The sounds are synthed sounds (I used fluidsynth) and the haxophone just uses the sound pressure to infer velocity of the notes.

The mouthpiece is optional: you can blow on the neck of the device and will get the exact same sound. But as a sax player, I really prefer to use it with a mouthpiece blowing through it but without making the reed vibrate (so no sound). I find that it helps me maintain proper embouchure and feels more comfortable. And after a solid practice session, I still get that gratifying tingling lower lip feeling.

Thanks for the feedback!

Very cool! Awesome project

The design says that it measures air pressure. So it's just blowing into a tube, much like e.g. the Yamaha BC-1. I've got one, and in the demo video, I hear the same rapid changes in volume/pressure. I would guess it could benefit from having a small, adjustable opening (like the BC-1), which makes it a bit easier to control.

Yeah and is the pressure sensor closed so you're actually not blowing but just increasing and decreasing pressure?

No, not really. There is sensing tube (which terminates on the sensor) and a venting tube (which lets the air flow through). This is the same technique used in other similar commercial instruments. You can see both tubes in the assembly instructions: https://github.com/jcard0na/haxo-hw/blob/main/docs/assembly....

Ahh that makes sense! So is this actually sensing a lower pressure than ambient? Since moving air results in lower pressure?