elkies@walsh.harvard.edu (Noam Elkies) (07/30/90)
THORNTON JOHAN A, in <1341@fs1.ee.ubc.ca>: >A better example of the "fundamental tone reconstruction" is the 60Hz buzz >we're all familiar with. Rarely is the fundamental present. Actually, as I noted a few months ago [on a thread that involved a George Crumb piece with two double basses holding a 60Hz B-flat throughout], I've always heard the so-called 60Hz buzz at about the B-flat an octave below middle C, indicating a frequency of about 120Hz, rather than the B-flat an octave below that which would be 60Hz; and indeed it stands to reason that in a system such as a power line or neon light without moving parts the electric hum would be driven not by the AC waveform itself but by its amplitude, whose fundamental frequency is twice the AC frequency (this assuming that physical AC current is a pure sine wave with negligible higher partials). In other words, not only is the 60Hz ``fundamental'' not present, but neither are the higher odd partials, and ``fundamental tone reconstruction'' does *not* take place. With something like an electric motor driven by AC current the situation should be more complicated. What's your source for the spectral analysis of electric hum (or rather electric hums --- I see no reason that a power line and a neon light should give rise to identical soundwaves)? --Noam D. Elkies (elkies@zariski.harvard.edu) Department of Mathematics, Harvard University