me and my friend were experimenting with the voice box a few weeks ago. running a stylophone in gave us a weird church organ, and a coffee grinder sounded like an air raid siren. the voice box doesn’t really KNOW what to do with stuff like that, but it still harmonized nicely. the stylophone was a tad glitchy but we weren’t holding the mic very steady so im pretty sure it was only glitching because it wasn’t receiving a strong enough signal.

playing a trumpet would be identical to singing oooohs and ahhhhs as far as the voice box is concerned and it will harmonize them accordingly; the only issue is that the harmonies MIGHT sound funny because the vb is meant to duplicate the human voice.

that being said, it sounded fine with the weird stuff i’ve put through it, and it will still sound less ‘synthy’ than the hog/pog/whammy will. just hook a guitarist into the instrument input and have fun!