Difference without en train de

Hi Johanna,

The difference between the two is minimal in this example -

J'écoute de la musique = I am listening to music

Je suis en train d'écouter de la musique =  I am ( in the middle of) listening to music 

You might use the second example if someone is trying to interrupt you, to say what you are in the process of doing.

Hope this helps!