These days, a lot of the new music is based on samples. This is where you take a snippet of some other song then manipulate and incorporate it into your song. However, from the moment people started doing this in the late 70s, there has been a big fight over the legality of sampling.
The centre of the case is this: if you take a piece of someone else’s creative work, should you have to (a) ask permission and (b) pay for the privilege of using this sample? There have been countless court cases over the last twenty-five years. It basically comes down to this: all samples, regardless of their length, must be paid for.
Even if you sample just one beat, you’ve gotta pay. Or at the very, very least, you must ask permission to use that sounds. Skip that step and you could end up getting sued for a LOT of money.