Frequency detection (audio)

[HankMcSpank]

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!!

No...I hadn't so put a toggle in my ISR (top tip - tks!)

I've scoped the ISR 'toggled' pin & I'm seeing 250hz on there?!! (therefore 2 x 250hz = an interrupt rate of 500Hz ....this for a 1kHz audio signal?!)

I confirmed my input to the comparator was 1Khz...and also the output from the PIC comparator is definitely 1khz (since I've brought it out on a PIC external pin & scoped it).

So it looks like my comparator interrupt isn't working properly and my interrupt is only happening at half the rate it should???

Any ideas?!!