Questions tagged [ifft]
The ifft tag has no usage guidance.
192
questions
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1answer
41 views
MATLAB: Applying Inverse Fast Fourier Transform to an array of real numbers
I'm trying to understand the difference between applying the Discrete Cosine Transform (DCT) and the Inverse Discrete Fourier Transform (IDFT) to the log Mel-filterbank energies as explained in the ...
0
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0answers
39 views
Getting back the original x axis after IFFT-FFT in Python
I have an analitically generated spectrum $I(\omega)$, x axis represents angular frequency, y represents intensity. The spectrum is centered around some frequency value, which is often called central ...
2
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2answers
116 views
how I can use the FFT data to compute the convolution?
First,I have a vector A of length N,through process
...
0
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0answers
42 views
Stolt interpolation and ifft in range migration algorithm
I am using range migration algorithm for focusing stripmap synthetic aperture radar data. I have successfully tested my algorithm using the following steps after range compression (similar to this ...
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0answers
14 views
What is the correct input format to perform IFFT on a spectrum?
Say I have response of a band pass $\left(f_1-f_2\right)$ or a lowpass filter $\left(0-f\right)$ and if I want to estimate filter length then I may take the inverse transform of the frequency response ...
0
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0answers
36 views
How to applly Hanning window on S parameter results?
I am working on Time domain computation. I have S parameter results simulated, using these results I do the Inverse FFT to get results in time domain.
I want to filter/window results using Hanning ...
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0answers
28 views
Cepstrum calculation with 5-smoothing zero padding
I am trying to compute cepstrum of a signal x
An implementation of this in python is:
...
0
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1answer
140 views
FFT of square wave: maths and actual numbers do not coincide
this fact is driving me insane... Theory states that the Fourier transform of a square wave is a sinc function, but if I compute the fft of a synthetic (perfect) square wave of amplitude 1 and ...
0
votes
2answers
100 views
What is the meaning of the length of diagonal lines in FFT
I am relatively new to FFT analysis of images and have a question about them. I like to think I understand the basics but many of the properties shown in a FFT image are beyond me.
My main question ...
1
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0answers
67 views
White noise generation in frequency domain (stfft) produces a periodic pattern
I have created a set of spectral processing modules for SynthEdit next to be released, implenting short time fft, so I am now quite experienced with the matter, but recently encounteted an unexpected ...
1
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0answers
55 views
Scaling issue after doing manipulations in FFT
I have two filters which must apply (in series) to same input data $x[n]$ e.g of length 256 (real time asio input buffers). One filter is e.g. an impulse response $h_1[n]$ of a speaker and other one ...
0
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1answer
48 views
0
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1answer
54 views
IFFT of a complex, conjugate-symmetric transfer function - Value at Nyquist frequency
Using the MATLAB 'symmetric' flag to compute the IFFT of a complex-valued, length-N (with N even), transfer function, the imaginary part of the complex value at the index ((N/2)+1) corresponding to ...
1
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3answers
92 views
fft and inverse fft error size and applying impulse response matlab
I have a signal called noise. I am using the following command to calculate the mean squared error after fft and inverse fft process:
...
0
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1answer
46 views
What happens if I zero out the initial terms of the fft output and take inverse fft? [duplicate]
I am new to signal processing domain. When I run fft on data of length 1000, I get 1000 complex numbers. Now, if I want to extract the low frequency information or signal approximation, I take the ...
0
votes
1answer
648 views
inverse discrete fourier transform with plain python
I am trying to calculate inverse discrete fourier transform for an array of signals.
I am using the following formula:
$$ x[n] = \tfrac1N \sum\limits_{k=0}^{N-1} X[k] \, e^{j 2 \pi k n/N} $$
And my ...
2
votes
1answer
64 views
What is the proper way to filter out unwanted noise from accelerometers?
I'm a beginner in signal processing and have a hard time to filter out environmental noise from the floor vibration data collected using accelerometers.
I have tried using butterworth filter (IIR) ...
0
votes
2answers
95 views
My impulse response does not tend to zero
I am doing an IFFT of frequency response data achieved with Simulation tools.
When I plot my impulse response it looks wrong as the response does not tend to zero as it should. Instead there seems ...
0
votes
1answer
108 views
Inverse FFT of complex exponential with time delay - window leakage?
I am working in MATLAB with a frequency domain signal that is a sum of complex exponentials, e.g.
$X(\omega) = \sum_i e^{-j\omega t_i} $ where $t_i > 0$ $ \forall $ $ i $
I expect the output to ...
2
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0answers
88 views
Correct way of derivating in frequency domain with FFT
I believe I am very close to the answer and only need a small nudge to get to the answer.
What I want:
I want to take a signal, use FFT to transform it to the frequency domain (FD), multiply it by $...
0
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0answers
38 views
IFFT, negative frequencies and noncausal impulse
When using the IFFT to compute an approximation to the IDTFT, frequency range is 0 to 2$\pi$ versus $-\pi$ to $\pi$. This produces a different impulse sequence(causal I think).
How do you calculate ...
3
votes
1answer
126 views
Is it possible to approximate given skewness and kurtosis values using an IFFT?
I have time domain data for a signal that behaves randomly but has non-random (non-Gaussian?) skewness and kurtosis values of ~0.9 and ~7.4, respectively.
The FFT of the signal shows that it's not ...
0
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0answers
39 views
How to relate power spectral density with the number of resource blocks in LTE?
I am running a simulation with 100 Resource blocks for LTE OFDM and I plotted a PSD for it. Now I am able to bring down the out of band emissions when I perform an algorithm on it. Based on the ...
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1answer
109 views
How is the decay of a signal exemplified in a Fourier Transform?
Is there any way to tell if a signal is decaying from its fourier transform?
4
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1answer
73 views
Multidimensional FFT with mixed directions
Let's say I have three-dimensional complex array $X[m,n,p]$, $m \in \{0, 1, \ldots, M-1\}$, $n \in \{0, 1, \ldots, N-1\}$, $p \in \{0, 1, \ldots, P-1\}$; i.e. $X \in \mathbb C^{M \times N \times P}$. ...
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0answers
47 views
Zero padding frequency domain data for improving time domain resolution before inverse FFT
I am working in MATLAB with measured data from a VNA. The bandwidth is 1 GHz from 5-6 GHz with 801 samples in the frequency domain. Everywhere I have read that I need to split the data into 2 parts at ...
1
vote
1answer
51 views
Quantized error in scatter plots for a hamming windowed LTE signal
I have a time domain signal based on LTE standards.
Carrier spacing = 15KHz, Symbols per slot = 6, extended Cyclic Prefix = 512 samples
FFT size = 2048, No. of sub carriers = 1200, channel BW = 20MHz, ...
1
vote
1answer
207 views
Best way to resample an OFDM signal without interpolating + filtering?
I am working on a custom transceiver with a sampling rate of 3.84 MHz (256 OFDM subcarriers at 15 kHz, although 56 subcarriers are null). I would like to resample the signal to 5 MHz, in order to use ...
0
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0answers
91 views
Why convolution in time and frequency domain are not equal?
I was writing this Jupyter Notebook. Then, I unexpectedly faced two visually similar output, but their numerical results were very different.
This is the code I used for convolution in the time ...
0
votes
1answer
65 views
Irregularities in tone generated using FFT data
I am implementing a simple program to generate tone in MATLAB using FFT/iFFT by zeroing all frequency bins except for the one frequency that I'd like to generate a tone in.
Sampling frequency is ...
-1
votes
1answer
40 views
Applying window function to reduce out of band emission for a symbol in LTE simulation?
I have to apply a window to an IFFT'ed signal (based on LTE standards, simulated for 1 symbol - 100 resource blocks - 1200 subcarriers). I have a signal which I have simulated till the IFFT. Now I ...
0
votes
1answer
174 views
Ambiguity in the IFFT process in OFDM
I am still trying to iron out some ambiguities in my understanding of the IFFT component of OFDM modulation schemes.
So here we have a QAM symbol $s_0$ being multiplied with the subcarrier for that ...
1
vote
1answer
115 views
OFDM Simulation process
I'm trying to understand OFDM by making a simulation. Are these steps correct?
generate M random complex QAM symbols. example: (1+j,1-j,-1-j,1-j....)
Split my M samples into a N 2048 sized arrays
...
0
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1answer
143 views
Phase wrap when computing impulse response from frequency response [closed]
Short:
I have the frequency response of a system as a set of complex numbers.
I want the impulse response for that system.
Problem: The phase of my frequency response wraps around 2pi multiple times....
0
votes
1answer
82 views
How to get the MLSEEqualizer work with IFFT and FFT blocks in the communication system?
Matlab MLSEE equalizer works fine with the QPSK modulated signal when the signal is propagated
over the multipath channel. However, if there are IFFT and FFT blocks used at TX and RX sides, ...
1
vote
1answer
1k views
Computation of the Inverse DCT (IDCT) Using DCT Or IFFT
Is there a way to compute the inverse discrete cosine transform (type-2) by leveraging either a DCT, FFT, or IFFT algorithm? I have seen ways to compute the DCT using FFTs, and I've seen ways to ...
3
votes
3answers
757 views
Calculate ifft using only REAL forward FFT
There are already questions on this topic here and here. I am trying to calculate the ifft using a DSP that only has a library function for a forward REAL (assumes conjugate symmetry) fft. For a given ...
1
vote
1answer
191 views
How to calibrate a signal with respect to frequency
I have recordings from accelerometers (non-flat response with respect to frequency) and I'd like to convert my voltage time series into acceleration values. Is there a standard method for doing this?
...
0
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2answers
468 views
Orthogonal signals in frequency and time domains [closed]
I have 3 orthogonal signals obtained by Fourier transformation. But when I do the inverse Fourier transform in Matlab, my signals are no longer orthogonal in the time domain.
Here is my question:
...
1
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2answers
208 views
How to compute the impulse response from incomplete frequency response data?
I need to compute the impulse response of a system, but I only have access to the frequency response data.
This data contains the output magnitude of the system (for a fixed input amplitude) at ...
0
votes
1answer
140 views
methods of crest factor minimization
i am studying the methodes CF minimization. and have a doubt.
in each methods there are steps with DFT and IDFT or like this FFT and IFFT.
Everyone provides the fact, that they use DFT and IDFT for ...
0
votes
1answer
291 views
How can I show DTFT result in MATLAB? [closed]
I wanna show DTFT result and convolution result in f-domain are same.
Additionally, I wanna show sampled function and inverse fourier transform result are same too.
How can I show this? If I use ...
0
votes
2answers
649 views
Ifft through Matrix multiplication
I am still new to MATLAB, so apologies if I sound lazy to you. I am attempting to model a transformation as a set of matrix operations. I start with a vector, up-sample it by $U$ (up-sampling rate), ...
0
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0answers
82 views
Making longer a time domain signal by adding values on its frequency domain. What am I doing wrong?
Background
Here's the thing: using software for Finite Element Acoustic Simulation I got the dataset of frequency response from a room; software works by solving the wave equation in the interval $`[...
0
votes
2answers
150 views
How to implement discretized CWT with FFT?
I tried to make circular convolution (correlation actually because it is easier to understand for me) look like the Continuous Wavelet Transform (CWT) but got stuck because the conjugation was on the ...
1
vote
3answers
992 views
OFDM - why do we need IFFT?
This question is really related to - is there any need for IFFT in the first place?
If we want to send a bunch of complex-numbers (vectors), then most OFDM discussions involve presenting those ...
4
votes
1answer
290 views
Zero padding effect on a FFT of gaussian noise
I have a gaussian noise $\nu(t)$ with variance $\sigma^2$. After a FFT I get $X(\omega)$. If now I do the IFFT on the $X(\omega)$ can I say that the result is still a gaussian noise of variance $\...
0
votes
1answer
98 views
Inverse FFT - synch the phase
Is there any way to synchronise phase of output of inverse DFT in each buffer?
When I send the output of inverse DFT to the speaker it sounds nasty.
Of course I know the „windowing functions” but it ...
0
votes
2answers
1k views
How to “rotate the phase”?
I have problem, not sure how to call it but I think it's something called "phase rotating", but not sure.
I make fast Fourier transform on simply square wave, and then I make inverse fast Fourier ...
1
vote
1answer
136 views
Inverse DFT to a real signal when only odd harmonics are present
There is an old paper by L.R. Rabiner, "On the Use of Symmetry in FFT Computation" which describes (among other things) an optimized method to calculate the DFT of a real signal $x_n$, $n=0,\dots, N-1$...
