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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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Compute (x^2 + 1)^3 using FFT and IFFT

So far I managed to run the FFT and I got the next table of coefficients: [2, 1 + i, 0, 1 - i, 2, 1 + i, 0, 1 - i] The problem I have is to compute the inverse and get the polynomial in its coefficient form. Can you please help me by explaining how…
Mark
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IFFT Synthesis from an empty spectrum

I'm trying to generate a sawtooth wave using the IFFT. I can do this successfully by first performing an FFT and then putting that analysed spectrum into the IFFT, however I would really like to be able to write a UI that enables me to draw the…
cixelsyd
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Translating an FFT function from Python 2.x to Python 3.x, and computing the IFFT from it

I have an Fast Fourier Transform function in Python for versions 2.x. I want to make it in Python 3.x, but I have some problems with "xrange" and list identifiers(as my compiler said). I also have no idea how to compute Inversed FFT from my FFT…
Reodont
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Type mismatch when using Numpy's ifft

guys. Im performing some FFT's in python to test a vocoder algorithm, but in this code line for i in range(0, duration_s, Nfft): output_time[i:i+Nfft] = np.fft.ifft( np.multiply(carr_fft, np.fft.fft(in_samples[i:i+Nfft]) , Nfft) ) It yields the…
José Fonseca
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Inverse fourier transform

I'm trying to write IFT algorithm. Here is my code: %% Fourier Analysis N = 20; T1 = 0.25*N; T0 = N; x = [zeros(T1,1); ones(T0/2,1); zeros(T1,1)]'; omega = 2*pi*1/T0; ak = zeros(1,2*N+1); for k = -N:N if k == 0 ak(k+N+1) = 2*T1/T0; …
Kulis
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IFFT of a Gaussian power spectrum - Python

I want to calculate the Inverse Fourier Transform of a Gaussian power spectrum, thus obtaining a Gaussian again. I want to use this fact to check that the IFFT of my Gaussian power spectrum is sensible, in the sense that it produces an array of data…
johnhenry
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How can i make GNU Octave ifft2 command work?

I'm trying to do some image processing in GNU Octave using fft2 command, but i'm having problem with the inverse transform. I can calculate the transform with no problem, do whatever i want with it, but when i return to space domain and try to plot…
ebernardes
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Fourier transform and filtering frequencies with negative fft values

I'm looking for the most abundant frequency in a periodic signal. I'm trying to understand what do I get if I perform a Fourier transformation on a periodic signal and filter for frequencies which have negative fft values. In other words, what do…
afrendeiro
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increase / decrease the frequency of a signal using fft and ifft in matlab / octave

I'm trying to increase / decrease the frequency of a signal using fft and ifft. The first plot is 1hz and the second plot is 2hz which I'm trying to get by altering the fft and ifft values. I can go between the frequency domain and time domain but…
Rick T
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Inverse FT of a filter in Matlab

I am trying to find the inverse Fourier transform of a simple filter in Matlab. In the first case (sinc filter / "brick wall"), I use the ifft function to find the time-domain function, which is a sinc, centered at t = 0. I now want to now find the…
Graham
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Matlab: Fourier Transform After changing phase matrix

I am working on some signals project and all I want to do is apply the fourier transform on a signal, get magnitude and phases and then change the phase matrix to something else say phasenew and then get the signal from magnitude and phasenew. I am…
Ayush
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Matlab,DSP: How to check if an array has hermitian symmetry

I have a rather large piece of code at the end of which I need to apply ifft to an array ZF. ZF is the fft of the columns of a matrix Z. The problem is, the ifft turns out to be a complex double array (which it shouldn't if I did everything…
Sobeit
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Is this part of a real IFFT process really optimal?

When calculating (I)FFT it is possible to calculate "N*2 real" data points using a ordinary complex (I)FFT of N data points. Not sure about my terminology here, but this is how I've read it described. There are several posts about this on…
Ronald McFüglethorn
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How to get an inverse fourier transform of a experimental frequency domain signal?

I just use digital processing signal punctually and right know I need a just simple thing. I have an IFR in time domain that magnitude and phase are known and the angular frequency as well. I mean, I just know: w = w0:dw:wf; H(jw) =…
Agaeme
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how to use ifft function in MATLAB with experimental data

I am trying to use the ifft function in MATLAB on some experimental data, but I don't get the expected results. I have frequency data of a logarithmic sine sweep excitation, therefore I know the amplitude [g's], the frequency [Hz] and the phase…
Rhei
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