It's all up there in black and white, but we'll be happy to spell it out again here -- it seems that Apple has decided to extend the length of iTunes song previews from 30 seconds to 90 seconds. Sounds just fine to us, but not to the recipients of this letter, who are told the change is happening whether they like it or not and it's for their own good. "We believe that giving potential customers more time to listen to your music will lead to more purchases," the document reads, but without giving the music labels any way to say no. We don't actually know the origin of this particular document, so we're not saying this is a done deal by any means, but if the letter's legit you're looking at the world's largest online music store telling the labels to put up and shut up -- or else peddle their tunes somewhere else.It's worth noting that CNET reported that iTunes song previews might double in length about two months ago.