The 415 has three selectors. One is for the mic's pickup pattern, the second is the 10db pad, the last is the low frequency roll-off.
The mic has dual diaphrams, meaning it can pick up...
A. Only what's in front of it (cardiod - the heart shaped pattern).
B. Omnidirectional (the round pattern), which will pick up evenly 360 degrees around the mic. This has no proximity effect. (more bass the closer you are to the mic)
C. Figure 8 (the 8 symbol) which will pick up front and back WITH the proximity effect (more bass the closer you are to the mic). There is some off axis rejection at the sides of the mic, but not too noticable.
The 10db pad is for recording LOUD sources. When you switch it on, it reduces the input level by 10 decibels. This prevents overload of the mic's preamp.
The low frequency roll-off, or "high-pass filter" allows only the higher frequencies above 80-100hz to pass through. This reduces the lowest frequencies substantialy and eliminates "boomy-ness" and low frequency rumble.