Audiobus: Use your music apps together.
What is Audiobus? — Audiobus is an award-winning music app for iPhone and iPad which lets you use your other music apps together. Chain effects on your favourite synth, run the output of apps or Audio Units into an app like GarageBand or Loopy, or select a different audio interface output for each app. Route MIDI between apps — drive a synth from a MIDI sequencer, or add an arpeggiator to your MIDI keyboard — or sync with your external MIDI gear. And control your entire setup from a MIDI controller.Download on the App Store
Audiobus is the app that makes the rest of your setup better.
SunVox synth engine available to developers
From SunVox developer Alexander Zolotov on Facebook:
You can freely use the SunVox synth engine in your applications (even commercial ones).
* load and play several SunVox/XM/MOD music files simultaneously;
* play interactive/generative/microtonal music;
* play synths, apply effects;
* load samples (WAV,AIFF,XI), synths and effects created by other users;
* change any project parameters (synth controllers, pattern notes, etc.).
Supported systems: Windows, Linux, macOS, iOS, Android.
Here is the complete SunVox library documentation with description of functions for different programming languages (C, Java, JS, Pixilang): https://warmplace.ru/soft/sunvox/sunvox_lib.php