"A music" -> how should I fix it?

Question

1. This is the book I used.

2. This is a book I used.

3. This is the music I listened to.

4. This is a music I listened to.

1 and 2 are implying that the book and the music were mentioned before at least once, so the listener already knows some part of the stories.

Whereas, 2 is implying that the listener is hearing about them having studied that book for the first time.

I want to make 4 the same as 2, but I can't use determiner 'a' in front of non-countable noun. What should I do? What am I missing?

Answer 1

"Some music" or "a piece of music".