High Pass Filter

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 chosen always defines the point at which the audio is reduced by 3 dB. Thus if a cutoff frequency of 100 Hz is chosen with a rolloff of -24 dB, the 100 Hz frequency will be reduced in volume by 3 dB and a frequency of 50 Hz will be reduced by 24 dB.

Additionally there will always 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.