The documentation advise on setting Registered Param LSB and Registered Param MSB to 0.
The Data Entry MSB has been set to 14.
Those changes are done in the constructor of FluidSynthSoundBackend right after the definition of m_synth.

In D2713#52416, @sandroandrade wrote:

Actually, there is a much simpler implementation, with no need for using pitch bend events.
Just add the pitch drift in FluidSynthSoundBackend::prepareFromExerciseOptions. Something like:

...
appendEvent(1, chosenRootNote + m_pitch, 127, 1000*(60.0/m_tempo));
...
foreach ...
appendEvent(1, chosenRootNote + additionalNote.toInt() + m_pitch, 127, ((m_playMode == "scale") ? 1000:4000)*(60.0/m_tempo));

I've followed your recommendations.
Sliders have been set to:

• 12/-12/0 for pitch
• 200/50/100 for volume

The corresponding tunning for the fluidsynth lib are done in the setters.

Volume, change volume from 0 to 127 using the slider.
fluid_synth_cc(m_synth, 1, 7, m_volume) // change the volume (command 7), on the channel 1