Live Mixing... EQ "roll off"?

[Call-Of-Ktulu]

I had to take over for the sound guy at the last show I was at when the other bands were playing and on the mixer its got the gain at the top, then high frequencies, mid frequencies, EQ roll off, and then lows. The EQ roll off nob has different frequences around it starting at about 80hz at the far left. I didn't touch it cause I dont' know what it does.... what does it do?

 

[Massive Master]

It just tells you where the rolloff is - Lower numbers = lower frequencies.

 

[masteringhouse]

Expanding on what John said, it sounds like a high pass filter. Basically it attenuates any frequencies below the one that you dial in. Good for protecting speakers.