Decay Mode is used to get a fade out-like effect on UTAU with no need to use external editing nor need to use the Envelope Editor of UTAU.
In order to use Decay Mode, the only thing to do is adding a [*] to the actual phoneme, like for example [yo*].
Look the picture below to see the generated wav files using Decay Mode:
While this feature is more noticeable in long notes than in short notes, Decay Mode is also useful to make softer and smoother transitions between (C)V-V short sounds, resulting in a more realistic sound.
