So basically, a raise on silence doesn't give you an additional numerical bonus, but if your stealth roll is based on hearing only (e.g. sneaking past a closed door), then you get an auto-success. Aside from that, you just add the numbers up.

Source

So basically, a raise on silence doesn't give you an additional numerical bonus, but if your stealth roll is based on hearing only (e.g. sneaking past a closed door), then you get an auto-success. Aside from that, you just add the numbers up.

Source

To quote the source:

The net result being that Silence always applies a –4 penalty to Notice rolls at least partially based on hearing, but with a raise, it's an auto-fail if the Notice roll is based solely on hearing.