Most of my drum kits come with a midi map. You can refer to this map when trying to convert an existing multi-part midi file to a BB capable midi file. If there is no map with a kit, load the kit into BB manager (File>Import>Drumset), and then click the check box in front of the kit’s name in the BB Manager drum kit’s list. After that, double click on the kit’s name, and this will open the drum set maker/editor window.
From this window, you can scroll through the kit to see where notes are laid out, relative to their midi value, from 0 to 127. In a typical kit of mine, the bass is set at 0 through 31. Drum kit pieces are at 32, 33, 34, or 35 through 59, 71, or in some extreme cases 83. If there is a keyboard, it will generally be mapped starting at 60 or 72. A fourth instrument, when included, will generally be in the range of 96 to 127. These are not absolutes, but they are good starting points, and it points ou the need to refer to the kit map or the actual kit itself.
When converting a midi file to the BB, it is imperative to consider the range of the part in the midi file. I have used 0 through 31, as this translates to range covering a dropped C tuning, up through the 12th fret on the G string. If the bass part is written to go being the 12th fret G, you need to first lower by one octave any notes that would be beyond the 12th fret G. Bass is rarely a problem, but this issue is definitely a problem with keys and other instruments.
In my largest keyboard kits, the keys range from 60 through 127. That is 68 notes. A full size piano has 88 notes. So, you can see some compromises have to be made in arranging. First, very low notes can be deleted, as this may be double the bass. Where this is a keyboard with no bass accompaniment in the original midi, you can move the bass part of the keyboard to the bass guitar. But, it has to be in the 60 to end of keyboard range. Otherwise, your keyboard part will trigger drum kit pieces.
When I make arrangements on the BB for 4 instruments, I am constantly editing and deleting parts to get everything to fit into the 128 notes available on the BB. It is an extreme exercise in working with a limited palette of sounds, and it is not something that can be reduce to a set of universal guidelines.
I learned the process by looking at “with bass” arrangements and seeing how they were made. But, I already knew something about midi as it related to part creation.
If you think this is difficult, or too much work, it’s probably best to make requests for the files you want done, as this portion of the process is probably the simplest part of creating an OPB or OPBK arrangement for the BB. I don’t mean to discourage you, but I do want you expectations to be realistic. It takes time to make these arrangements. When I have a great midi file to work with, I am really happy when I get a song done in less than an hour. And we haven’t even addressed setting levels by adjusting velocities, which frequently takes even more time. There’s an art to it, and there’s craft involved. You’ll need to know how to use your tools (Studio One), to make it work.