2 Answers

As a musician I can say that you can hear the notes in your head the same as reading text, you hear the word in your head. 

In this case, a pen transfers text to paper of the words you hear in your head-- A musical instrument transfers the notes you hear in your head to the ears of those that listen.  

A person that plays by  'Ear' and doesn't read, must always hear the music before they play it, and also remember it for the next time.  a person that plays by ear and can play a performance all night has a very vast musical filing in their head, most amazing.  A person that plays by ear must always think several notes ahead of what they are actually playing.   A person reading music must read ahead of where they are actually playing.

LA--LA---LA That's how musical I am!   I know! Don't give me any awards! LA__LA__!!

Ducky

I know that song very well.