On Aug 12, 2010, at 5:58 AM, Olin Lathrop wrote:

> FILT <-- FILT + FF(NEW - FILT)
>
> And voila, we have the basic standard digital low pass filter =20
> algorithm
> from Digital Filtering for Dummies Made Easy 101.

That was lovely.  Thanks!

Rather than talk about digital low pass filters, this is easily =20
related to the simple averages we all learned in grade school.  The =20
average of N samples of a signal is simply:

   S1 + S2 + ... + Sk
   ------------------
            k

Which can be re-written:

   S1 + S2 + ... + S(k-1)       Sk
   ----------------------  +   ----
             k                   k

Now, if you already have an existing average value ("FILT"), this =20
becomes exactly Olin's earlier equation:

>            (K-1) * FILT   NEW
>            ------------ + ---
>                  K         K

So you can give it new names, but you're really just computing the =20
average of the last N samples.  (now, if there's a lot of difference =20
in samples, you might notice that recent samples have more "weight" =20
than older samples, but that's just a little detail...)

BillW

--=20
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