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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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Gaussian wave generation with a given central frequency

The formula for gaussian wave is 1/[sqrt(2* pi* variance)]*exp{-[(x-xo).^2/(2*variance)]}; I have this question in 3 parts: 1) How to generate a time domain Gaussian signal with a given central frequency. (I tried to control it by changing the…
Amartya
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a saw-shaped IFFT in matlab

I have a problem with the inverse fourier transform of a function that is supposed to be smooth, but practically it becomes saw-shaped. The function in Fourier domain is: f(m,n)=im(heavisede(m)+heaviside(-m))/(m^2+n^2). Applying the ifft2 to this…
Mohammad Bazrafshan
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Fourier transform of multiple rows

I want to take FFT of 10 measurements. That means I have 10 rows in my data with each row having dimension [1*2000]. In the code below, I am doing in a wrong way. Can anybody tell me what mistake I am making? load('fb2010'); …
Mayank Lakhani
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IFFT: symmetric flag

Can anyone please explain the algorithm of performing the symmetric IFFT in MATLAB? As an example: out_signal = ifft(X,'symmetric'); Here, X is complex symmetric signal.
Kanak
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MatLab - IFFT of an image is complex

I'm taking the fft2 of an image which gives me a complex matrix, but when I transform it back with ifft2 the result is also a complex matrix and it is not the original image. What can be happening…
Pythonice
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inverse fft of fft not returning expected data

I'm trying to make sure FFTW does what I think it should do, but am having problems. I'm using OpenCV's cv::Mat. I made a test program that, given a Mat f, computes ifft(fft(f)) and compares the result to f. I would expect the difference between…
Sveltely
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Time Series from spectrum

I am having a samll problem while converting a spectrum to a time series. I have read many article sand I htink I am applying the right procedure but I do not get the right results. Could you help to find the error? I have a time series like: When…
JPV
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Python: convert frequency response to impulse response

I'm using an acoustic simulator that gives me a (complex) frequency response for any (positive real) frequency I feed in. I would like to generate a 1024 point impulse response. I believe I have the basic technique here:…
P i
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"Frequency" shift in discrete FFT in MATLAB

(Disclaimer: I thought about posting this on math.statsexchange, but found similar questions there that were moved to SO, so here I am) The context: I'm using fft/ifft to determine probability distributions for sums of random variables. So e.g. I'm…
sebastian
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Crossing clock domains within a device

I am working on designing a Pilot Insertion module in VHDL to be implemented on an FPGA which is part of an OFDM system. For every 48 words coming from the modulation components, the pilot insertion will add pilot tones and NULLs to fill the…
technocratic
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Converting an algorithm using numpy.irfft to JavaScript

I am trying to convert an algorithm initially written with numpy to JavaScript, and I don't manage to reproduce the results from a reverse FFT. The original algorithm uses numpy.fft.rfft and numpy.fft.irfft : # Get the amplitude amplitudes =…
sebpiq
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OPENCV convolution for big kernels with size nearly equal to image

My image is of size 107x149. And my filter kernel is of size 75x75. What is the best way(in terms of speed) to convolve the image with kernel? Note : filters are non-separable.
Ravi
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blurred image removal in an image database

I have a dataset of about 2000 images. This database contains some blurred images. How can I automatically remove the blurred images from this database? I read about fourier transformation to remove the blurred images. First I need to transform my…
user570593
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I want to use MATLAB fft2 function for electromagnetic wave propagation

I want to do EM (ELECTROMAGNETIC) wave propagation by find the field Fourier transform in plane z==d , A = fft2(F(x,y,d)) PS(phaseshift) kz = k^2 -(kx^2+ky^2) where kx = 2*pi*1/dx ,ky = 2*pi*1/dy C = IFFT2(A*EXP(i*PS) but I dont get the…
Yasaman
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Using Periodogram to detect seasonality of time series

I am working on capturing seasonality of time series using periodogram plot, I want to use the top ten frequency components to create the seasonality time series, so far, I plotted the periodogram: data=elec_price[:48*365] from scipy.signal…
mohamed elhafiz
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