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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What Are the Units of a Fourier Transform?

I know that a Fourier transform (FT) outputs a distribution of how much of each frequency is present in a signal, but what would be the units of that distribution? It's not a proportion or a percent ...
Data2Dollars's user avatar
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Is it possible to reconstruct the continuous frequency spectra from DFT/FFT?

Given the output of some FFT (lets call it X) with N bins (lets say 2048) is it possible to recover the values in between the bins in the same way that I can recover the values in between samples of a ...
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Pixel Shift when using Fourier Downsampling

I am working on a Super-Resolution network, and want to try to use Fourier downsampling, different from the normally used bicubic downsampling as it relates to MRI imaging. I have tried using this ...
Christoffer Overgaard's user avatar
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Excel FFT of Two Sine Waves Not Giving Expected Results

I did an FFT in Excel on a 440 Hz time domain sine wave, $y_1(t) = \sin(2\pi\cdot440\cdot t)$, and got the expected output in the frequency domain: a single-spike distribution with 100% of the signal ...
Data2Dollars's user avatar
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Discussion on the relationship between the FFT magnitude spectrum and the corresponding actual amplitude

This might be a bit long, but it's a question that has troubled me for a long time, and I hope to get everyone's help. When studying signals and systems, we usually only pay attention to the relative ...
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Why doesnt DFT Padding cause sinc like features

I'm new to the land of DSP so any incorrect terms please let me know. It seems padding the time domain signal can make the magnitude spectrum look 'nicer', the fact it doesn't gain any more useful ...
George kirby's user avatar
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Jitter model does not behave as expected after FFT

So I'm currently trying to understand the relationship between jitter and phase noise. To help my understanding I did write a little simulation in matlab. I used this model in the time domain, relying ...
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Peak FFT Frequency Off By One Bin

I used Excel's FFT feature to compute an FFT of a 440Hz sine wave that I also generated with Excel. The peak FFT value should occur at 440 Hz. Instead, it occurred one bin later at 528 Hz, so I'm ...
Data2Dollars's user avatar
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What's Nyquist frequency in DFT?

I'm currently studying digital signal processing at university but I can't figure out what the Nyquist frequency means in the DFT coefficients, I know what the Nyquist frequency is in the sampling ...
minghierid's user avatar
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Possible to combine and/or compare a swept Sine and a wide band noise signal?

I am working on a problem where two profiles need to be compared. One is a swept sine in $m/s^2$ (Acceleration) and the other is a sine-on-random signal composed of a swept sine $m/s^2$ and a random ...
SpillTheFFTea's user avatar
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Can a bad quality sound be measured via THD?

I'm trying to create an app that measures the audio quality, this is ideally to filter out blown out or cracking speaker who has different types of distortions, what would be the best measurement ...
Priyank Joshi's user avatar
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How to find frequency , location and phase of two sinusoid signal buried in noise?

There is a data set which has two different sinusoids buried in noise. Data record has following properties: A data records with a total data length of 2048 points. The sampling frequency is 100 Hz. ...
Thouhidul Islam's user avatar
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Ignoring Negative Frequencies from FFT on Real Time Series Seems Inconsistent With Time Series

I ran an FFT on real financial monthly time series data. If I plot the FFT frequency domain output on the interval $[0, f_s)$, the dominant frequency pair peaks occur at $f_{A1}$ $\approx$ $0.02 \ ...
Data2Dollars's user avatar
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Binning and Frequency for FFT on Financial Time Series Data

I'm trying to analyze financial market time series data, so are there any particular concerns in using FFT for that kind of data? The data seems to be relatively covariance stationary. My sampling ...
Data2Dollars's user avatar
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How do you properly cut out negative frequencies from FFT of a real signal if it reduces sample size?

If a real time signal has $N$ samples, then the magnitude of its FFT will also have $N$ samples--half of which will have positive frequencies and half of which will have negative frequencies. The ...
Data2Dollars's user avatar
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Frequency decomposition of forecast error variance

I think my question concerns statistical signal processing. I was referred to this site by a user at Cross Validated. I want to do a frequency-domain decomposition of generalized forecast error ...
Pavel Filip's user avatar
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How does background noise affect the fft results for a pure tone

When I am recording a pure tone and conduct a fft, I receive a peak in the spectrum for this certain tone. Let's say the peak is 5 Now I am recording a pure tone with additional white noise. Does this ...
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Non-uniform FFT

I'm looking for a form of a FFT where the samples in the frequency-domain don't represent uniform spaced frequencies. What I would like to get is a frequency-domain with samples that are unevenly ...
wimalopaan's user avatar
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Program to compare output and input streams to verify volume

I'm trying to wright a program to compare, two sound signals, output (speakers) and input (mic) streams and verify/adjust the volume. I'm using Microsoft Visual Studio C# forms project with the ...
djangocoder5925's user avatar
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Is there any way to make the FFT more efficient for continuously sampling a signal?

So I want to continuously estimate the frequency content of a signal using the FFT such that at every sample timestep, I add a new sample to my current set of samples and remove the oldest sample in ...
Quéston Questioneer Esquerie's user avatar
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How can i add overlap-add into this

Im new to DSP and i wanna know how i can add overlap-add into this to remove artifacts. ...
SignalWhisperer's user avatar
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Zoom FFT shifting region of interest to be centered at zero Hz

So using this resource: https://flylib.com/books/en/2.729.1/the_zoom_fft.html I think I understand that the zoom FFT allows you to calculate the FFT for a region of interest with a lower order FFT by ...
Quéston Questioneer Esquerie's user avatar
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Losing my mind over simple conversion of common Acceleration PSD-Units: g²/Hz to (m/s²)²/Hz

Because it causes confusion within my team I wanted to create a simple overview on how to convert from one PSD Unit to another. I know it is really simple but I've obsessed over it for a few hours. I ...
SpillTheFFTea's user avatar
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Signal level from its FFT

Suppose I have the FFT of an arbitrary real audio signal z samples long. Is there a way to discover the signal level (intended as the largest absolute value of its samples) from the FFT without ...
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Min. sample duration for FFT of low frequent signals obtained from zeroIF receiver

I am new here and a beginner with SDR & FFT. For antenna pattern measurements, a flying probe antenna is to be used to sample the electromagnetic near-field in front of an antenna. A lightweight ...
Tom944's user avatar
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Is it possible to compute a 2D-FFT if the input size is not a power of 2? [duplicate]

Let us suppose to have an image with size $28\times28$, and that we want to apply a 2D-FFT without any padding operation. Does exist any algorithm which allows to perform the 2D-DFT calculation with ...
Giorgio Bianchi's user avatar
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Filter coefficients hamming window for low-complexity Welch PSD computation

I am trying to implement the proposed method from this paper 1, to eventually have a more efficient PSD computation for feature extraction on a microcontroller. The method is suitable since I am using ...
michael's user avatar
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Why a sampling frequency would distort a signal even if it meets nyquist theorem [duplicate]

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giraffe123's user avatar
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Predicting the "amplitude" of a damped sine wave from FFT

For a sine wave, $A \sin(\omega_0 t)$, with an amplitude $A$, after FFT and calculating the magnitude spectrum we can get a single peak with a height also equal to $A$. This requires proper scaling. ...
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How am I supposed to acquire/measure vertical and horizontal effective resolution from my images?

I apologize first for some questions that might be dumb. Unfortunately, I am only a bachelor student (writing my bachelor thesis in physics) and have almost zero image processing experience. And I ...
Anothernewbie's user avatar
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Is the noise at different sampling points related? [closed]

Given the power spectral density of noise, if the values at different sampling points of the same noise are added, what is the power spectral density at this time? Is there any correlation between the ...
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Influence of phase discontinuity on power spectrum density

I was wondering about the influence of phase discontinuities on a power spectrum density calculated with f.e. Welch's method. I know you shouldn't have any phase discontinuities in your signal, but I'...
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How to produce a noise spectrum from an rms velocity specification?

For a dynamic model I am looking at the appropriate input to analyse the performance under the influence of floor vibrations. The norm is an ISO VC-C floor spectrum as displayed in the image. However, ...
Jan's user avatar
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Forecasting of a periodic movement based on sensor data

I need your help. Unfortunately I don't have background in signal processing, but have a problem in this field. I'm helping a friend with an interactive art project. It has parts that move based on ...
Alexander Jasper's user avatar
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Can we implement polyphase fft for N point even when filter coeffients length is 4N for example?

This paper https://ieeexplore.ieee.org/document/10051908 tells that we can implement polyphase fft even when data length is less than filter coefficients length. I am confused how can we implement the ...
Purushothama T S's user avatar
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writing from STFT to audio using ISTFT adding harmonics to audio not present before

I'm doing quite a bit of the samething as I wrote in this post here : Shifting frequency peaks such that w[i] moves to w[i/n] using STFT and IFFT I'll quote from it here to present the issue I now ...
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Shifting frequency peaks such that w[i] moves to w[i/n] using STFT and IFFT

I am trying to do a kind of frequency compression on say 20 most energetic frequencies in a particular slice of a STFT. If w[i] is the frequency peak for a slice of STFT at a particular time, then I ...
Vrisk's user avatar
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4 votes
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Why are my frequency bins oscillating?

I am working on a personal project that maps bass notes to colors in real-time. However, I'm encountering some issues with oscillations in my frequency bins. I visualized my frequency bins to ...
Alex Larson's user avatar
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Noise at Corners of MATLAB's ifft2

I'm trying to implement the code in this tutorial in MATLAB using MATLAB's ifft2() function instead of the algorithm used in the shader (looks to be some type of Radix-2 algorithm). It is used to ...
eball's user avatar
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FFT analysis of signals that were combined

I have a dataset with ECG artefacts, noise and EMG activations. Now I want to analyse the EMG activation using Welch's and Burg's method. The EMG realizations are approximately 0.25 s long, resulting ...
Stijn's user avatar
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Why are these excess frequency components in my FFT spectrum? [duplicate]

I am experimenting with digital signal processing and I took the FFT of a sinusoid in Matlab. I got the frequency components that I expected to be present but there are two excess spikes that mirror ...
Michael's user avatar
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1 answer
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Polyphase FFT example implementation

How can I implement a 256-point polyphase FFT whose sidelobe level is 40db down and main lobe width of rectangular window? If we perform FFT of 256 point with some window, The window will have effect ...
Purushothama T S's user avatar
1 vote
2 answers
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do closer peaks Leak more to each other (spectral leakage in FFT)

I am familiar with the spectral leakage problem in FFT due to a rectangle window for a sin signal giving two peaks that leak to each other. My question is will the leakage to the frequency bins near ...
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How do I isolate a part of this signal in time-domain in Matlab?

I want to isolate a reflection part of a signal which I've transformed from Frequency to Time-Domain (see Picture). So far, I've tried to create a Hamming-Window with the specific window-width for the ...
Anne-Mary's user avatar
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How does the shape of a FMCW radar work in Python?

I’m a beginner to this field, so sorry if my questions aren’t the best, or if I’m missing information. Anyways, I’m working with raw data samples from a FMCW radar. Basically, a frame constitutes of [...
Aquelae's user avatar
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3 votes
2 answers
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FIR filter insufficient stopband attenuation

I used PyFDA to design a low-pass FIR filter for the final stage of decimation of a complex (I/Q) stream, from 2048 MHz to 16kHz. The last stage, 32kHz to 16kHz is the only non half-band filter, as ...
Deepstop's user avatar
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Issue with cudafft library and fftshift on odd image dimensions

I'm facing with a code I'm implementing for an exam using the GPU. Specifically, the code I'm writing is in C++, and I'm using the CUFFT library to perform the Fast Fourier Transform (FFT). The ...
overflow''s user avatar
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How to accurately estimate the quality factor of a noisy signal

I'm currently interested in measuring the quality factor of a noisy signal. For the purposes of example, consider a single degree of freedom mechanical system excited by white noise: \begin{equation} \...
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NUFFT of non-uniform sampling spectrometer

I am looking to apply Matlab's nufft.m function to a signal non-uniformly sampled with a spectrometer, hence measuring values at discrete frequencies. In this case I believe my sample points t will be ...
liamando's user avatar
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Debug the difference between two Frft implementations

I need help to understand the difference between two fractional Fourier transform implementations. On this website two different implementations for the fractional Fourier transform are presented (...
Laszlo Korte's user avatar

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