## FFT

Started by in Matlab DSP13 years ago

This is my Question: I am performing fast Fourier transform (matlab> fft) of a time series of a load (with a certain magnitude) converting it...

This is my Question: I am performing fast Fourier transform (matlab> fft) of a time series of a load (with a certain magnitude) converting it into a load spectrum (frequency dependent). How can I understand the spectrum amplitude....in respect to the time load... what is the relation.... Thanks in advance... best regards, Josif

## FFT2 question

Started by in Matlab DSP18 years ago

Hi friends, we have a problem. We've an image of 576x768 pixels reconstructed with a CCD camera of 6.35x7.4 micron/pixel. ...

Hi friends, we have a problem. We've an image of 576x768 pixels reconstructed with a CCD camera of 6.35x7.4 micron/pixel. We need make the image FFT2 to know the frequencies of that. We need make a change of phase of Fourier transform of the image because we need

## wavelets (windowing)

Started by in Matlab DSP18 years ago

I would like to ask the people who have experiences in wavelets. I am doing frame by frame wavelet packet decomposition , im...

I would like to ask the people who have experiences in wavelets. I am doing frame by frame wavelet packet decomposition , im just wondering whether overlap windowing should be done like that in taking frame by frame fourier transform ( does it apply to fram by frame wav

## how to get spectrogram like plot using wavelets

Started by in Matlab DSP14 years ago

Hi everyone, i did short time fourier transform(STFT) on 1-D speech signals, and did spectrogram analysis. On one paper I found that it is...

Hi everyone, i did short time fourier transform(STFT) on 1-D speech signals, and did spectrogram analysis. On one paper I found that it is possible to come up with a wavelet based analogy of spectrograms, it was called "scalogram" at that paper. So, I set about trying to figure out a way to come up with scalogram code in matlab. After coding a matlab program which does a full decomposition...

## Square signal

Started by in Matlab DSP19 years ago 1 reply

Hi all :) Does anyone know how to generate a square wave as a sum of sine waves using matlab code? I know how to generate a...

Hi all :) Does anyone know how to generate a square wave as a sum of sine waves using matlab code? I know how to generate a square wave using the "square" command but I have NO IDEA how to do it using fourier series. Won't someone PLEEEAAASE help me out? I'm re

## IDFT

Started by in Matlab DSP14 years ago

Hello I've written this programme to compute idft but for some reason it doesnt work... can someone please help me with that??? I know its...

Hello I've written this programme to compute idft but for some reason it doesnt work... can someone please help me with that??? I know its probably something there i dont see... % % Inverse Discrete Fourier Transform % function x = idft(Xn) N = input('Type the lenght of the sequence ='); M = input('Type the lenght of the transform ='); [N,M] = size(Xn); if M ~= 1, % ...

## Fast Fourier Transform

Started by in Matlab DSP15 years ago 1 reply

HI All, Could you please let me know how I can calculate FFT to biary image? The image is Interfile file, that is raw data, in short integer...

HI All, Could you please let me know how I can calculate FFT to biary image? The image is Interfile file, that is raw data, in short integer coded on 2 bytes. The matric size is 128*128. Please help me as I am not familiar with MatLab. Khalid Alzimami Department of Physics School of Electronics & Physical Sciences University of Surrey Guildford, Surrey, GU2 7XH UK tel. +4...

## test fourier fft

Started by in Matlab DSP21 years ago

hi, I have found differents periods in a time serie with the fft function. I wonder how to test and validate these periods. ...

hi, I have found differents periods in a time serie with the fft function. I wonder how to test and validate these periods. thanks pierre Pierre Fouillaron DEA Oc?anologie biologique Laboratoire LEMAR IUEM place Nicolas Copernic, 29280 Plou

## RE: short time fast fourier transform and waterfall mode l

Started by in Matlab DSP20 years ago

In the Signal Processing Toolbox, there's a function called specgram() that does STFT. It has an option to output a 2D matrix which...

In the Signal Processing Toolbox, there's a function called specgram() that does STFT. It has an option to output a 2D matrix which can be plotted using a 3d plot like mesh(). By default, it produces a nice color contour-plot of the Time-Frequency plane. > -----Original Mes

## Help on IFFT

Started by in Matlab DSP14 years ago

Hi, All I have original mass spectrom which is time domain signal. Then I use fft in Matlab to fourier transform into powerspectrum. Code as...

Hi, All I have original mass spectrom which is time domain signal. Then I use fft in Matlab to fourier transform into powerspectrum. Code as below: a=textread(C:\notebook\070111.txt') %load data into a single column matrix called "a" A=fft(a,65536); %built in m file, fft of matrix a for 2^16 element. Pa=A.*conj(A)/65536; %calculate the intensity of A f = (0:32768)/65536; % create the freq...

## Re: Discrete Fourier Transform of a signal containing only dirac impulses

Started by in Matlab DSP15 years ago

Mirco- > It's perhaps a silly question, but I don't see what I'm doing wrong. I'm > trying to calculate the FT of a signal containing only...

Mirco- > It's perhaps a silly question, but I don't see what I'm doing wrong. I'm > trying to calculate the FT of a signal containing only dirac impulses. To > avoid aliasing I first low pass the signal with a Butterworth filter Why will there be aliasing in a signal with pulses? If you look at a magnitude plot, you should get something like a dense comb filter. One pulse would give you

## help me in sampling a bandpass signal...

Started by in Matlab DSP14 years ago

hi, how can i generate an impulse train(time domain of period T) in matlab whose fourier transform gives me the same impulses of period...

hi, how can i generate an impulse train(time domain of period T) in matlab whose fourier transform gives me the same impulses of period 2?/T... actually i have generated an impulse train(of limited length) in time domain, but when i take its FFT, the result gives me a discrete impulse of high amplitude at t=zero and zero for all other values. infact m trying to do imulse train sa...

Started by in Matlab DSP12 years ago

hi all. for my project im creating a voice recognition system using d.s.p in matlab. i will input voice samples into matlab and apply discrete...

hi all. for my project im creating a voice recognition system using d.s.p in matlab. i will input voice samples into matlab and apply discrete fourier transform. i need to know which method of inputting voice samples is better, record and save audio as wav file and use wavread or simply use wavrecord function directly. any opinions on the matter is appreciated. thanks in advance.

## impulse train sampling

Started by in Matlab DSP14 years ago

hi, how can i generate an impulse train(time domain of period T) in matlab whose fourier transform gives me the same impulses of period...

hi, how can i generate an impulse train(time domain of period T) in matlab whose fourier transform gives me the same impulses of period 1/2*pi*T... actually i have generated an impulse train(of limited length) in time domain, but when i take its FFT, the result gives me a discrete impulse of high amplitude at t=zero and zero for all other values. infact m trying to do imulse trai...

## Unknown phase delay after fft of rect

Started by in Matlab DSP13 years ago

Hi, My goal is to normalize out a linear phase shift from the Fourier transform of a rectangle with settable delay and width. I have a...

Hi, My goal is to normalize out a linear phase shift from the Fourier transform of a rectangle with settable delay and width. I have a strange phenomena that I have not been able to track down. I want to take the fft of a rectangular pulse (with settable delay (tah) and width (pw)) and then look at the magnitude and phase response versus time. Mathematically taking my representation of the r...

## Discrete Fourier Transform of a signal containing only dirac impulses

Started by in Matlab DSP15 years ago

It's perhaps a silly question, but I don't see what I'm doing wrong. I'm trying to calculate the FT of a signal containing only dirac impulses. To...

It's perhaps a silly question, but I don't see what I'm doing wrong. I'm trying to calculate the FT of a signal containing only dirac impulses. To avoid aliasing I first low pass the signal with a Butterworth filter (should I take another one?) and than use the matlab function "fft" to transform the signal. Here an example: %The signal with two pulses: x=[zeros(1,1000) 1 zeros(1,800) 1 zeros(1...

## IFFT in OFDM, real output requires conjugate symmetric

Started by in Matlab DSP16 years ago 1 reply

Hi, i've forgotten where i read about this but i know for OFDM, if i want the output of my IFFT to be real, i can only use half of...

Hi, i've forgotten where i read about this but i know for OFDM, if i want the output of my IFFT to be real, i can only use half of the subcarriers with the other half the complex conjugate mirror of the 1st half. It apparantly got to do with the properties of Fourier transform or something like that. I'm currently writing my report on OFDM. Can someone direct me to references or literature...

## help me sample this modulated signal

Started by in Matlab DSP14 years ago

hi, i m attaching my code kindly help me sample this modulated signal consisting of four channels each at carriers 400,1000,1600 and 2600HZ...

hi, i m attaching my code kindly help me sample this modulated signal consisting of four channels each at carriers 400,1000,1600 and 2600HZ respectively. see also the time domain envelope of the composite signal being AM modulated at these four carriers and the fourier spectrum... how can i implement sample rate variation to extract these four channels??? (impulse train sampling is pref...

## truncating the function and taking fft

Started by in Matlab DSP17 years ago

% Rectangular pulse,FFT shifted N=400; t=linspace(-10,10,2000); n=0:N-1;%index x = [zeros(1,220) ones(1,60)...

% Rectangular pulse,FFT shifted N=400; t=linspace(-10,10,2000); n=0:N-1;%index x = [zeros(1,220) ones(1,60) zeros(1,120)];%rectangular pulse % plot(n,x);axis([0 400 -0.5 1.5]);grid on xlabel('n');ylabel('x[n]');%pause; X = ifft(x,2000);%fourier transfo

## Applying FFT on the data obtained from oscilloscope

Started by in Matlab DSP15 years ago 2 replies

Hi all, Firstly I would like to apologise if this message appears to be a repost. Anyway I saved data of a sine wave from the Agilent...

Hi all, Firstly I would like to apologise if this message appears to be a repost. Anyway I saved data of a sine wave from the Agilent oscilloscope and imported it into MATLAB. I have 2 sets of data, one is the timing data and one is the amplitude data. My task is to obtain the fourier transform for the sine wave and analyse the harmonic content of the wave. I can apply the fft function in...