Estou tendo problemas para plotar o FFT de um arquivo wav. Consegui plotar os espectros de magnitude e fase do sinal, porém preciso repetir isso no intervalo-fs/2:fs/2.

%read sound files 
%'y' is the vector holding the original samples & 'fs' refers to the sampling frequency 
[y,fs] = wavread('handel.wav'); 
ydft = fft(y); %fft to transform the original signal into frequency domain 
n = length (y); %length of the original signal 
%  y has even length 
ydft = ydft(1:length(y)/2+1); 
% create a frequency vector 
freq = 0:fs/length(y):fs/2; 
shiftfreq = fftshift(freq); 

%plot original signal in time domain; 
figure; 
plot ((1:n)/fs, y); 
title('handel.wav in time domain'); 
xlabel ('second'); 
grid on; 

% plot magnitude in frequency domain 
figure; 
plot(freq,abs(ydft)); 
title('handel.wav in frequency domain'); 
xlabel ('Hz'); 
ylabel('Magnitude'); 
grid on; 

% plot phase in frequency domain 
figure; 
plot(freq,unwrap(angle(ydft))); 
title ('handel.wav in frequency domain'); 
xlabel ('Hz'); 
ylabel ('Phase'); 
grid on;