## fourier transform

Started by in Matlab DSP14 years ago

hi all, i have one function, x = (e^-2t) cos (4t) u(t) and i suppose to compute this fourier transform for the continuous signal and plot...

hi all, i have one function, x = (e^-2t) cos (4t) u(t) and i suppose to compute this fourier transform for the continuous signal and plot the frequency spectrum. these are the step that i figure out that can verified my answer that i calculated myself (correct me if im wrong) 1- plot the signal 2- use fft command 3- use fftshift command 4- use stem command but, in the first ste...

## ~~~ Filtering ~~~

Started by in Matlab DSP18 years ago

dear krishnamachary, filtering in the "frequency domain" does not mean convolution in this domain. filtering means u are ...

dear krishnamachary, filtering in the "frequency domain" does not mean convolution in this domain. filtering means u are taking a product of the Fourier transforms of the signal x(n) and the system impulse response h(n). the fourier transforms are X(n) and H(n)

## ~~~ Filtering ~~~

Started by in Matlab DSP18 years ago

dear krishnamachary, filtering in the "frequency domain" does not mean convolution in this domain. filtering means u are ...

dear krishnamachary, filtering in the "frequency domain" does not mean convolution in this domain. filtering means u are taking a product of the Fourier transforms of the signal x(n) and the system impulse response h(n). the fourier transforms are X(n) and H(n)

## ~~~ Filtering ~~~

Started by in Matlab DSP18 years ago

dear krishnamachary, filtering in the "frequency domain" does not mean convolution in this domain. filtering means u are ...

dear krishnamachary, filtering in the "frequency domain" does not mean convolution in this domain. filtering means u are taking a product of the Fourier transforms of the signal x(n) and the system impulse response h(n). the fourier transforms are X(n) and H(n)

## Organisation of spatial frequencies in FFT2 matrix

Started by in Matlab DSP17 years ago

Dear all, My questions relate to the filtering of the 2-d Fourier transform of a square image for a certain range of spatial...

Dear all, My questions relate to the filtering of the 2-d Fourier transform of a square image for a certain range of spatial frequencies, using Matlab. The image is Fourier analysed using FFT2 and is arranged with the zero-frequency component in the middle of the spectrum us

## prewhitening a signal in matlab

Started by in Matlab DSP11 years ago 4 replies

Hello, I am looking at a time series that doesn't have a white spectrum, and I would like to whiten it. In theory, I understand whitening as...

Hello, I am looking at a time series that doesn't have a white spectrum, and I would like to whiten it. In theory, I understand whitening as taking a signal which is not white, fourier transforming it, then dividing its magnitude by its magnitude (so that it is 1 = white) and then inverse fourier transforming it. I know that for a signal which is discrete and finite, that this division by its...

## DFT and rectangular pulse

Started by in Matlab DSP18 years ago 1 reply

hello there... i have this Discrete fourier transform function as below and a function to generate a rectangular wave but the dft...

hello there... i have this Discrete fourier transform function as below and a function to generate a rectangular wave but the dft function isnt accepting the rectangular wave as the xn function so as to calculate its fourier transform....how do i equal the matrix dimension here.

## short time fast fourier transform and waterfall model

Started by in Matlab DSP20 years ago 1 reply

HI Everybody how to plot short fast fourier transform of a signal.Is there any other command other than fft.also how to plot...

HI Everybody how to plot short fast fourier transform of a signal.Is there any other command other than fft.also how to plot waterfall model(3d plot)for a speech spectrum,the 3 parameters r amplitude,time and frequency. thank u

## Problem with fourier transform

Started by in Matlab DSP12 years ago 3 replies

Hello all, I have a problem about period amplitude and phase distortion when performing a fourier trasform. The problem arise when I have two...

Hello all, I have a problem about period amplitude and phase distortion when performing a fourier trasform. The problem arise when I have two periods with different amplitude but very close. An example; I create one cosine function with period=90 amp=60 and phase 2.2 rad, another one with period= 75 amp=30 phase=1.1 and then sum togheter. If I perform an FT on this sum of cosines I get...

## Request for FHT/IFHT matlab code

Started by in Matlab DSP16 years ago

Hi all my name is Ganesh, I am looking for matlab code on Fourier Hartley Transform(FHT) and Inverse Fourier Hartley Transform(IFHT)....

Hi all my name is Ganesh, I am looking for matlab code on Fourier Hartley Transform(FHT) and Inverse Fourier Hartley Transform(IFHT). Could any one help me with this. Your help will be highly appreciated. You can send me the code on my email ganeshrnaik@gane... Thanks in advance regards Gane

## calculating Instantaneous frequency (IF) using fft

Started by in Matlab DSP14 years ago 2 replies

Hi, i have a big problem, i need to calculate Instantaneous frequency (IF) using fft (Fast Fourier Transform) and STFT (Short Time Fourier...

Hi, i have a big problem, i need to calculate Instantaneous frequency (IF) using fft (Fast Fourier Transform) and STFT (Short Time Fourier Transform). I have a discrete sinusoidal signal: n=1:1024; omega=0.2; X=exp(j*omega*n); To calculate clear signal IF using fft i should find max(fft(X)) and that would be the IF. the quetsion is, would be the IF=0.2? Becouse this is a discrete sig...

## Fwd: Fourier mellin transform

Started by in Matlab DSP17 years ago

Note: forwarded message attached. Date:   Mon Dec 6, 2004  9:17 pm Subject:   Fourier mellin transform ...

Note: forwarded message attached. Date:   Mon Dec 6, 2004  9:17 pm Subject:   Fourier mellin transform To:   matlab <> Hi

## Problem with Fourier transform phase shift

Started by in Matlab DSP13 years ago 1 reply

Hello everybody, I have a problem in phase shift with Fourier transform: what I did is to create a cosine function with known period, in...

Hello everybody, I have a problem in phase shift with Fourier transform: what I did is to create a cosine function with known period, in example T=40 and perform an FT on that signal. FT give me correct period but phase is correct only if I perform FT on an integer multiple data points, in example T=40 and num.points 400 or any x*40. I get max phase shift (180?) with T/2, so in previous e...

## Increasing the amplitude of a select range of frequencies by a factor of 5 and plotting the Fourier spectrum and the time domain signal

Started by in Matlab DSP13 years ago 2 replies

Hi all, I am new to matlab and I am using it to try and accomplish the following... Increasing the amplitude of all frequencies below...

Hi all, I am new to matlab and I am using it to try and accomplish the following... Increasing the amplitude of all frequencies below 200Hz and above 5kHz by a factor of 5 for a simple and short audio file and plotting the Fourier spectrum and the time domain signal. This sounds like very basic stuff but for a newbie like me it looks ....well difficult. Will gladly accomplish all the he...

## FFT algoritm

Started by in Matlab DSP15 years ago

Appendix A. DFT (Discrete Fourier Transform) _/* Direct fourier transform some in the group ask for this code. */ int...

Appendix A. DFT (Discrete Fourier Transform) _/* Direct fourier transform some in the group ask for this code. */ int DFT(int dir,int m,double *x1,double *y1) { long i,k; double arg; double cosarg,sinarg; double *x2=NULL,*y2=NULL; x2 = malloc(m*sizeof(double)); y2 = malloc(m*sizeof(double)); if (x2 == NULL || y2 == NULL) return(FALSE); ...

## Fourier Transform

Started by in Matlab DSP17 years ago 1 reply

hi everybody I just apply a FFT with 1024 samples (k=1024), to function (i.e): y=sin(2*pi*2.48e9*x+0.1*rand(1,1025))+1 ...

hi everybody I just apply a FFT with 1024 samples (k=1024), to function (i.e): y=sin(2*pi*2.48e9*x+0.1*rand(1,1025))+1 After calculating those 1024 values, how can I draw its power spectrum? How define frequency axis? Thanks.

## Fourier wavelet regularised deconvolution

Started by in Matlab DSP12 years ago

hello , While searching for some dsp projects to study I found a topic "forward" in http://www.dsp.rice.edu/software.i found out...

hello , While searching for some dsp projects to study I found a topic "forward" in http://www.dsp.rice.edu/software.i found out some codes from that project but still i'm unable to use it.I hope some of you could help me out of this problem.

## fast fourier code

Started by in Matlab DSP18 years ago 1 reply

hello everyone, i am performing fft,ifft & nested for loops on 21x1985 matrix. it is taking a lot of time. is there any...

hello everyone, i am performing fft,ifft & nested for loops on 21x1985 matrix. it is taking a lot of time. is there any function that i can use to do it faster. i'v heard of something called vectorization but couldnt find it anywhere. This is very urgent . tha

## Image Registration..

Started by in Matlab DSP17 years ago

Hai everybody, I am trying to register two color images(one is the reference and the other is the rotated as well as shifted and...

Hai everybody, I am trying to register two color images(one is the reference and the other is the rotated as well as shifted and scaled) using Log polar transform.Here is the algorithm: I first converted the color to gray scale image Then applied fourier transform

## fourier transform and phase velocity

Started by in Matlab DSP17 years ago

dear all, I am new to MATLAB and am running into difficulties. I am working on laser ultrasonic surface waves. I have the...

dear all, I am new to MATLAB and am running into difficulties. I am working on laser ultrasonic surface waves. I have the out-of-plane displacement data over time, and i am attempting to perform a 2d-fft to calculate the phase velocity dispersion curves. I am wanting to do this upto a frequency of upto 10MHz. If anyone can help me of give me som