Fft Definition and 181 Threads

hello! i'm given a signal h(t) = v(t)*g(t) where g(t) is a distortion/noise that got added and has a very low frequency compared to v(t) i need to devise a method to clean up g(t) i'm thinking of to do the fft on the signal h(t), and remove the lower frequencies and do the inverse...

Hi, As part of my homework, I wrote a MatLab code to solve a Poisson equation Uxx +Uyy = F(x,y) with periodic boundary condition in the Y direction and Neumann boundary condition in the X direction. I used the finite difference method in the X direction and FFT in the Y direction to...

Im trying to perform an FFT on a set of sampled data to determine the frequency of a person humming. Im using the MCF51AC256 on the DEMOACKIT, coding with Codewarrior using Processor Expert which has a FFT bean included, so all I need to do is pass it values and it performs the FFT. So I...

Hi, I'm using a version of daqacquire to acquire a sample of sound data. This program also uses daqdocfft to perform a Fourier transform, allowing me to view the frequencies that are present in my data sample. My problem is that I don't understand how the function is calculating the...

So, let's say you have a signal, bandpass filtered between 10Hz and 1000Hz. The signal is then sampled at 2000Hz. A window of 20 samples is then FFT:d. You then get a frequency resolution of 2000/20 = 100Hz (the FFT contains 20 points). One consequently doesn't know anything about any other...

Hello, I have a question regarding fft's. My experience with working with Fourier transforms is pretty much limited to transforming contrived functions pen and paper style, not dft's. But now I need something and I think the fft is the appropriate tool, but I'm having a hard time understanding...

Hello, I have a question regarding fft's. My experience with working with Fourier transforms is pretty much limited to transforming contrived functions pen and paper style. But now I need something and I think the fft is the appropriate tool, but I'm having a hard time understanding some...

Homework Statement I need to speed up a image alignment function using FFT Homework Equations FFT, correlation coefficient (for deciding best alignment) The Attempt at a Solution This function works but a fail to see how it is any better that a naive evaluation of the correlation...

Hello everyone, Finding a good query to find an answer in www search engines isn't as easy as I thought. The subject is very narrow and sophisticated. When one performs a FFT, he/she/IT ;) gets the amplitude and phase spectra. The phase spectrum ranges from -PI to PI. Then, there are of course...

Hi all, First a warning: my Mathematica skills, and computery-type skills in general, are not very hot. My problem is thus: I have a function which I know: \hat{f}(k) I'd like mathematica to approximate the inverse Fourier transform of this function for me and plot the result. I've...

Homework Statement From what I understand, the array output of the FFT of a function in time represents the frequency contributions of different frequencies with the first output coming from 0 freqeuncy, 2nf from the 1st fundamental frequency and so on.. if so, then why does this code(which...

Hey everyone, first of all id just like to clarify this isn't a homework or coursework related problem, its part of my personal MatLab learning for future years. I obtained a nice little siganls and systems question off a friend, it looked fairly simple but I've come across a problem which i...

Homework Statement How i will write the code for fft Homework Equations ACos(ωt+φ) The Attempt at a Solution n = 100; n = 0:n; nodd = 2*n + 1; T=n*pi/2w w=2*pi*1.93*10^14; phi= 0; A=-6:6; X= A*cos(w*T+pi) %Here it generates error " ? Error using ==> mtimes Inner matrix...

Hi, I have a question about the FFT. I'm starting to learn the concepts behind it, but I'm struggling at this one particular thing... Ok, let's say you have this diagram. http://www.ece.uvic.ca/499/2004a/group05/image/radix2.jpg Can someone explain to me exactly what "N-point" means? Also...

I got some data which is in equal time stamps. When I do the Fast Fourier Transform for the data using MATLAB I get the graph below. Now I understand how to do the fast Fourier transform but I have no idea what information the FFT graph gives. I am confused as to what the peak at 1...

Hello all. how to find relative phases, strengths of a signal by using Matlab.

Hey, This may seem very stupid but how the heck are you supposed to use FFT? The FFT transformations take a vector as in input but I want to use it to work out FT of a perticular value. I have the charecteristic function of a distribution and wish to numericaly work out values for the...

well, that's the heading of a project i am doing...i need some help on neutron detectors... how they are dectected and what is the probable graph of count rate vs, pulse height that i might get for a nuclar fission reaction of U-235... can anyone help?

Hello I have a Gaussian Pulse in the frequency domain and transform it with the IFFT into the time-domain. My Problem is now that I can't figure out a way to give the sample points the correct time-scale. What kind of formula do I need to use? Thank You for helping me!

Hi all, I am currently looking into the energy correction factor of the Hann window. So far I have found that to correct for the application of Hann-window and Fourier transform the result needs to be multiplied by sqrt(32)/sqrt(3). Can any of you explain how to get that factor ? The...

Homework Statement Hi, I hope someone could help me, I have been trying to solve this problem with FFT in matlab, why?, because my teacher gave it as homework. The problem is the following. Obtain the value of the following integer using FFT: Homework Equations the integer goes...

Hi, I hope someone could help me, I have been trying to solve this problem with FFT in matlab, why?, because my teacher gave it as homework. The problem is the following. Obtain the value of the following integer using FFT: the integer goes from [-infinte, infinite], and the function is...

Hello all. I am working on a problem for class that is taking some time data and changing it to frequency data. I am using excel and the fast Fourier transform(fft). I am having a problem graphing the results. I am very new to signal processing. I am only given the data which is 1024...

Hi! How can I time shift (ts) a real signal (N samples, T time period, dt sample rate, Fs sampling frequency) using matlab: Timeshift signal = ifft (fft(signal)*exp(2*i*pi*Fs*ts)) ? I am trying to do it this way and it is not working? For example how would you shift a Cos signal to...

What I want to do is apply a frequency-independent phase shift to a Gaussian Noise signal. Obviously I can just invert it to get a pi shift. Also I can take the Hilbert transform to get a pi/2 shift and I can invert that to give myself in effect a 3/2pi shift. BUT... what I want to do is to be...

Hi, I wasn't really sure whether to put this post under Physics or Engineering. I was just wondering whether someone can gimme some help or info or guidance... I am currently working on a project in which I am using the FFT (Fast Fourier transform) algorithm. In a nutshell, I am trying to use...

Does anyone know of any good texts that cover Discrete Fourier Analysis and the Fast Fourier Transform? *I don't know if this belongs here in the HW help or in General Math section.

Hi! This is my first post on these forums. I'm having some problems with the split operator + FFT algorithm to solve the Schrödinger equation in time. A real Gauss curve in a zero potential environment should simply flatten out, but I get two peaks as the following Matlab run shows...

I start with calculating psi(x,0). Then i use fft(psi(x,0)) to get the Fourier coefficients. and with fftshift i get the terms with negative index in the beginning. Then i multiply with the timedependent factor and use ifftshift and ifft to get the wavefunction psi(x,t). Here is the code...

This is part of my senior project. Please help! I'm trying to use a code to FFT a real, even set of data, but the results are not real and even as would be expected. The code I'm using is availabe http://www.koders.com/c++/fid1C48DD8DBB45CA4B87C9A38DAFC532E793443862.aspx (and...

Could somone possibly describe this http://home.bak.rr.com/berlin/088821368-guess1.jpg FFT. I need to know the properties and frequency. Thanks for anyone's time who helps. (BTW, if this is in the wrong forum, I could use some redirection).