I have posted an Xcode project for a bare-bones iOS app called Oscillator. It plays a sine tone and allows the user to adjust the amplitude and the frequency (exponentially from -40 dB to 0 dB and from A-110 Hz to A-1760 Hz). It’s not very sophisticated conceptually, technically, or aesthetically, but it does demonstrate the basics of a) mapping user interface objects to methods, b) writing an audio callback function, and c) implementing wavetable synthesis. There’s a fair bit of commentary in the .h and .m files.