Averaging AtoD samples

[Darrel Taylor]

Thanks Ioannis.

And I'll say ... cncmachineguy's rules were pretty darn close to how I modified the averaging routine.

[HankMcSpank]

Wow ...what can I say?!!

DT you truly rock...and without a doubt you're my most favouritiest E-personage on the whole of this global network!

I'll give this runout at the weekend...once again, thanks....just brilliant!!

cnc machine guy - great input too ...many thanks.. re the arriving frequencies (or more importantly, what the PIC sees for incoming signal frequency - comparator 'count'), well, on a std tuned guitar, the lowest note is 82.4Hz...which @20Mhz clock gives a comparator interrupt 'count' of about 60700 per 82.4Hz period' ...the highest note on a guitar is about 1.4Khz & gives a comparator count of about 3500 1.4khz 'period'. Each musical note has about 5% difference...but the problem with guitar 'pitch detection' is you can bend a note, which will obviously fall somewhere in between the 5% between notes.

I'd like to be able to eventually get the PIC discern not just which note is being played but also when it is s being bent - but for that I need good solid incoming samples to process...and these spurious samples were really screwing me up - hence I relish having a dabble with what DT has just posted!

[HankMcSpank]

An old thread & just revisiting this issue again ...re the spurious rejection, there's a setting as follows....

Reject          CON  2          ' Spurious Rejection level

Presumably that setting is the amount of samples, before the averaging code accepts/adopts the new incoming sample (vs just throwing away a sample that diverges too much) ....but what is deemed a 'spurious' sample ..in other words what in the Darrel's code a couple of posts above decides that the incoming sample was spurious ...and can this 'sprurious diversion amount' be adjusted?

To help explain, consider the following trail of ADC samples...

99
101
100
91 ------ not spurious, just a low sample
97
101
50 -----------spurious
98
100

How is the spurious rejection set so as to accept the ADC rsample of 91, but to just reject the sample of 50?

[cncmachineguy]

Ok Hank, I'll give this a go. BTW, it only took me 15 mins to remember what I was thinking when I posted almost a year ago!

Anyway, this is what I think is going on. Every sample with a difference greater then 50 in DT's code gets rejected the first and second time through. The 50 can be set with the FAspread constant. the number of times it get rejected is set by Reject constant.

The way it gets rejected is really pretty. Int the avg routine, the value gets tested against FAspread, if it is bigger, the flow jumps to FastAvg, where reject count gets incremented by 1. then reject count gets tested to see if it is now 3

IF RejCount = Reject + 1 THEN

if it is, the new value is accepted as good. It also becomes the new average. and everything moves on from there.
If it is not, then the running average is left as is and the current value is rejected.

BTW, I think using DT's FAspread con 50, 91 would never be considered as spurious since it is within 50

Does this help?

[HankMcSpank]

Thanks Bert....let me see - so it's the FAspread that sets how far the deviation from mean that can be accepted .... with the RejCount counting how many 'deviations from mean' there have been - once the Rejcount number is met, then the new level of incoming sample becomes a valid sample to average against?

[cncmachineguy]

Thats my understanding Hank. It sounds so much better when you say it.
Do you get the code now?

[HankMcSpank]

Yes, I get it - tks (as ever) for the input Bert.