I ment CTDT!

Been reading the Stephen Desper thred and i came across this interesting technique for recording vocals but,for the life of me,i just can't get a grip on it.How do you record something using CDTD?I know it's been covered in Sthepen's book.I tried to contact Mr.Desper to buy the book but he is not answering my e-mails.Can anyone help me on this matter?

Thank you