As I understand this,

Damper resonance: Holding down the damper pedal, playing a note causes additional resonance effects.

String resonance: While silently holding a chord, playing a note may cause additional resonance effects.

Correct? Then what is "acoustic resonance" as listed in some specs?

You're right on the first two definitions as they're normally given by DP sellers. 'String resonance' comes from specific harmonics in one note causing sympathetic resonance in other notes, within the same harmonic range.

But it is impossible to imagine what kind of resonance would NOT be, in some form or other, acoustic. Seems like a complete contradiction in terms.

I don't know about "acoustic resonance" (wahtever that is) but I don't understand the distinction between string and damper resonance. Physically they are the same phenomenon, right? One string is undamped (because of pedal or becaause it is pressed) and another is played. They are perhaps implemented differently and therefore listed as two different "features" although it is actually one.

Right, it's just a programming distinction. There's a generic algorithm for damper down, and another for individual keys down.

Casio lists my PX-330 as "acoustic resonance", but I've never noticed anything. I noticed the PX-150/PX-350 list damper resonance (fixed setting for piano sounds) -- now I have to go back to GC and check.

I would consider them to be two different features. If you hold a C major chord down with your left hand, and play a C note with your right hand (no pedal involved), that lower C will resonate, and to a lesser extent, the E and G will resonate as well. If instead you hit that low C chord and then depress the pedal and then play that higher C note, many strings will resonate. So the results sound different, the samples employed are different, the programming needed is different. The phenomena are based on the same acoustic principle, but the sound and required implementation are different, which is why a keyboard can have one and not the other.

Damper resonance can be captured quite realistically with pedal down layers in a sampled piano. I believe string resonance needs a separate DSP algorithm to exist in a purely sampled piano, even pedal events can create very complex resonance situations. Purely modeled pianos can excite the string models for both types of resonance.

That sounds right. The "damper up" sound is _one sample_. The sound of "key X down, with dampers up" is _one sample_.

To get "string resonance" -- the correct sound for "hold down key X, and strike key Y" -- you must sample _pairwise_ each pair of notes! And then sum them:

. . . A 6-note chord will have (I think) 18 combinations
. . . of keys.

Which, I suppose, is why it's only modeled in high-cost DP's, and in software pianos.

The DPBSD thread has definitions for all these things. But that doesn't necessarily match with the manufacturer's meaning.

. Charles

There doesn't seem to be an industry standard for this terminology, and what exists is ambiguously named.

You're being quite generous calling it simply "ambiguous".

On my Kawai ES6, the string resonance seems to be accomplished by triggering softly any of the keys that are held down that fall within the 2nd and 3rd partial of other notes being struck. I imagine this can be termed an algorhythm. Kawai calls it Harmonic Imaging. It is not however a dsp generation of resonance.
A number of the initial high end piano vst's did, with Kontakt, use an actual DSP generation of soundboard and string resonance I'm pretty sure. It was always one of the features that crashed the program:)

I think "Harmonic Imaging" is what Kawai calls the entire process of sample playback and resonance effects in the ES6. I believe "string resonance" is most likely a DSP effect in there.

For example, if I hold down the G above middle C and strike middle C, a G an octave above the depressed G sounds. To me, when I subsequently strike that octave G on it's key, I am convinced its the same sample. I been all over the keyboard doing that, it's alot of fun, until family members start telling me to knock it off!
Kawai's Harmonic Imaging, as far as string resonance is concerned, seems to be a sophisticated triggering matrix.
The damper resonance however is far subtler.

Okay so the PX-330's "acoustic" resonance is some form of damper resonance. It's most easily noticed hammering an upper key.

One of the big features of string resonance on the kawai is the blooming effect of the resonance and the way it makes the sonorities bigger than just the notes being played. The resonance also effectively obscures looping effects and contributes to evolving sonorities that also lay over the notes being played.
-Without damper pedal-