Lawrence Yates <[email protected]> wrote: That's possible - we're talking over thirty years ago. On 13 February 2011 01:24, David A. Jewell <[email protected]> wrote: > my thought would be that if it was a tube [valve in british] > amplifier then it might be a non-power related harmonic. If it is > a solid-state amp then I don't know what could be causing it except > to say that it would be another component within the system that is > perhaps resonating.
I don't think we need to invoke magic oscillations to explain this anecdote. By the way, tube amplifiers are very susceptible to power-line hum because the low voltage used to heat the filament is usually AC, direct from a step-down transformer, but the carefully filtered DC used for the actual audio pathways. The thermal oscillation (at twice the power main frequency) can sometimes be enough to feed through to the audio. It doesn't take much to be perceivable to the ear! And tubes may perform worse as they age. (Audio amplifier design, especially in pre-solid-state power supply and pre-semiconductor-op-amp days was an extremely sophisticated area of engineering. It wasn't rocket science -- it was much more critical.) > >"I always switched on the stereo", he said. "Try it next time > >you're there and listen - it hums a perfect concert A" > Something,s not right here. > If in England where the power is 50 Hz, the hum harmonics would be > 100 Hz, 200 Hz, 400 Hz. Huh??? The harmonics would be 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, etc. Hz. To determine mistuning from A440 it doesn't matter which we use, but the 450 Hz 9th harmonic is easiest to compare with A440. > That's not very close to 440. > If in the US with 60 Hz power, the hum harmonics would be 120, 240, 480 > Still not very close to 440. > Not what I'd call a "perfect" concert A. > What' up with that? > Or > Are they close enough that nobody can tell the difference? Power in the UK is indeed 50 Hz. If the piano is perfectly tuned to A440, and if we compare the ninth harmonic of 50 Hz, we find: (cents 450/440) => 38.9 In other words, 50Hz is a little more than 1/3 of a semitone sharp from A440. That's nowhere near close enough to sound in tune if the notes were played simultaneously, but it is quite close enough to be identified as the "same" note as the piano A. The classroom trick might not have been a demonstration of perfect pitch and fine tuning (which many victims of perfect pitch indeed seem to have). It might have been about the question "Where is concert A?" And the lecturer might have learned over time to drop his pitch a little from the amplifier A. As an aside, sometimes one hears the statement that 60Hz power-line hum (as is found in the U.S. and most other places) is a Bb. But consider the 8th harmonic of 60 Hz: (cents 480/440) => 150.6 In other words, 60Hz is almost _exactly_ on the quarter tone betweer B and Bb. It isn't just somewhere in the crack -- it is essentially _exactly_ in the crack! This is mere coincidence, of course. _______________________________________________ post: [email protected] unsubscribe or set options at https://pegasus.memphis.edu/cgi-bin/mailman/options/horn/archive%40jab.org
