Please see this post

1. Would you recommend me cut-off parameter value to make more accurate to real grand piano?

2. I think.. soft pedal in real grand piano doesnt change only volume also velocity dynamics.. toward soften touch feeling..
So.. soft pedal can Assign to modify velocity curve??? Even change the sound tone Toward soft.. feeling less dynamic

I don’t happen to think that there is any change in the velocity curve that occurs in emulating a soft pedal. Stepping on a pedal doesn’t have anything to do with how hard you must play on the keyboard of an acoustic piano.

The reduction of the volume is exactly “less dynamic”. By lowering the output level when the pedal is applied reduces the soft to loud range. Soft-to-loud is “dynamics”, by definition.

We invite you to experiment - because you can make the sound do whatever you want. We mentioned if you would like to affect some timbre change you could apply a LPF (Low Pass Filter)... this also could be accomplished by using an Insert Effect Set to EQ. By applying a very slight negative gain value you can darken the tone to taste. An EQ is a device that includes both filters and amplifiers... so it is also a candidate for use in darkening the tone if applied properly.
Knowing what frequency to apply the filter is knowing the range of frequencies involved in the instrument we can Piano.
Typically, mid-range frequencies with a broad bandwidth... because you are going to apply a negative value, this will also have the ability to soften the sound. But it’s character is different.

Good ears and good Monitors will allow you to hear this difference rather clearly. Lowering the Volume by applying a change to the Part Volume parameter will sound different from changing the EQ ... both can be used to decrease output level, one changes the tonal balance more dramatically than the other. It is subtle but really different.

How much of each you apply is really “personal taste”... but don’t go changing “velocity curve”, at least not if you are going after acoustic piano behavior. Una corda, simply shifts the acoustic piano action so that the hammers strike less strings... it does not do any adjustment to how the instrument responds to how hard you play.

Stepping on a pedal doesn’t have anything to do with how hard you must play on the keyboard of an acoustic piano.

Wait - what? Can you elaborate.

I agree with the OP that pressing the soft pedal does, for some acoustic pianos (depends), require more velocity to get the same volume.

Grand Pianos will generally shift over the keys and hammers so that one string is not struck and the remaining strings are struck with a more "fleshy" part of the hammer since this area is not compressed by constant normal use. So the sound at the same velocity is a bit muffled vs. non-soft-pedal. In combination, since only 2 strings (not all 3) are resonating - the volume is decreased. So it's different than turning the volume down - although probably the closest thing to it and emulating such a grand piano digitally is probably "close enough for jazz" by just turning the volume down.

Upright pianos - at least most I've dealt with (probably not upright grands - but the more mainstream type) do not shift side-to-side the hammers. They push the hammers closer to the strings in their resting position. The result is that there is not as much of a "full swing" and thus the hammers are traveling at a slower velocity when keys are struck with the same force. In this acoustic piano action type - the result is very different from just turning the volume down. This type of action would be modeled by applying a negative offset to the velocity of the piano key strikes. It wouldn't be right to just decrease the volume of a matching velocity sample. When the soft pedal is pressed, it would be appropriate to lessen the velocity and have that means lower the volume.

I think that either of these can be modeled in different ways. The upright piano is "expensive" to model.

The grand piano style: using a foot switch as a source used with Mod/Control->Control Assign destinations. EQ can be offset along with volume in order to simulate the grand piano. Both volume and EQ using Mod/Control is a bit "problematic" because the sound will instantly change volume and EQ for all notes - not just new ones - when pressing the pedal. It's an approximation with limitations. Certainly unsatisfactory if enough scrutiny is applied.

You can solve this by "burning" more resources and simulating the grand piano by using two sets of PARTs. One set with a different EQ and different velocity setting (probably easiest to use velocity offset). Use A.SW1 or 2 tied to a pedal as the upright suggestion below. This will not suffer from existing notes suddenly changing volume/color.

Unfortunately, velocity offset and related parameters are not assignable destinations. I've had previous applications for this missing feature. The way you'd have to accomplish this with what you have is switch between two sets of samples. One set that responds to one set of velocities and another set that has different/offset values. If you have space in one PART (enough elements) - you can copy elements and change the velocity settings for the samples. Then use A.SW1 or 2 to switch between the two. You can use a footswitch to trigger A.SW1 or 2 - so a pedal can be used ultimately to control this. Or you can use two PARTs and switch between the PARTs similar to switching elements. A.SW should be used here too so that letting go or pressing the soft pedal while notes are sustaining (still held) won't jump in velocity.

Even though you could build a better una-corda mousetrap - you begin to see it's prohibitively expensive in many situations and start to appreciate why "just turn down the volume" is the go-to compromise. When you're not building a Performance filled with other instruments - simulating the grand-style soft pedal can make sense using a 2nd set of PARTs.

The "best" simulation would have each of the 88 keys sampled with the soft pedal pressed at various velocities. So your sample picks up the sound of the instrument with the soft pedal applied (which, depending on state of the hammers, could be quite different in tone). Using EQ is OK - but sampled would be more realistic. This is how your favorite software sampled pianos work. I haven't combed through the waveforms to see if there's a set of samples with the soft pedal pressed. Even though best - it may not be different enough to warrant tracking down the samples if the instrument doesn't have them in the factory set.