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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 do i apply the fft to an image, display the image, and then do the same with the ifft?

The question is a bit broad. Here is what I have done: I have a method for applying the fft. I'm not going to post it because whether it is correct or incorrect is not really the point here. I run an image through the method and then try to display…
Mason
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KissFFT (kiss_fftr to kiss_fftri) - How to reconstruct the original signal?

I'm having some trouble understanding how to use KissFFT (1.2.9) correctly. All I am trying to achieve for now is to perform an FFT and then immediately perform an iFFT to reconstruct the original signal again. The code snippet below demonstrates…
protectedmember
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FFTW: Trouble with real to complex and complex to real 2D tranfsorms

As the title states I'm using FFTW (version 3.2.2) with Fortran 90/95 to perform a 2D FFT of real data (actually a field of random numbers). I think the forward step is working (at least I am getting some ouput). However I wanted to check…
JRC
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simultaneous inverse fast fourier transform of two real functions

I'm trying to calculate the inverse Fourier Transform of two real functions with a single IFFT. The best and most straightforward explanation I've found so far is here, where it says: Use the fact that the FFT is linear and form the sum of the…
Trap
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Scaling problems with IFFT in Matlab

I'm studying the IFFT in Matlab by applying it to a Gaussian. According to Wikipedia tables, the Fourier transform pair would be F(w) = sqrt(pi/a) * exp(-w^2/(4a)) in frequency, and f(t) = exp(-at^2) in time. I modified the code in a previous…
Medulla Oblongata
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How is the one-dimensional inverse discrete Fourier Transform calculated in numpy?

I have an array of complex numbers (waves), which is ordered in the same way as is returned by fft. If I call ifft on this array, it returns an approximation of the original samples. I would like to implement ifft myself in python. I've found the…
Iter Ator
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Why does zero padding in Fourier domain lead to an inverse transform which is complex?

If I start off with a signal which has only real values, performing an fft and ifft returns the exact signal back with no complex entries as expected. But if I pad the fft with zeros to obtain interpolated values in the time domain, the inverse fft…
Sachu17
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Doing IFFT and saving back to wavfile doesn't work

I have the following function where I'm trying to do FFT on a audio file and reset the phases and putting it all back together as a new audio file. First I do the FFT on both channels and then normalize the amplitudes. When I'm trying to do the…
bnc
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MATLAB FFT -> Equalizer -> iFFT

I’m trying to implement a 32 point FFT - Equalizer - iFFT On a step by step basis. I input a Time domain signal to a FFT block and then used iFFT to obtain the original data back. Naturally after FFT, I get 32 points of symmetrical real and…
Big Head
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compute derivative fourier coefficient Julia

I am trying to calculate the derivative of a function from the fourier coefficients of this function with IJulia. for that, i there is a link between the fourier coefficient of the function and the fourier coefficient of the derivative , being…
ChrlTsr
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Recovering time function from its single-sided spectrum + its Hermitian

I am trying to get a real wavelet, w, which is a column vector, from its single-sided Discrete Fourier Transform. According to the theory, the negative frequency side is complex-conjugate of the positive frequency side, but in implementing it in…
Turhan Tisinli
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Linear and circular convolution in Python

I'm trying to perform linear convolutions in Python by comparing the results from FFTs and convolution functions. Python's scipy.signal.fftconvolve automatically does the necessary zero padding. If we do the calculation using only FFTs, we add a…
Medulla Oblongata
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Ifft and fft for sparse vectors

I am trying to optimize some code for performance and i notice that i am forced to make a conversion from sparse to full vectors since the built-in ifft and fft functions do not support the sparse matrix type. My signal is however sparse and I want…
Nithin Govindarajan
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rfft or irfft increasing wav file volume in python

I have just started writing a program to manipulate some audio in python. Before I write any filtering functions, I wanted to do a test to compare the input signal to the output signal after having the input signal go through an rfft and irfft. For…
Elon Ullman
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right way of performing inverse FFT in MATLAB?

I've red through the matlabcentral discussion on fftshift and ifftshift but I don't understand completely what's the right thing to do for me. A bit more helpful for one aspect is this answer on stackoverflow. I have an array A with (equally-spaced)…
riddleculous
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