The following is a discussion about various aspects of the WL loudness meters from some time ago (but the loudness meters are much the same in WL9):
While I would agree that most loudness meters are rather similar, the Wavelab Loudness meters are among the more adaptable, since you can colour code to your own preferences and set the thresholds according to your own loudness requirements. Loudness meters can be helpful for music but there is no ‘official’ loudness level for music on CD (for example) but there are guidelines for what might be considered healthy. The R128 -23LUFS standard level is relevant mainly for broadcast applications. Various other loudness guidelines are also in the process of being encouraged (for example, internet streaming services).
Before you start using the Wavelab loudness meters it’s hepful to have a basic idea of the function of the three meters, integrated (I), short-term (S) amd momentary (M). The integrated meter is a ‘long term program’ reading measured over the whole program signal, the short term is measured over 3secs, and the momentary is measured over 400ms. Used in combination they give you a good aural ‘picture’ of the loudness profile of the audio you are monitoring. The meters don’t show transient peaks like digital peak meters and more closely follow how we perceive loudness. And Wavelab’s loudness meter also has the loudness histogram which helps with viewing how the loudness is distributed.