Alesis ANDROMEDA A6 Reference Manual page 87

Chapter 3: Basics of Analog Synthesis
Here's a graphical representation of a typical envelope. We'll be covering the details
of how an envelope works, what you can do with it and what all those labels mean in
a later chapter. For now, we just want to show you how an envelope is graphed
(especially since the A6's screen will display something like this when you're editing
an envelope in a Program).
Since sound waves have polarity – both positive and negative properties (a kind of
"pushing and pulling") when moving air – a sound's envelope also has polarity.
Using the envelope above to shape a sound wave's volume, the wave as we might
hear it could look like this:
A A6 R M 85
NDROMEDA EFERENCE ANUAL