Can I use koala with an audio interface?

YES!!!

All you need is the appropriate adaptor to adapt your USB interface to your phone/tablet. Also, your audio interface needs to be “class compliant” – which is another way of saying one that you don’t need to install drivers to use. Most usb interfaces are “class compliant”, but I would definitely check before buying.

iOS

If you have a lightning connector on your phone/iPad, you will need Apple’s “Lightning to USB 3 Camera adaptor” – it’s expensive, but all the cheap copies on ebay have problems, pretty much without exception – if you buy one and it doesn’t work, I told you so!

If you have an iPad with a USB-C connector, all you need is any old USB to USB-C adaptor – it should cost $3-9 on amazon or ebay.

Android

If your android has a USB-c connector – you just need any old USB to USB-C adaptor as shown above for iPad.

If your phone has the older micro-usb, you need a USB OTG cable, that looks like this: