You're right. For an objective measurement of the sound levels you'd need a calibrated measurement device. But that's not the point. That racket before the match was loud, distorted and uncomfortable and did nothing to enhance the atmosphere of the game. A large part of the problem is that the PA system is not up to the job and distorts when it is overdriven.
Do you really believe that a bit of loud music makes for an atmospheric event? You'll be asking for an electronic organ next like they have in American ice hockey. From your comments I would assume that you are relatively young and possibly don't have the experience of attending a passionate, exciting game of football. Unfortunately Saints' games have fallen a long way short of that in recent times. We never needed loud music at the Dell.