Reply To: I know the Audient iD4 box is low-noise, but this is pushing it
Blackhole only connects the audio of one app with another. Nothing else, specially no amplification. If you don’t need it (and don’t know how to use it) don’t use it.
It is unclear what you had before and also how you enter the interface. You might have an electric bowed instrument or a mic (and what kind of). That would be very different to handle. But since you have level with other apps it seems that it is working at least in some way.
The VU meter of soundjack might not be as sensitive as the indicators of other apps. The optimum level is rather in the middle than 3/4 full, I think.
If you use a mic, check if it is a condenser which needs phantom power (48V) or a dynamic one (if it is a ribbon mic don’t activate phantom power because it would kill the ribbon immediately). Dynamic mics have a lower output level and might need to have the gain almost fully open.
Have you checked the mirrors? The signal from the mirrors is usually a bit quieter than the direct one because of the lower volume setting (which you can change).
The iD4 is not made for passive electronic instruments as it has no Hi-Z (high impedance) input, only mic and line. So for electric guitar or bass or, even worse, a piezoelectric pickup (violin, viola, cello, double bass, classical guitar) that interface won’t be of much use without a high impedance buffer or preamp.
A screenshot of your left part of the stage might be helpful.