What it says on the tin, basically. I've been using MIDI for over ten years, and only now feel pushed to go right into SysEx. For something obviously so critical and precise, I'm finding it hard to find a good introduction.
The slightly fuller background is that I use the Ketron SD2, and I am interested in 'layering' patches to create complex sounds which are responsive to careful use of touch on a touch-sensitive keyboard. 'Attack' and 'Rise' are particularly useful in this, since they allow a time dimension.
The software I have long preferred to control direct-play has a number of 'sliders' to control the various common effects. Several of these - volume, modulation, chorus, reverb, for example - do produce marked responses from the SD2. Those for Attack and Rise do not. I suspect there may be no effect at all - hence my interest in using sysex direct to try to achieve an effect.