Welcome to part 1 of my new series of blogs to help musicians from a non engineering background understand some of the things they will encounter with audio formats. First up is CD Audio.
First of all, so we have an understanding of how CD Audio differs to other consumer formats, we will look at the specifications for CD Audio, which are as follows:
2 Channel Stereo Audio
Sample Rate : 44.1kHz
Bit Depth : 16 Bit
Length (Recommended by Sony) : 74 minutes
Length (Theoretically possible) : around 85 minutes (most plants will reject anything close to this!)
Maximum Track Count : 99
What is the disc itself actually made up of?
The data on a CD is split into three parts:
1. Lead In – This contains the Table of Contents, which is easiest described as the index of the tracks on the CD
2. Program Area – Where the audio data is contained
3. Lead Out – describes the last area of non audio data stored on the CD
What IS a “Red Book” CD?
“Red Book” describes a compact disc which conforms to the original CD Audio standards developed in 1980 by Sony and Phillips. Non Red Book conforming CDs will play on most CD players, although some of the specifications deal with the physical capacity of a disc (length of audio), and non-conforming lengths are not guaranteed to play back on all systems.
The “Red Book” standard is the officially recognised standard by the IEC for consumer and duplication systems.
The name comes from the original manual for CD-DA standards used by engineers and designers which had a red cover, apparently!
The term for this format was originally CD-DA (Compact Disc – Digital Audio), but some times you see Audio CD or simply just CD being used on sales descriptives for this format.
Almost all the CDs you will have ever bought for music will be CD-DA, although they are various additional formats which came after the initial wave of commercial CD.
What non audio data can be added to a standard audio CD?
CD Text is a specific addition to the Red Book standard which allows extra user defined text to be displayed on compatible players.
The correct name for data within a CD Audio master which isn’t audio is its “meta-data”.
CD Text allows these to be displayed on CD Text compatible CD players and computer audio programs.
Areas of the user definable additional meta-data available on a modern CD Audio product are:
Product identifying information –
UPC/EAN (or Bar-code, for entire CD):
ISRC Code (per track on CD):
CD Text information –
What is a DDP?
DDP stands for “Disc Description Protocol” and is a file set format used for the delivery of audio CDs. We use these as they are not prone to errors like transferring audio files via the internet and re encoding them without being able to check to CD Audio at the last stage and errors such as can occur in physical CDr masters.
It is a folder (often in a ZIP or RAR when delivered) and must contain the following:
Audio image(s) (.DAT file(s))
DDP Identifier (DDPID)
DDP Stream descriptor (DDPMS)
Subcode descriptor (PQDESCR)
These are all created by the mastering software and are not adjusted by the recipient.
Sometimes an additional text file (often called a PQ read out or Cue) can be founding inside these folders for checking against the resulting manufactured CD.
You cannot play a DDP like an audio file!
Most DDP programs allow us to create digital masters which correspond exactly with the DDP as a reference. This plus a text file allows you to confirm the information inside the DDP without actually playing or accidentally damaging it!
HOFA are an excellent company for mastering software and provide a DDP player, which is also great for reading back DDPs where they are the only surviving master.
Although digital streaming services currently outnumber CD in term of consumer usage they very much still exist and are part of the audio product market. I hope now people who are not audio engineers and technicians have a good idea of the language and technologies applied!