Bass and guitar are written an octave higher than they sound. For example a true concert middle C, on a piano it is on the first ledger line below the treble staff C, is on the third space of the treble staff for a guitarist, i.e. written an octave higher than it sounds.

So if your MIDI bass line is for it's actual notes (concert middle C) and your sound source is expecting an octave higher bass line (written) you may loose the lower notes. Sometimes it is visa-versa. Every sound source and MIDI base line is either one way of the other and it's up to you to match them. But all you have to do is to transpose the bass line either up or down an octave so it matches your sound source.

For the in-depth Midiots I know there is some controversy over what is middle C. I am using the most common C5 MIDI note 60, read here:

http://www.electronics.dit.ie/staff/tscarff/Music_technology/midi/midi_note_numbers_for_octaves.htm

https://en.wikipedia.org/wiki/C_%28musical_note%29

I hope this helps and is not too confusing.

My goal this weekend is to move just enough each day so that no one pokes me to see if I'm dead or not.

64 bit Win 10 Pro, the latest BiaB/RB, Roland Octa-Capture audio interface, a ton of software/hardware