Stack Overflow
Stack Overflow

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

224 questions
0
votes
1 answer

FFTW non-symetric inverse transform c2r

Suppose I have a real 2D matrix A(MxN), by using the FFTW3 r2c transform I take the matrix into Fourier space where B is the complex array B=fft(A(Mx(N/2+1))). I know that B has Hermetian redundancy, so I perform some operations (left-right, up-down…
Brani
  • 25
  • 3
0
votes
1 answer

Inverse STFT of spectrogram without phase information

Trying to train a neural network to deal with audio data, I would like to assess some of its inner representations. One of them is very much a magnitude spectrogram without phase information, but with high overlap between Hann windows. Is there a…
Anaphory
  • 6,045
  • 4
  • 37
  • 68
0
votes
1 answer

Inverse Fourier of a Discrete and Finite Sampling Window

I am trying to find the inverse Fourier of a discrete sampling window with N_f = 11 elements. I am expecting to see a periodic Sinc-like signal in the time-domain: However, this is the output I get: Why the number of observed oscillations in my…
SaraG
  • 179
  • 2
  • 11
0
votes
0 answers

Hann Filter in Spatial Domain

So, Hann filter is: H(k)=(1+cos(2*pi*k/W))/2 , W=2*kmax and based on this, the inverse Fourier of Hann filter is supposed to be: h(x) = 1/2delt(x) + 1/4(delta(x-1)+delta(x+1)) where delta(.) is the Dirac Delta function. So, if Hk and hx denotes…
SaraG
  • 179
  • 2
  • 11
0
votes
1 answer

C++ Image 2D Fast Fourier Transform

I have to implement 2D FFT transform on the image (I cannot use library to do it for me - part of the course). I use CImg to load and save images. I have made the following code: CImg FastFourier(CImg &originalImage) { …
mgrzellak
  • 11
  • 1
  • 7
0
votes
2 answers

Matlab fft2 anomaly (bug or stupid user error?)

In trying to replicate an optical Fourier transform within Matlab I did the following: I loaded this 512x512 image as "dot512r": Then did: >> whos dot512r Name Size Bytes Class Attributes dot512r …
EddingtonsMonkey
  • 112
  • 7
0
votes
1 answer

How to make a wavetable with Inverse FFT in web-audio api or any other tool

I would like to know how one could generate a wavetable out of a wav file for example. I know a wavetable can be used in web audio api with setPerdiodic wave and I know how to use it. But what do I need to do to create my own wavetables? I read…
Kilian Hertel
  • 166
  • 1
  • 14
0
votes
2 answers

call matlab ifft from c

I have a short question: I would like to call the matlab fuction ifft from c code （inverse fast fourier transform） I was trying to understand the matlab api for c , but I could not find any example on how to pass the arguments or how to call an…
Julia Fischer
  • 21
  • 3
0
votes
1 answer

IFFT Matlab symmetric vs Java math commons

iam translating matlab code to java and i have a problem where i dont understand the difference betweent a normal X = ifft(___)function in matlab compared to a X = ifft(___,symmetric) . Matlab Docs they write: For nearly conjugate symmetric…
Khan
  • 1,418
  • 1
  • 25
  • 49
0
votes
1 answer

Compute the FFT inverse without using the FFT forward

I'm trying to compute the FFT inverse without using the FFT forward, but it returns just a black image. I'm using EmguCV in C#. I'm using this code: Matrix reverseDft = new Matrix(m_rows, m_cols, 2); CvInvoke.cvDFT(data, reverseDft,…
Maria Laura Brzezinski Meyer
  • 1
  • 2
0
votes
1 answer

fft matlab time to freq and back

I'm trying a simple (Fast Fourier Transform) fft and convert it back, but it doesn't work. I need to start with this in order to proceed with adding phase to each component. Can you please take a look and see where I go wrong with…
elis02
  • 13
  • 7
0
votes
0 answers

Why there is not dxdy factor in fft2() function of MATLAB?

In analytical 2D Fourier Transform, integrand is multiplied by dxdy. In algorithm of MATLAB function fft2(), this is not done. In discrete case, dx is Lx/Nx and dy = Ly/Ny, where Lx,Ly are lengths in metres and Nx,Ny are number of samples in x,y…
atom
  • 153
  • 1
  • 9
0
votes
0 answers

derivative in two dimensions using FFT2 in python

I want to calculate derivative of a function of two variables f(x,y) = exp(sin(sqrt(x^2+y^2))) [which for 1D case reduces to f(x) = exp(sin(x)) well covered under this post Finding first derivative using DFT in Python ] using fourier…
snano
  • 23
  • 7
0
votes
0 answers

Using IFFT to get original signal and Parseval's Theorem

I have a current signal (extracted in csv) which I obtained from cadence simulation over 30ns time. I have removed DC offset and applied windowing function before FFT. And normalized FFT by sqrt(N). I have shift zero-frequency component to center of…
aguntuk
  • 127
  • 9
0
votes
1 answer

How to do inverse fft symmetric with CUFFT

I need to convert this line (MATLAB) to CUDA: picTimeFiltered = ifft((picFFT_filt), size(I,3), 3 ,'symmetric'); My current implementation is for this line (without 'symmetric' flag): picTimeFiltered = ifft((picFFT_filt), size(I,3), 3); This is my…
Matan Marciano
  • 333
  • 4
  • 13
1 2 3
…
14 15