3 ms·
That's a good point re. the crystal oscillator. Maybe I'm wrong re. the sample rate then, I found this paper - http://www.forensic.to/ENF%20processed.pdf http:
by anfractuosity 4y ago
That's a good point re. the crystal oscillator.
Maybe I'm wrong re. the sample rate then, I found this paper - http://www.forensic.to/ENF%20processed.pdf http://www.forensic.to/ENF%20processed.pdf , where they mentioned 8kHz as the sample rate.
I think what I was thinking is commercial systems such as https://synectic.co.uk/product/sd037-frequency-monitor-html/ https://synectic.co.uk/product/sd037-frequency-monitor-html/
mention specs such as 'The frequency monitor units are supplied pre-calibrated to an accuracy of +/-0.0001Hz'
- sgtnoodle 4y agoI was mainly responding to the hobby experiment of connecting a 12V transformer to an audio input on a computer. Even then, it seems like 8Khz sampling would be plenty to fingerprint a 60Hz signal. 8Khz sampling can capture information up to 4Khz, per the Nyquist frequency. That frequency monitor spec sheet mentions 90ms response and filtering, which would imply it averages information across 5 periods. Also, because it's a purpose built device, it's likely not periodically sampling the waveform with an ADC, but rather has a dedicated zero-crossing detection circuit that feeds into a capture input on a digital timer with at least microsecond resolution.