[s060872]

看来你真是初学者，
clear all
fs=200;
nfft=200;
order=20;
t=0:1/fs:1;
f1=20;

x=sin(2*pi*f1*t)+sqrt(0.1)*randn(size(t));
[p,f]=pburg(x,order,nfft,fs);
p1=10*log10(p);
figure,
plot(f,p1)
grid on;
xlabel('Frequency(Hz)');
ylabel('相对功率谱密度(dB/Hz)');
title('Burg PSD Estimate');