Basic function

A biquad filter can process the sound in the frequency domain.

Channel

If it is a low pass, it will only pass the lower part of the spectrum (i.e. low frequencies) and if it is a high pass, it will only pass the higher part.
A notch is a filter which passes the frequencies outside of a given range.
Low shelf, high shelf, and peaking EQ are filters that adjust the amplitude of the spectrum in the low frequencies, in the high frequencies, and around a center frequency respectively, by the specified gain.
For a low pass for example, decreasing the gain produces a muffled sound while increasing it produces a lower, louder sound.
By adjusting the Q, the amplitude of the frequencies around the cutoff frequency (or center frequency, depending on the type of the filter) can be emphasized.

Item	Description	Initial Value	Upper Limit	Lower Limit
Type	Type of the filter.	Low Pass	-	-
Cof	Specifies cutoff frequency.	0 Hz	0 Hz	24000 Hz
Gain	Gain for low shelf, high shelf, or peaking EQ.	0.00	0.00	5.00
Q	Quality factor. A value below 1.0 broadly and gently affects the range around the specified frequency, and a value above 1.0 emphasizes the range around the specified frequency.	1.00	0.01	10.00

Item	Description
Low Pass	It is a filter which passes only the frequency components lower than the cutoff frequency.
High Pass	It is a filter which passes only the frequency components higher than the cutoff specified frequency.
Notch	It is a filter which passes the frequency component outside of a range centered around the specified frequency.
Low Shelf	Adjusts the amplitudes of the frequencies higher than the specified frequency by gain.
High Shelf	Adjusts the amplitudes of the frequencies lower than the specified frequency by gain.
Peaking	Adjusts the amplitudes of the frequencies around the specified frequency by gain.