High Pass Filter
|High Pass Filter allows through (passes) frequencies above its cutoff frequency and attenuates frequencies below its cutoff frequency.
Sound below the cutoff frequency is not eliminated but increasingly attenuated as the frequency falls further below the cutoff. The steepness of the attenuation is set by the rolloff value. For example, with a rolloff of 6 dB per octave, the sound decreases by 6 dB for each octave below the cutoff frequency (an octave below is half the frequency).
It is hard to design a pass filter with a sharp cutoff, so the cutoff or corner frequency defines the point at which the audio is reduced by 3 dB. Thus there will also be a small and decreasing amount of attenuation just above the cutoff frequency.
To achieve more attenuation you can run the effect again or use a greater rolloff.
There is a more detailed explanation in this Forum topic.