Yamaha CS-30L Owner's Manual page 4

CHARACTERISTIC
POINTS OF
SYNTHESIZERS
The
function of
the
synthesizer
is
to
electrically
synthesize and control
the three
elements of sound,
that
is,
interval,
tone
and volume
as well
as
the timewise
change from
the instant a
sound
is
generated
to
the
point
it
fades away.
The
interval
is
controlled
by
the
VCO,
tone
by
the
VCF,
volume by
the
VCA
and
the
timewise
variation
of
sound by
the
EG,
"VC"
in
VCO,
VCF
and
VCA
stands for "voltage-controlled".
Now,
let
us consider
what
kind of function
this
voltage control has
in
the
synthesizer.
The drawing
at the right
is
the block
diagram showing
the basic
composition of
a
synthesizer.
•
KEYBOARD
CIRCUIT
This
circuit generates the key's voltage
(KEY
VOLT)
that corresponds
to
the
interval,
and
the
signal voltage
(TRIGGER)
that indicates that the
key
is
being depressed. Although
the
TRIGGER
will
become "o"
volt
when
the finger
is
released
from
the key, the
KEY VOLT
that indicates the interval
will
be
memorized
by
the
SAMPLE
AND HOLD
(S/II) circuit until
the next
key
is
depressed.
The drawing
at
the
right
shows
the relationship
between
the key's
interval
and
KEY VOLT
voltage
together with
the
wave forms of
the
TRIGGER
and
KEY VOLT
signals
mi
(E) do
(C)
-*
sol
(G)
are
depressed.
•
VCO
(Voltage control
oscillator)
The
VCO
makes
a
sound
source of
a
frequency
that corresponds
to the
KEY VOLT
of
the
key-
board
circuit.
It
oscillates
simultaneously such sound
source
wave forms
as
saw-tooth waves and
square
waves
that
have
a great
number
of harmonics and
sine
waves
of
a
single
frequency.
Although
the
oscillator
frequency corresponds
linearly
to the
KEY
VOLT
value,
if
the
oscillator
should be controlled
while
adding an
AC
voltage
such
as
low
frequency
oscillator
(LFO)
to
the
KEY VOLT
voltage,
it
will
be
possible to
modulate
the
key
interval with the
LFO,
or
the like.
The
function of adding
this
voltage
is
carried
out by an
adder.
Regarding
this
voltage
value that
is
used to control the
VCO,
it is
possible
to freely
control the
VCO's
oscillating
frequency
in
accordance with the voltage value
since a syn-
thetic voltage
formed by
several
AC
wave forms
is
used
instead
of
a
fixed
DC
voltage.
The
drawing
at
the right
shows
a case
of
VCO
control
in
which
the
sine
waves of
the
LFO
is
added
to the
KEY
VOLT.
Needless
to say,
it
is
also possible to
add
an
EG
voltage
in
place
of,
or
simultaneously
with, the
LFO.
•
VCF
(Voltage controlled
filter)
The
VCF,
which
is
the heart of the
synthesizer,
VCO VCF
VCA
KEYBOARD FOLLOW
EG
KEY VOLT
KEYBOARD
EG
TRIGGER
VOLTAGE
KEY VOLT
C
PITCH
HOLD
HOLD
mm
TRIGGER
E|
I
[c
EG
C
1
3
2
^
KEYON
L
-KEY OFF
-KEYON
L
KEY OFF
PITCH
VCO MOD
CONTROL VOLT
LFO
KEY VOLT
VCO OUT