On Mon, Dec 24, 2012 at 9:27 AM, Fons Adriaensen <fons@linuxaudio.org> wrote:

Violins (and many other instruments) can and do produce harmonics
above 20 kHz. As long as these are vibrations inside the instrument
they could even interact in non-linear ways and produce something that
is audible. Once they are 'in the air', they don't interact and you
can't hear them.

Correct, but when it comes to recording the sound of that particular violin you don't need to capture the ultrasonic frequencies, just what we can hear for it to be a perfect reproduction for the listener. I was simplifying things a little in my explanation, as in the end only what we can hear makes up any of the identifying information about the instrument, which you obviously state later on.

Seablade