我有以下代码：

// input: speech segment
[y,Fs,bits]= wavread('/media/A03036C33036A068/scilab/30msec_voiced.wav');
max_value=max(abs(y));
y=y/max_value;
t=(1/Fs:1/Fs:(length(y)/Fs))*1000;
subplot(2,1,1);
plot(t,y);
xtitle('A 30 millisecond segment of speech','time in milliseconds');
sum1=0;autocorrelation=0;
for l=0:(length(y)-1)
    sum1=0;
    for u=1:(length(y)-l)
        s=y(u)*y(u+l);
        sum1=sum1+s;
    end
    autocor(l+1)=sum1;
end
kk=(1/Fs:1/Fs:(length(autocor)/Fs))*1000;
subplot(2,1,2);
plot(kk,autocor);
xtitle('Autocorrelation of the 30 millisecond segment of speech','time in milliseconds');
auto=autocor(21:160);
max1=0;
for uu=1:140
    if(auto(uu)>max1)
        max1=auto(uu);
        sample_no=uu;
    end
end
pitch_period_To=(20+sample_no)*(1/Fs)
pitch_freq_Fo=1/pitch_period_To

在这方面，我没有理解pitch_period_To=(20+sample_no)*(1/Fs). 他们为什么要加 20 个？