It's pretty clear in the documentation. Did you go get all the PDF docs on the Roland site?
https://www.roland.com/us/products/system-8/support/
Make sure you get that Reference manual.
I'll spell it out, but I'm going to make it quick. It's really very easy if you reference the doc.
First, realize that when you go into Performance mode, you then choose to make it Dual or Single mode:
Dual - can be two layered patches that equally share all keys, or split by assigning different Key Ranges to each ("Lower" and "Upper")
Single - you still have access to two patches, but only one at a time. They're still called Lower and Upper, but only one is active on the keyboard at a time.
Here's a super simple and fast Split Performance creation. If I put brackets around it, it's a button.
1. Change to [Performance] mode
2. Go to a blank Performance Bank, like [E] [1]
3. Assign the [Lower] patch (in Panel Select). Go to [Menu] and navigate to [Performance Edit]. [Enter]. Confirm Common Perf Mode is set to DUAL. If not, change it.
4. Press [Exit]
5. Navigate [>] to Part Edit, hit [Enter]. You are now in the Lower Part Edit menu.
6. Choose the patch you want for Lower. We'll assign [System-8] [A] [7], "BS Pedal Bass"
7. Now to set its range. Press the [>] button to navigate to the Range settings. Range Lower is already set to C-. Leave it there. Press [>] again for Range Upper. Use the Value dial to change it way down to B2. Now you have set a bass patch as the Lower Split to just the first 12 keys.
8. Now to do the same for the Upper Split. Press [Upper] on Panel Select, and press [<] a few times to navigate back to the Patch select. We'll assign [Jupiter-8] [A] [6], "LD Jupiter Lead". Press the [>] button to navigate to the Range settings. Range Lower is set to C-. But we've got the Lower there, so change it to C3. Range Upper is already set at Eb9. Now you have set a lead patch as the Upper Split to the rest of the keys.
9. You can confirm all of this by playing at any time.
10. Press [Exit] and [Exit] again. You probably saw that there are a lot more settings like setting the individual sounds Levels, whether or not Arps and the Pitch lever assign to both Lower and Upper or just one, panning and so on. I'll leave it to you to read the doc and experiment to find the right balance, but...
11. IMPORTANT! **SAVE** [Write] the Performance, as you have changed it, to E1 so as not to lose your work. Now you have your very basic split, and you can go back and tweak its sound and behavior. You can go in and change the Lower and Upper patches to different tones entirely. And if you want that perfect "50/50" split on the keyboard, set the Lower patch Range Upper to B3, and the Upper patch Range Lower to C4. Just be sure to consider saving your work as you go along, to the same bank or another.
Hope that helped to get you started.
