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
~
(signal to be modulated),
Sound signal
1\J'V
FM signal (modulated signal)
IMMNNMN
'-1~
Loose wave Dense wave
(modulator signal)
Extremely high carrier/
modulator frequency
ratio. The "density" of
the transmitted carrier
waveform varies accord-
ing to the modulating
signal.
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
1\J'V
(sound to be modulated)
Modulator
1\J'V
(modulator signal)
FM sound (modulated sound)
Close carrier/modulator
frequency ratio results
in FM sound.
<9>
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.
Operator
Pitch
Modulation data
The frequency data and
modulation data are
combined here
1) Pitch Frequency Data
Output
Envelope 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.
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
Operator
1\f\!V\JV
Sine wave
!'----\
Envelope data