How close is anyone to making a working electronic filter for the sound of the vuvuzela horn which is plaguing television broadcasts of the world cup?
"If we consider a vuvuzela to be a tuba with a 1 meter tube length, then the fundamental tone would have a wavelength of 2 meters, which corresponds to a frequency of 172 Hz. Using the modern Western standard of A440, this would be between 4 and 5 half-steps below A an octave below middle A, or somewhere between E and F (I suspect that the instrument typically isn't exactly a meter long, but calibrated to fall exactly on one of these two). But most players probably aren't hitting the fundamental; the first or second harmonic is generally easier to blow. The first harmonic would be at double the fundamental, 343 Hz, and would likewise be an E or F, one octave higher. The second harmonic would be triple the fundamental, 515 Hz, which between two and three half-steps above middle A, which would put it somewhere between B and C.
Or, going about it the other way, if as Wikipedia says the note is B flat, and if we assume that that's the second harmonic, then that means that the length of the instrument should actually be 110 cm. A ten percent error is probably reasonable for trying to estimate the length from pictures, so that's probably correct."