Frequency detection (audio)

[cncmachineguy]

Hi Hank, just stabbing at this, you second set of numbers is not really all over, every other one is close to the last. I am guessing here maybe timer is overflowing with the lower freq?

[HankMcSpank]

Hi Hank, just stabbing at this, you second set of numbers is not really all over, every other one is close to the last. I am guessing here maybe timer is overflowing with the lower freq?

hi bert,

Very plausible/good idea, but alas, it's not down to Timer1 overflowing (I worked out that with a 16 bit timer @16Mhz oscillator I can go down to about 58hz before worrying about overflows), for example if i take the frequency even lower than 800hz, it goes fairly stable again, here's 500Hz...

3120
3218
3212
3208
3202
3198
3194
3184
3182
3179
3173
3168
3163
3154
3151
3150

[cncmachineguy]

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

BTW Nice to be back and looking at hanks fun stuff

[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]

[Archangel]

500 hz is the first harmonic negative of 1 Khz. some Pi filters might help or lower the input gain

[HankMcSpank]

500 hz is the first harmonic negative of 1 Khz. some Pi filters might help or lower the input gain

I don't think that's the issue, here's a scope screenshot of what the PIC's internal comparator is seeing internally...





The white parameters window to the right is my scope's take on the waveform it is displaying (1khz)

The green text on the left is the PIC spitting out the TMR1 counts it's counted between comparator2 interrupts serially to my PC com port.

[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.

[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?!!