It seems weird that Murdock turned his stereo all the way up when he was getting ready in the morning. With his sensitive ears, wouldn't that hurt? But he sees via sound. He wasn't just putting on music to wake himself up, he was effectively turning on the lights.
Matt also uses loud noises as a way to concentrate, oddly enough. He's constantly hearing everything so one single noise drowning out the others is preferable.
One of the accepted flaws in the film is the soundtrack which promoted groups and was very loud during the whole movie leaving little to no moments of silence. It's actually a device to make you feel a little like the character in a world full of disturbing sounds.
A relatively minor example, but consider this; the moment Kingpin unmasks Daredevil as Matt Murdock, when Matt asks why Fisk killed the only two people he ever loved, Fisk immediately knows that the other person he killed important to Matt was his father. Considering the number of people that Fisk has likely killed over the course of his criminal career, what does it say about him if he can remember even a victim as long ago as Jack Murdock that easily? Does he just remember every single person he's killed and consider them just "business" he had to deal with to get to the top?
On top of that, it adds a potential deeper meaning to his earlier interest in hiring Matt and Foggy; was Fisk basically trying to score a further victory over Jack by corrupting his son to become part of the life Jack tried to reject?
