iPhone will only record in mono from external microphone(s)
This needs to be explained somewhere prominent because existing threads don't make this clear and it took me too long to work this out.
The iPhone audio inputs (TRRS format), including how lightning cables handle audio by default only include a single mono channel. This means even if you have two microphones mapped to stereo coming in, by the time it reaches the iphone it will have been re-mapped to that standard (i.e. either merged into mono, or more likely, one of the channels dropped entirely).
The only workaround is some external devices that send the audio over lightning in their own way (I assume just as data streams), then some apps can decode that. Which is why this OP may have had success using the Blue Yeti stereo mic with Filmic Pro. Or why you can record 2 tracks using an iRig Pro DUO and their proprietary app.
Tested with iPhone 14. I hope this helps someone.
