Yamaha Electone EL-900 Owner's Manual page 122

Envelope Parameters
By using the modulators and setting them to various output levels, you
can create all kinds of sounds. These sounds will be static, however,
unless you have the output levels change in time. That is precisely what
an envelope does. It varies the output of an Operator in time so that you
can vary the tone or the level. If the output of the modulator changes, the
tone will change. If the output level of the carrier changes, the volume
will change.
2 3 5 6
AR D1R D2R RR
1
OUTPUT
4
LEVEL
D1L
Key on Key off
Feedback
The output of a modulator can also be circled back to its input, allowing
it to modulate itself as well as the Operator below it. This is called feedback,
and it adds harmonic complexity to the tone. Operators using feedback
are indicated by a line that encircles the right side of the Operator.
Feedback cannot be directly controlled; however, you can adjust the
parameters of Operators that have feedback to change the characteristics
8
of the feedback sound.
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