title: Units for Matlab PSD
body: <p>Im new to matlab and as part of my university assignment,im supposed to draw up these signals on matlab.and i have some problems regarding the units of the psd plots.</p>
  
  <pre><code>1)j=0:1/100:1; %time index
  z=sin(2*pi*5*j); %sine wave signal
  z=z*2;
  plot(z),xlabel('Sampling Points'),ylabe;('Amplitude');
  figure,psd(z)
  
  2)noise=rand(1,100);
  plot(noise);
  figure,psd(noise);
  
  3)[B,A]=butter(10,3/50,'low');
  LPFz=filtfilt(B,A,z);
  plot(LPFz)
  figure,psd(LPFz)
  
  4)y=wavread('sp1.wav');
  
  Fs=44100; %sampling frequency
  wavplay(y,Fs);
  
  save sp1.mat y
  plot(y(:,1)),title('Waveform of Speech'),xlabel('Sample Points'),ylabel('Amplitude')
  figure,psd(y(:,1))
  </code></pre>
  
  <p>i would be extremely grateful to anyone who can help my by telling me the units i should use for the x axis of the psd spectrum,y axis is in dB ,that i got.i dont know what to out for x</p>