KDFX Reference
KDFX Algorithm Specifications
10-71
161 Allpass Phaser 3
Allpass filter phasers
PAUs: 3
The allpass phasers are algorithms that use allpass filters to achieve a phaser effect. These algorithms do
not have built in LFOs, so like Manual Phaser, any motion must be supplied with an FXMod. Unlike the
other phasers, the allpass phasers use high order allpass filters. The order of the allpass filters sets the
number of notches that will appear in the frequency response when the dry and filtered signals are mixed.
The number of notches in the frequency response ranges from 3 to 6 for Allpass Phaser 3 . The allpass
phaser algorithms use a typical signal routing with wet/dry and cross-coupled feedback. A different
number of notches may be chosen for the feedback path than for the direct output.
Figure 25 An allpass phaser
A phaser uses a special filter called an allpass filter to modify the phase response of a signal’s spectrum
without changing the amplitude of the spectrum. Okay, that was a bit of a mouthful—so what does it
mean? As the term “allpass filter” suggests, the filter by itself does not change the amplitude response of a
signal passing through it. An allpass filter does not cut or boost any frequencies. An allpass filter does
cause some frequencies to be delayed a little in time, and this small time shift is also known as a phase
change. The frequency where the phase change has its greatest effect is a parameter that you can control.
By modulating the frequency of the phaser, you get the swishy phaser sound. With a modulation rate of
around 6 Hz, an effect similar to vibrato may be obtained, but only in a limited range of filter frequencies.
X-Couple
Feedback
Out
FB
Dry
Dry
Wet
Wet
Allpass
Allpass
L Input
R Input
L Output
R Output
Out Gain
Out Gain
Out
FB
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