Questions tagged [ifft]
The ifft tag has no usage guidance.
292
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How to evaluate inverser fourier transform?
A function $f(\tilde{\phi}_i,\tilde{\theta}_j)$ defined on the sphere. The interpolation or filtering of the function is depending on $K$. I am confused on how to perform inverse-transformation using $...
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OFDM Problem with Simulink IFFT
I'm studying OFDM modulation and trying to implement the Tx system on Simulink. I did what is shown in the picture.
I was expecting to see subcarriers but I got "nothing".
What am I doing ...
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Impulse response aquired by ifft seems to require circshift
On the system below:
I have found W by inputing 20-1000 frequency and found amplitude and phase for each frequency. I've tested for minimum phase and none min S. But the answer is not logical for me. ...
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49
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Understanding FFT size in OFDM
The number of subcarriers = the size of the FFT?
The size may be the same or different depending on the document.
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129
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Generating time-domain noise from PSD
I have a question regarding generating a time-domain noise from the power spectral density (PSD), this was addressed in this question (How to generate time-series from a given one-sided PSD?) but I ...
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Need to write a simple code in matlab of training sequence or zadoff Chu sequence for my OFDM signal-synchronization
I have written a complete code, in matlab, for my ofdm signal for the transmitter and receiver. Now I want to transmit my ofdm signal via wireless channel using SDR.
Now, I need to combine a simple ...
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How to Eliminate Clicking Sounds in WAV File Generated from NFM Demodulation using FFTW?
I am working on a Digital Signal Processing (DSP) project where I am processing signals received from an SDR (Software Defined Radio) device. I am using the SoapySDR library to interface with the SDR ...
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Why does FFTPack 5.1 not give the same complex numbers as Matlab's FFT2 command does?
I'm doing FFT2 with FFTPack 5.1 and it's working great. But it does not give the same result as Matlab's FFT2 command.
Turning Time domain -> Frequency domain -> Time Domain give the same result ...
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How to do FFT with complex numbers - Ansi C code
I have a small issue.
I'm going to do FFT2 onto a matrix $X$, and the only library I have is FFTPack. FFTPack is the oldest FFT library, but it's one of the fastest and 100% portable too.
The problem ...
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214
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Xilinx ISE IP Core 7.1 - FFT (settings) give incorrect results, whats missing
I am quite new to the VHDL domain and totally new to using its ip core. I'm trying to implement an 8 point FFT using the ip core FFT 7.1 but my results are a bit off and I cannot figure out why that ...
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160
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how to convert s-parameters in frequency domain to time domain?
How to convert s-parameters in Matlab's frequency domain to the time domain with code example?
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37
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GNSS Acquisition in time domain: Why is conjugate of FFT replica used for the mixer?
Pretty new on all this GNSS stuff, I'm just studying from scratch an acquisition unit based in time domain using a parallel FFT structure. Just like the image got from "Acquisition Strategies of ...
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46
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pffft equivalent of fftwf_plan_dft_r2c_1d function from fftw
I am trying to convert my project from using FFTW to pffft. I only need to call the following two functions:
...
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145
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3D convolution product with Fourier transforms, FFTW and MPI in C
My question is not really from the field of signal processing but I think you are the most suited for answering my question.
I am willing to compute the gravitational potential which can be written as ...
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How to compute the ifft of a constant value?
I am clearly missing something obvious here because I am trying to do something that ought to be very simple: compute the ifft of a continuous signal.
My understanding is that the ifft of a continuous ...
- 296
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98
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Perfect channel estimation for OFDM (via H=Y/X) in MATLAB
Despite using the same channel for convolution, each time I get a different estimated channel. Could you please tell me what I'm doing wrong? I want to demonstrate that I can estimate the same channel ...
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334
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How can I generate a OFDM baseband signal with the output of the ifft?
I have some understanding problems with OFDM. I think I have understood most of the theoretical concept. At the moment, I am trying to write some Python code to simulate the transmitter part. This is ...
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The correct way to perform signal processing on S-parameter data
I have a question to ask you which has been bugging me as of late.
I have s-parameter data with 5001 samples acquired from a vector network analyzer. I am trying to 'gate' this s parameter data, i.e. ...
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Power spectral density of melodic contours
DESCRIPTION OF SIGNALS
I have several sung melodies under each of nine experimental contexts ("conditions"). The melodies are all of slightly different lengths (ranging more or less from 3s ...
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112
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How to process a signal in frequency domain then convert it bakc to time domain?
Maybe a example of coupling effect in frequency modulated continuous (FMCW) radar will be helpful to better demonstrate my problem.
Let us consider a FMCW radar system. We have a complex transmitted ...
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124
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IFFT confusion, sampling frequency
I made a previous post about what I am trying to do
Previous Post
I have band-limited data in the frequency domain from a VNA and I am trying to convert it into the time domain. VNA data saved in .s2p ...
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48
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Creating infinite continuous time series out of a finite discrete spectrum
I have a power spectrum $S(\omega)$: a $1 \times N$ real vector that matches frequencies from 0 to 125Hz. I would like to create a time series $S(t)$ $[-\infty<t<\infty]$ that matches this ...
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72
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Do the direct multiplication of a matrix with vector and divided matrix with part of vector have the same complexity?
According to my understanding the FFT operation for a vector whose length is $N$ has a complexity of $ \frac{N}{2}\log_{2}{N}$ complex multiplication and $ N\log_{2}{N}$ complex addition. I was ...
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518
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IFFT gives complex values in Matlab
I have frequency data from a VNA. I am trying to convert to time domain, and I can't figure out why I am getting complex valued time domain data. This is for ISAR measurements, and I can't get passed ...
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129
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Artefactual results in the Welch PSD (FFT) of melodic contours (pitch profiles)
DESCRIPTION OF SIGNALS
I have several sung melodies under each of nine conditions. The melodies are all of slightly different lengths (ranging more or less from 3s to 12s), and each is encoded as a ...
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1
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966
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Inverse Fourier transform in Python not yielding the original signal
I am trying to do a Fourier Transform and Inverse Fourier Transform. The problem is that I am not getting the original signal after inverse transform.
...
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67
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Bandpass function in Matlab inverting the Frequency spectrum when using a hermitic transformed signal
I have a VNA response (S11 parameters) from 3.5 to 40 GHz. Then I apply a hermitic transformation (complex conjugate) to it since we only have the spectrum for the positive frequencies. Then I use ...
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144
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FFT, why my program works but doesn't?
I'm working on a simple 1D FFT and iFFT for two days now but no matter what I do, the code fails. I'm using FFTW library and libsndfile on linux and my goal is to use FFT for filtering audio.
The code ...
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108
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Unstable deconvolution in frequency domain (spurious high frequency component?)
I have a black box-like deterministic model $h(t)$, which provided with a real-valued input $x(t)$ returns a real-valued response $y(t)$. The model should produce little to no noise. My goal is to ...
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Azimuth image extent in frequency domain SAR algorithms (RDA, omega-k)
When looking at the practical implementation of frequency domain SAR imaging algorithms like the range Doppler algorithm (RDA) and the omega-k algorithm (also called range migration algorithm, RMA) as ...
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878
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Order of using FFT, IFFT, FFT shift and IFFT shift
I considered a time sequence of sine wave t = [0,0.707,1,0.707,0,-0.707,-1,-0.707]
I took spectrum = fft(t) and got the ...
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366
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What is inverse Fourier transform of real spectrum?
I am trying to retrieve the origin signal in time domain (or path-length domain) from a spectrum obtained by CCD-matrix of interferometer.
I understand how to transform a real signal in the time ...
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88
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What steps are necessary to get the same impulse as before a FFT + IFFT
What steps are necessary to get the same impulse as before a FFT + IFFT.
At the moment I am trying out my code a bit and would like to do an FFT from an impulse response followed by an IFFT to ...
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Reason for "buzzing" artifact over processed audio after IFFT
I made a program that can change pitch of a recorded audio clip while maintaining its duration. Basically, it takes the FFT of windowed segments of a recorded signal, processes them using phases to ...
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Trying to get an FFT to work on an fpga to get sound data
I am trying to get an FFT to work with Verilog to bin frequency data to be able to tell what note is being played.
I am using an FPGA BASYS3 with a pmodmic3 which samples at $20\,KHz$ and outputs 12-...
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397
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How to reconstruct original signal using IFFT after cutting past Nyquist limit
I'm working on a pitch shifting program. Everything works up to the point where I try to do the IDFT. Because I cut the DFT array past the Nyquist limit, when I run the IDFT, I don't get the same ...
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Is the negative spectrum (by DFT) of a real signal "needed" to reconstruct it?
I'm trying to grasp the "ah-ha!" moment for the DFT/FFT. One of the points I struggle with is: if the original time signal $x[n]$ is real, then the values of the DFT $X[k]$ are (correct me ...
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How can I learn more about this equation?
I have come across an undocumented slide detailing the system response based on a time vs amplitude input signal.
The transfer function $$G(jw)$$ and $$w_{n} = 2\pi f_{n} $$
$$h(t) = \sum_{k=0}^{n} A(...
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Using FFT, iFFT separate instead of FFT2, iFFT2 for a convolution? is it possible?
I'm testing implementing a convolution by using an FFT way. Reference Link: Replicate MATLAB's `conv2()` in Frequency Domain
as you see, he uses fft2 & ifft2 and it works perfectly. But I want ...
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263
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Detecting a known alarm signal in an audio stream
I am going to detect alarm sounds (like from a fire detector) in a live stream. (I have asked similar questions here before, I'm now at the stage of actually doing it).
I will not really want to ...
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201
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FIR filter phase response at fs/2
I am currently building a FIR filter based on frequency sweeping data (0 Hz to Fs/2), i.e., transfer curve in frequency with the sampling rate of Fs.
The phase response is shown in the following ...
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How to properly filter offline data by zeroing the unwanted frequencies after FFT?
I am new to the field of DSP. I have a measured signal, and I wanted to apply a low pass filter on the data. I just simply applied FFT, wrote zeroes at the unwanted frequencies then applied inverse ...
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How to convert discrete-time QAM pulses to a continuous-time signal using the IFFT (for OFDM)?
So I've run into some trouble in trying to plot the PSD of an OFDM signal. Specifically, I cant see how we go from the discrete domain to the continuous in time domain.
I have a time vector, which is ...
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148
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My summed sin waves seems to only work if my wavelength is divisible with the time steps. A problem with phase likely
I have created a program in python that can create any generic signal and a time range to display it as shown by the red '--' line below. I then created a way to calculate the phase, amplitude, and ...
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1k
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Delay/Lag calculation using cross correlation in frequency domain
I need to compute cross correlation of two signals using frequency domain. Hence, I am using the below equation for calculation.
max(IFFT(FFT(a)*conj(FFT(b))))
...
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281
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Why signal add noise cause signal undiscoverable after `fft` and `ifft`？
As we all know, Fourier transform of the sinc(t) is rect(f).
Simple python script to discover signal after fft and ifft with ...
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816
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Are there any reasons to use overlap algorithm when one could do ifft(X * Y) from the complete signal as well in similiar time complexity
We learned that overlap add and overlap save are used as fast convolution methods, because they can be applied with fft due to the formula $x[n] * y[n] = \text{IFFT}(X[k] Y[k])$
So now I was wondering ...
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How to zero pad and do overlapping block convolution to reconstruct audio for frequency filtering in time-frequency domain
I am doing STFT (short-time Fourier transform) on real-time audio to filter frequencies by magnitudes (to reduce noise) which have certain drawbacks like noise spikes in reconstructed audio in the ...
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40
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How to define u to solve greens equation
this is doing my nut in. I need to define u in the following equation (there is a lot more to it but this is a sample):
$$G(x,x',z,z') = \int_{-\infty}^{\infty} \exp\left(-ju(x'-x)\right)exp(-jk|z-z'|)...
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382
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MATLAB: ifft after fft does not give the original result
I apply ifft after fft, but the result is not the same (x-fft(ifft(x)) is different from ...
