Just a few ideas for the envelopes.
1) Sustain slope: raise/fall in percent (over time)
Lets the sound gently fall (or rise) in volume as it is the sustain phase
2) Hold level: positive dB -> louder than initial attack
3) Hold shape: independent of decay shape
I know that this can already be done with a custom shape, but that's a bit cumbersome for my taste. The standard UI has still room for two elements.
Masi
