# Questions tagged [ifft]

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415 views

### Is it possible to reconstruct an image using its magnitude only?

Let us take any image like Lena or cameraman. I know that when Fourier transform is applied on image,spatially global features like amplitude and phase are obtained locally. My question is whether it ...
457 views

### Efficient calculation of correlation function every $N^{\rm th}$ point

I would like to calculate a long correlation function of length say, 1e6 points. I have a prior knowledge that the correlation peak will be in point k*1000. Is there an efficient way to apply this ...
156 views

### Microphone Array null steering unexpected results after IFFT

I am writing an open source microphone array simulation program:SharpEar. When I give uniform weight to microphone array elements, the result in the angle is a sinc function as expected. There are 41 ...
941 views

### Frequency Domain Filtering with big kernel size

I use FFT to do filtering in frequency domain, but when I use big kernel I got shift on border, I think it's due to nature of cyclical convolution and I need to do more zero padding. But how to ...
843 views

### Simple FFT convolution with impulse response wav file doesn't give the right results

I have been trying to find a solution to my FFT convolution problem but everything that I have found while searching hasn't been helping me. I have a working forward and backward FFT function, that I ...
453 views

### How to narrow the frequency band of a wavelet

I have a ricker wavelet with a dominant frequency of 15 Hz. The fourier transform shows its frequency band is almost to 50 Hz. How can I narrow the frequency band of this 15 Hz ricker wavelet? I have ...
225 views

### Conceptual question on FFT/IFFT (IFFT existence)

I was reading "Discrete and continuous Fourier transforms: analysis, applications and fast algorithms" written by E.Chu and, at some point, I found something that I could not completly understand. ...
3k views

### Using only positive frequencies in fourier domain, How will it affect the ifft?

I am going to do some kind of transformation and transform a data to another domain, and again back to the first domain. For this, I take a fourier transform of the data and separate the positive part ...
769 views

### Get data ready for IFFT

I am having troubles applying the IFFT function to some data I have. I already had a look here Complex conjugate and IFFT and here What assumptions should be used to invert spectrum into time domain ...
504 views

### Spectral location of individual OFDM symbols

The generic IFFT OFDM transmitter takes $N$ serial input data symbols, parallelizes them, maps them to their signal constellation points, and processes all $N$ resultant complex values using the IFFT ...
180 views

### Complex numbers in $\tt ifft$ of an MMSE amplitude estimator

I am trying to reconstruct a signal from a noisy speech using an MMSE algorithm proposed long time ago by Ephraim and Malah (1984). After going through the algorithm, I got a matrix A which represents ...
924 views

### Is magnitude information enough to reconstruct an audio signal

I have used an MMSE STSA estimator to obtain the magnitude of an audio signal. The original signal is combined with white noise and I used an algorithm given in an old research paper by Ephraim and ...
295 views

### Problem executing RIFFT in Cortex-M4

I'm implementing an Speech Recognition System over a Cortex-M4 processor (STM32F4-Discovery) and I'm facing a problem when a compute the RIFFT. I believe that I'm passing to the function the vector ...
2k views

### Inverse fourier transform by using a random phase and an original magnitude (matlab)

I want a image. Firstly I want to do fourier transform and get the magnitude and phase information. And then make a new random phase, finally use the changed random phase and original magnitude to ...
5k views

### fft of a complex signal

I am new to dsp and just have a vague understanding of fft process. i know fft is used to convert time to freq domain.... i need to generate a sequence of frequencies such that F=[F1,F2,.....Fn-1] ...
787 views

### Why does a phase shift in the frequency domain not produce a time delay in the time domain?

Suppose I have an input signal which represents a vehicle front suspension response that has been measured using an accelerometer. It is seen that the measured rear suspension response is effectively ...
1k views

### How does the number of frequency-domain sampling points influence the outcome of an inverse FFT?

Given some frequency-domain representation of an impulse response. How does the number of frequency-domain sampling points influence the outcome of an inverse FFT, if I keep the sampling frequency ...
625 views

### Inverse FFT data format with FFTW

I perform FFT of two real sequences using "two for the price of one" - array $x[n]$ and $y[n]$ is packed as a complex number - $z[n] = x[n] + j y[n]$ - using FFT2 and FFTW. I am able to decode the ...
2k views

### How to transmit the real+imaginary output of an IFFT over a transmission channel?

I'm working on a modem system using a 16-QAM scheme. The transmitter runs an IFFT to modulate the signal, and has a 12-bit DAC. The receiver runs an FFT to demodulate the signal, and has a 12-bit ADC. ...
619 views

### fft(x) different from fft(ifft(fft(x))?

I normalized the spectrum of a time series and windowed the spectrum, then something strange happened. The code below can run in MATLAB or Octave. ...
854 views

### Alamouti code after or before IFFT block in OFDM

We are trying to implement Alamouti STBC on underlying ofdm signal. We were thinking as to where to write alamouti coder block. I thought we could write it after the cyclic prefixer block as we get a ...
472 views

### A problem about whitening of a signal

I intend to whiten the spectrum of a time series using a point-wise normalization in the frequency domain. In my first test, it looks pretty good. ...
1k views

### Bit reversal on twiddle factors on inverse FFT

I am currently working on a application which requires an inverse Fourier transform (IFFT) and am using a function library provided by Texas Instruments, in the datasheet they give an example on how ...
2k views

### IFFT and OFDM upconversion

I am trying to understand some basic concepts with IFFT as represented here OFDM Modem page 50-53, and 108-114. Some basics that are represented - The base sampling rate is 8khz. The symbol period ...
2k views

159 views

### Inverse Fast Fourier Transform Hard Way

I'm reading "Digital Signal Processing", written by Michael Weeks. In section Representing a Digital Signal as a Sum of Sinusoids, there is this Matlab code that I cannot understand. (code given below)...
17k views

### Cross correlation with FFT and fftshift

When I calculate the cross correlation between two vectors with the following code ...
76 views

### Get excitation from two signals

I have two signals, one whisper data and one normal voice data of the same sentence. I'm trying to build a voice conversion, but just want to start off with some simple signal manipulations. I ...
427 views

### inverse FFT when only a few time points are needed

I am developing C++ code to do some modeling that will take as input a parametric model of the complex frequency response (amplitude, phase) and produce as output an impulse response, e.g. using the ...
202 views

### what I'll get if I take FFT of a frequency domain data

What I'll get if I take FFT of a frequency domain data. I have two questions related to this. For ex, x is a time domain data where X = fft(x), now fft(X)= what i'll get ? While reading SCFDMA, data ...
416 views

### spectral division

Sorry if this is elementary. If I add a small sinusoidal signal to my data and then take FFT of both my original and the modified one and then inverse FFT the division of the two, I should then be ...
497 views

### Image processing free open source libraries

This is the first time that I post a question here so excuse me for asking such a beginner question. what free open source <...
23k views

### Reconstruction of audio signal from Spectrogram

I have a set of songs for which I extracted the magnitude spectrogram using a Hamming Window with 50% overlap. After extracting the spectrogram, I did some dimensionality reduction using Principal ...
2k views

### what does the output of ifft in ofdm look like?

i have a problem in ofdm modulation .... there is a stream of bits that is converted from serial to parallel and is applied to an IFFT block. based on the definition of IFFT the output should be an ...
3k views

### Frequency response <-> Impulse response

I am trying to calculate an actual frequency response from a desired frequency response. fftSize = 128; fs = 8000; I have 2 input arrays: f[] and aDesired[], ...