N = 128;
M = 10;
PSD1 = zeros(N,1);
for n = 1:M
   m1 = ((n-1)*N)+1;
   m2 = m1 + N-1;
   a = wavread('pipe1.wav', [m1 m2]);
   b = abs(fft(a)).^2;
   PSD1 = PSD1 + b;
end;
PSD1 = PSD1./ M;