Frequency detection (audio)

[cncmachineguy]

Hank,, how bout toggling a pin in your ISR to show when the PIC thinks it should start and stop counting.
EDIT : OK I see youo have done that already DOH!!

The numbers should be linear IMHO. so 330 HZ is about half of 600, but your numbers are *4. 330 = 7300 and 600 = 1800. Now between 600 and 650, we have a difference of 600. So that would say the count shoud be 600 per 50hz. so to get to 100hz, we would expect the count to be 10*600=6000 difference. or 7800 (ish). but you are at 49,000 for 82.4. either I am way off on my linear assumption (most likely) or something is really amiss.