There are too many clashing walkthrough;s on the web >.<!

Here's my situation, i'm after Barret's Ultimate Weapon, the Missing Score (and it's been missing through my past playthroughs), and I really, really want it!

Tifa has currently woken up after Sephiroth has gone into the Lifestream and Cloud is missing - just before the public executions, and i was wondering if the Missing Score is around here, because all the key words i can find associated with the weapon is "The Sister Ray" and as i'm close to the sister ray, i thought it was near.

So, could someone, anyone, help, and it's urgent! (game is currently paused on some text!)

All help welcome!