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Questions tagged [fft]

The fast Fourier transform is an efficient algorithm to compute the discrete Fourier transform (DFT) and its inverse.

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which is the relationship between domains (x and k) in FFT?

I need to plot an escalar field f(x,y) in an interval xv= (xmin,xmax) in Nx steps and ...
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1answer
79 views

Precompute parts of an FFT on streamed data inputs

I've implemented Radix-2 & Radix-4, DIT & DIF variants of the cooley-tukey FFT algorithm and they perform well on test data. Now for a project, my algorithms will be applied to a real-time ...
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58 views

How does this Odd stacking DFT work?

I have just read on page 3 of this paper: https://www.onsemi.com/site/pdf/Filtering_Hearing_Ai.pdf That an "odd stacking" DFT can be created, essentially sacrificing the DC and Nyquist bands to ...
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1answer
57 views

Remove Frequency Range

I got a signal and I would like to remove a specific frequency range. I am a frequency noob, so I will explain it by images: I have a frequency filter (butter bandpass): I have a signal and it's ...
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59 views

how to plot log intensity of a 2D image wrt frequency?

I'm reading an article about frequency filtering and I came across this figure which represents log intensity of an image wrt frequency. I want to code this function with ...
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2answers
93 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 ...
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1answer
85 views

Measuring Amplitude of sound wave FFT

Please, pardon my ignorance. This may be a simple question, but I am still unable to explain what is happening. I am using a turtlebot to listen to sound emitted from a stationary sound source. My ...
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118 views

Edge effects in cross-correlation

This is a follow-up of this question. The problem explained in the linked question has been in part solved by the mean of a windowing function. But my cross-corrleation still exhibits strong edge-...
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4answers
519 views

DFT (FFT) of a Real Even Function Doesn't Yield Real Only DFT Signal

There are a lot of similar questions already, but I can't find one answering this problem. I used the following MATLAB code to perform the FFT on a Lorentzian input signal ...
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153 views

Phase Noise in OFDM simulation

I am trying to simulate phase noise in OFDM and in search of a mathematically tractable model. So far, I have managed to get phase noise by multiplicating $e^{j\phi(n)}$ in frequency domain where $\...
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1answer
51 views

Improvement of SNR by sampling different number of cycles using FFT of a fixed length singal

My question relates to Fourier transform of signals with different lengths in time but the same fixed length of the digitized signal with different sampling rates. Specifically, how does the number ...
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109 views

Compare twoo Arraylists that contains peaks (fingerprint) of an audio files using python

My main idea is to compare the similarity of twoo audio files,so i already did detected the peaks elements (as shown bellow) of my files -Soud A & Soud B- and put those peaks on an ArrayList -...
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3answers
106 views

Decreasing Sample Rate in DFT (FFT) for Audio Analysis

I'm working with audio data analysis through FFT algorithm. My example audio is a sine wave at 440 Hz and 44100 Hz sampling rate. FFT methods in programming, like ...
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192 views

Getting the velocity in Radar FMCW

I have managed to get the frequency (the beat) frequency from an FMCW. Here is a screen shot of a wall that's detected by the Radar. I performed an FFT of complex I,Q data. My questions are 1. How ...
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1answer
4k views

Apply Low pass Butterworth filter in Python

I want to use a low pass Butterworth filter on my data but on applying the filter I don't get the intended signal. Here is the dummy code: Signal A: ...
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1answer
126 views

Measuring acoustic phase difference between two receivers

I am trying to measure the acoustic phase difference between two sensors 30cm apart each other. The sampling frequency is 20kHz, and my interest frequency is about 1700 Hz. The below is how I ...
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1answer
337 views

Scale FFT frequency range for a bars graph

I'm trying to show frequency spectrum for audio data as a bars graph using FFT. If I have data for a sine wave at 440 Hz and with sampling rate 44100 Hz and analyze its first 1024 samples I get an ...
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1answer
70 views

In a periodogram, why is the modulus squared of the DFT taken rather than the DFT itself? [duplicate]

Why can't you just take the DFT itself? And how accurate is this method in spectral density estimation? Are there cases in which it is very accurate?
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1answer
145 views

How to shift FFT spectrum by half a bin?

I am trying to find a way to shift the outputs of the FFT (any algorithm implementation, currently using radix-2) by half a bin with the same bandwidth. To put it another way, say you have a 512pt ...
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1answer
128 views

Morphing between two FFTs

I'm a musician and I'm making a script that takes a wave file and snaps each of its frequencies from the fourier transforms to the nearest musical harmonic. Thanks to help from another question I ...
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41 views

Detection over a few number of bins

In Periodogram Can I take only few frequency bins (nFFT bins) , sum and compare it with threshold in stead of whole bins . if yes why? with knowledge I pass the data through the window before fft ...
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1answer
195 views

FFT - preferred way of tone detection

I am using FFT to detect certain frequencies (DTMF). I can clearly see the frequencies in the spectrum. Is there a preferred / optimal way to decide if a certain frequency is present or not by looking ...
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1answer
142 views

Band energy and Parseval theorem

In Python, I consider a dummy signal as follows: fs = 512 sig = np.random.standard_normal((fs,)) sig corresponds to 1s of ...
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1answer
130 views

Wavelet transform and FFT using to extract feature power bands with EEG signals

I am using 5 channels [ fz , cz , c3 , c4 , pz] to detect drowsiness of driver My First Question is, what is the right input to get feature power band ( Theta , alpha , gamma , beta ) to wavelet ...
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1answer
157 views

Windowing a signal for FFT

I am actually working on a project involving the cross-correlation of two signals. My cross-correlation code is working fine, but I suspect that I should apply a window to my data set in order to ...
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1answer
39 views

How to Calculate the number of DFTs taken in a STFT

Given variables of window size (W), overlap (O), and length of the Signal (S) (in my case, length of a song) and I am trying to determine an equation that gives me the number of DFTs that would be ...
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51 views

2D - FFT using Xilinx System Generator

I have searched the 2D-FFT implementation using 1D-FFT. Is there a reference design for 2D-FFT implementation in the System Generator of Xilinx ? Espeacially effectively use of FPGA resources. i.e : ...
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1answer
135 views

Phase Modulation and Intermodulation Anomaly ? (Spectrum plots inside - **Updated**)

I have a MATLAB script for modelling a two tone signal (a sum of two sinusoids) going through a non linear transfer function (such as an amplifier). The amplitude of a signal is amplified non linearly,...
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1answer
40 views

psd of an ac voltage signal

In an lab class experiment who's subject of interest was Johnson's noise I measured the ac voltage of a battery. Now I wish to find the psd of the measurement and show that it is constant. 1.Is such ...
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1answer
114 views

Arbitrary Phase FIR design using FFT

I want to design a digital FIR filter to cancel the phase of an analog Butterworth filter (i.e. the phase is smooth) i.e. the filter has unity gain with just an inverted phase component. The ...
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2answers
126 views

Adding phase to a signal that has multiple frequencies

An amplifier changes the phase at different amplitudes of asignal. I am using amplifier data in a MATLAB model. I have constructed a signal that is a sum of sinusoids of different frequencies with ...
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2answers
223 views

pdf of the sum of gaussian distributions using fft Ask [closed]

I am trying to derive the pdf of the sum of independent random variables. At first i would like to do this for a simple case: sum of gaussian random variables. I was surprised to see that i don't get ...
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1answer
119 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 $\...
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2answers
63 views

Is there such thing as harmony independent timbre characteristic of a sound?

I was wondering if any of you know about any technique to extract a harmony (e.g. harmony in a shape of a chromagram) independent timbre characteristic of a sound frame. What I'm after is a version ...
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1answer
95 views

Signal squared in time domain

In some publication I have found a formula that for some reason squares signal in time domain. I am analyzing it now. What should be the Fourier transform of a signal that was squared in time domain? ...
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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 ...
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1answer
98 views

Sum of Diracs in Frequency Domain

I am attempting to compute the sum of dirac functions in the frequency domain via the following formulas: $$ ReLu(f(x)) = f(x) * \sum_{i} \delta(x-x_i) $$ $$ x_i : f(x_i) > 0 $$ $$ F(ReLu(f(x)))(k)...
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1answer
89 views

temporal high-pass filtering to approximate phase derivative

I am currently following the algorithm as based on a previously published research article "A Motion Detection Algorithm Using Local Phase Information" by Lazar et al. The basic overview of the ...
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0answers
56 views

How to catch the peaks from a signal [duplicate]

I am trying to get the peaks from a signal after I had applied FFT function. So I am trying to get only the high frequences along the signal, but with findpeaks I get alot of frequences that I dont ...
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1answer
64 views

Conjugate symmetry Problem

I'm seeing something very curious in the Matlab code below. X = fft(x); Xt = X; Xt( (end/2+1):end ) = 0; xr = 2 * real( ifft( Xt ) ); Xr = fft(xr); where ...
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2answers
374 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 ...
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1answer
53 views

changing circular shift in hologram reconstruction

I'm trying to write a very simple code for the reconstruction of an in-line hologram of particles in a micro channel (digital holographic microscopy), but I'm getting some results that are hard for me ...
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2answers
115 views

Phase difference b/w two sinusoidal signals using FFT

I am trying to understand how to find phase difference b/w two real sinusoidal signals and then align the phases of two sinusoidal signals using this difference. In the first step, however, i have to ...
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2answers
48 views

What should I do with FFT result array from microphone input? [duplicate]

I currently want to create a small pitch detector and I have to say that I am very new in this topic of signal processing. At the moment I implemented the FFt algorithm and I got an array of window ...
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1answer
98 views

Summing magnitudes of individual frequency bins

I am working on signal analyser and have problem with understanding relationship between display resolution and frequency resolution (range). My frequency range is $ 1-20000\quad [ H z ] $ so to ...
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1answer
186 views

Apply windowing before FFT or after?

I am computing a spectrogram and I've found a code example online which goes like this: ...
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0answers
80 views

Find cepstrum of a function with dirac function

$$x[n] = d[n] + a\cdot d[n − N_p]\ ,\ \ |a| < 1$$ I need the complex and real cepstrum of this function as well as what would happen for $N=N_p/6$ for the DFT approximation $$x_p[n] = \frac{1}{N} ...
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3answers
302 views

real time overlapping buffer for FFT

I am currently using overlap-and-add method for a noise cancellation project. Everything works well so far except that when it comes to the real time, I need to overlap the input signals for FFT input....
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15 views

What is the best spline to interpolate freq analiser graph

the question is as it is in the topic: What is the best spline to interpolate freq analiser graph? I am looking something simply and fast to implement. I read about catmull-rom it looks it could be ...
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0answers
143 views

FFT Data loss during IFFT

I am working on image encryption using FFT mask. (not fractional) For the start, I applied a series of pseudorandom phase masks to the results of FFT (512*512 elements). (used logistic map for random ...