Itunes sound quality

Hey guys just had a quick question. Do you guys notice that songs bought from the itunes store the sound quality isn't as loud as say songs downloaded from cough cough other sites haha. Like I noticed that songs that were download somewhere else the sound is much louder on the high volume but for itunes songs even on high volumes it's not as loud. Is it just me or what????

 

ohhhhh so what does everyone use to make a difference I think mine is just on rock or something