What's the latest and greatest for reducing the sustain time?

If the effect is primarily noticeable with the sustain pedal down, the first thing I would try is decreasing the Sympathetic resonance.

Also, try different instruments. Among the instruments I have, I’ve noticed the C. Bechstein DG has particularly strong sustain/resonance — I can easily get a big, blurry mess unless I go light on the pedal.

Agree with Pianistically - pedalling can be the single most noticeable difference between making the piano do what we want, and having it seem to ring out, or act too full of noise. A lot of people who grew through the dpianos of the past knew "this is not real piano behavior" - but it was OK for pop, rock etc.. but now Pianoteq gets to a place where the behaviors of its pianos can be interesting, to either side of the piano reality divide - I'm for both worlds - and you can make Pianoteq sound like a real piano with some effort to break from old habits (If like me, you mostly used to play pianos on dpianos from the 80s/90s.. before dynamics were more than a few layers etc.).. But if you're not stuck with that (not assuming, just trying to cover a lot of things since it's not clear to readers perhaps exactly what you're trying to tame..)

First thing I'd check would be compressor (not all presets will have one 'on' - but some might). If it's on, turn it off or lessen its effect (particularly its mix amount - although some compression types are aesthetically supposed to be a certain way - but instantly reduce it with its 'mix' slider if it's still desired to an extent).

Noticing you mention 'turning it down in FX' - not sure what you mean by 'it' there (which is possibly more fun to guess! though).. but if you mean what I think you might mean by 'it' there, you certainly could be making your perceived issue more problematic, here's why..

If you mean you turn down the main FX "Gain" level slider, that will turn everything down (just the whole signal path volume level - it doesn't just feed IN the FX.. it's an overall level.. a great way to make a final volume adjustment whilst working on FX which might boost or cut the level in various ways.. it's a nice to have last finishing item, rather than a way to remove 'some FX' - BUT I DO like the idea of there being a way to feed the FX in - however.. most individual FX do already have a mix of their own.. much more nuance etc.. just thought this might interest others wondering about the 'gain' in the FX section, esp. if it's causing some to think it's about 'the level of FX'.)..

so because of that?? (if so, just making assumptions) you might be kind of fooling your ears until they tell you "no that doesn't work". But maybe you turned down the bass in FX (EQ?).. either way, those are design choices for sure - but might not hit the spot for shortening duration of sustain.

Pianos can 'sustain' for like, minutes. So indeed that's a thing.. but I feel that your issue might be about shorter term 'busy' nature of so much sound together, whilst playing chords? (That kind of length.. which you'd maybe like to drain away faster, like steeper waves, in some matter of seconds?), that would require different edits - like some mentioned above.

The others above already gave good examples of things to do. Definitely a mixture of Impedance AND Direct duration might be the most direct way to quickly and importantly, 'realistically' bring down unwanted sustained energy. (with those 2 sliders, you can make quite a tubby boing like a poor old dumpster piano find OR increase the droning everlasting note durations like an impossible kind of solid diamond cabinet with tungsten harp and tantalum strings or something).

I'm happily supporting the idea of Modartt adding more 'envelope' functions (inside "Note FX" panel, to go with "Attack"). Has been brought up before iirc - but forum member 'moontan' suggested this recently.. So, I really do hope sometime it may be possible to add in 'artificially short' notes with those 'old school' tools. (I hope believe many sound designers will enjoy that). In 'Note FX', it is possible to add 'modulation' either per note, or just a single wave (singular time unit across all notes).. so it's seemingly possible for an envelope (beyond transient) to engage on a per-note basis.. it would be super for various reasons beyond the cause of piano realism of course.

Absolutely, you could move mics back further, so they capture more ambience and less direct piano signal.. and the piano can 'seem' farther away 'in space' because of placement.

Think of the most obvious 2 types of distances..

if the mics are right up close inside the cabinet up against the strings, that will be the most energy from the piano to the signal path (and you can alter how Pianoteq mics respond in various ways, like engaging "Proximity effect" which is a real-world factor in play).. and the opposite, if you move mics way back from the piano, it may sound of course distant - but you find the spot which works best for your aesthetic choices.

You can load microphone default presets, to speed up your discovery of the mic panel.. with any mic 'array', we can link and unlink them, so as to drag them around as a pair (or up to 5)... or place them individually in different ways. There is a lot of existing 'know how' around mic arrays (and very good reasons for the existence of some arrays).. but esp. for modern/personal/experimental or art music etc. the rules are fewer - simply because the market doesn't require the same kind of mic array (like for example many classical recordings use fewer, but 'best of' kinds of mic arrays - listeners don't wish to experience 'novelty' when listening to their classical music via speakers.

But definitely, sticking to the default mic arrays in Pianoteq, (which you can still alter and save as your own etc.) would be time well spent for many users. (mics are not easy - they can be fun, a learning experience, but for sure, it doesn't seem that everyone will enjoy it or gain much improvement to their own mic arrays). There is the problem of making stuff worse for ourselves - but in sound design or contemporary music... tamed 'mistakes' can be the very things which make up, or inspire elements of a mix.

My ongoing advice, is to keep trying things out - break the pianos - move the sliders (all of them) WAY too far - (*you can always 'undo' to return - or just reload the clean preset.. don't fear ruining anything.. just don't 'save' presets you ruined, and you don't have to hear your terrible preset experiments if you don't want to) - remember at times, it can seem counter intuitive, to mess with certain physical elements of a real piano with sliders. But they are named well, are component parts of what really happens with a piano when played - and you really can do so much, if you choose, to alter how it sounds.. from within the bounds of realism, through to the realms of.. cyber punk and beyond.

I like to put this into some posts about editing - you can reduce (or increase) some 'singing' in the notes by altering Unison width as mentioned by dv above - always I want to add, for any alteration to unison width, try this... "Right-click" on the Unison width slider to reveal 'Unison balance'. By putting 'negative numbers' in there, you can reduce some singing energy.. not enough to really solidly dampen a real piano's sustain.. but can be a nice touch on any piano.

Definitely try right-clicking on various sliders as you try things out - there are some beautiful last mile touches you can make to your main changes on a slider, to make it seem more 'realistic' or beyond. Hope this inspires anyone interested (the old right-click trick can be overlooked) - and I wish always the best in your enjoyment of this remarkable software instrument machine!

Posted my first ever youtube video today to provide an example.

Note the sound does not start for a minute or so while I set up two pianos.  If you can spot the mouse you can see me mess with various options.  I start with stretch string tuning, then Full Rebuild which is more piano-like, then back to stretch strings again.  Sometimes the droning is a non-issue, other times you can really hear it go on and on. 

Note the tuning is unusual in that I have two pianos sharing the strings.  One piano has 2/1, 5/4 and 3/2, which is basically a piano dedicated exclusively to the pure major chord.  I find these smaller sets of strings with pure and simple ratio relationships sound very resonant and have specific character.  The other piano is based on 7s in the numerators, 2/1, 7/6, 21/16 and 7/4.  The two pianos sound surprisingly good together and the two drones together sound better than one Pianoteq piano, imo.  The two pianos with simple tunings is of interest here in and of itself, but not necessarily related to my perception of looong sustain (although possibly).

https://youtu.be/ax89sQOSjRA

Thanks folks, great feedback, all!

Glad you liked the example, Qexl!