>> > Two cascaded single pole filters each with a filter fraction of 1/256 > A divide by 256 is a shift right of 8 bits, which is just moving bytes around > new filt val = - /256 + /256 This looks so simple but something goes terrible wrong for me ... << See my response to your other post. I was out of town for two days, which is why I am only replying now. Please switch your mailer to send as PLAIN TEXT only. You are apparently sending MIME-encoded text. I am using Outlook Express, and it won't put the ">" in front of the text I'm replying to when it is MIME encoded. I'm getting tired of manually adding the ">" in front of your text lines. I have some specific things to say about your message below, but I'll wait until you stop using MIME encoding. ******************************************************************** Olin Lathrop, embedded systems consultant in Littleton Massachusetts (978) 742-9014, olin@embedinc.com, http://www.embedinc.com -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.