> 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.
Monty
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Received on Thu Oct 27 16:15:01 2011
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