MAC users cannot do normalization this way. I use a mac and it was frustrating until I figure out I could set up special effects to change the volume of each person individually (and it saves between uses).
To set up a special effect for a person: Right click on the user's name, select miscellaneous, then Special effects. This gives you a slide bar where the volume is set at 100% Move it above 100 for higher volume, below to dial it down a bit.
This will get you a perk from your shy susans and a rest from your chatty cathys.