This is tuba (in B flat).
I made the application assuming that the app play with Surface Pro.
*I don’t recommend playing with iPhone due to playback sound delay in iOS.
movie (from Twitter)
https://twitter.com/KodamaJn/status/1112757392150679552
[control]
This app have 4 valves (same as real tuba fingering) for right hand and some buttons that act as a lip buzzing for left hand.
The sound keeps while any button of left hand is pressed. On the other hand, the right hand uses only change the tone.
Please see below about the structure of the tuba:
https://www.yamaha.com/en/musical_instrument_guide/tuba/
[material]
I use the free tuba sound file obtained from the website below (University of Iowa Electronic Music Studios).
http://theremin.music.uiowa.edu/MIS-Pitches-2012/MISTuba2012.html
Play fun!!