Synthia is a small but powerful polyphonic synthesizer for the iPhone and iPod Touch.

N.B. RECOMMENDED FOR IPHONE 3GS and 4.

A bank of cascaded-triple-oscillator frequency modulation (FM) synthesizers provides a broad palette of sounds from percussion to strings with over 170 million variations.

The keyboard can be scrolled across the full 88 keys of a piano from A0 to C8. You can even change the size of the keys to suit the size of your fingers. The keys are touch sensitive - the harder you tap a key the louder the sound.

There are 14 synthesizer controls:

Amplitude attack
Amplitude decay
Register (octave) shift
Portamento (for "sliding" from note to note)
Modulator 1 attack
Modulator 1 decay
Modulator 1 frequency ratio
Modulator 1 modulation index
Modulator 1 and dynamic modulation
Modulator 2 attack
Modulator 2 decay
Modulator 2 frequency ratio
Modulator 2 modulation index
Modulator 2 and dynamic modulation

The FM frequency ratio defines the harmonic frequencies, modulation index controls the number of harmonics, and dynamic modulation defines how the harmonics change in time.

For a demo, go to:
http://www.youtube.com/watch?v=QDOoJ0Qiut4