I think we discussed this before. In a real piano, there are many sources of vibration, primarily the open strings and the duplex scaling. If the dampers are down, the strings are damped (and not open) and not allowed to vibrate much, if at all. If you press the damper pedal, the dampers go up and all strings are available for vibration, either by being struck or sympathetic vibration. For a sample library, there are pedal up samples - the dampers are all down except for the keys that are played. The SR in this scenario include the main string that vibrates and the duplex scale SR, which are picked up by the recording. Additional SR also occurs because other strings are undamped (by multiple strings being played at the same time) must be modeled because you can't record all of these combinations.
For pedal down samples, all strings are available to sympathetically vibrate. So when a recording is made with one struck note, All of the possible SR is already recorded. Key combinations don't matter because all strings can vibrate and no selectivity is necessary.
Anyway, PTQ models both. I'm pretty sure that the pedal up SR is modeled much like mine, and the pedal down "body resonance" is what everyone on the forums talk about as they are a group of harmonics that are excited because of the input frequencies. This body resonance is unnecessary with sampled instruments, and layering PTQ on a sampled instrument to enhance this effect maybe is nice, but as I have said before, hyper -real and not realistic. The sample recording already picks up all of the SR caused when the pedal is down.
I think the difference this time is that PTQ now allows an input signal to "excite" the body resonance engine.
I took the bait @Del Vento 🙂