This is a track recorded using the iPhone Filtatron app. I started off using the app as a delay with my guitar, and then it gradually got into feedback and self oscillation. At some point I hit record, and at another I hit stop. This track is around 12 minutes and it’s fairly modular-sounding and satisfying.
Watch your audio levels. Most sounds come in fairly gradually, but if you jump around, turn the volume down first. Some parts are quite a bit louder than others.