Allen&Heath XONE 4D - Manual (Page 42)

Allen & Heath 42 XONE:4D User Guide
FILTER REFERENCE
The VCF Filters
A voltage controlled filter is an audio filter where
the cut-off frequency is altered by a DC control
voltage rather than a variable resistor. This
produces a much wider operating range and more
control over the filter response to create
unlimited combinations of tonal effect.
Two stereo VCFs are provided, one either side of
the crossfader. Each can be switched in or out
and has its own frequency sweep control. A Low
Frequency Oscillator (LFO) provides filter
modulation.
LFO modulation
The LFO automatically sweeps the cut-off
frequency up and down according to the beat
entered by tapping the tap tempo button or
locking to the analysed BPM. The LFO can be
applied to Filter 1, Filter 2, or both filters together
for additional cyclic filter modulation effects.
Filter Type Select
The filters are ‘state variable’. This means that
they provide three simultaneous filter types, high-
pass, band-pass and low-pass. Three large
illuminated switches select which type is active.
You can press any combination together to create
different response types such as ‘notch’ and an
interesting ‘all-pass’ effect. The switches are ‘soft
switched’ for live performance, meaning that the
audio signal is ramped between filter states to
prevent audible clicks.
Note that the last selected type is lost when
power is removed from the console. The LPF is
always selected when power is applied.
The graphs below show the effect on the audio
frequency response for the three filter types. The
range of sweep from low to high frequency is
shown together with the effect of adjusting
RESONANCE (one frequency with several
resonance settings shown).
The vertical scale shows the amount of cut or
boost around the normal 0dB operating level. The
horizontal scale shows the change in frequency
from low (bass) to high (treble).
10k 20 1kHz 100 20k
0dB
+ 5
+ 10
+ 15
+ 20
-5
-10
-15
-20
LO-PASS FILTER
LO HI
BAND-PASS FILTER
LO HI
10k 20 1kHz 100 20k
0dB
+ 5
+ 10
+ 15
+ 20
-5
-10
-15
-20
10k 20 1kHz 100 20k
0dB
+ 5
+ 10
+ 15
+ 20
-5
-10
-15
-20
HI-PASS FILTER
LO HI