Frequency detection (audio)

[HankMcSpank]

Are my eyes lying to me or are they the same-ish as for 1K? One must ask them selves How can this be?

Good spot!

Here's approx the Timer counts I'm seeing for different frequencies...

82.4Hz (lowest note on a guitar) - 42,900 (ish)
330Hz (top E) - 7,300(ish)
600Hz - 1800 (ish)

650Hz -1200(ish)

& then when I go higher in frequency, the timer1 counts start going all over the place ..

Here's 800 hz...

4924
177
4940
177
4965
179
4987

Oddly, when I dial 1000hz in, yep the counts go to 3,200 again ....so clearly something is wrong with my detection method using interrupts & timer1 counts

(btw I know the frequencies the PIC is handling internally are correct, as I'm outputting the PIC's comparator output to an external pin & attaching a frequency counter to the pin)

Hmm [strokes chin]