DJs are highly skilled and sought after musicians. They travel the world in caravans that carry the instruments they play with. They can perform live as bands, or they can hook up into an existing electrical grid and play music from Before. The music from Before is all stored on small electronic boxes that only DJs know how to run. The box and speakers are hooked up to a grid and can be played for days on end.
DJs are trained in a school in the east. They’re taught how to play a variety of instruments and how to run the electrical equipment. Before leaving the school they are allowed to select a number of songs from a seemingly vast and limitless archive that is tightly guarded by the school. More songs can be taken for a fee. The DJs are only limited by the memory of their storage boxes (souped up ipods) and the amount of money they earn playing for the crowds.
The richest DJs are often kept by the ruling class and have permanent setups with them. Holding a DJs electronics hostage is a good way to get money and/or get stabbed by a very angry DJ. Sabotage is rife among the young DJs and there are tales of some having everything destroyed by others jealousy.
This info dump was brought to you by an overactive imagination that plots out the tiny little things that will never matter in a short story so why the hell am I stuck on it anyway?