sympathetic resonance not working as expected?

Eran, you are right, there are some particular computations, including the ones that you mention, that are by-passed for optimization reasons. This optimization is justified by the fact that in normal conditions (default value for the sympathetic resonance parameter), the sympathetic harmonics that are by-passed would be masked by the harmonics of the notes that are played: in experiment 2, G4 sympathetic resonance is masked by the 3rd harmonic of the C3 which has been played, and in experiment 3, the normal level of the sympathetic resonance is low because the main part of the energy comes from the stroke, absent in this case. The rule that we usually follow is: compute what can be heard in normal conditions. However nothing is definitive in our model, we are constantly working on improvements.

In a review in the swedish magazin MM the author thought that the middle octaves of Pianoteq are a bit synthetic. He thought that maybe it will be better if the different tones in an accord affected each other. I don't know if the subject in this topic have to do with it?

Hi Eran,
I've been experimenting with sympathetic resonance too and think it works OK.

Your experiment No 1 is indeed correct. When the (silent) C3 note is held the damper is removed from the C3 string, which although free to vibrate at its resonant (and harmonic) frequencies has nothing to excite it. The G3 note is rich in harmonics for a relatively short period after after the G3 hammer strikes the strings. This period is long enough for G3's second harmonic (G4) to propagate through the instrument and excite the undamped C3 string with a standing wave pattern which is C3's third harmonic.

Your experiment number 2 the C3 string is vibrating predominately at its fundamental frequency by the time you release G3. Any remaining 3rd harmonic of C3 is now a (dying) overtone of the (already resonating) fundamental. In reality you would not hear G4 as a separate note anyway (otherwise you would hear a chord comprising C3 and G4).

Experiment no 3. If anything I would have expected a (very weak) G4 from the C3 string but I can't even hear C3. Are you sure you are playing C3 softly enough?

The important point is that it is the percussive action of a hammer striking a string which produces harmonics which die away much more quickly than a fundamental. A string will only be excited to resonate sympathetically if it is undamped (key held down) during the percussive action of striking another key.

If you want to try something really wierd to test out the sympathetic resonance try this :

Gently press C3, E3 and G3 so they do not sound. With these notes held down hit F#3 (or A#3) staccato FFF.

Try and do that with a sampled instrument.

Hi John,

Well, I have tried all three experiments on my acoustic Yamaha as well. So seems both I and my Yamaha disagree with you :-)
Regarding experiment 3 - on PTQ i heard the C3 very softly as I played it softly. You are right I didn't mention that.
My understanding is that when two strings are free to resonate and have common overtones, they will eventually (quite quickly) resonate together with these overtones - even in the same phases. It's not the hammer stike on one string causing the other sting to resonate. It's the fact that these strings are vibrating freely simultaneously - their sound waves affecting each other.

Thanks,
Eran