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A low-pass ﬁlter is used to remove the higher spectral components of the signal while leaving

the lower components unchanged. The frequency at which attenuation begins to take effect is called

the cutoff frequency and it is controlled using the Frequency knob. In a resonant ﬁlter, frequencies

located around the cutoff frequency can also be emphasized by an amount called the quality factor

or Q-factor of the ﬁlter as illustrated by Figure 10. This parameter is adjusted using the Resonance

knob. The higher the Q-factor, the louder and sharper the response of the ﬁlter around the cutoff

frequency. When the Q-factor is set to 1 (Q knob fully turned to the left), there is no emphasis

around the cutoff frequency and the attenuation is -3dB at the cutoff frequency. The attenuation for

frequencies located above the cutoff frequency depends on the order of the ﬁlter which is set by the

Order menu, a slope of -12dB/Oct corresponding to a second order ﬁlter and a slope of -24dB/Oct

to a fourth order ﬁlter.

Resonant High-Pass Filter

Amplitude (dB)

Frequency (Hz)

0dB

−3dB

Cutoff

Frequency

Slope (dB/Oct)

Q=2

Q=1

Q=4

Q=10

Figure 11: Frequency response of the high-pass ﬁlter.

The high-pass resonant ﬁlter works exactly in the opposite manner as the low-pass resonant

ﬁlter by removing the frequency component of a signal located below the cutoff frequency while

leaving those above the cutoff frequency unchanged. Similarly to the low-pass ﬁlter, the Q-factor

controls the emphasis of frequencies located around the cut-off frequency.

Band-Pass Filter

The behavior of a band-pass ﬁlter is to let the frequencies in a band located around a center fre-

quency and to attenuate the frequencies outside of this band as shown in Figure 12. The bandwidth

of the band-pass ﬁlter is set with the Resonance knob while the center frequency is set with the

Frequency knob. The Order control sets the order of the ﬁlter. This parameter affects the slope of

the roll-off on both sides of the center frequency. For a second order ﬁlter the slope is -6dB/Oct

while for a fourth order ﬁlter it is -12dB/Oct.

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