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Questions tagged [ifft]

NOTE: please use the FFT tag instead. The FFT is a type of algorithm for quickly computing the Inverse Discrete Fourier Transform.

The IFFT is an FFT algorithm with some different initial permutation of data samples, and often an additional normalization, such that the algorithm computes the IDFT rather than the DFT. The FFT and IFFT are always implemented by the same code.

Related topics include , , , .

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

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How to write fftshift and ifftshift in R?

In numpy, we have the following functions : import numpy from numpy.fft import fft2, ifft2, fftshift, ifftshift I would like to rewrite these functions in R. fft in R works just as fft or fft2 in python. Also for ifft2, we have to do…
John Smith
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Manually inverting FFT using Numpy

I have a little script for calculating the Fourier Transform of a square wave which works well and returns the square wave correctly when I invert the fft using numpy.fft.ifft(). However, I am unable to invert the transform by manually adding up…
Deniz
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Inverse FFT in C#

I am writing an application for procedural audiofiles, I have to analyze my new file, get its frequency spectrum and change it in its calculated. I want to do this with the Fast Fourier Transform (FFT). This is my recursive C# FFT: void ft(float n,…
Just Kauser
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Weird but close fft and ifft of image in c++

I wrote a program that loads, saves, and performs the fft and ifft on black and white png images. After much debugging headache, I finally got some coherent output only to find that it distorted the original image. input: fft: ifft: As far as I…
Justa Ghost
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Comparing Naive Inverse Filter to Wiener Filter for Deconvolution in Matlab

I am currently trying to compare a simple inverse filter to the wiener filter for deconvolution using matlab. My starting signal is exp(-t^2) and this is to be convolved with a rect that is nonzero for times -.5 to .5. I am introducing noise with…
John Cast
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Point-product with fft

According to the convolution theorem, a convolution in the time domain is a product in the fft domain. With correct zero-padding, it works: % convolution in time domain a = [1 2 3]; b = [4 5 6]; c = conv(a,b); a_padded=[a 0 0]; b_padded=[b 0…
jerome.dubuk
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Signal Relationships and Conversion: Transforming one Signal into another?

I'm trying to relate a near shore tidal signal (point A) to 3 points along a long model boundary (points B C D). I want to possibly have a relationship between B C D with which we can convert A predictions into B C and D. At the moment I'm doing a…
Alex Byasse
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Correct usage of fft2 and fftshift for shape from shading

I am attempting to recreate a classical shape from shading algorithm seen in the Trucco/Verri text "Introductory Techniques for 3d Computer Vision", but I am having a hard time understanding the fft function in matlab. Essentially, I need to use the…
user2009114
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inverse of FFT not the same as original function

I don't understand why the ifft(fft(myFunction)) is not the same as my function. It seems to be the same shape but a factor of 2 out (ignoring the constant y-offset). All the documentation I can see says there is some normalisation that fft doesn't…
nrob
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fftshift/ifftshift

Please, see the the description of both fftshift and ifftshift. I would like to understand how to call the above two functions in relationship with fft and fftn in Matlab. Let say that my signal has a certain frequency content; now, the frequency…
fpe
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Fundamental Frequency by Cepstral Method

I'm trying to find frequencies by the Cepstral method. For my tests I got the following file http://www.mediacollege.com/audio/tone/files/440Hz_44100Hz_16bit_05sec.wav, an audio signal with a frequency of 440Hz. I've applied the following…
ederwander
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Time Domain / Spectrum / DSP

I perform an iFFT on a complex-valued spectrum and change the corresponding time domain-signal by lets say nulling the first sample. Finally I transform it back to frequency domain via FFT. I wonder where is the (physically) difference between using…
user1177816
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Amplitude and phase spectrum. Shifting the phase leaving amplitude untouched

I have the data that has equivalent intervals and corresponding measurements at relevant points. As an example, here is the excerpt of the data I have: y =[2.118, 2.1289, 2.1374, 2.1458, 2.1542, 2.1615, 2.1627, 2.165 …
akkab
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Recursive Inverse FFT

I have implemented two functions FFT and InverseFFT in recursive mode. These are the functions: def rfft(a): n = a.size if n == 1: return a i = 1j w_n = e ** (-2 * i * pi / float(n)) w = 1 a_0 =…
mpourreza
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Matlab: for even real functions, FFT complex result, IFFT real result

I am testing the validity of the FFT and IFFT functions in Matlab. I can compare the outputs of these functions to a well-known mathematical fact: the Fourier transform of an even, real function (like a Gaussian centered at 0), is another even,…
Liz Salander
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