Yeah Rich, it's mainly the harmonics of the fundamental tone which make instruments sound different. Without them, for example, a flute playing at 400Hz would sound like a trumpet at the same frequency. So, although the fundamental tones of the instruments don't go much above 4KHz, the harmonics up to our limit of hearing(20KHz possibly, but less for most of us at realistic levels)are an important part of the musical experience.

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Enjoy the music, not the equipment.