On Thu, Oct 27, 2011 at 07:40:36AM -0400, Monty Montgomery wrote:
> > 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.
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.
> ...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 _______________________________________________ Linux-audio-user mailing list Linux-audio-user@email-addr-hidden http://lists.linuxaudio.org/listinfo/linux-audio-userReceived on Thu Oct 27 20:15:01 2011
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