I love my MODX, it's one of the best purchases I've made this year
but I've noticed that in general all the Acoustic Piano sounds ( that I use a lot in my work) with the same setting of the Master Volume knob compared to other sound families like strings, synths and so on : Pianos sound have always a lower Volume in comparison, I'm forced to turn up the Master Volume knob, how can I fix it?
Also I often hear them "muddy", can you give me some advice to make the acoustic piano sounds sound good?

Thanks for the question and your interest in the MODX. Acoustic Pianos may indeed sound lower in Volume compared to other sound families, this is in part due to the velocity sensitivity. As you increase the Velocity Sensitivity, the output level decreases, this is a natural thing, as it demands more effort to get the same output. This will be particularly true versus synth sounds which may not be responsive to velocity change, at all.

There are several ways to overcome this... you know the first one, turn up... another would be to increase the amount of effort used in playing the sound.

Because a Velocity response is such a personal thing (take any ten piano players you will get at least 9 different responses to what makes a proper response concerning ‘input effort’ versus ‘output level’...) I recommend you attempt adjust your (extremely) programmable synth to match your playing preference. While this can be a very involved subject, the following should get you started:

Recall the Factory Performance: “Acoustic Piano DA”
I chose this because it is a Single Part, single Element acoustic piano which will make it clear what is happening.
The main Volume is set conservatively at a value of 70 (most sounds with conservative levels are set so that they make good partners when merging them into your own creations. If every Part was stored at 127, combining sounds would be problematic (particularly for those who don’t ever turn anything down), you can always turn up the Volume.

But the Velocity Sensitivity setting within the program will take place at the Edit - Element - Amplitude level of the architecture:
Press [EDIT]
Select PART 1
Touch “Elem1” > “Amplitude” > “Level/Pan” > move the cursor to highlight “Level/Vel”

Set this to +0 this removes all Velocity Sensitivity. This is a typical setting for organs, analog synths, harpsichords, etc, instruments that do not respond to velocity, at all.

Play at a steady input effort with one hand and slowly increase “Level/Vel” with the other, you should observe that the sound gets softer as you increase the value.
This means to get the same Output Level now requires more effort (input) from YOU.
By the time you reach +32 you have reached the point where it maxes: the sound output increase for an increase in effort.

Play soft (piano) then play loud (forte) and you will experience the maximum change from soft to loud
As you increase beyond +32, and finally reach +63, you can only get sound with a maximum effort.
All values +33 thru +63 are used when programming velocity crossfades (for example, say you do not want the piano to sound when you play softly). At +33 you can actually touch a key softly enough to produce no sound output. And by the time you reach +63 only your maximum effort will be rewarded with sound output.

To the right of the “Level/Vel” parameter you have an "Offset", and a "Curve".
On this sound Curve #3 is the preset value — this is considered the ‘Soft’ curve. The x-axis (left to right) is effort increasing. The y-axis (up/down) is output increasing as you go up. With Curve #3 = it is easy to get loud (never break a fingernail)

Curve 1 is the converse, it takes more effort to get loud. This is considered the 'Hard' curve (for the heavy-handed)
Curve 2 is linear... effort in = level out (for a unit increase in effort, you get a unit increase in output)
Curve 0 is easy at low effort and harder to get very loud (wide)
Curve 4 is hard at first and easy at higher effort.

Each Element (AWM2) can be programmed to respond individually to your playing style.
There is a global Velocity Curve that affects the overall response of your instrument - but the "Level/Vel" setting is where the rubber meets the road for the individual program.

That should get your started... Hope that helps
Adjusting Volume is always subjective - and quite normal thing to do. Change it whenever you require... Because so many synth players started on piano, you will find that most of the sounds give you plenty of room to "lean in" - the instrument, the pianoforte, is the first keyboard that had touch sensitivity. You can adjust how much engery it requires to get loud!

Thanks for the excellent explanation, I will give it a try!

Also I often hear them "muddy", can you give me some advice to make the acoustic piano sounds sound good?

Muddy is a descriptive word that has usually to do with Equalization of the sound system. Muddy is the opposite of 'clear' - the Acoustic Pianos of the MODX will suffer in mono, when I say suffer, I mean they will not be heard in their full glory (Stereo).

We recommend stereo whenever possible. On the "Amplitude" > "Level/Pan" - try experimenting with the "Scaling Pan" parameter... when set to positive values +0 and above, you will be placing the lower end of the piano in the left channel, and the upper end of the piano in the right channel (great for solo piano pieces where you can make it feel like you are sitting at a piano).

Are you listening through studio monitors? (highly recommended).

Yes I'm listening through studio monitors : two Yamaha HS-7
also I hear the Acoustic Pianos in full stereo because my MODX outputs are connected to two Mixer channels and hard pan left and right

Ok, so having said that, that is, I am listening to the acoustic piano sound through studio monitors and in stereo, what are the other tips for having a less artificial/ more natural piano sound?

Eliminate the mixer, first, see if it improves your sound. The MODX is on display in literally hundreds of stores across this country connected directly to HS7 monitors, and literally thousands of MODX’s are auditioned and purchased through this very system. So the issue is your connection (cables), your mixer, mixer settings, a blown tweeter, or check your hearing (can’t eliminate that).

Things to try
_Verify all cables. are you using recommended unbalanced TS cabling? Or balanced TRS cabling?
_Eliminate the mixer just to check if it is degrading your signal path
_Plug headphones directly to the Keyboard.
_Move the same headphones to the Mixer. Compare.
_Verify your monitors are aimed at your sitting position, (if you can’t see the tweeter you can’t hear the tweeter)
_Make sure your tweeters are not blown.
_Call up a friend, they do not have to be a musician, but it might help if they were, and have them judge the sound — if none of the above work, you might consider its your ears. Particularly if “all the Acoustic Pianos” sound that way to you, we have to consider it might be you, or your expectations.

Hopefully you can hear the difference between them... try the following...
Press [CATEGORY]
Set “Bank/Favorite” = Preset
Set “Attribute” = All
Set “Main” = Piano
Select the first piano “CFX Concert”
Press the [AUDITION] button, listen
Let the Audition Phrase play the instrument - set your volume to a level equal to the volume of a piano in the room
Move through each of the pianos.

Hopefully you hear a dramatic difference between the pianos.
Are you aware the Super Knob often changes EQ, and room size?
Many times the ASSIGN KNOBs are set to do EQ? Learn to explore, the Assign Knob EQ is there to make adjustments for the room you are in... eliminate reflective surfaces that degrade your sound, like glass, rugs, etc.
Consider you speaker placement. Try to avoid corners, speakers should be ear level.
“All the pianos” don’t, or shouldn’t sound similar at all.
Ask your friend to evaluate what they hear, try not to prejudice their opinion with yours, so without your comments, let them decide based on their own expectations. Do they hear what you hear?

If they play keyboards, let them play while you listen... this, because your hearing perception changes when you are playing versus when you are listening only.

If “all the Acoustic Pianos” sound low in volume and muddy, and you determine the gear is fine, then you may want consider the above tests. Start by BYPASSING your mixer... just to ensure you’re not degrading the sound.

Let us know.