applied-acoustics-systems ultra analog Manual Do Utilizador
4.3
The Filter Module
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4.3
The Filter Module
Ultra Analog is equipped with two multi-mode filters. The fil-
ters are patched in a flexible way in order to allow their use in
parallel, in series or any combination of both. For even more flexi-
bility, the cutoff frequency of the Filter 2 can also be locked to that
of Filter 1.
parallel, in series or any combination of both. For even more flexi-
bility, the cutoff frequency of the Filter 2 can also be locked to that
of Filter 1.
Each of the multi-mode filters include a resonant low-pass,
band-pass, high-pass, notch and a formant filter which can be se-
lected using the Type drop-down menu. The order of the filters can
be adjusted to 2 (-12 dB/oct for low-pass and high-pass and -6 db/oct for band-pass) or 4 (-24
dB/oct for low-pass and high-pass and -12 db/oct for band-pass) with the help of the Order drop-
down menu. Furthermore, different saturation algorithms selected with the Drive drop-down menu
can be applied to the filters. The resonance frequency of the filters is adjusted with the Cutoff knob
while its resonance is controlled with the Q knob. When the formant filter is used, the Q knob is
used to cycle between the vowels (a, e, i, o, u).
lected using the Type drop-down menu. The order of the filters can
be adjusted to 2 (-12 dB/oct for low-pass and high-pass and -6 db/oct for band-pass) or 4 (-24
dB/oct for low-pass and high-pass and -12 db/oct for band-pass) with the help of the Order drop-
down menu. Furthermore, different saturation algorithms selected with the Drive drop-down menu
can be applied to the filters. The resonance frequency of the filters is adjusted with the Cutoff knob
while its resonance is controlled with the Q knob. When the formant filter is used, the Q knob is
used to cycle between the vowels (a, e, i, o, u).
The cutoff frequency and resonance of the filters can be modulated with different modulation
sources. The modulation sources are the Keyboard, the Filter Env and LFO modules which
are each controlled by the Kbd, Env and LFO gain knob respectively. Modulation signals with a
positive value will increase the cutoff frequency and Q-factor of the filters while a negative value
will decrease them. Note that the filter parameters can further be modulated by the velocity signal
from the keyboard through the use of the velocity modulation parameter of the Filter Env modules.
are each controlled by the Kbd, Env and LFO gain knob respectively. Modulation signals with a
positive value will increase the cutoff frequency and Q-factor of the filters while a negative value
will decrease them. Note that the filter parameters can further be modulated by the velocity signal
from the keyboard through the use of the velocity modulation parameter of the Filter Env modules.
The three gain knobs associated with the cutoff frequency can be adjusted to their center po-
sition by clicking on the green LED located above the knob. In this position, the cutoff frequency
will exactly follow the pitch of the note played on the keyboard in the case of the Kbd modulation,
it will vary exactly one octave higher and lower in the case of the LFO modulation and will vary
one octave higher or lower depending on the position of the inv switch with the Env modulation.
Let’s now have a closer look at the different filter types available.
will exactly follow the pitch of the note played on the keyboard in the case of the Kbd modulation,
it will vary exactly one octave higher and lower in the case of the LFO modulation and will vary
one octave higher or lower depending on the position of the inv switch with the Env modulation.
Let’s now have a closer look at the different filter types available.
4.3.1
Resonant Low-Pass Filter
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. 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 5. The higher the Q-factor, the louder and sharper the response of the filter around the cut-
off 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 cut-off 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.
lower components unchanged. The frequency at which attenuation begins to take effect is called
the cutoff frequency. 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 5. The higher the Q-factor, the louder and sharper the response of the filter around the cut-
off 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 cut-off 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.