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SOUND SYNTHESIS
3.4.5 VCF
‘.
The Voltage Controlled Filter
(VCF)
controls tonal quality (tim-
bre) by selectively removing and emphasizing different over-
tones of the
DC0
waveforms. The VCF used in the
Poly-800
IS
a LOW PASS filter: it passes
oval
tones BELOW the Cutoff
Frequency and reduces or removes completely the overtones
ABOVE
rhe
Cutoff Frequency. When RESONANCE is turn-
ed up, any overtones very close to
rhe
Cutoff Frequency will
be emphaslzed.
Cutoff Frequency is the most imponant parameter of the
VCF
Varying the Cutoff Frequency changes the blend of overtones.
resulting In a timbre change (which helps create dynamic and
“lifelike” sounds). Cutoff Frequency is determined by the
CUTOFF (‘-: :
).
KBD
TRACK ( ‘-:3
).
POLARITY
(
‘Y’-:
)
and
EG
INT(
L;S
)
parameters. It can be also be affected by DEG
3 and/or by the Modulation Generator (MG).
PARAMETER NAMES AND FUNCTIONS
p-J
CUTOFF
This parameter directly sets the Cutoff Frequency of
the low pass filter.
When
the Cutoff Value is set to
7s
(assuming both
KBDTRACK
(1’3)
and EG
INT(SS)
ares6lto
2).
all wavelorm overtones from
lhe
DCOs
are passed
without any effect. and the sound Is very brighl.
,
As
Cutoff Value is reduced. more and more harmonics
are cut off, producing a more rounded or less bright
sound.
When the Cutoff Frequency Value is near
c,
nearly
all of the waveform is filtered out. resulting in almost
no sound.
/Q
RESONANCE
Resonance emphasizes Ihe harmonics near the Cutoff
Frequency, producing a characteristic
“wah”
or “band
pass” type of sound.
Harmonics near
The higher Ihe Value, the stronger the effect of the
Filler on the tonal quality (timbre). Resonance can
prc-
duce
lypical
synthesizer “wah-wah” sounds, helps
make instrumental sounds
more
real&tic.
and general-
ly provides a good variety of subtle and dramatic
etfects.
Effect on tone
qUdity
(
Value
Large (very pesky sound)
1
Small
f
!
None
w
,
KBD
TRACK
Keyboard Tracking controls how the VCF Cutoff
Fre-
quency changes as you play up and down the
keyboard. There are three Values: Full. Half and Off.
Full (
z
)
Cutoff
Frequenq
rises and falls in EXACT
PROPORTION to the pitch of the HIGH-
EST note sounding at any given time
(whether played on
Ihe
keyboard or
ptc+
duced by the Chord Memory feature).
This tends to keep timbre (tonal quality)
relatively constant as you play up and
down the keyboard.
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