The video below discusses the Motion Synth App's use of three zones of vertical orientation to control note octave.
See further instructions below this video for configuring octave control in the Notes Tab (Main Menu).
Once you are in the Main Menu, ensure that the Notes Tab is selected:
The “Octave (neutral position)“ setting changes the octave value of the middle octave zone, thereby raising or lowering the octave values of the top and bottom octave zones.
If Octave Control is switched off, then “Octave (neutral position)” will set the octave value.
Use this switch to activate audio feedback that is triggered each time the user transitions from the middle octave zone to either the lower or upper octave zone (no sound triggered by transitions to the middle zone).
This audio feedback may be useful for some users in learning where the vertical orientation thresholds are between the octave zones.
The audio feedback will be deactivated if an audio app running in the background assumes control of iOS sound output.