Yamaha DX7 II FD Reference Manual page 12

Each operator's EG is specified by four rates and four levels. These parameters are
explained in detail below. The following diagram illustrates the output of a typical EG.
Output
Level
99
Key on
L1
L3
L4
------------------------------------------~Tme
The EG button
(#9)
provides access to the following envelope parameters in a single LCD
display.
Ll-L4 Each envelope consists of four levels which affect the output level of the selected
operator. These envelope levels are relative to the overall output level specified by the
oscillator level parameter.
0 Level is 0 (silent)
99 Maximum level value
If an EG level is set to 0, the operator with which it is associated will produce no signal
once that level is reached. Once an EG level of 99 is reached, the operator's signal will be
at the amplitude specified by the oscillator output level parameter.
Levell (Ll) is the first level reached after pressing a key. L2 and L3 are intermediate
levels reached while a key is held down. Once L3 is reached, the operator output remains
at this level until the key is released. L4 is reached after the key is released. Since most
sounds fade to silence after a key is released, IA in a carrier EG is almost always set
to
0.
The time it takes to reach each of the EG levels is determined by the rates, which are
described below.
The envelope architecture employed by the EGs provides much more flexibility than the
ADSR (Attack-Decay-Sustain-Release) envelopes found on older analog synthesizers. For
example, the volume envelope of a flute cannot be simulated using an ADSR EG.
However, it is a simple matter to simulate such an envelope with the EGs found on the
DX7 II.
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