I have just bought BIAB 2018 Megapak. How do I set up to input midi by playing in the notes on a keyboard (Casio CDP-120 and /or
CDP-220R).

You need a USB to MIDI interface. There are many models out there, with different price points. If all you want to do is use the Casio for MIDI input, an inexpensive model with only the basic features should do.

Insights and incites by Notes

HI
After you have got your keyboard connected as above .
This is how to proceed with recording.

To hear what you are playing in via BIAB.

The play thru uses channel 5, if you decided to record this it will Automaticaly record on the Melody track . as you play.
However the melody track uses channel 4 so if you want to hear the same voice on playback make sure that your thru patch and your melody patch are the same.
Hope this helps more than confuse
Mike

I have two different Casio's connected to my computer. One uses standard MIDI cables (and I connect it to my computer through my external Audio/MIDI interface, although previously it connect to a dedicated E-Mu XMIDI 2x2 MIDI-to-USB interface) and the other is a direct USB connection. Both keyboards work well for input into BIAB and RealBand, as well as any other DAW, and support hardware MIDI output from those applications as well.

And Mike Head is spot-on. Just remember that in BIAB, MIDI input is via the Thru track, so what you hear will be based on the settings for the Thru track. But when you play it back, it will be recorded on either the melody or soloist track, so you have to assign appropriate instruments and settings to those tracks to ensure you hear the same thing as when you recorded it.

Let us know if you have any difficulties.