Questions tagged [ifft]
The ifft tag has no usage guidance.
186
questions
0
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1answer
80 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
70 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
39 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
38 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
41 views
0
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1answer
31 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
70 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
votes
1answer
39 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
158 views
inverse discrete fourier transfor with plain python
I am trying to calculate inverse discrete fourier transform for an array of signals.
I am using the following formula:
And my python code looks as follow.
...
2
votes
1answer
61 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
85 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
87 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
votes
0answers
72 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 $...
0
votes
0answers
23 views
IFFT, negative frequencies and noncausal impulse
When using the IFFT to compute an approximation to the IDTFT, frequency range is 0 to 2$\pi$ versus $-\pi$ to $\pi$. This produces a different impulse sequence(causal I think).
How do you calculate ...
3
votes
1answer
80 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
votes
0answers
27 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 ...
-1
votes
1answer
75 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
votes
1answer
62 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. $X \in \mathbb C^{M \times N \times P}$. ...
0
votes
0answers
40 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
46 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
130 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
87 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
50 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
31 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
144 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
98 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
votes
1answer
116 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
76 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
862 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
568 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
141 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
votes
2answers
386 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
vote
2answers
162 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
112 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
261 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
516 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
77 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
126 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
763 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
229 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
93 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
942 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
114 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 $x_n$, $n=0,\dots, N-1$...
1
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0answers
169 views
Frequency Domain Variant of Pearson's Sample Correlation Coefficient?
Suppose that you need to find (i.e. acquire) $x_1$, a short data packet with a known bit sequence preamble (i.e. a PRBS BPSK), in $x_2$, quantized samples recorded from the output of an ADC. You don'...
1
vote
1answer
431 views
1D convolution and deconvolution using FFT
The task: there is some original signal, and there is some response function. I need to convolve them using FFT and then do deconvolution to restore original signal.
The task graphical illustration ( ...
0
votes
2answers
212 views
How to reconstruct an image from s-parameters in Matlab?
I have a set of data which is the s-parameter (s11), consisting of 2 columns ($1001 \times 2$). The first column represents the frequency and the second column is the magnitude in dB. I need to use ...
1
vote
1answer
418 views
Cepstrum: IFFT or FFT to enter the cepstral domain?
I'm trying to implement source-filter separation of some pre-recorded speech in Max/MSP. I'm unsure of whether one uses an FFT to enter the cepstral domain, or an IFFT. Some of the textbooks and ...
1
vote
1answer
113 views
Problems with IFFT not being symmetrical
I have two signals, a measurement and a reference which I have performed an FFT on. They have both been windowed with a Hanning window, and now I would like to deconvolve these to get the impulse ...
0
votes
1answer
630 views
Inverse Fast Fourier with overlap
I had to work with sound(denoising algorithms), when I read about an algorithm it said that we do DTSTFT(Discrete-time short-time fourier transform) we will create an overlap between each "chunk" of ...
0
votes
1answer
246 views
taking FFT from DCT
There is a speech signal, $y[n]$, in the time-domain.
To take it to the frequency-domain, DCT has been got from $y[n]$ (w = dct(y) in MATLAB).
After it, I applied ...
