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
15
votes
1 answer

fft division for fast polynomial division

I'm trying to implement fast polynomial division using Fast Fourier Transform (fft). Here is what I have got so far: from numpy.fft import fft, ifft def fft_div(C1, C2): # fft expects right-most for significant coefficients C1 = C1[::-1] …
gaborous
  • 15,832
  • 10
  • 83
  • 102
14
votes
1 answer

FFT and IFFT in C++

I'm using C++/C to perform forwards and reverse FFT on some data which is supposed to be the pulsed output of a laser. The idea is to take the output, use a forward FFT to convert to the frequency domain, apply a linear best fit to the phase ( first…
KRS-fun
  • 696
  • 3
  • 9
  • 20
9
votes
3 answers

changing frequency using fft and ifft not using whole numbers

I know I can change frequency by whole numbers by changing the variable shift but how can I change the frequency using numbers with decimal places like .754 or 1.2345 or 67.456. If I change the variable 'shift' to a non-whole like number like 5.1 I…
Rick T
  • 3,349
  • 10
  • 54
  • 119
8
votes
2 answers

Filtering signal frequency in Python

I tried to filter some signal with fft. The signal I am working on is quite complicated and im not really experienced in this topic. That's why I created a simple sin wave 3Hz and tried to cut off the 3 Hz. and so far, so good import numpy as…
Kev
  • 577
  • 1
  • 10
  • 29
8
votes
1 answer

MatLab - Shifting an image using FFT

I want to shift an image (represented by a 2D matrix) using the multiplication of its fft by exp(-j*2*pi*x*F), where x is the displacement. I…
Pythonice
  • 313
  • 2
  • 6
  • 8
7
votes
1 answer

use of fft, ifft and fftshift in matlab

I am trying to implement the split-step fourier method to solve the nonlinear schrodinger equation in optics. It basically treats the linear part and nonlinear part separately. It solves the linear part by using fourier transform and the nonlinear…
Physicist
  • 2,848
  • 8
  • 33
  • 62
7
votes
3 answers

"extended" IFFT

If I have a waveform x such as x = [math.sin(W*t + Ph) for t in range(16)] with arbitrary W and Ph, and I calculate its (Real) FFT f with f = numpy.fft.rfft(x) I can get the original x with numpy.fft.irfft(f) Now, what if I need to extend the…
Martin Blech
  • 13,135
  • 6
  • 31
  • 35
6
votes
1 answer

Using scipy fft and ifft to solve ordinary differential equation numerically

I have an ordinary differential equation in time domain as follows: C*du/dt = -g*u + I where I = A*t/tau*exp^(1-t/tau) in the freq domain: u(w) = I(w)/(g*(1+C/g*j*w)) j being the complex number sqrt(-1) hence i can get u(t) by going into the freq…
user1854231
  • 61
  • 1
  • 2
5
votes
2 answers

2D Deconvolution using FFT in Matlab Problems

I have convoluted an image I created in matlab with a 2D Gaussian function which I have also defined in matlab and now I am trying to deconvolve the resultant matrix to see if I get the 2D Gaussian function back using the fft2 and ifft2 commands.…
Sean James Jamieson
  • 101
  • 1
  • 2
  • 11
5
votes
1 answer

ifft(fft(audio)) is just noise

whether i just nest them (iff(fft(audio))) or try window-by-window (window the audio, do the fft, do the ifft, then invert the window, replacing zero with eps, then merge the samples back (trying abs here and there in the pipelines)) i get only…
sam boosalis
  • 1,997
  • 4
  • 20
  • 32
5
votes
1 answer

fft/ifft: Sampling Frequency and Length of Signal

This is partly taken from the Matlab fft-documentation: Fs = 30; % Sampling frequency T = 1/Fs; % Sample time L = 130; % Length of signal t = (0:L-1)*T; % Time vector x =…
Tobias
  • 4,034
  • 1
  • 28
  • 35
4
votes
1 answer

iFFT of symmetric spectrum

I perform the iFFT on a symmetric spectrum (using Python). Why is the result not an real-valued signal but contains complex values? # My symmetric spectrum spectrum = numpy.array( [1+1j,2+2j,3+3j,3-3j,2-2j] ) # Perform the iFFT print…
user1177816
  • 73
  • 1
  • 4
4
votes
1 answer

How to perform FFT2D (Fast Fourier Transform 2D) R, G, B color component

I am new in fast fourier transform (FFT) and does not have much idea, how it calculate in programming language such as C++. Here is method of FFT2D void FFT2D(Complex *f, Complex *F, int width, int height); It takes an input image f…
user553710
  • 210
  • 2
  • 9
  • 16
4
votes
0 answers

Changing definition of FFT in Python

The Fourier transform operations defined in Wikipedia are which is analogous to the numerical algorithms in Python (and Matlab). However I want to use this alternative definition: in order to numerically show that the following equations are FT…
Medulla Oblongata
  • 3,771
  • 8
  • 36
  • 75
4
votes
1 answer

Generate a quasi periodic signal

Is there a way to generate a quasi periodic signal (a signal with a specific frequency distribution, like a normal distribution)? In addition, the signal should not have a stationary frequency distribution since the inverse Fourier transform of a…
WANG Guosheng
  • 73
  • 7
1
2 3
…
14 15