42Advanced features
Oscillators - FM Synthesis
Referring to the diagram on the last page, it can be seen that
the output waveform begins the same as the carrier, and
becomes more complex (harmonics are added) as the amount
of FM modulation increases via the envelope. It then returns to
a simple wave again as the envelope decays.
The timbre of the Waveform is changing with time. This is the
opposite of subtractive synthesis where a low pass Filter is
used to remove harmonics.
To complete a simple synthesizer, a further envelope is added
to control the output volume.
The complete FM building block is illustrated below.
OSC 2 is able to FM OSC 3 via a dedicated FM envelope. The
diagram below shows in block diagram format how the
A-Station can produce FM sounds.
The easiest way to be totally familiar with FM is to take one of
the factory preset FM sounds, for example Bank 2 - 49 (Sound
249) and modify it.
Setting OSC 2 - 3 manual FM amount
Ensure the function switch is set to SHIFT. Repeatedly press
KEY 7 (Oscillator Menu) until the display shows F L (Osc 2-3
Manual Level) and an alternating value. Whilst playing a note,
adjust the PORTA/DATA knob. Notice that increasing amounts
of modulation level make the sound more metallic.
Programming FM sounds
Modulator
OSC 2
FM Envelope
OSC 3
AMP ENV
Carrier
Envelope used
to control FM
modulation
amount
Envelope used
to control ampli-
tude
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