Hi,

Edson Brusque wrote:
>    some months ago Olin posted the formula that changed DSP world: :)
>        Filt <-- Filt + (New - Filt)*FFrac
>
>    Saddly, my 8 bit implementation have a problem that I can't
surpass:
>        filt =3D filt + ((sig16)new - (sig16)filt) / 2;
>
>    The value never goes to 255 because of integer roundings:
>        filt =3D 254 + (255 - 254) / 2;
>        filt =3D 254 + (1)/2;
>        filt =3D 254;
<snip>

Well this is one of the drawbacks with (standard) IIR filters, you're
only
affecting 1/x part of the difference to the output each pass.
In this case it easy:

Change:        Filt <-- Filt + (New - Filt)*FFrac

to:         Filt <-- Filt + (New - Filt)+1*FFrac

Assuming you truncate the result.
If FFRac is of another magnitude then change the '1' to
reflect it, i.e. FFRac=3D4 means that you should add 2 instead.
( i.e. an 'halfbit' of the output ).

/Tony

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body