If a user's instrument is not tuned to the standard A = 440Hz concert pitch, it is possible that BIAB might need to be brought into tune with the instrument if BIAB is going to accompany the user playing that instrument.
How to tune BIAB in relation to this, there are three possibilities to consider. (A) MIDI Styles
BIAB does have MIDI tuning. If a soundcard supports this, and one is using a MIDI style (as opposed to a style containing Realtracks), it should be able to be tuned.
The option is found under "Options | GM Settings".(B) Styles with All Realtracks
If one uses Realtracks, it's still possible to tune. I just tried the following approach and it worked for me.
1. I downloaded a free pitch shifting VST from the below URL. (One that I found on the web is called PitchProof and comes in 32-bit and 64-bit dll files.)https://aegeanmusic.com/pitchproof-specs
2. I tried this VST with BIAB 64-bit. Before doing any thing else, I needed to put the 64-bit pitchproof .dll file in my VST folder (using copy and paste).
3. Next I loaded the song I wanted to work on.
4. Then I opened the MIDI/VST-DXi dialogue window (#1 on the image below).
5. I selected "Combo" (this affects all output) -- #2 on image.
6. Using the dropdown listbox that I've number #3, I clicked on "Add VST plugin" -- this is at the bottom of the list.
NOTE: It's important not to use the top dropdown list box because this is usually reserved for a software synthesiser.
7. I navigated to where I'd put the PitchProof dll and selected it.
8. I then set the blend (#4) to Wet so that only the processed signal could be heard.
9. I set the "Pitch" to zero (#6)
10. I set the key to that of my song (#7) -- this is probably not needed.
11. I then tuned the output using the dial labelled #5.
This worked fine for me and sounded good.(C) Styles that mix MIDI and Realtracks
I haven't tried this but I suspect that it will be more challenging to tune these styles because of the two different types of sounds.
In this instance, I suggest...
1. Render the song to Audio
2. Mute all tracks except the Audio and follow the method given in part (B).
Alternatively, transferring the song to a DAW will allow for easy pitch manipulation of both audio and MIDI.