The only focus with music is focusing on the music. To focus on something that is not the music is listening to the void. Focus requires peace of mind and the absence of distractions. Controlling focus is easy only if the object of your focus is the one that is the easiest to focus on. The only song that can truly help you focus is silence. When you hear music you must respect it. Listen to the music or have no music playing at all, any other way is an abomination.