Siri Plays a Grand Piano With Some Help From AirPlay and Yamaha, it used some technological trickery to enable Siri to play a concerto on a Yamaha Disklavier Grand Piano.
The MIDI songfile converted into an audio file that the iPhone can play and connecting the audio output of an Airport Express to the analog input of a MIDI-enabled Disklavier piano, the iPhone can "play" the MIDI file via AirPlay and control the multi-thousand dollar piano.
According to the Loop's Jim Dalrymple:Then, you simply ask Siri to play your favorite song from your iTunes library, and Siri responds immediately, by making the Disklavier’s keys and pedal move up and down, recreating the performance, including full orchestration.
How the Siri App works with Piano:
You can say the Siri app, which song you want to play, its simply look into your song library, it send the data witlessly to the piano through apple express, and the reproduce the performance as exactly the real performer.