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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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How do i Show this in the Frequency domain with Matlab

Convert time domain to frequency domain in Matlab, these ECGs are plotted together in the time domain and i wish to duplicate the 3 in 1 window in Matlab by doing the fft. My graphs look weird, any ...
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Remove constant noise from Goertzel output

I'm trying to analyze a signal recorded from an analogue phone line and do DTMF recognition using a Goertzel algorithm. However, due to a fault in the hardware, there is a constant 50Hz power line ...
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10 views

Spectrogram of chirp sequence radar signals

I am confused as to whether SFFT makes sense to process chirp sequence signals. The radar fires up a sequence of 100 linear ramps with that are only interrupted by the very short period in which the ...
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7 views

Calculating noise floor of digitization system using FFT

I am trying to calculate self noise of a digitization system with differential inputs.For this purpose, i select a differential channel, set input range to +/-5 V, short both differential inputs and ...
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17 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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24 views

How to achieve a smoothed frequency phase response with no outliers

I have two sampled signals, which I then perform wavelet analysis on, by synthesising the Filterbank, perform the dft on each kernel, and the dft on the sampled signals, and multiply together. ...
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43 views

Detecting a three-tone signal in real-time

I'm new to digital signal processing, and I've been looking into FFT, filtering, Matlab etc. What I'd like is to build a program which will detect when a certain BEEP is transmitted through a trunked ...
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27 views

Is it possible to approximate certain 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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22 views

Matlab: Different 1-D FFT results with and without zero-padded

Recently I am implementing FFT with C code. So I use Matlab for algorithm verification. As Radix-2 FFT was chosen, I've learned that zero-padding technique could help to reach 2^N limitation without ...
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29 views

Taking FFT of a signal with lots of “holes”

I have a time series that is spotty (more 'no sample' than 'sample' at each second, which is the sample rate). There are obvious trends when viewed visually. However since there are holes, the FFT ...
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6 views

PSD to single frequency - MIDAS files - python

New to signal processing, but I've been forced into it a bit as part of my education. I'm collecting low frequency samples in the magnetic field, from 1 to 1000 Hz. It is stored in MIDAS files, ...
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Aperiodic Correlation function using FFT Method

Periodic correlation function between two binary sequences say x and y can be computed using FFT. corr_value = ifft(fft(x).*conj(fft(y)); Can some one please help on how to compute aperiodic ...
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34 views

Matlab FFT not producing symmetric spectrum

I am plotting a FFT of a sampled RC pulse but my resulting spectrum isn't symmetric - it's offset. ...
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1answer
43 views

PSD subtraction

I am interested seeing the difference between two power spectral densities (PSD) as a noise reduction exercise The blue line is the psd of my signal, and the the orange line is the psd of the ...
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14 views

Signal ECG Noise correction

in order to make the correction of an ECG signal full of collector noises from a sensor, I use the fast Fourier transform (FFT) method and it sends me complex numbers, my problem is that I do not know ...
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6 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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46 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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32 views

Phase differences between DFT and FFT (in MatLab)

I have implemented a (direct) DFT in MatLab (following script) and compared it to the built-in FFT routine. The magnitude response seems to be identical (excluding some possibly round-off errors), but ...
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20 views

Strange phase for gaussian beam 2D

I have a 2D Gaussian beam : After doing FFT2 and angle I get strange results: This is the code I'm using (Python 3) ...
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1answer
35 views

DTFT frequency range

$$X(e^{j\omega}) = \sum_{n=-\infty}^\infty x[n] e^{-j\omega n} $$ The frequency term $\omega$ in DTFT is normalized as $\omega = \frac{\Omega}{f_\mathrm{s}}$ $\Omega= 2 \pi f$ is the angular ...
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Restoration problem with numpy fft function and self-made high-pass filter

Hi, I am using numpy.fft functions to do CV assignments in univ. But while implementing the high-pass and low-pass filter, I found something wrong during the process. The difference should converge ...
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1answer
79 views

Purpose of multiplying fft output by Hann window?

I'm working with some acoustic propagation models at the moment. A feature I've noticed in 2 of these models is that the output of the model is often multiplied by a Hann window in the frequency ...
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1answer
27 views

Zero padding and 2D Fourier transforms: how does zero-padding affect phase?

It's pretty clear that zero-padding an image before performing Fourier transform simply enlarges the magnitude image (stretching it to the new, padded size). What I can't understand is how it affects ...
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66 views

FFT Heart Rate Monitor on Arduino

Part of my project is to build heart rate monitor from Nano and a PulseSensor. I am having trouble working with the Fast Fourier Transform part of the code. This code here is from a library (...
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1answer
37 views

Electret microphone RC filter design contradiction among information sources

I'm building a circuit for an electret microphone and I want to build a bandpass filter around the op-amp. I was using this source until I have found that most sources ( e.g. here and here) indicate ...
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1answer
56 views

Why Does 2D FFT of Gaussian Looks More Sharper than Gaussian Itself?

I am trying to understand why 2D FFT is done on a Gaussian process in a particular code. From my understanding from these posts: https://www.researchgate.net/post/...
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58 views

Amplitude and Phase of FFT gives messy results - Matlab [closed]

I'm trying to calculate the spectrum magnitude and phase of a signal, but when I plot them I get pretty messy results: The signal is displayed on the right, then I have the magnitude and phase of ...
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16 views

Wavelet Transform Implementation Method

I have been watching the wonderful youtube videos here: https://www.youtube.com/watch?v=4TTpwIZrUAo&list=PLn0OLiymPak2G__qvavn3T8k7R8ssKxVr&index=3 detailing morlet wavelets and fit ...
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25 views

Zero-padding vs. nonzero-padding in computation of auto-correlation with FFT

Isn't the usual zero-padding in the computation of the auto-correlation function with FFT just one of many possible extrapolations of the original signal? If I have a measured signal which has good ...
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2answers
50 views

What should my reference value be when converting FFT bin amplitudes to dB?

I want to transform my FFT output values into a dB scale, but I'm struggling to determine the function I should run each bin amplitude through. My understanding of the decibel scale is that a value ...
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2answers
58 views

Multiple different length Windows for high resolution realtime FFT

I am looking at trying to achieve a 'realtime' (as quick as possible to acquire, process and present data) FFT application to analyse audio. I have setup my app to acquire a set of samples, apply a ...
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2answers
59 views

Is there a rule of thumb for zero padding in image processing?

I see there are a lot of answers on why zero padding is necessary and how it avoids wrapping around the sides of images. However is there a rule of thumb on how much padding will be good for the image ...
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37 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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36 views

How to Extract frequency bands from Short-time Fourier Transform?

I am reproducing the results reported by the author in a research paper. In which he takes the STFT of EEG signals. The input data has a shape of (1 X500) and I used Scipy library built-in function to ...
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29 views

Zero padding frequency domain data for improving time domain resolution before inverse FFT

I am working in MATLAB with measured data from a VNA. The bandwidth is 1 GHz from 5-6 GHz with 801 samples in the frequency domain. Everywhere I have read that I need to split the data into 2 parts at ...
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31 views

Image from Inverse FFT operation is sparse

I'm trying to train a deep nerual network that takes in input, an signal in the frequency domain, and attempts to learn a mapping to another signal in the frequency domain. Basically, the input to ...
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2answers
46 views

How to select the sampling frequency when the input signal frequency is not known

I am trying to observe the noise produced by UPS present in our lab, under no load (a normal running condition when its power is on). As I don't know its frequency range, I have randomly chosen 4 ...
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1answer
54 views

FFT: do I need to include gaps in data in my FFT domain?

I am currently doing an FFT on a very large amount of vibration data, which I am going to sample with no pattern which I want to PSD eventually My question is in essence can I go from my data ...
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42 views

Frequency analysis : relation between FFT size and sampling

I am currently trying to perform an experiment given an audio signal. I am therefore sampling the audio frequency range (0 to 22kHz) with a 48k sampling rate. When performing a FFT on my signal, I ...
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1answer
54 views

What's the formula for choosing FFT sample rate and window length to make sure the frequency I want is in the center of a bin?

I don't know why I am having such a hard time with this math, but I am. I am doing phase-sensitive detection of a few sensors, which are triggered by a modulated light source. The modulation frequency ...
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1answer
68 views

How to set STFT-parameters to visualize woodpecker / Sawtooth Signal? ​

I always wanted to work with FFTs and Spectrograms to characterise sounds and their frequencies using python. Lately I recorded a woodpecker at his work. Woodpecker Wav File To know where to look ...
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51 views

Understanding FFT size in OFDM modulation

I know that the FFT size is the the number of subcarriers OFDM system have. But I also know that the FFT has to be $ 2^N $ big (in order to process N samples from time domain to frequency domain). ...
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1answer
31 views

How to classify the movement type of a target into two categories(direct motion or else) by using a doppler radar?

How to classify the movement type of a target just into two categories(one is direct motion which is almost straight line movement and the other is anything else) by using a doppler radar with a ...
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29 views

N-dimensional Cooley-Tukey FFT

I am trying to formulate an n-dimension algorithm for the Cooley-Tukey FFT. In two dimensions, it is very clear: $$ Y[k_1 + k_2 n_1] = \sum_{l_2 = 0}^{n_2} \Biggl[ \Biggl( \sum_{l_1 = 0}^{n_1 - 1} X ...
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1answer
42 views

Incorrect dominant frequency from FFT

DATA source: Bearing vibration data FEMTO IEEE PHM 2012 challenge. DATA context: Sample rate: 25.6 kHz Sample period: 0.1 Seconds (2560 points) Motor runs at 1800 rpm Steps taken: Low pass butter ...
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49 views

Spatial smoothing - 2D MUSIC [FMCW MIMO radar processing]

I'm using a 2D Music algorithm for the estimation of Range-Azimuth info in a ULA FMCW MIMO radar. The algorithm procedure is pretty simple as per Belfiori F., Application of 2D MUSIC Algorithm to ...
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3answers
48 views

In case of Complex DFT spectrum, why the x axis range from N/2 to N point mean a negative frequency?

When we transform a complex signal into frequency signal by using a complex DFT, The range from N/2 to N point on the X axis of the spectrum mean a negative frequency... But i cant understand why ...
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51 views

OFDM modulator: Transmission time calculation

I have a problem with a certain task. The frequency of the signal sampling at the OFDM modulator output is 20 MHz. The length of the protection period is 2 microseconds and it is 20% of the ...
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2answers
48 views

Checking Parseval's Theorem for Gaussian Signal by Using Scipy

I'm trying to check Parseval's theorm for Gaussian signal. It's well known that fourier transform of $\exp(-t^2)$ is $\sqrt{\pi}\exp(-\pi^2 k^2)$. So I implement it by using quad and simps. I think ...
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87 views

GCC-PHAT (Generalized cross correlation) always peak at delay=0 on real audio signal

I have studied the GCC-PHAT algorithm to estimate TDOA on audio signals at 2 mics. Here is my MATLAB implementation: ...