Kurzweil K2661 Musician's Manual page 514

DSP Functions
The DSP Functions
Two-pole Allpass Filter (2POLE ALLPASS)
Using 2POLE ALLPASS is very similar to using ALPASS, with two differences. First, the phase
shift is -180 degrees for partials at the center frequency, approaching 0 degrees for partials at low
frequencies, and approaching -360 degrees for partials at high frequencies.
Second, since this is a two-stage function, there's an additional control-input page (F2 WID)
which controls the filter width. The parameters on this page affect the frequency range,
measured in octaves, where most of the phase shifting occurs. Small values cause a drop from 0
to -360 in the phase shift to occur near the center frequency, while large values spread the drop
in the phase shift over a broader frequency range. Small values tend to affect just a few partials,
leaving others mostly untouched. The affected partials seem to become detached from the
others, creating the illusion of an additional sound source.
16-18
10 100
0
-20
-40
-60
-80
-100
C 4
-120
-140
-160
-180
-200
-220
-240
-260
-280
-300
Width = 2 octaves;
-320
Cutoff frequency
-340
from C 4 to C 10
-360
10 100
0
-20
-40
4
-60
-80
-100
-120
-140
-160
-180
-200
-220
-240
-260
-280
-300
-320
-340
-360
Frequency in Hertz
1000 10000
C 10
Frequency in Hertz
1000 10000
.1
Cutoff frequency = C 6;
width from .1 to 4 octaves
100000
100000