27 Oct
2011
27 Oct
'11
5:41 p.m.
On Thu, Oct 27, 2011 at 07:40:36AM -0400, Monty Montgomery wrote:
Yes, the long-term stability will be very good, as the frequency is
adjusted to keep clocks in sync. But there are small short-term
variations all the time which you won't notice on a clock, but can
be measured easily.
A variation on
this is used to check the authenticity of some
recordings in forensic audio. Almost all 'surveillance' audio
contains some low level 50/60 Hz. If the recording is done on
a digital device then its clock can be assumed to be more stable
than the mains frequency
At least in NA, mains frequency is very very stable. The entire
continent is in phase and clocked with very high precision. It's more
stable than a free-running digital clock. ...I used this fact to 'cheat' in a high
school physics contest where
we had to build a clock and the winner was the most stable. Ours had
a CdS cell that watched the 120Hz flicker of the lights in the room.
And if the lights were switched off ... :-)
Ciao,
--
FA