title: how to convert normalized frequency to actual frequency
body: <p>suppose that we have following code</p>
  
  <pre><code>function [ x ] = generate1(N,m,A3)
  f1 = 100;
  f2 = 200;
  T = 1./f1;
  t = (0:(N*T/m):(N*T))'; %'
  wn = randn(length(t),1); %zero mean variance 1
  x = 20.*sin(2.*pi.*f1.*t) + 30.*cos(2.*pi.*f2.*t) + A3.*wn;
  %[pks,locs] = findpeaks(x);
   plot(x)
  end
  </code></pre>
  
  <p>i have generated signal using following command</p>
  
  <pre><code>y=generate1(3,500,1);
  </code></pre>
  
  <p>and i have got 501  length sample,now i want to use  music method to detect frequencies,namely 100 and 200,assume that number of  parameter is 2,so i have tried</p>
  
  <pre><code>pmusic(y,4)
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/bNAfP.png" alt="enter image description here"></p>
  
  <p>how  determine actually frequencies from this picture?i think that i need to convert a from normalized  frequency to actual frequency,as i know normalized frequency is same as $f/f_s$ where $f_s$ is sampling frequency,but in this case what i should do?</p>