Questions tagged [ifft]
The ifft tag has no usage guidance.
203
questions
0
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2answers
20 views
Am I supposed to normalize FFT in Python?
I'm sorry if this question is posed often, I can't seem to understand the answers already out there. I'm working with several forms of the Fourier transform, including the FFT, PSD, and spectrograms. ...
0
votes
1answer
53 views
Fourier Transform of sampled reflectance measurements
Goal:
Calculate the complex index of refraction ($\hat n = n +jk)$ from reflectance measurements.
Data:
Reflectance measurements for various materials were taken with a FTIR (Nicolet™ iS50 FTIR, ...
0
votes
1answer
63 views
On the use of Permutation matrix to perform iFFT
I have a question about using the permutation matrix for performing $iFFT$ for such matrix and then reshape it row-wise and column-wise way.
Let's say that we have a random matrix $x$ whose size is (...
1
vote
3answers
95 views
Frequency domain samples to time domain without knowing the sampling rate?
I have some frequency response data from 802.11a OFDM communication in channel 8 of the 5 GHz band, and I would like to inverse transform this to produce the corresponding time domain response. That ...
0
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1answer
28 views
Hamming window in frequency domain and back
I can't figure out the scaling and slight artifact in fourth plot.
...
0
votes
1answer
68 views
Windowed N-point FFT
In the previous question,
Smoothing in frequency domain and impulse reponse of the filter in time-domain
I guess I have made a mistake in-terms for applying windowing to FFT.
After reading "...
0
votes
2answers
84 views
Converting PSD to Time Domain Signal
I am currently using MATLAB and I'm thinking if I can reconstruct PSD back to time domain signal using MATLAB's ifft. I found a link in solving this problem but it's in Phyton and when I tried it in ...
0
votes
2answers
51 views
Is there any other method to get the DFT of a signal without actually computing it using normal calculation
Is there any other method to get the DFT of a signal without actually computing it using a normal calculation.
Please help me out in this query
0
votes
0answers
57 views
If you are given an inverse DFT, then how do you convert it back to the DFT without actually computing any DFT?
If you are given an inverse DFT, then how do you convert it back to the DFT without actually computing any DFT?
0
votes
1answer
48 views
Can we use discrete cosine transform with imaginary part
I have been reading about the difference between the use of iFFT and iDCT with OFDM.
What I understood that iDCT can only be used with one phase modulated symbol which is PAM/BPSK modulation.
It ...
0
votes
2answers
47 views
What is Magnitude and Phase actually represents in Fast Fourier Transform?
When we reconstruct the image from its magnitude only using Inverse Fast Fourier Transform, then why the resulting image looks nothing like but the original image? Can someone please explain me in ...
0
votes
1answer
40 views
bandpass waveform detector?
I am hoping that somebody might have a good idea for detecting low-frequency pulses in some rather noisy data (I'm working on improving the snr). I have repurposed a "Raspberry Shake 1D" to record the ...
0
votes
1answer
53 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
55 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
votes
2answers
117 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
52 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 ...
0
votes
0answers
15 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
votes
0answers
37 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 ...
0
votes
0answers
31 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
votes
1answer
167 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
121 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
vote
0answers
79 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
vote
0answers
59 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
50 views
0
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1answer
63 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
vote
3answers
100 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
49 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
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1answer
826 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
68 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
117 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
119 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
90 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 $...
0
votes
0answers
39 views
IFFT, negative frequencies and noncausal impulse
When using the IFFT to compute an approximation to the IDTFT, frequency range is 0 to 2$\pi$ versus $-\pi$ to $\pi$. This produces a different impulse sequence(causal I think).
How do you calculate ...
3
votes
1answer
133 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
48 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
118 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
79 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. $X \in \mathbb C^{M \times N \times P}$. ...
1
vote
1answer
58 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
226 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
93 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
67 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
46 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
182 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
117 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
147 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
83 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, ...
2
votes
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
791 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
3answers
231 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
491 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:
...
