wish there was a way to kind of "normalize" the output volume of this demos  ...

Not 100% like a normalize button, but you can increase and decrease the "fxgain" in PT Effects window until the graphical output max loudness (PT main screen) for whatever midi demo you are playing is at the top of the yellow (or to taste).

Its confusing because the original request here sounds like an issue with velocity output from your keyboard or the velocity curve in PT, which you basically just confirmed. There is a calibration tool you can use for PT. However, velocity can't be normalized per say because its MIDI, which is back end data that triggers sound generation, not the sound generation (or the sound itself). Good luck!

I found a (partial) solution ...

It has nothing to do with the Behringer UCA222, which is perfectly fine for my setup.

The key was brundledfly's hint to "velocity differences".

While i had set my Velocity Curve in Pteq, i didn't pay much attention to some other parameters of my HP605 until now.

I "discovered" that adjusting the "Input Vol" parameter helped adjusting the output vol from my notebook to match the "loudness" of the inbuild piano sounds.

Secondly - and more crucial - was adjusting the HP605's "Key Touch" parameter, which i had set and forgot shortly after i had received the piano. By lowering this value, i was able to get the same "loudness" from my own playing, than the Pteq demos.

While i'm quite happy with this solution, it is imho only a partial one.

Because the loudness of PTeq's internal Preset Midi demos still differs greatly between some Instruments / Presets.

Thus i'd wish there was a way to kind of "normalize" the output volume of this demos in PTeq.
Perhaps there is?

As always, thank you in advance for your valued thoughts and suggestions ...

     Input jacks: Stereo miniature phone type

And this spec for the Behringer:

     Line Out Connectors: RCA, Unbalanced

Presumably you're either using  a Y-plug to get the two mono outputs from the Behringer into the stereo mini jack or you're using an 1/8" phone cable from the Behinger's headphone out. Either way, my guess is the Behringer's output level is weak and/or impedance mismatching between the unbalanced ouputs and inputs is probably contributing to a less-than-ideal input signal level.

There isn't a lot you can do about that other than making sure Pianoteq's level control is maxed without clipping the Behringer's DAC. And if you're using the headphone out, try getting a Y connector/cables to use the RCA ouputs which may work better.

Going forward, you might want to consider setting up a conventional stereo monitoring system - possibly with a small mixer to handle signals from the Behringer, the Roland, and your notebook's onboard sound - rather than using the Roland's speakers. And next time, look for gear that has +10dBu balanced I/O.

i run PTeq on a notebook, which is connected via a Behringer UCA222 to my Roland HP605.

I find it higly annoying that there is a big difference in loudness between PTeq's internal Preset Midi demos itself when played over the speakers my HP605, but also between a PTeq Preset Midi demo and playing the Preset on the piano.

Mostly the demo is way louder than the Preset sound of notes payed on the piano.
(Pteq Preset Sounds played on the piano are also way quieter than the HP605 inbuild pianos)

Therefore i almost always need to tweak volume / settings when switching presets.

And when i want to hear the preset playing live on the same level than the HP605 inbuild pianos, i need to raise the Piano's speaker volume very high, which produces a buzzing sound (imho caused by the connected notebook)

1. Am i the only one experiencing such issues?

2. Is this perhaps a Roland specific problem?

3. Is there perhaps a way to fix the loudness on an acceptable level (without buzzing)?

As always, thank you in advance for your valued thoughts and suggestions ...