis) kernel function. My goal is to convolve the kernel with the population density such that the output captures the transmission…
neither-nor
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Fourier transform on Green function - Difference between 2 signals almost identical

I am performing FFT with Matlab on the Green function, and I get a strange result that I can't explain. With the definition of Green function (G(r)=-1/(4*pi*r) and taking G(0)=1 to avoid divergence, I am doing two different samplings, one defined on…
user1773603
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Filtering harmonic from signal (python)

I saw similar questions partially solved but in matlab ref1, ref2, but I'm working with python. I am new processing signals and I am trying to remove harmonics from the following signals. These are radio observations (at 3 and 7 THz). So first,…
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Problems calulating FFT in Swift

I am trying to use this algorithm to give me a Fast Fourier Transform. My compiler is choking on the sqrt() function inside vDSP_vsmul() function when i copy it over. line 41 of enter link description here The error says cannot find overload for…
Kevin
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a saw-shaped IFFT in matlab

I have a problem with the inverse fourier transform of a function that is supposed to be smooth, but practically it becomes saw-shaped. The function in Fourier domain is: f(m,n)=im(heavisede(m)+heaviside(-m))/(m^2+n^2). Applying the ifft2 to this…
Mohammad Bazrafshan
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How to implement 1D FFT filter for each horizontal line data from image

I wish to apply a frequency-domain filter, such as a Low Pass or Band Pass, to each horizontal line of an image. Is this possible using opencv?
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FFT-results in python dependend on linspace chosen?

I'm very new to Python and I have a basic understanding problem. To me it seems that the result of an FFT is just based on the linspace chosen by oneself. # Number of samplepoints N = 600 # sample spacing T = 1.0 / 800.0 x = p.linspace(0.0, N*T,…
Thore
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Fourier transform of multiple rows

I want to take FFT of 10 measurements. That means I have 10 rows in my data with each row having dimension [1*2000]. In the code below, I am doing in a wrong way. Can anybody tell me what mistake I am making? load('fb2010'); …
Mayank Lakhani
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