@Lars, just speaking from my exp. of making various extreme preset types.. I am guessing the engine could be capable of including a lot of the things associated - but, I'd also guess, it would be some work to give users a panel with logical controls (like the prepared piano software kindly shared by Yves! Pretty fine and vast control there, actually pretty sweet, thank you Yves!). But I love the idea of a group of controls for doing controlled preparations/treatments (like being able to follow Cage's instructions for example, rather than doing what I do now and wing it when I'm making extreme settings by ear - it is a fascinating idea).
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For @shem.. there will be different ways to interpret 'soft'. Maybe moving mics way back and adjusting reverb (lowering hammer noise, key noise etc to hyper realize distance) is one POV on that kind of thing which you may be seeking.. but if not that..
what you describe doesn't seem normal.. as if something is bugging out there in your audio setup or something (it's not my experience that you cannot make things extremely soft).. you can right-click the velocity curve pane, and paste its text into a post here.. others can copy/paste it into their velocity curve.. just wondering if you're actually editing it the opposite way to what you are aiming for?
Next guess (knowing nothing of your experiences/setup etc.. - forgive if any of the suggestions are things you already know/tried).. Sometimes, I overlook something like we all can, so I try to post things which might help beginners and experts alike without meaning to bug anyone..
I'd like to help.. can only begin at guessing why you're hearing aggressive stomping notes with a heap of things set for softness. No way of knowing your situation/gear.. Absolutely the best way to know it's not something strange - if nothing below heps you, maybe consider uploading an audio snip of what you hear, along with the FXP you're using.
but to start kind of at the beginning.. some things to rule out..
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Lowering hammer noise can help with creating soft pianos - even try it at zero - who knows, with other elements adjusted it could be a benchmark for less transient in your shaping.. and adjusting up from nothing might help you gage where you prefer a soft hammer noise (not talking here about the 3 hammer hardness controls as you mention you altered those - but things in combination are like secret sauce. Hope that's just one you overlooked. If not..
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Check "Local Control" (dpianos may have a button for it, or a setting in it's menu or software it might come with).. "Local Off" is a button on mine for example.. click it so it's off and it no longer sends its own internal sound into the PC (along with MIDI).. in essence, to be sure, your dpiano should only be firing MIDI, not also sending its own audio. It's not super common that somehow people end up hearing both piano software and dpiano sounds together, but it seems it happens enough to be the cause of weird audio issues occasionally.
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Not sure if you tried "Felt" piano presets, those are like the closest thing usually to a very soft variant in the grand pianos. It can be made even more soft with the things you mentioned, as well as shaving off some attack (Note Effects button - 'Attack envelope'). Interestingly, you might find some nice tones by actually raising hammer noise along with shaving off some attack (keep the envelope at numbers like 0.0010 to 0.0050 or so.. you can be super subtle at 0.0001 or whatever but.. I think that you can balance extra hammer noise and slightly larger numbers there.. one reason is, it's a little like a fast compressor shaving off some of the 'clip' in normal transient data, but boosting associated overtones.. niche maybe - but I love balancing this, esp. with soft playing with compression with a bit of makeup gain. Not for every occasion - but I like things like that for intimate piano.)
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There are 2 different EQ types (Equalizer, large button and within the FX section you can line up 2 instances of EQ3 parametric type to do some extreme shaping.. leveraging these you can theoretically remove as much of any tones, like pass/shelf/notch/bump, cut/boost etc.
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Back to the main Equalizer, extra things you can do in there is to alter "Resonance EQ" (effecting the EQ of the resonances only), plus "Resonance Duration" (effecting length of any ranges of resonant EQ).. With those two extras, you could for example click to add a bunch of dots precisely, to notch out some/all resonances, like between 1kHz and 3kHz - or boost those, make them ring out way longer - and make dozens of cuts/boost wherever your ear takes you! - and on the front interface, raise/lower "Sympathetic resonance" so you 'mix in' the flavor in a general sense to taste).
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Move 'strike point' (where hammers hit stings, it's seen as a measurement) - depending on desired tones, move the slider left/right until you get more deep tones.. like strumming a guitar close to the bridge vs. strumming over the sound hole.
There are going to be other things I'm overlooking just now - but you've mentioned some things.. but like up top.. the issue of still hearing loudly stomping notes with all kinds of settings softened seems like either a 'have you turned it off and back on again' thing, or something like 'Local OFF'... or maybe something else. Hope some of that helps out.
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Many presets will have extremely subtle, or zero compression engaged - but the compressor in the FX section is pretty good. There are a number of things you might do with it but it would be a matter of taste - however, you can help make smoother, less stomping notes etc.. even if you set it to a subtle 'mix' amount, with a fairly low 'threshold', and maybe gently raise the compressor's 'gain' (there's also a main 'gain' in the FX too, which can be the fast way to lower the signal from the mics, if they are up high in vol).. honestly feel it's good at getting the piano very contained if required.
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Lower 'Dynamic' slider - like around 30. This will not be like compression - but it will adjust how deep the diff is between low velo and high velo strikes. With 'soft' piano sounds (ESP. IF played extremely softly), having a huge dynamic range without compression can be like way far from a good audio technique.. you can get lovely distant piano sounds by raising dynamic, no compression, just distant mics - and so on.. but I'm guessing you're meaning soft somewhere between.. but all the above could impact on any way you look at your goals.
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Altering other sliders top right including "Q factor" to adjust how much high overtone frequencies ring, and for how long generally.
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In a DAW there are infinite ways to alter things. You may be advanced etc.. again, no way to know - but if not.. I am one who encourages people to try.. some have great included tools easy to use. But Pianoteq has enough onboard to make a DAW usually a kind of next step thing..
Various things in combination, esp. when beginning maybe with a 'felt' preset - for sure you should not be stuck with profound notes.
Hope some of that might help make a difference. But for sure - when any subject about detailed editing comes up, it often becomes more about helping someone who is not benefiting in some way.. usually, it's just taste, sometimes exaggeration for impact, or something on their end.
Pianoteq Studio Bundle (Pro plus all instruments) - Kawai MP11 digital piano - Yamaha HS8 monitors