Re: Moving average filter ...


It looks like you are trying to invent a 1-st order exponential averager:

y += (x - y) >> shift

This is not the same thing as the moving average, although it is certainly useful algorithm.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com






group@xxxxxxxxxxxxxx wrote:
Hello -

I'm trying to implement a 'smart' moving average algorithm, which
consumes as little memory (RAM) as possible.

Imagine two 8bits registers reg_8_hi and reg_8_lo. These two registes
can be combined into a 16bit register, reg_16.

Algortihm is;

1 - Samples are added to reg_16.
2 - High order of reg_16, reg_8_hi is subtracted from reg_16.
3 - Average value is high order of reg_16, reg_8_hi.
4 - Registers are preloaded with reg_8_hi = 127, and reg_8_lo = 255.
Which is 'best guess' on average.

Code:
void MovingAvg(uchar sample)
{
reg_16 += sample; //add sample

reg_8_hi = reg_16 >> 8; //get high order
reg_16 -= reg_8_hi; //subtract high order from total

reg_8_hi = reg_16 >> 8; //new high order (average)
reg_8_lo = reg_16 & 0xFF; //new loworder
}

A statement is that # of samples is size of reg_8_lo (8 bit = 255
samples),

Questions are now:

1 - is this a valid moving average algortithm ?

2 - does this algorithm have a name ?

3 - if I need lower number of samples can this algorithm be changed
to; reg_8_hi and reg_3_lo. Which would then give me 8 samples.
Reason for this question is that if I do;

Code:
void MovingAvg(uchar sample)
{
reg_16 += sample; //add sample

reg_8_hi = reg_16 >> 3; //get high order
reg_16 -= reg_8_hi; //subtract high order from total

reg_8_hi = reg_16 >> 3; //new high order (average)
reg_3_lo = reg_16 & 0x07; //new loworder
}

I get an error on the average calculation, which I'm not really able
to compensate for.

Any comments ?


Best regards
.

Relevant Pages

  • Re: Moving average filter ...
    ... - is this a valid moving average algortithm? ... - does this algorithm have a name? ... not an FIR. ... I like to think of these things as an approximate digital RC filter - they have a similar effect on the signals, and are just as easy to implement. ...
    (comp.arch.embedded)
  • Re: Moving average filter ...
    ... Algortihm is; ... - is this a valid moving average algortithm? ... - does this algorithm have a name? ... "Applied Control Theory for Embedded Systems" gives you just what it says. ...
    (comp.arch.embedded)
  • Moving average filter ...
    ... Algortihm is; ... void MovingAvg ... - is this a valid moving average algortithm? ... - does this algorithm have a name? ...
    (comp.arch.embedded)
  • Re: Efficient Moving Average and Moving Variance Calculations
    ... efficient algorithm for computing a moving average. ... algorithm for computing "moving variance": ... Overwrite oldest value in X1 history buffer with X1. ...
    (comp.dsp)
  • Efficient Moving Average and Moving Variance Calculations
    ... efficient algorithm for computing a moving average. ... Overwrite oldest value in X1 history buffer with X1. ...
    (comp.dsp)