A high pass filter does what it sounds like it does. It's a filter that lets high frequencies through. In other words, low frequencies are cut out. On mixing consoles you often find a 100Hz High Pass Filter. This is a filter that lets frequencies above 100Hz through and cuts the very low bass frequencies. The purpose of a 100Hz High Pass Filter is that it cuts out unwanted stage noise, and rumble/pops from the microphone. However, beatboxers like sub-bass and so we rarely want to use a High Pass Filter.