This may be of interest to the Picaxe community - judging from the number of times someone asks about how to choose reasonable parameters for PWM frequency and low pass filter:
http://www.designnews.com/author.asp?section_id=1365&doc_id=238089&cid=NL_Newsletters+-+DN+Daily
Wolfgang
http://www.designnews.com/author.asp?section_id=1365&doc_id=238089&cid=NL_Newsletters+-+DN+Daily
Wolfgang