Hello again, everyone!
I was recently introduced to Audiobus, a system for inter-app audio on iOS. You can configure various inputs, outputs, and filters in between, much like a musician has their guitar and amplifier with effects boxes. The app costs $5. I wanted to see if I could use it to replace my guitar setup, which is a few cheap ($30-$40) effects pedals and a Marshall practice amp I bought for $10 and fixed.
Several years ago I bought a Behringer UCG102 Guitar-to-USB Interface, which I believe was released before the iPhone. The nice thing about this device is that it uses the “standard” interface for a USB sound card (if there is such a thing) so it works on iOS and OS X without drivers, being detected simply as “USB AUDIO CODEC”. It has a 1/4” plug for both input and output. I’m connecting it to my phone with the Lightning to USB Camera Adapter, which is possibly the most underwhelmingly named product of all time, given it’s non-camera use cases. I tried using the 30-pin to Lightning and 30-pin to USB adapters together but that didn’t work.
iOS gets a little bit funky when it has multiple inputs and outputs, and since the USB interface has an output also, sound wouldn’t play through the device speakers. Plugging in headphones would work, but I ran into another issue. Since my headphones have a built-in microphone, that took over and I no longer got input from the guitar. Running the headphones through a 1/8” extension cable with only two pins (the cable I usually curse for disabling the microphone) allowed the headphones to take over the output while leaving input over USB. I probably could have also used the output from the USB interface if I had a 1/4” to 1/8” adapter handy.
Since the Behringer interface has a long USB cable you can use a 3-6” instrument cable. With the instrument cable, USB interface, cheap headphones, and your iPhone, you can carry an entire guitar rig in your pocket (minus the guitar). Check out JamUp or GarageBand to begin exploring your effects options with AudioBus.