Fft Definition and 163 Threads

Hello, I have a simple cosine f = 50Hz. When I generate Matlab code to produce 1/2 second of this signal and take the FFT, the response correctly shows a spike at 50 Hz. However, when I bracket the signal with 1/2 seconds of zeros on either side, the frequency response is showing a spike at...

I am new to Fortran. Is there an ultimate best library for FFT for Fortran (95)? I found this one FFTPACK. I am not sure if this is the best one. Is there anywhere a simple example how to use it? I have huge time files (260 MB each) that I like to read in Fortran and perform FFT and...

Hi, I have a complex time signal x(t)=X1*exp(i*∅)+X2*exp(i*2*∅). On converting to frequency domain, i expect frequency components at ω and twice of ω (when ∅=ω*t). FFT gives the desired frequencies, but the amplitudes don't correspond to X1 and X2. I understand that this is due to the phase...

I am trying to compute the Fourier transform of a square pulse with MATLAB's FFT. Code: Fs=1000; %Sampling rate (Hz) T=1/Fs; %Sampling time interval P=10; %Period of pulse t=0:1/Fs:P/2; %Time axis N=length(t); x=rectpuls(t,P); %Pulse amplitude n=pow2(nextpow2(N)); %Number of frequency...

Spatial Frequency Transform by doing FFT twice ?? This is for my own knowledge in relations to acoustics. I am trying to determine the location of sound using an array of sensors. Very similar to what they are doing in the webpage given. Im looking at the material at...

Hi, I have the following problem that I would like to solve by using the 'fft' function in matlab. Some background on the problem: The evolution of sea surface height is given, to first order, by \eta_o(x,t)=A\cos\left(kx-\omega t\right) From this, we see that there are three parameters...

I'm attempting to use Matlab fft functionality to reconstruct Fourier transform tables in my textbook (brigham), but to little success. Here is code to take the Fourier transform of cos(2*\pi*x*f_0), which should be \frac{\delta (f + f_0) + \delta (f - f_0)}{2} I can *almost* get it, but...

it seems like a pretty commonly used computational/mathematical method in analyzing experimental data, such as voltage signals

Matching orientations of 2-d arrays of values -- using fft? I was discussing the following problem (a subproblem of a personal project I'm working on) with a professor: we're given two 2-d arrays of values. We know them to be identical, but they might not be oriented corrected -- i.e., 0 0...

I am using an FFT package (GFT) to analyze a signal from a pressure sensor. I am unsure of the results I am getting, so I decided to try to verify the FFT package using a known input. I am using a signal generator to produce a sine wave of +/- 5V @ 5 and 100 Hz. When I run the FFT on the...

Hello. I've made a lab experiment of interference and with a CCD camera photographed fringe pattern which one can understand as a periodic signal. My question is: When I apply an FFT to the image is there any limit to the amplitude information I may get from lower frequencies? I read in the...

I was browsing another topic, and I suddenly remembered that I've never quite figured out what units matlab's fft returns. I've used the fft before and found where I had signal noise by taking the power density of the Fourier coefficients, which is all I really wanted to use the fft for in the...

Suppose you have the FFT of a sinusoidal signal sampled at 100 kHz and it has energy peaks at k = 100 and k = 412. How many points is the FFT? What is the frequency of the signal?

Fourier Transform -- Completely Flustered About Recursive FFT Hi all. I have been banging my head about this problem for the last week and a half-- Fourier Transform. Some background about me: I am a rising Junior at an accredited university majoring in Computer Engineering & Computer...

Confusion with 2D DFT Hello everyone, I'm trying to figure out why the third transform in the picture I attach here is different to the other ones, why it's 'distorted'. I know that it's related with the fact that if you copy the image in a grid the resulting image has discontinuous lines...

Does a PNA show FFT If I'm looking at gain across a band on a PNA could one say that I'm looking at an FFT or is that complete nonsense?

Homework Statement The following is the output of a 16 point computation of the discrete Fourier Transform for data taken at 10 kHz. Complete the table below by determining the frequencies associated with each of the FFT values. I attached an Excel workbook with the table. Homework...

Homework Statement Find the Fourier Transform of a unity amplitude rectangular pulse of width 2T, where T=[ims]. Use MATLAB to plot the magnitude response of this signal's FT. Homework Equations The Attempt at a Solution I got something that LOOKS right, but the first...

I understand that for the FFT the resolution or bin size is a function of the number of samples in your signal and that while padding the signal with zeros will make the graph look more precise it will not enable you to resolve between two frequencies if they are contained in the same bin. What...

I am wondering what the minimum sampling duration must be in order to accurately resolve a 60Hz wave. I know the FFT works with periodic waves about the number N but I am not sure how this relates to say a sampling duration that is 1 half the sampling period of a 60 Hz wave. I'm worried that the...

I took the FFT of a signal that was taken at non constant time period (T), but at a sampling frequency(Fs) of 6.5 hz. Can I take the FFT of a signal with non constant T, and does it mean anything? Please see attachment. Ps. I used Matlabs, FFT command, which i think uses the Cooley–Tukey FFT...

I have about 40 tabs open on this right now and something important is slipping my grasp. I know this has been covered a million and a half times, but for some reason I cannot seem to find a straight answer (or more probably realize and understand it when I see it). When I take the Continuous...

Hi, everyone: As I am sure will be clear from my post, I am not--nor have I ever been-- an EE :). (For the sake of giving some context to help taylor the answer, I am a mathematician-in-training. I only know the most basic ideas of signal-processing but I do know...

I have data in excel file and want to convert that to frequency domain. I wrote the following code but its giving me the wrong results. If my data is 2,2,2,5,5,6 Shouldn't Amplitude =2 and frequency =3 Amplitude =5 and frequency =2 Amplitude =6 and frequency =1 %Read in the...

Does anyone know a good free library to do Fourier Transforms (FFT or DFT). I know FFTW but I'm having some problems with it. I want an alternative that do FFT in two dimensions with complex numbers. The libraries I have found doesn't fulfill this requirements. Thank you

Hello, I have a very basic FFT question. Correct me if I am wrong, but the FFT is a fast implementation of the DFT (which is essentially the same as Discrete Time Fourier series). The DFT is periodic in time and frequency. Thus if you input a time domain made of 4 times samples for example to...

Im writing a program in python to simulate the propagation of a gaussian beam through a thick lens and to the focussing point using Fourier optics. Due to the strength of the focussing I need a lot of data points so that I have a decent resolution at the focus. To speed things up and to...

Hi, I have to solve a FFT problem by mathematica.I have attached my problem(exercise 2) here. I do not understand fft algorithm well.I also try to solve it by mathematica but mathematica can not solve this by forier transform directly.It will be great if anyone help me to solve this problem.

I have collected time-domain acceleration signals from the test rig through an accelerometer. Voltage signals are scaled to acceleration signals based on voltage sensitivity of accelerometer. Please refer the link given at the last to get the link for PDF attachment to see the time domain...

Hello, Please help me with the following problem. Given a measured signal which has to be smoothed. A lowpass filter has to be applied. The signal is available as measured data (a data file on the hard disk, numerical, not real-time) ( it has to be applied in C or C++). The filter...

Hi All, Its my first post here. I want to know how the digital output which comes out of an ADC can be used to calculate FFT. Because FFT algorithms usually needs real and imaginary parts of a sampled signal? Thanks.

Hi, I'm analyzing a laser diffraction experiment. Does Matlab has a reverse FFT function? Thank you Naftali

I'm trying to do FFT convolution via the FFTW3 library for image processing purposes. Basically I have a kernel and I am convolving it with an image. A problem I encountered has to do with the dimensions of the image. When the width is not equal to the height, the pixel values I get, seem to...

Hi, I am a bit confused regarding using FFT to calculate the 1D single slit diffraction pattern.. Let's take the simple setup shown here: http://electron9.phys.utk.edu/optics421/modules/m6/images/sslit.gif" If I wanted to do a quick calculation using Matlab, I would create a 1xN matrix...

Homework Statement 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) The Attempt at a Solution i'm thinking of to do the fft on the signal h(t)...

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...

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...

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...