Questions tagged [ifft]
The ifft tag has no usage guidance.
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1answer
20 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 ...
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0answers
38 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
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1answer
23 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
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1answer
18 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 ...
-1
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0answers
23 views
Generated time-signal from PSD is correct or not?
I have PSD data of noise, from which I want to get time series. Phase of the different frequency does not matter in the time-signal. Similar type of codding I used in Mathematica and in MatLab. First ...
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0answers
55 views
Discrete Fourier Transform: Can't get the correct amplitude in frequency domain
I've gone through this link.
I've generated a signal using two sine waves, one with an amplitude of 1000 and with a frequency of ...
-1
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0answers
22 views
Spatial equivalent of frequency domain filter
I have been doing image filtering in frequency (fourier domain) which simply requires element-wise multiplication. I already know my filter in frequency domain. Now I want to have an equivalent filter ...
0
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1answer
62 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
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1answer
62 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
...
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0answers
20 views
Common Cyclic prefix for a set of cascaded OFDM symbols
I've seen research papers / baseband systems that deal with synchronization using a common CP(Cyclic Prefix).
The transmission structure comprises , a family of complex orthogonal sequences, with ...
0
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1answer
68 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
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1answer
64 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, ...
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0answers
73 views
Hilbert transform “pass band”
I sample a human speech at 24kHz, to make the Hilbert transform using FFT and iFFT. What are the minimum and maximum frequencies (or range of frequencies), which will be 90 degrees shifted?
Maximum ...
0
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1answer
310 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
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3answers
236 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
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1answer
61 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
172 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
78 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
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1answer
52 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
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1answer
146 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
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0answers
35 views
Confused about obtaining impulse response from overlapped FFT'd signal
I have two audio signals which I have performed an FFT to plot the magnitude vs frequency response in realtime.
To do this I have divided the incoming signal into small blocks of size 2048, ...
0
votes
2answers
161 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), ...
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0answers
65 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 $`[...
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0answers
79 views
Hilbert transform spectrum and discrete impulse response
The impulse response of a filter implementing the hilbert transform is $ f_H(t)=\frac{1}{\pi t} $ (see hilbert transform on wikipedia) which seems to be kind of a "smooth" function as long as $ t \neq ...
0
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2answers
89 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
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1answer
286 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
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1answer
108 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
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1answer
81 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
322 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 ...
0
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0answers
33 views
Obtaining $x[n]$ from its periodogram [duplicate]
I'm trying to work out the following problem, but I'm missing something I hope I can get your support.
I'm using Matlab, and currently trying the following simple task: We have sampled discrete ...
0
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0answers
231 views
Spectra of a basic OFDM transmitter
I try to simulate a primary (or very basic) OFDM transmitter. The goal is to have spectra exactly like these:
But through my Matlab code:
...
1
vote
1answer
76 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 $x_n$, $n=0,\dots, N-1$...
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0answers
100 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
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1answer
215 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 ( ...
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0answers
65 views
How to recover signal after spectral subtraction
I have done spectral subtraction on noisy speech signal. I want recover original signal after the spectral subtraction. I have done reverse of FFT and deframing of signal using following code but ...
0
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2answers
100 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
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1answer
230 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 ...
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0answers
253 views
Zero Padding FFT: ifft(fft(x)) is unequal to x
I implemented an iterative radix-4 FFT and IFFT, and after performing these on zero padded, but further unchanged signal, the output differs.
What am i getting wrong?
Problem Description:
A signal ...
1
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1answer
90 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
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1answer
296 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 ...
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0answers
24 views
1 symbol=500 real values. how to take IFFT in OFDM?
in OFDM we take symbols, do serial to parallel conversion and then perform IFFT. Right? here the problem comes...
instead of using 'pskmod' builtin function, i've made a proper code using sinusoids. ...
0
votes
1answer
172 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 ...
1
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1answer
476 views
How does MATLAB recover picture from magnitude spectrum alone?
This is the transformation I did.
The code fft2() the Lena picture than ifft2() it back to the original. Add some ...
3
votes
2answers
200 views
What is the effect of the natural logarithm in the frequency domain?
I have read that taking the natural logarithm of a signal $x$ in the time domain will introduce a spectral broadening and hence "up-sampling" process before the logarithm is required. I tried to test ...
0
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0answers
289 views
Implementing convolution with fftw
UPDATE
I've now implemented a timeshift on both the filter and the input signal, but this does not remove the noise.
The plot below shows the original mono track in the upper panel.
The middle panel ...
1
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0answers
519 views
Vibration Acceleration Analysis with FFT and inverse FFT
I've been reading time series data off of an accelerometer, and converting it to one RMS acceleration in g. The sensor works in a range of 0-6.4 kHz approximately. Ideally i would like to restrict the ...
1
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1answer
229 views
Efficient computation of inverse FFT of real sequence using half sized FFT or inverse FFT
The inverse FFT of a folded real sequence yields a real symmetric sequence. Are there any ways to exploit this symmetry to perform a smaller complex FFT or complex inverse FFT?
Background: it's ...
0
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2answers
371 views
Signal reconstructed using IFFT: amplitude scale larger than input
I am trying to test reconstruction of signal from IFFT.
Below is the python program. I break the signal into overlapping windows and do FFT after multiplication with window function. Then I apply IFFT ...
1
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1answer
387 views
Bit-reversal equivalence on IFFT (radix-2 Cooley-Tukey)
From everything that I read on the internet, I understood that when performing FFT or IFFT, one should perform bit-reversal to obtain a result in natural order (Assuming input is also in natural order)...
2
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1answer
815 views
Inverse Fourier transform - porting from MATLAB to Python
I am porting a script from MATLAB to Python, but I am failing when it comes to the inverse Fourier transform.
The function in MATLAB (ifft) includes a 'symflag', which treats the data as conjugate ...
