I assume the sound needs to be a mainstream popular at certain point of time, then overshadowed by a newer trend.

Which made me question myself:

• Is nu-metal considered as classic now?
• Most Allan Holdsworth’s song are so far ahead of its time, can it be considered as classic?
• Also what’s modern rock nowadays? I know how modern metal sounds, but completely out of the loop with modern rock. Most pop songs have some elements of hip-hop instead of rock nowadays.