From BeepBox Wiki

Envelopes are a system of dynamic control of settings in BeepBox. They had existed for a while, albeit undirectly, but were properly given a system in BeepBox update V4.0.

Envelope Usage

Envelopes are seen as multiple buttons at the bottom of the instrument settings marked under text that says "Envelopes". To the right of this text, a "+" button is located, and when pressed, a new envelope is added to that instrument. Three buttons appear per envelope. One for selecting the target, another for selecting the envelope type, and the third for removing the envelope. Envelopes can be applied to multiple settings such as note filter points and note volume. Some mods of BeepBox like Slarmoo's Box offer many extra envelope targets for each setting that others may not have, like reverb. Envelope types on the other hand often follow a naming scheme which defines their type and then their speed (Example: Swell 3 or Tremolo 1). There are also special envelope types that don't follow the typical behavior of other envelopes such as "Note Size".

The list of selectable envelope targets/types, their behaviors, and where they are available are documented and explained in their own dedicated pages: Envelope Targets and Envelope Types.

JummBox Envelope Additions

JummBox update V2.6 introduced two more settings for envelopes that are contained in their own dropdown. The first of which is a checkbox named "Discrete". This checkbox toggles whether the envelopes are interpolated or not, thus when toggled off the envelopes sound sharper and/or click more. This change is more noticeable on faster envelopes. The second setting is an envelope speed slider which controls the speed of all envelopes on the instrument (has no effect on special behavior envelope types). The speed range goes from stopping all envelopes from playing completely, all the way up to 8x speed. This can be controlled during the song by its respective modulator.

Slarmoo's Box Envelope Additions

Slarmoo's Box 1.0 and VoxBox Alpha added the ability to individually invert the shape of Envelope Types. This checkbox can be found in a new dropdown present per envelope, and when toggled makes it so that where an envelope would previously output a value, it now outputs 1 - that value. A notable exception is punch, which is instead 2 - that value to avoid negative outputs. The pitch start and pitch end in Slarmoo's Box can also be found in this dropdown