Averaging AtoD samples

[Darrel Taylor]

I think the Fast Average section might be modified so that instead of jumping to the spurious noise point, it will reject the sample entirely.

That should only take commenting 1 line from the original code.

[HankMcSpank]

I think the Fast Average section might be modified so that instead of jumping to the spurious noise point, it will reject the sample entirely.

That should only take commenting 1 line from the original code.

I've broke the breadboard circuit up ....so can't test right yet. But this sounds cool.

How does the averging code decide whether what's coming in is spurious...or in fact the beginning of a new stream of samples (eg a new frequency arriving, which will generate a different comparator count - with it's own spurious counts).

I guess what I really need issome form of 'trigger' (or 'change' threshold) so that my program then knows that a new frequency is coming in (& is not just a spurious reading)...

For example, red test below is spurious count, blue is new frequency arriving (therefore count changes and starts coming in at around that new level)

5000,4999,5000,5001, 3956,5000,5001,5000,4999,5000,3789, 2570,2571,2569,2570,2571,18912569,2571....

[cncmachineguy]

Hank, It seems to me you need to set some rules, or rather conditions. something like this:

1) samples must be +- 10 of a target number to be included in the average
2) numbers outside the +- 10 will need to have 2 more samples within the new samples range to be considered a good sample.

That seems like it would weed out the rouge numbers. Now of course I have chosen random numbers. The 10 and 3. I don't really know what the numbers represent (I assume gutiar notes). Nor do I have a feel for how long a note will last. thats what drives the 10 number.

[Darrel Taylor]

We choose to go to the moon. We choose to go to the moon in this decade and do the other things, not because they are easy, but because they are hard, because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one which we intend to win, and the others, too.
            John F. Kennedy

Notice in the image that all spurious samples were rejected.
And where the samples changed from 6798 to 3899, the average caught up after 2 samples (adjustable with a constant).

DEFINE OSC 20

DEFINE LCD_DREG PORTB 'LCD data port 
DEFINE LCD_DBIT 0 'LCD data starting bit 0 or 4 
DEFINE LCD_RSREG PORTB 'LCD register select port 
DEFINE LCD_RSBIT 4 'LCD register select bit 
DEFINE LCD_EREG PORTB 'LCD enable port 
DEFINE LCD_EBIT 5 'LCD enable bit 
DEFINE LCD_BITS 4 'LCD bus size 4 or 8 
DEFINE LCD_LINES 2 'Number lines on LCD 
DEFINE LCD_COMMANDUS 2000 'Command delay time in us 
DEFINE LCD_DATAUS 50 'Data delay time in us 

DEFINE HSER_RCSTA 90h ' Enable serial port & continuous receive
DEFINE HSER_TXSTA 24h ' Enable transmit, BRGH = 1
DEFINE HSER_SPBRG 129 ' 9600 Baud @ 20MHz, 0.16%
DEFINE HSER_CLROERR 1 ' Clear overflow automatically

'----[Averaging Options]------------------------------------------------------------------
AvgCount	CON  16		' Number of samples to average
FAspread	CON  50 	' Fast Average threshold +/-
Reject          CON  2          ' Spurious Rejection level

;----[Variables]--------------------------------------------------------------------------
Value		VAR  WORD
RejCount        VAR  BYTE
ADavg		VAR  WORD

;----[Initialize]-------------------------------------------------------------------------
RejCount = 0
ADavg = 0

;----[Main Program Loop]------------------------------------------------------------------
Main:
    HSERIN [wait($FF),DEC Value]                                   ; get a sample
    HSEROUT ["Smpl= ",DEC Value]
    LCDOUT $FE,$80,"Smpl= ",DEC Value,"    "
    GOSUB Average                                                  ; average it
    HSEROUT ["  Avg= ",DEC ADavg] ;   ,"  Avg2= ",DEC ADavg2,13,10]
    IF RejCount > 0 THEN HSEROUT ["  Rejected"]                    ; indicate if rejected
    HSEROUT [13,10]
    LCDOUT $FE,$C0,"Avg = ",DEC Value,"    "
    LCDOUT $FE,$94,"FC  = ",DEC RejCount,"    "
GOTO Main

' -=-=-=-=-=-=  Average Sample values -=-=-=-=-=-=-=-=-=-=
Average:
    IF Value = ADavg Then RejCount = 0 : RETURN  ; NoChange
    IF ABS (Value - ADavg) > FAspread OR Value < AvgCount Then FastAvg
    IF ABS (Value - ADavg) < AvgCount Then RealClose
    ADavg = ADavg - (ADavg/AvgCount)
    ADavg = ADavg + (Value/AvgCount)
    RejCount = 0
    GoTo AVGok
  FastAvg:
    RejCount = RejCount + 1
    IF RejCount = Reject + 1 THEN 
        ADavg = Value
        RejCount = 0
    ENDIF
    GoTo AVGok
  RealClose:
    RejCount = 0
    ADavg = ADavg - (ADavg/(AvgCount/4))
    ADavg = ADavg + (Value/(AvgCount/4))
  AVGok:
    Value = ADavg			' Put Average back into Value
  NoChange:
Return

[Ioannis]

What filters and what rules?

Darrel rules!

A masterpiece, if I may say.

Ioannis

[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!