You forgot the modifiers for it being on the same floor, having other odors present (we're smoking a cigar), the listener having on gloves and wiping his nose with a cold.
The perception test modifiers are seperated for a reason. However, here's how I view it:
1) The characters make a perception test.
2) Look at their numbers
3) If they get high enough to hit a TN of 4 + all sound modifiers they hear it.
4) If they get high enough to see it past all sight modifiers, they see it.
5) If its something they can smell and they get high enough, they smell it.
6) If its something in their mouth, they can taste it if they roll high enouhg.
So if you have a force 9 spirit hiding a rocker and his band in the same room with you, you'll roll your perception test. Say you get 1,2, 4, 5, 8, and 13
The target numbers are:
- visual: 4 + 9/force - 4/action is obvious = 9
- sound: 4 + 9/force -6/drums are like autofire -2/lead singer's yell = 5-
- smell: 4 + 9/force -4/the guitarist is into grunge and hasn't bathed in a month +2/other odors (our cigar) are present = 11
- taste: lets skip this one for now
That means you got
visual: 1 success, there's something there but you're not sure what it is. Just a faint purple haze over the stage
Sound: 3 successes, Its definitely a band, and you're pretty sure its Jimmy and the Whalers
smell: 1 success, something in this room reeks and it isn't your cigar, but you can't quite tell if its sewage, someone that didn't bathe, or a toxic water elemental.