psd vs pwelch in matlab

hi there,

I have a problem,

I compare the result of psd and pwelch, but they showed the different result, why this happened? My matlab version is R2009, unfortunately the matlab delete the description of psd, so would someone tell me why the result of psd and pwelch differs even use the same window? here is my code: ----------------

clear;
Fs=1000;
n=0:1/Fs:1;
y=cos(2*pi*40*n)+3*cos(2*pi*100*n)+randn(size(n));
Nfft=1000;
window=hanning(100);   
noverlap=20;   
dflag='none';  
[Pxx,f]=psd(y,Nfft,Fs,window,noverlap);   
figure
plot(f,10*log10(Pxx));  
xlabel('frequency/Hz');ylabel('PSD/dB');
title('PSD-Welch method')
hold on;
[Pxx1,f1]=pwelch(y,window,noverlap,Nfft,Fs); 
plot(f1,10*log10(Pxx1),'r');

Answer 1

[Jun]

If someone knows the answer, please tell me, thanks again.

Answer 2

[Honglei Chen]

You should use pwelch. In R2009b, psd is deprecated because the resulting power spectral density is not properly normalized. The shape is correct though.

[Jun]

Thank you Honglei, That really helps.