Re:The “432 Hz vs. 440 Hz” conspiracy theory
by gaur on Monday October 24, 2016 @04:50PM
(#12782766)
I wonder why they decided it was better to design and build an 11x multiplier and a 25x divider rather than cut a 440 kHz crystal and run it with a copy of the 1000x divider electronics they already had.
Re:The “432 Hz vs. 440 Hz” conspiracy theory
by zokier on Monday October 24, 2016 @05:07PM
(#12782910)
Because 1MHz crystals are common off-the-shelf items, 440kHz are not?
Re:The “432 Hz vs. 440 Hz” conspiracy theory
by gaur on Monday October 24, 2016 @06:18PM
(#12783405)
In order for that explanation to make sense, one has to assume that 11x multipliers and 25x dividers were common off-the-shelf items during the time period in question.
If the choice is between a custom crystal and two custom boards, the custom crystal is going to be the far less painful choice.
Re:The “432 Hz vs. 440 Hz” conspiracy theory
by Turing_Machine on Monday October 24, 2016 @07:49PM
(#12783952)
I would bet that the BBC was using the 1 MHz crystal and the associated division/multiplication circuitry for other frequency control purposes, not just the musical test tone. 1 MHz is smack-dab in the middle of the medium wave band usually used for AM broadcasting, and the BBC has always broadcast on many different frequencies at the same time.
Having all the broadcast frequencies controlled by a single reference crystal would have some obvious advantages (and a few disadvantages too, of course).
> The B.B.C. tuning-note is derived from an oscillator controlled by a piezo-electric crystal that vibrates with a frequency of one million Hz. This is reduced to a frequency of 1,000 Hz by electronic dividers; it is then multiplied eleven times and divided by twenty-five, so producing the required frequency of 440 Hz. As 439 Hz is a prime number a frequency of 439 Hz could not be broadcast by such means as this (http://www.wam.hr/sadrzaj/us/Cavanagh_440Hz.pdf)
Since 1000 Hz also was (is?) a broadcasted test tone, it makes sense that it is much easier to get perfectly matching 440 and 1000 Hz from the same high-frequency source than it is to get 439 and 1000 Hz. A more precise way of describing the problem is then that it's hard to generate since it doesn't share any divisors with other desired test frequencies.
If they only required 439 Hz they could have just used a slightly differently tuned source oscillator, yes.