The question as it appears in the 01/22 edition of Specs & Techs from GlobalSpec:
A physics professor stated to his class that a live performance of an orchestral piece will always sound different from a high-quality Hi-Fi reproduction. He claims this is because in the live performance, the listener will be able to hear some beat frequencies between some higher frequency harmonics (above the hearing range), whereas in the recorded reproduction (unable to record the original, high harmonics), the beat frequencies will not exist. A student said, "Nonsense!" Is the student correct?
Thanks to Lleros MaHarg who submitted the original question (which we revised a bit).
(Update: Jan 29, 8:50 AM EST) And the Answer is...
The student is correct, because the beat frequency between harmonics above the hearing range will not be heard in either the live performance, nor recorded version, because the beat frequency is a modulation of the original frequencies, and is not a real note in itself. To hear the beat frequency in the live performance one would have to have a non linear device (eg a diode detector) in the path to the ear to cut off one half of the modulated waveform, in a similar way to an AM radio. If the original high harmonics are recorded, they will not be heard for the same reason above, and if they are not recorded the beat will not exist.
Links: http://hyperphysics.phy-astr.gsu.edu/hbase/sound/beat.html
http://en.wikipedia.org/wiki/Beat_(acoustics)
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