Yamaha Electone EL-57 Owner's Manual page 85

Adjust the RR (Release Rate) parameter.
Play a note on the keyboard and then release it. Notice how the
changes affect the tail end of the sound, just after you release the
key. By changing this parameter, you can make the sound
sustain beyond the release point (lower settings).
Keeping Operator 1 on, select and turn on Operator 2, then
adjust the Operator level.
Adjust the OL (Output Level) parameter.
Use the Data Control buttons below OL (Output Level) to
change the level of Operator 2. Notice that the volume of the
sound doesn't change, but the tone does. Increasing the level of
one of the top row Operators generally makes the tone of the
Operator below it brighter or more metallic. Decreasing the
level has the opposite effect.
Turn off Operators 1 and 2, and turn on Operators 3 and 4.
Make some changes to their parameters, as you did with
Operators 1 and 2 in steps #1 and #2 above. Set the OL of the
Operator 3 to 110.
The relationshp between Operators 3 and 4 is similar to that
between Operators 1 and 2.
About the Operators
Changing the level of one of the top row Operators (2 and 4 here) affects
the tone of the Operator below it.
Changing the level of one of the bottom row Operators (1 and 3) affects
the volume of the related top row Operator.
NOTE:
Raising the OL of the Operator 2 (to
113 - 127) to make the sound brighter
and lowering the AR of the Operator 2
(to 1 - 10) can produce a distinctive
effect.
NOTE:
No sound will be produced nor will
adjusting the top row Operators have
any effect if all of the bottom row
Operators have been turned off or set
to their minimum level. Be sure to
turn on the bottom row of Operators
and set them to a suitable level before
changing the parameters of the top
row Operators.
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