title: how to transform frequency domain into time domain
body: <p>I had created a 3 three different frequency signal and filter out the signal i don't want. But when i using ifft in matlab, it shows a wrong graph.How to transform my frequency domain spectrum back into my 3 second time domain graph? Below my code is as below:</p>
  
  <pre><code>clc
  clear all
  Fs = 8192;
  T = 1/Fs;                                             
  %create tones with different frequency
  t=0:T:1;
  t2=1:T:2;
  t3=2:T:3;
  
  y1 = sin(2*pi*220*t); 
  y2 = sin(2*pi*300*t2);
  y3 = sin(2*pi*440*t3);                          
  
  at=y1+y2+y3;
  
  
  figure;
  plot(t,y1,t2,y2,t3,y3),title('Tones with noise');
  
  [b,a]=butter(2,[2*290/Fs,2*350/Fs],'stop');
  e=filter(b,a,at);
  et=(ifft(abs(e)));
  figure,
  plot(et)
  </code></pre>