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Questions tagged [dft]

Discrete Fourier transform (DFT) is a specific kind of discrete transform, used in Fourier analysis.

Given a sequence of N samples f(n), indexed by n = 0..N-1, the discrete Fourier transform (DFT) is defined as F(k), where k=0..N-1:

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Source: engineeringproductivitytools

428 questions
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Image compression with FFT causes patchy areas

I am trying to implement image compression using fft. I follow these steps: Pad the height and weight of the input image to be powers of two (for easier DFT application) For each of the red, green and blue channels: Transform each row to its…
Mushegh
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Fastest DFT method for Javascript?

I'm working on a "studio" website where you can perform different sound edits on a clip of audio you record. In order to do the sound editing, Fourier Transforms have to be performed on windows of the recorded sound. This is the code for recording…
BigChungus443
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Way to calculate vibration

I am reading a paper about synthesis. One of the parts is talking about calculating vibrato, and I want to follow their way to do the same thing. However, I am new to signal processing and am not sure whether the method I found is correct or…
Megan
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What causes these periodic spikes when computing Fourier Transform from scratch?

I recently wrote a little python program to compute a fourier transform of a signal from the basics for the sake of learning and checking my understanding of how this function works: import numpy as np from scipy import integrate import…
Drake Mossman
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fft of a constant function in python

I want to calculate the DFT(FFT) of a constant signal. Here is the code import matplotlib.pyplot as plt import numpy as np from scipy.fftpack import fft, ifft def constant_function(x): return 1 t = np.arange(0.0,1,0.1) print(type(t1)) print(…
Gunners
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Why is the Number of Frequency Bins Determined by the Frame Size in the DFT?

I'm currently working with Fourier transforms and I notice that the output of an FFT usually has the dimensions (n_fft, ) where n_fft is the number of samples to consider in the FFT, though some implementations discard frequency bins above the…
AlePouroullis
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How to plot the result of 1D DFT on an image with sinus gratings when it only shows completely dark image instead

I have been playing around a little bit to understand how the 2D DFT works. As far as my understanding goes the 2D-DFT performs a columns wise fft and then a row wise fft afterwards. So now I wanted to check what the result looks like after…
OuttaSpaceTime
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How to code the discrete Fourier transform in python

[I am having trouble coding this in Python, I don't really know where to start. The DFT Version 3 is the one pasted below][1] ![1]: https://i.stack.imgur.com/0J7T0.png ![1]: https://i.stack.imgur.com/JXR4i.png
need_help12
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How can I transfer a discrete set of data into the frequency domain and back (preferrably losslessly)

I would like to take an array of bytes of roughly size 70-80k and transform them from the time domain to the frequency domain (probably using a DFT). I have been following wiki and gotten this code so far. for (int k = 0; k < windows.length; k++) { …
Matt
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2D FFT convolution or 1D?

For my research, I have a lot of different images A, which I want to convolve with kernel B as fast as possible. The images are (M x N) and the kernel (M x P), in the normal convolution (which I have implemented right now) I slide them over each…
Taliebram
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Simple Windowing DFT code -ValueError: setting an array element with a sequence

I was expecting to make simple code windowing DFT for my assignment but, i thing i have problem with formating DFT signal realX[k] and imj[k]. Here is my code below: import numpy as np import matplotlib.pyplot as plt import random realX =…
zief26
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Inverse Discrete Fourier Transform

I have been attempting to implement a Inverse DFT (without using a FFT), but struggle a bit with the maths. From the implementations and pseudo codes I have read I cannot figure out the issue with my…
Cameron Richards
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R: Inverse fft() to confirm my manual DFT algorithm inaccurate?

Using R, before assessing some metric of accuracy on my own manual implementation of DFT, I wanted to do a sanity check on how well stats::fft() performs by doing the following: sig.ts = ts( sin(2*pi*freq1*t) + sin(2*pi*freq2*t) ); sig.rt =…
Christian
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STFT(Short-Time Fourier Transform) & DFT(or FFT) in Matlab

I want to try STFT & FFT using Matlab. What I wonder is STFT of signal computes the result that FFT(DFT) of each windowed signal and I can see the change of each frequency value over time. If I calculate the average of each frequency over the total…
Hak-Min Lee
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No instance of overloaded function when resizing

I got an error of "No instance of overloaded function" when I used resize(). I'm aware that what's inside of resize() might be wrong as well. I'm trying to resize x, an array of floats to all zeros. Not sure if std::vector>(0, 0) would be the right…
linda meng
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