sf2 note on/off velocity and aftertouch vs adsr envelope?`

[superfury]

How do I apply a velocity from a MIDI note on/off and note/channel aftertouch to the adsr envelope? Simply multiply the pcm samples with the volume specified by the adsr, multiplied in the same way with velocity and aftertouch? (All factors between 0.0f-2.0f?) Or does the velocity only affect the attack/decay time and the aftertouch the sustain/release time? (With 0x3f doing nothing, factor 1.0f) Does the velocity/aftertouch only affect volume, playback speed, asdr speed or a combination of them?`