Yamaha DX9 Operating Manual page 10

FM TONE GENERATION
FM
Tone
Generation .... Understanding the
Basics
The
DX9
is
an
entirely
new
type
of synthesizer
employing
an
entirely
new
FM
digital
tone generation system. This
unique
Yamaha
system permits
finer control over subtle
musical nuances and
vastly
expanded
voice creation poten-
tial
compared
to conventional
synthesizers.
1.
The
Meaning
of
FM
FM
stands for
Frequency
Modulation.
FM
radio broadcasts
use the
same
principle.
One
signal-the
modulator-modu-
lates
a
second
signal— the
carrier.
In
FM
radio the
carrier
is
an extremely
high "ratio"
fre-
quency and
the
modulator
is
the music
signal to
be
braod-
cast.
In
effect, the
carrier "carries" the
modulator
signal
through the atmosphere
to
your
receiving antenna.
FM
broadcasting
Carrier
wave
Sound
signal
(signal to be modulated)
(modulator
signal)
Extremely
high
carrier/
FM
signal (modulated
signal) modulator frequency
ratio.
The
"density" of
the transmitted
carrier
waveform
varies accord-
ing
to the modulating
signal.
~r
2.
FM
Tone
Generation
In
the
DX9
In
the
DX9,
the
carrier signal
determines
the pitch of the
note
produced and modulator
determines
the shape of the
waveform
produced and
therefore
its
timbre. This explana-
tion
may make
it
look
like
the
carrier
and modulator
are
two
entirely
separate
things. In fact,
they
are
one and
the
same.
A
special oscillator unit called an "operator" can be
used
as either a
carrier or
modulator
in
the
DX9.
Pitch
frequency
data
Operator
ata
I
I
Modulation
data
\Y
osc
AMP
-m!)—
^
EG
Output
The
frequency data
and
modulation
data
are
combined
here
Envelope
data
Loose
wave
Dense wave
1
)
Pitch
Frequency Data
Pitch
frequency
data from
the DX9's microcomputer
sys-
tem
determines
the operator's
oscillation
frequency.
When
the operator
is
used
as a carrier, this frequency
is
equivalent
to the pitch of the note produced. When
the operator
is
being used
as a
modulator,
the
ratio
of
its
frequency
to that
of the
carrier
determines the timbre
of the note produced.
2)
Modulation Data
This
is
the
modulation
data received from
the previous
operator's (modulator) output.
The
FM
tone
generator system
is
similar
in principle, but
in
this
case
both
the
carrier
and modulator
are audible
signals,
and
their
frequencies
can be almost
equal.
FM
tone
generation
Carrier
(sound to be modulated)
Modulator
(modulator
signal)
FM
sound
(modulated sound)
Close carrier/modulator
frequency
ratio results
In
FM
sound.
3)
Envelope Data
When
the operator
Is
used
as a carrier the
envelope
data de-
termines the volume
envelope
of the note produced.
When
the operator
is
used
as a
modulator
the
envelope
data
de-
termines the timbre envelope of the note produced.
For example,
the pitch frequency
data applied to an oper-
ator used
as a carrier determines the frequency
of the
sine
wave output from
the operator. Inputting
envelope
data
results
in
an output waveform
similar to that
shown
in
the
figure.
Numerical
value
—
M^
Operator
W
mj Sine wave
J—
^
+
,
PITCH
^*-
—
OSC
—
^
AMP
,i
MOD.c
EG
/"^
Envelope
data
^
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