Audio CDs...What is a DDP???

When supplying Audio files for manufacture there are a few things to get your head around. DDP/DDPi is a big one, then we start mentioning, 44.1KHz 16bit Stereo,  ISRC codes, CD text and PQ sheets making the entire affair seem like a secret club that has several handshakes to learn. It's not a secret club, it's just an education, so settle down class and we shall begin...

If you are a band or artist recording independently it's important to understand some of the process before we get to manufacturing because it can ensure a painless process - given some time, organisation and budget. Once you have your songs ready, one would naturally get excited to head to a studio, get in front of a microphone or plug in and record them. After that, they need to be mixed until you are happy with the result and for many this is done by the same engineer or studio. The result at this stage is a hopefully a perfectly listenable format that all involved are happy with and manufacturing is the next step. But wait...

...the next stage is often missed out or "included" in the mixing as a quick bolt on and that is the process of Mastering. The Mastering stage is why we are going back to these pre-manufacturing stages. It's an incredible important stage and (on several team members personal experiences) can change everything. Many first hand experiences  would advise using a separate specific specialist Mastering service aside from the Recording and Mixing, so that the audio is looked at objectively, but many studios do have reputable Mastering Services in house, so we suggest doing your homework and listening to some pre and post master examples from your studio to use the right avenue.

Firstly, in the right hands, this process can amplify your mixed recording 100 fold and even fix some parts of mixing that you may not be as happy with now you have listened on a few different speaker systems. This brings up the next positive for your audio's post mastering as the process focuses on achieving the closest possible listening experience across sound systems and really shows off the talent of your Mastering Engineer. It's worth mentioning here that a good Mastering Engineer will ask what format your music is for and will master it accordingly. Not only is the file type and composition of files different for CD, Cassette and Vinyl Mastering, but the dynamics are considerably different for each format too - but what has this got to do with all these file types and acronyms? In our experience with regard to the CD format, good Mastering Services manage all the file formatting for you in a process called "Authoring"  so it's a really good place to start when planning your recording because it can save far more time and pain later down the line if you can budget for it. Note, like many manufacturers, we can offering Authoring Services for customers in need, but we do not offer any Mastering Services. 

So the actual technical stuff then:

44.1KHz 16bit Stereo means...three different things. The simple bit is Stereo, meaning 2 channels of audio, one for left and one for right. Stereo Sound feeds sounds into each of our ears independently to create a virtual spatial awareness for the recording. In music, this is used to give the feeling that different sounds are in different places. For example a band with two guitarists often make one guitarist dominant in one ear and the other guitarist more dominant in the other ear to separate sounds and simulate a "live" scenario making it easier for the listener to hear both guitar lines clearly. Equally Drum kits often have their set-ups reflected in the stereo pair in such a way that you could even work out if they were left or right handed.

16 bit refers to dynamic range, or simply the volume range featuring the very quietest to very loudest and is capable of yielding a dynamic range of 65,536 different volume levels across 96Db.  Think of 16 bit as being the best best trade off between quality of information and file size. A form of resolution for sound. Imagine the early computer games industry where there was very limited storage space on game cartridges. They all have a similar sound quality as they were recorded at 8-bits to save space, but produced a lesser quality audio. The modern 8-bit Audio movement features some great uses of these low-fi tones, but for realistic audio playback, the 8bit obviously just doesn't give enough. 16-bit became the standard for quality sounding recording with "sensible" file sizes almost before the dawn of the disc.

44.1KHz then? So human hearing is capable of 20KHz and that basically means that we can hear and process 20,000 snapshots of audio in a second. Think of it like a flick book animation, or if you are familiar with it, the term "frame rate" in regards to a video. 44,1KHz is clearly over double the human hearing capacity, so high that any unwanted digital artifacts caused by minor data loss or mis- reading in the recording would be negligible in our ears. We understand this in Television by seeing the technology grow from graining, slightly static and jerky 50s black and white television sets to todays OLED 60" screens that don't miss a beat, showing smooth elegant images. For those interested, modern OLED television's operate a minimum of 120fps where as the human eye would detect flickering or strobing at 90fps or lower. Back to audio and the 44.1KHz is just the same principle, a high enough frame rate for us to experience smooth audio play back without interference.

International Standard Recording Code is your ISRC acronym unravelled and these are used to permanently identify audio tracks (even if bouncing between publishers) and can be used to distribute royalties to the proper creators - Very important in today's streaming platforms as it saves any guessing. The codes themselves are comprised of: 

• Country Code: 2 letters representing the country of the rights holder (e.g., GB for the UK)
• Registrant Code: 3 letters/numbers assigned to the record label or rights holder.
• Year of Reference: 2 digits representing the year the code was assigned.
• Designator: 5 digits assigned sequentially by the rights holder for that specific recording.

You can obtain ISRC codes wither through your distributor or, if you have a PPL account, through their portal. Each ISRC code represents a single recorded track. Those aware of "Taylor's Version" recordings in her legal battles for ownership will only need to dig a little to see that her tracks have different ISRC codes to the original ones. We are pleased she now owns all of them and this case demonstrates how these codes play an important part of the legal structure.

CD Text, although self explanatory for it's purpose still comes with the query of "How do I get it onto my disc so if shows up in every player?" A long time ago now, this was a bit like black magic, but as technology grows and generations pass, more and more people understand the term "Metadata" and CD Text is essentially metadata. To ensure the metadata is present it needs to be properly executed in the DDP using suitable CD Authorising Software and have an accompanying CDTEXT.bin file tying it all together. Note that some cheaper players don't play by the rules and can have difficulty displaying legitimate text information. There is no guarantee to get text onto every player out there, but this is the core method trusted by all major manufacturers.

A PQ sheet is simply a document showing the IRSC codes and other data associated with the production listing. Commonly it lists:

• Track Listing in order
• Index Points of when the tracks stop and start
• Pauses/Gaps if relevant
• ISRC Codes against each track
• Total Running Time

The PQ sheet is often contained within the DDP/DDPi as opposed to independent paper or digital documents that were present in times of old.

So we have rate, quality, type of audio and a load of data elements, so what on earth is a DDP/DDPi?? Well, it's the Disc Description Protocol, (obviously!) or Disc Description Protocol Image (Essentially the same thing) and is the standard format for manufacturing - it took a long time to get there but eventually a "standard" emerged! DDP is not a format, parse, but is actually a collection of files that are EVERYTHING  required for the CD to be produced. Generally speaking it does or can contain the following:

• Audio data,
• Metadata
• ISRC codes
• PQ subcode data

but MUST contain the following 4 parts to function:

• Audio image(s) (.DAT file(s))
• DDP Identifier (DDPID)
• DDP Stream descriptor (DDPMS)
• Subcode descriptor (PQDESCR)

The latter list is a little harder to comprehend, but essentially without them the file won't work. Simple things like a "0" or "1" in the wrong place can do things like loose the CD text data or even skip a track, so it is always best not to guess. If in doubt ask. No manufacturer would suggest cobbling the DDP together yourself unless you have a high understanding of all the elements and use of high quality Authoring Software.

Why not just send a copied CDR master to the factory? Well, manufacturers still can and do accept CD masters, .wav files and scrawled notes, but much like any other manufacturing, this is all about ensuring a good product and where the responsibilities between manufacturer and client lie. Copying a CDR comes with risks where the CDR itself does not necessarily keep a reliable set of files and can throw third party problems into the mix as CDR discs themselves can be of a lesser physical quality to other disc types. Equally a manufacturer can author the CD for you, but this carries the old human error risk or a lack of comprehension in the technical language between a customer and a manufacturer.

DDP Images are the way to convey a true image of the product from Mastering to Manufacture. As we visited at the beginning class, the advise will always be to have a look at your chosen Mastering Service and ensure they offer the whole package in Audio and Authoring services. It's the smoothest way to get your audio into production.