Solved the problem with BiasFX with its muffled sound (or I was using it wrong, who knows) by ditching the app and learning a new one: Harmonizr!
It does a really good job self-harmonizing or transforming that tweety flute sound to bass. Yes, maybe using the bass option I sound like a bari-sax made of paper, but for once it's a clear bass line.
Reasons to love Harmonizr:
- Harmonizes hands-free (no need to hold a chord on the keyboard while playing flute with two additional hands)
- Bass mode doesn't record your actual sound, only the transformed one
- Fun harmonic modes
I made a loop with a bass line and harmonizer to hear how it works together. I like it! Still used BiasFX for extra crunchy negative 2 octaves bass line though.