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# Questions tagged [ifft]

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13 views

"I would like to create a hidden suggestion, for which I want to use monoaural masking. This involves masking a calculated frequency for 200 microseconds. Specifically, if the signal level ...
64 views

### Explanation to layman on the effect of zero-ing in frequency domain

Unable to understand the answer to Why is it a bad idea to filter by zeroing out FFT bins?. Please elaborate and explain in layman's term what the answer is saying. Also by any chance is it related to ...
• 161
1 vote
78 views

### Phase Slope Distance Calcuation

After trying to implement IFFT algorithms for phase-based ranging, as outlined in this very interesting and descriptive blog post; I've been getting horrendous results (orders of magnitude inaccurate),...
41 views

### Convolution with the Inverse FFT of a Box Filter

I read through this post here on an example of filtering using the box function in fourier space. The example makes sense and I was able to follow it and implement it in Julia (I did in space instead ...
• 103
209 views

### Generate a Time Series from Power Spectral Density Python

I am trying to generate a time series from a defined PSD function, however i tried to do this in python , with the following steps: Define the Power Spectral Density Define the time parameters Define ...
71 views

### Confusion over deconvolution cost function gradient

A basic deconvolution problem is defined by the cost function $C(f) = ||f \star h - g||^2_2$, where $f$ and $g$ are unknown latent and measured images, $h$ is known kernel. I want to derive the ...
• 23
1 vote
153 views

### Why is reconstruction of window function from its DFT difficult/noisy when the sidelobes of DFT are higher?

I am able to use the DFT and IDFT formulae to get the DFT of a window and reconstruct it but only if the sidelobes is very low (or the main lobe is narrow) as shown in the image below: Why does this ...
1 vote
106 views

• 669
74 views

### 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 ...
25 views

### 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. ...
108 views

### 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.
313 views

### 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 ...
110 views

### 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 ...
• 41
93 views

### 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 ...
47 views

### 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 ...
• 417
1 vote
430 views

### 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 ...
• 417
385 views

### 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 ...
• 195
1 vote
529 views

### 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?
65 views

### 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 ...
• 103
72 views

### 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: ...
• 25
1 vote
242 views

### 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 ...
58 views

### 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
1 vote
121 views

### 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 ...
• 13
701 views

### 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 ...
1 vote
140 views

### 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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74 views

### 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 ...
• 51
126 views

### 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 ...
• 155
1 vote
198 views

### 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 ...
• 33
87 views

### 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 ...
• 187
834 views

### 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 ...
• 33
131 views

### 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 ...
• 51
2k views

### 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. ...
82 views

### 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 ...
177 views

### 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 ...
• 131
129 views

### 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 ...
1 vote
97 views

### 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 ...
1 vote