Questions tagged [ifft]

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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. ...
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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, ...
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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 (...
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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 ...
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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. ...
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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 "...
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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 ...
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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
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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?
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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: ...
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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 ...
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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 ...
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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 ...
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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 ...
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1answer
50 views

Yet another fft question - a vocoder

Lets assume a pipeline X: ...
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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 ...
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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: ...
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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 ...
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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 ...
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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) ...
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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 ...
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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 ...
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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 $...
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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 ...
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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 ...
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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 ...
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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?
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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. $X \in \mathbb C^{M \times N \times P}$. ...
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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, ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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....
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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, ...
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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 ...
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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 ...
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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? ...
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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: ...

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