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@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/listinfo/linux-audio-user
