Conversation so far:
what was the band Pendulum's initial musical style?
When Pendulum was formed, their musical style was considerably more drum and bass sounding than the work they were known for later in their career.
What type of style did Pendulum adopt after their initial drum and bass sound?
Pendulum's newer work is regarded as generally leaning heavily towards a mainstream, dance-driven sound.

Question: When did they change styles?
Self-contained rewrite: When did the band Pendulum change musical styles?