In recent years DDP images have become a popular format for supplying CD masters, one of the advantages of a DDP image is that it can be transferred over the internet as a data file. However if you wish to send your master as a DDP image to your CD manufacturing company, you will be asked to supply an MD5 checksum of the the files, and if you are not asked for one, consider using another company.
WHAT IS AN MD5 CHECKSUM AND WHY IS IT SO IMPORTANT FOR DDP IMAGES?
For our purposes an MD5 checksum is important as it allows us to check the integrity of the data once it has been transferred. When you create an MD5 of the files used in the DDP image you are basically taking a fingerprint of the files, once file has been downloaded on the receiving end the recipient creates an MD5 file of the same files their end. If the senders and the receivers MD5 checksums match, then we can be assured that the file transfer has been successful and the data is an exact match.
Without this checking stage it is not possible to be confident that the data has not corrupted during the transfer. If an upload or download ends prematurely, that would result in audio being missing from the master. Or data corruption could result in a glitch or loud pop in the audio.This is why it is so important that you as the sender and the CD pressing plant as the receiver insist on using MD5 checksums.
How do I make an MD5 checksum?
Some CD mastering software automatically creates the MD5 checksum at the same time as the DDP image. In your DDP folder you should check to see if you have a text file that contains the text “MD5” or sometimes “Checksum”, or has the extension “.md5”. If your folder does not have a file with a name similar to this, then you will probably need to create an MD5 of the files.
A quick web search will come up with quote a few applications for PC and Mac that are free and will create the checksum files for you. However to make life a little easier for you I have given links below to download two of the easiest to use programs available.
Which files in the DDP need an MD5 Checksum?
This will vary from company to company, some may require a checksum of all of the DDP files, some may only need the “AUDIO.DAT” or “IMAGE.DAT” (the actual file name will depend on the software use to create the master). You may be able to compress the entire folder into 1 ZIP file and supply an MD5 of the ZIP folder.
You are best checking with the company manufacturing your CD’s what they prefer before supplying the DDP files. At Pure Music we would like an MD5 of each file or a an MD5 of a ZIP file containing the DDP image.
How to use MD5 for PC
Once you have downloaded the link, unzip the folder and double click on MD5 For PC to launch the application. All you now need to do is simply drag the file that you want to create the MD5 of and drop it into the application window. The software will create the MD5 checksum. Now you can go to the “Edit” menu and select “copy”. You can now paste this MD5 into a text document to save with your DDP image.
How to use DropHash for Mac
Once you have downloaded the link, unzip the folder and double click on DropHash to launch the application. You will need to make sure the section called “Hash” is set to MD5, by default it is set to SHA/1.
All you need to do is simply drag and drop the file that you want to create the MD5 of into the application window. The software will create the MD5 checksum. Now you can go to the “Edit” menu and select “copy”. You can now paste this MD5 into a text document to save with your DDP image.
Sending audio data files over the internet.
If you are sending audio files over the internet we recommend using an MD5 checksum, as the you maybe sending a large amount of files I would recommend compressing all of the files into 1 ZIP folder before uploading, and sending the resulting MD5 in a text file or email.
Go forth and multiply!
So now you know what an MD5 checksum is and how to make an MD5 file, you can go forth and send you master all over the world with confidence that it will sound just as good as when you created it. One final word of advice, this article covers general good practice in supplying MD5 checksums and DDP images, however if you are not using Pure Music for your CD Replication, then please check with your supplier on their particular requirements for supplying DDP images.