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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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 ...
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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 ...
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Why a sampling frequency would distort a signal even if it meets nyquist theorem [duplicate]

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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 ...
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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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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 ...
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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 ...
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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 ...
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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 ...
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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
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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 [...
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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 ...
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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 ...
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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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1 answer
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What are the theoretical maximum values of the complex bins in an unscaled FFT of size N?

I am using FFTs to perform real-time convolution of audio signals on small embedded microcontrollers. I am thinking about testing different/smaller data types to represent the complex bins. I am ...
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Discrepancy between time & frequency domain RMS magnitude

I'm looking at complex baseband RF at a sample rate of 2.56 MHz. I've plotted the FFT of the entire spectrum, a 16 kHz segment of that spectrum, and the output of 160 decimation low pass filter that ...
Deepstop's user avatar
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What are the spikes here in the spectral analyser?

I'm learning to use the spectral analyser in Simulink, and tested it with a 500kHz square wave (sampled at 1MHz). When I set the Resolution Bandwidth (RBW) to 700Hz, the plot was beautiful and shows ...
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Elevation angle estimation from L-shaped antenna array

I have TI IWR6843ISK-ODS radar sensor and need point cloud data as output from it. The antenna arrangement is as follows: I would like to know how to estimate elevation angle with this antenna ...
Pushkar Mahajan's user avatar
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(graphic) Relation between FFT and complex signal

I have a complex signal with a frequency between 0 and 16 (16 not included). I have made four plots (in python) to show four examples. For each example I provide the signal, its FFT in both real, imag ...
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parallel FFT resources on FPGA

Given my FPGA working frequency and the input data throughput to it I need to parallelise my FFT algorithm. For instance: input throughput = 40 Gsps fclock = 400 MHz Parallelization = 40 Gsps/400 MHz =...
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2D Fourier downsampling to even number of points gives incorrect modes in the last column

I would like to downsample an image in the frequency domain to an even shape, similar to what is described in this post. I have been able to do this successfully with a 1D signal to both an odd and ...
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Radix-4 DIT Inverse Transform Reordering Issue

I am trying to implement a radix-4 DIT FFT. It looks like the forward transform is working correctly, but the backward transform output is not in the correct order. I'm pretty sure that the ...
Tobias Hienzsch's user avatar
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Do you have to receive a whole OFDM signal to be able to demodulate?

An OFDM signal is made of subcarriers that are orthogonal to each other. This terminology makes me think that if one is only interested in information on a specific subcarrier, only that subcarrier ...
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Does the length of DFT points (duration of a signal) affect the "amplitude" of the power spectral density?

For example, performing a DFT on a 10-second-long and 20-second-long signal with the same sampling frequencies will change the "amplitude" of the power spectral density (PSD) at each ...
Tom's user avatar
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Strange spectra of different volume sines

I am simulating mic input with a sine of 100 values that would, in q4_28 look like this (full period): ...
Øyvind Teig's user avatar
6 votes
1 answer
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Bandwidth of an entire song

My question has to do with the difference between the frequencies of a single note, and the frequencies of an entire song. If I have a 5 second signal of the form: $x(t)=\sin(8\pi t)$, here is the ...
Levi's user avatar
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2 votes
1 answer
167 views

How to interpret FFT output?

I want to perform a spectrum analysis of my own voice using the code below. ...
walter's user avatar
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1 answer
66 views

What would be my new sample time when applying small-size IFFT to a big-size FFT?

I have a signal sampled at $Fs$ [Hz], a big size FFT is used to detect some signals, then a small size IFFT is use to transform that portion of the spectrum in the time domain, my question is what ...
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I am trying to plot range of a target in a FMCW radar

I am working on the simulation of FMCW radar, and I am trying to figure out how to plot the target range using the impulse response of the beat signal. I have successfully generated the chirps and the ...
Raj Patil's user avatar
4 votes
0 answers
82 views

Recover the first half of the time-domain signal of the N-point frequency domain signal using an N/2-point FFT

Let X be an N-point sequence in the frequency domain (where N is a power of two): $$ X = (X[0], ..., X[N-1]) $$ where $X$ is the complex and conjugate symmetric forward DFT of the real sequence $x = (...
keith's user avatar
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Correction Factor for np.fft.rfft

I tested the function np.fft.rfft using the following code and determined the magnitude of a $50 \, \textrm{Hz}$ sine wave. ...
Tom's user avatar
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FFT-based phase estimation better than CRLB in MATLAB simulation

I am trying to understand the concept of CRLB for a simple sinusoid in AWGN with a simulation in MATLAB. According to Kay (p. 57) the CRLB for phase estimation is: $var\{\phi\}=\frac{2(2N-1)}{SNR\cdot ...
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Is it possible to use np.fft.fft to pick out the Fourier coefficients from one timepoint, at a specific frequency?

I am trying to apply np.fft.fft on a 2D array of data of shape (98, 1024), where 98 is the number of trials and 1024 is the sampling rate in Hz. I am trying to find ...
Lisa Duan's user avatar
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Finding oscillation frequency in a harmonic polluted signal [duplicate]

I would like to find periodicity and the oscillation frequency in a signal. I used this simple MATLAB code which works find for some signals, but for a harmonic polluted signal like the one given ...
user70703's user avatar
2 votes
1 answer
91 views

what does librosa.stft do that makes it different?

My understanding of the Short Time Fourier Transform is that first I need to frame the signal and window it, after that apply an fft on these windowed frames. Using Librosa: ...
kulon one's user avatar
1 vote
1 answer
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Summation interchange in DFT/FFT

Let $x(n)$ be a sequence of length $N = LM, n = 0,\dots,N-1$.$N$ and $M$ are integers. The Discrete Fourier Transform (DFT) of $x(n)$ is given by $X(k) = \sum_{n = 0}^{N-1}x(n)W^{nk}_N$ where $W_N = e^...
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Musical Instrument Characterization

I am doing an undergraduate project where I want to first characterize an instrument based on its pitch and timbre and make an instrument recognition system afterward. Pitch characterization is pretty ...
Flash's user avatar
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2 votes
2 answers
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Signal power depending on FFT bin size

I have read the following quote from a different post: If the noise is white (spread evenly across frequency), then the power will be distributed equally to each bin, and as we increase the number of ...
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