Yamaha CS-30L Owner's Manual page 5

creates the tone
by
changing
the
harmonic
structure
by
cutting, or emphasizing, with the
filter
a part
of
the
harmonics
of
VCO-produced
sound
source having
a large
number
of harmonics.
The
VCF
creates the tone
by
changing
the
cut-
off frequency
(existing
on
the borderline between
the
passage
and
shield-off sections) by
controlling
the
voltage.
To
eliminate any harmonics
structure
deviation
f
KEY
BOARD
FOLLOW)
caused
by
the
difference
in intervals,
it is
designed so that the
cut-off
frequency
will shift
along with the
shift in
the
interval,
by adding
the
KEY VOLT
voltage
of
the
keyboard
circuit
to the
DC
voltage generated
with
the use
of the
control.
The
tone can be rendered
with
a
timewise
variation
by
adding
to these con-
trol
voltages
a voltage
such
as that
of
the
LFO,
or
EG,
that
changes with time
as
in
the case
of
the
VCO.
The drawing
at
the
right illustrates the
mode
in
which
the cut-off
frequency of
the
LPF
is
controlled
by
the
EG.
VCA
(Voltage controlled
amplifier)
The
VCA
is
an amplifier block
whose
amplifica-
tion
degree
is
varied by the control voltage.
The drawing
at
the
right
shows
a case
in
which
the amplification degree of
the amplifier
is
controlled
by
the
EG
voltage
to
give
a
timewise
variation
(envelope) to the
volume, from
the point the sound
starts
up
to the point
it
fades
away.
Naturally,
as
in
the cases of the
VCO
and
VCF,
it is
possible
to
add
a
voltage such
as
of the
LFO
to the
EG
voltage
and
use the
resulting
voltage
as
VGA's
con-
trol
voltage.
CUT OFF FRO.
-
KEY VOLT
AMPLITUDE
INPUT
OUTPUT
EG
(Envelope Generator)
The
EG
has the function
of producing
the voltage
curve that indicates
the
condition
in
which
the
sound
changes
in
order
to
render the
sound
with
a
timewise variation.
Given
a
signal to initiate the
start
and end
of the
envelope
by
the
TRIGGER
voltage
of
the
keyboard
circuit,
the
EG
generates
signals
that will
be used
as
the control
signals for
the
VCO, VCF,
VCA,
etc.
In
addition
to
the
elements described above,
the
synthesizer
has such elements
as
the
LFO
(low
frequency oscillator) that functions to give
a peri-
odical variation,
and
controls to
enhance
the effects
of the
performance. But
in
any
case,
the
fact re-
mains
the
same
that
something
is
controlled
by
changing the voltage.
In this
way, since
all
controls
in a
synthesizer
are
effected
by
using the voltage value
as a
medium,
the
synthesizer
is
capable of producing various
variations
of sounds with
ease.
EG 1,1
TRIGGER
KEY-ON KEY-OFF ON OFF
ON
Difference
in
envelope
waveforms
caused
by
trigger
waveforms.