What periods of time are implied?

These mean at first glance pretty much the same but do they really do?

1 I studied a lot before taking this exam.
2 I had been studying a lot before taking the exam.
3 I had studied a lot before taking this exam.

Can you illustrate when “studying” takes place in each of them.
My attempt.
1 implies that it took me a lot of time to get ready for the exam
2 implies that I spent some hours leading to the start of the exam.
3 implies that I had studied a lot (in general, bot specifically for this exam)

Waiting for your ideas.