taking FFT from a part of the signal

Hello all, I have a sound signal in time domain , How can I take the FFT of a excerpt of it, say a 40ms section from 0.026sec to 0.3sec? Ive just been able to plot that segment in time domain, but I can not figure out how to plot its spectrum.. Here is my code, I hope someone can make it done.. Cheers,

clear all
close all
clc

%%Loading,Plotting and Listening to the signal
figure
[signal,Fs,nbits,opts] = wavread('stry.wav');  % Load
tSampling=1/Fs;
n=length(signal);
t=(0:n-1)*tSampling; %Making the time vector
plot(t,signal);    % Plot
sound(signal,Fs);  % Listen

%%2)Plot a 40ms section in the middle of the vowel /iy/ 
figure
plot(t,signal)
axis([0.3 0.34 -0.2  0.2]);

%%Taking FFT

signalF=fft(signal(0.03:0.34),1024);
fAxis=-Fs/2:Fs/1024:Fs/2-Fs/1024;   %Making the frequency vector
plot(fAxis,abs(signalF));
title('Spectrum of signal(t)');
xlabel('Frequency (Hz)');
ylabel('|signal(f)|');

Answer 1

[Matt J]

You mean you want to do a Short Time Fourier Transform (STFT)? If so, there are a number of offerings on the File Exchange, e.g.

http://www.mathworks.com/matlabcentral/fileexchange/38035-stft-short-time-fourier-transform

[Negar]

Thank you , but I think my problem is much more basic than STFT: Having a signal of length n (e.g. n= 7438) in time domain, I want to plot a part of it, e.g. from t1= 300ms to t2=340ms. I can not relate between n and time here ! I have plotted the signal at that duration by help of Axis. However, I need to know about the signal samples at this duration since I'm going to take its fft later..

[Matt J]

 signal(t>=300 & t<=340)

[Negar]

Thank you Matt J :)