With SFX you can create cues to change the volume of other playing cues.  These Volume Change cues not only modify the volume of a cue, but they can also be used to pan cues among outputs.  Some examples of situations that call for a Volume Change cue would be to fade in or out a piece of music, or "move" a helicopter around the theatre. In this way, all volume modifications occur within SFX, reliably. 

When you create a Volume Change cue you also have the ability to select a custom fade curve. The Volume Change Curve editor is shown below:

When you create a Volume Change cue you specify how many seconds the fade will occur as well as which cue or cues the Volume Change will affect. To select a custom curve for a crosspoint, you open the Volume Change cue's Matrix and select the curve by clicking on the "x" symbol for a crosspoint

You can choose different curves for each crosspoint!

The Volume Change cue is a very powerful tool that allows you to handle all of your volume modifications from within SFX.  This promotes reliable playback night-after-night and reduces operator error and inconsistencies.