Questions about signal analysis

[Ahmed Husain ?Abbas Mohamed Sahrab]

Hello

I've got a question about finding the PSD (Power Spectral Density) in octave, I looked at the documentation and used the following code to find it.

[y, fs] = audioread("song1.wav");

NFFT=32768;  %Sample Size

F=fft(y,NFFT);

F_Shift=fftshift(F); %Shifting the FFT

fVals=fs*(-NFFT/2:NFFT/2-1)/NFFT; %To adjust the X axis to suit the plot

hold on

L=length(y); %Finds the length of the y variable which is a vector

Px=F_Shift.*conj(F_Shift)/(NFFT*L);   

figure  

plot(fVals,Px,'r'); 

title('Power Spectral Density');  

xlabel('Frequency in Hertz')  

ylabel('Power');

I'm wondering if there is a separate command to commute the PSD and the power spectrum, and my second question is how to pick the frame size. 

Best Wishes

Ahmed Suhrab