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FM Tone Generation
(3) FEEDBACK LEVEL
By raising the feedback level, the modulation deepens, and the timbre of the sound be-
comes brighter.
(4) Envelope Generator (EG)
The EG creates the changes over time in the output level from the instant a key on the
keyboard is pressed to the time that the sound disappears.
If you listen to various musical instruments, you soon realize that besides the differences
in the timbre of the sounds they create, there is a large difference in the way that the sound
first comes out, and in the way in which it fades away. For example, the sound from a
piano gets very loud the instant a key is struck, then the volume gradually fades away, even
if you continue pressing down the key. Also, if you look at the change in tone over time,
there is a bright sound with a lot of overtones the moment the key is struck, but the over-
tones soon fade away, and the tone takes on a darker aspect.
The function that produces the instrument’s change in volume and timbre over time is the
EG.
In an FM tone generator, an EG is built into each operator. The EG for the carrier changes
its volume over time, while the EG for the modulator changes the timbre of the sound over
time.