LinPlug Spectral - Manual (Page 37)

An Envelope which is not synced to tempo
Hold
If the AHDSR envelope is used, this dial controls the time gap between end
of the Attack phase and start of the Decay phase. In classic ADSR
envelopes these phases are connected, as soon as Attack is finished,
Decay will start. With the Hold parameter however the envelope can remain
at maximum level for a certain amount of time. The effect of that is
somewhat a bit similar to applying a compressor. The range is 0
millisecond to 5 seconds.
Decay
The Decay dial setting determines the time it takes from the Attack peak to
the Sustain value of the envelope. Range: 1 milliseconds to 15 seconds.
Sustain
The Sustain dial setting determines value at which the Decay phase ends,
that can be something in the range 0 to 100%. If set to 100% it means that
the envelope wont fall from its maximum value, thus the decay is effectively
not taking place. A value of 0% means that the envelope is at minimum
value at the end of the Decay phase.
Fade
If the ADSFR envelope is used, the Fade determines the rate at which the
envelope moves from the Sustain level to either 0 (for negative Fade
values) or its maximum value (for positive Fade values). A Fade setting of 0
means that the envelope remains at the Sustain level until the key is
released. The more you turn the dial towards + or -, the faster it fades