ScreenSynth

If you want to try before you buy, check out the Lite version here:
https://itunes.apple.com/us/app/screensynth-lite/id1185432158

ScreenSynth is a keyboard, fretboard or fingerboard for playing music. You can connect to a MIDI synth app/device or use the app's internal DX7 synthesizer for sound output.

Features:
- Configurable note layouts based on piano/fretboard/fingerboard instruments (e.g. piano/guitar/bass/violin).
- Touch force sensitive, for piano-like control over the volume of each note played.
- Drag your finger over the screen to create vibrato or bend/gliss sounds between any pair of notes. Use this to play bluesy note bends or experiment with microtunings or carnatic music.
- Connect to other synthesizers (apps or devices) using MIDI output.
- Or use the app's internal low latency emulator for the DX7 line of synthesizers to produce a wide range of sounds.
- Your own DX7 6-operator FM patches (.SYX files) can be loaded and used so you can add more instrument sounds.
- Can show you how to play songs by highlighting sequences of notes that should be played.
- Import your own songs (.MIDI files) that you can then learn how to play.
- No ads or data harvesting!

Enjoy!