Frequency detection (audio)

[HankMcSpank]

Ok, so I took the HSEROUT command out of the ISR ...... & then my ISR 'toggle pin' frequency scoped correct up to around 900hz audio input ....however, above that 900Hz audio input, even with just a basic 'toggle pin' in the ISR, the toggle pin frequency as seen on a scope starts going awry again....so the conclusion here ...it seems that DT's interrupts are taking a bit too long to get in & out for anything above 800hz comparator interrupt rate (this is with a 16Mhz oscillator).

Anyone know of another way of approaching this? (I'd like to be able to to detect up to 1.5Khz)