Pressing a key does not tell the whole story of a synthesised note. The sound may rise slowly, settle to another level and continue fading after your finger leaves the key.
Ableton’s Learning Synths introduction to envelopes explains that an envelope controls how another aspect of a sound changes over time. The familiar ADSR labels refer to attack, decay, sustain and release. An envelope is a control shape, not a separate sound you hear by itself.
Use a simple sound and a low, comfortable playback level. If the instrument provides an amplitude envelope, begin with its documented default and change only attack. Compare a brief onset with a slower one while keeping your note length similar.
Next restore the original attack and change release. Notice what happens after you stop holding the note. A long tail caused by this setting should not automatically be described as room reverberation; different processes can create an extended ending.
Record the assignment as well as the shape
Write down what the envelope controls. A similar shape applied to loudness and to a filter can produce different experiences. “Long attack” is incomplete as a patch note when the destination is unknown.
Save two clearly named versions if your tool allows it, then alternate between them. This is more useful than moving several controls until you can no longer remember the starting point. The aim is a repeatable comparison you can explain in ordinary listening language.
Illustration selected from this site’s existing collection.