Joel Kolstad wrote:

I'm told that 'zero beating' typically has accuracy not much better than some
tens of Hz due to the limited lower frequency response of the human ear... has
anyone tried zero beating a signal from above and below and taking the average
to get what might be a more accurate frequency estimate?


Use an analog comparator to drive a LED so you can see the difference
when you can no longer hear it. Add a counter if you want to get fancy,
and you can count the number of beats per minute, hour or even day.
--
?

Michael A. Terrell
Central Florida