I read a bunch of discussion about the low pass filter on the lame maillist a while back. I can't remember all the specifics exactly though. Setting the lowpass a bit higher might not be a bad idea though...still kinda safe. I wish I could remember why they lop off the top, but I seem to recall that the main reason is to speed up the encoding process and reduce file size. those high frequencies might require more bits...etc... but more importantly, they definitely require more CPU cycles to compress...