Storing a "volSpeedTarget" on the channels and clearing volSpeed upon crossing it. "volSpeedTarget" gets cleared on all actions that set volSpeed (other than volume portamento).
notes
if effect value is 0 (D300), besides clearing volSpeed/volSpeedTarget it also applies any provided volume as normal (normally when D3/D4 are present on a row, volume doesn't get applied, because it's interpreted as data for the volume portamento)
caveats
no idea if these are good effect codes to choose
no idea if my implementation on the command stream side works
[re-opening since previously had a force-push]
Storing a "volSpeedTarget" on the channels and clearing volSpeed upon crossing it. "volSpeedTarget" gets cleared on all actions that set volSpeed (other than volume portamento).
notes
caveats