Number: 16, 17, 18, 19
Whatever the musician sets this controller to affect. There are 4 General Purpose Sliders, with the above controller numbers. Often, these are used to control parameters such as what Aftertouch can. If a MultiTimbral device, then each Part usually has its own responses to the 4 General Purpose Sliders. Note that these sliders don't have a fine adjustment.
0x00 to 0x7F where 0 is minimum effect.