Well , they have a choice. They could choose any signal to look at. I 've tried lookin but usually they look at the mixed. But I 've  I 've tried looking at the single signal and  and in order to judge when it  when it was speech and when it wasn't ,
Oh.
but the problem is then you have breaths which  which show up on the signal.
But the procedure that you 're imagining , I mean , people vary from this , is that they have the mixed signal wave form in front of them ,