Often a source of confusion is the .cda file. On a windows computer, when you insert a RedBook Audio CD, the tracks show up as .cda files. One might assume that these are the audio files on the disc because they are the only items that show up in the explorer window. . . that would be wrong. The .cda files are merely placeholders pointing to a place on the CD that the song starts.
This has to do with how audio, especially digital audio, is arranged and stored.
In the past few months, we've had several requests for masters to be sent over the internet to the manufacturing plant. DDP is the perfect format for this. Many plants will give you FTP information to send the DDP master to their facility or a login to a webpage that you can upload the file. I like this trend and recommend this for clients that have chosen replicators that accept DDP masters.
Red Book is the name given to the compact disc digital audio format.