simple locate question

[Florian Hengstberger]

How to creata a second locate database for private use?
(mp3 database or so).
I have tried
$ locate -U dir_with_mp3s -o database.dtb

Searching in this database doent work
$ locate -d database.dtb somesong.mp3
gives no result.
The database exists and it looks ok, seems to be a simple
ascii format.
What am I doing wrong?
I guess its simple, isn't it!

Thanks Florian