The Compact Disc was invented by Sony and Philips in 1981 in order to serve as a high-quality compact audio storage device which
allowed for direct access to digital sound tracks. It was officially launched in October 1982. In 1984, the Compact Disc's specifications
were extended (with the publication of the Yellow Book) so that it could store digital data. standards describing the ways in which
information must be stored on a compact disc, depending on how it is to be used. These standards are set out in documents called
books, each of which has a colour assigned to it:
This is the format used for encoding music on all commercial compact discs. If you buy a CD from a store, the music on that CD is stored in
CDA format. This means that the disc includes the encoding to bring it to the red book standard.
Digital audio material comes in many forms - Compact Discs (CD), MiniDiscs (MD), Digital Audio Tapes (DAT), Digital Compact Cassettes
(DCC) and Alesis ADAT.
When producing a compressed digital audio CD these files are written to disc just as they come and, depending upon the recording software
used, may be accompanied by MultiAudio or other navigational information. MultiAudio requires that, in addition to compressed digital audio
files, an appropriately formatted disc also must contain a defined table of contents (TOC) which the playing device will use for file navigation.
In addition, the specification allows playlists to be created to organize material so it can be accessed by categories such as genre, album,
artist or even in custom groupings (known as tagging) created by the user.
In the case of a Red Book audio CD, compressed files must first be uncompressed and translated into the correct format before recording.
Historically, this had to be accomplished manually but most recording software now performs the conversion process automatically during the
writing process. As with any audio recording it’s important to remember that the sound quality of a written disc will be no better than the source
Even though general purpose CD-R and CD-RW discs and their
consumer audio versions appear for all practical purposes identical, only blank media bearing the “Compact Disc Digital Audio
Recordable” (CD-DA Recordable) and “Compact Disc Digital Audio Rewritable” (CD-DA Rewritable) logos can be written in consumer
audio recorders. The reason for this restriction is to comply with international copyright agreements. A special Disc Application Code
present in the ATIP information of a CD-DA Recordable/Rewritable disc’s pregroove wobble identifies it specifically for audio use.
Consumer audio recorders (players) are programmed to reject discs not containing the correct code. This should be understood
that the audio quality on none-pressed CD-ROM discs will be compromised in comparison to the commercially produced pressed
audio CD-ROM discs.
Audio CDs do not use WAV as their sound format, using instead Red Book audio. The commonality is that both audio CDs and
WAV files have the audio data encoded in PCM. WAV is a data file format for a computer to use that can't be understood by CD players
directly. To record WAV files to an Audio CD the file headers must be stripped and the remaining PCM data written directly to the disc as
individual tracks with zero padding added to match the CD's sector size.
In the digital domain, PCM (Pulse Code Modulation) is the most straightforward mechanism to store audio. The analog audio is sampled in
accordance with the Nyquest theorem and the individual samples are stored sequentially in binary format.
The wave file is the most common format for storing PCM data.
The WAVE File Format supports a variety of bit resolutions, sample rates, and channels of audio. This is the most popular
format for storing PCM audio on the PC and has become synonymous with the term "raw digital audio." PCM and ADPCM are techniques
for storing analog audio data in a digital format, the Microsoft .WAV file. Other storage methods (for example, Mu- Law, A-Law, Transform
coding, CELP, and so on), are not supported by Windows Sound System 1.0. Higher resolution digital audio files obviously will produce better results.
Audio CDs have 8 subchannels of non-audio data interleaved with the audio data, called the P, Q, R, S, T, U, V, and W channels.
You can think of them as small, separate streams of data running alongside the audio, which can be read by a player at the same
time as the audio, if the player is "smart" enough to interpret them. For example, CD+Graphics discs (karaoke) store rudimentary
graphics and text in the subchannels, but you need a special player to read and display this information.
The P and Q channels are used to tell an audio player how to play back an audio disc. The Q channel contains the index markers.
In the pause (gap) before a track begins, the index marker is set to 0 (zero). When a track begins, the index marker changes to 1.
(If a track contains subindexes, these are incremented by 1 sequentially during the track. In this case the Q channel might contain
1, 2, 3, 4, etc.) When the track ends, the Q channel index marker goes back to 0, then re-starts at 1 when the next track begins.
Are identical in appearance to audio CDs (pressed), and data are stored and retrieved in a very similar manner (only differing from audio
CDs in the standards used to store the data). Discs are made from a 1.2 mm thick disc of polycarbonate plastic, with a thin layer of
aluminium to make a reflective surface.
The most common size of CD-ROM disc is 120 mm in diameter, though the smaller Mini CD
standard with an 80 mm diameter, as well as numerous non-standard sizes and shapes (e.g. business card-sized media) are also
available. Data is stored on the disc as a series of microscopic indentations. (Diagram below).
Layers of the CD disc.
TOC and CD text
Editing and burning software sometimes lets you specify a title and artist for each track – known as The Table of Contents (TOC).
There are CD players that support CD Text display the text during playback. You need to be writing in Disc-At-Once mode to enable
CD-Text writing. CD-Text is part of the CD+G extension to the Red Book standard for audio CDs. It allows for storage of additional
information (e.g. album name, song name, and artist) on a standards-compliant audio CD. You can cut a CD whose titles will be
read on a car player that reads CD text, but not on the computer, they don't read that information. The information is stored in the
lead-in area of the CD, where there is roughly five kilobytes of space available, in a format usable by the Interactive Text
Transmission System (ITTS). Information such as video material, pictures etc can also stored in the R through W Subchannels
on the disc, which are not used by strict Red Book CDs. About 31 megabytes of information can be stored there.
Is a writing mode that requires lead-in, program data and lead-out to be written in one (1) write event. Another name for this is "Single
Session" recording. All of the necessary information you wish to record needs to be staged on your computer hard disk prior to
recording in the Disc-at-Once mode. This mode is usually necessary for discs that are sent to a CD replication facility. By
recording in the Disc-at-Once mode, you eliminate the run-in and run-out blocks associated with multisession and packet
recording modes which often are interpreted as "uncorrectable" (E32) errors during the glass mastering process. The Lead-in Area
(sometimes called the LIA) only contains information which describes the contents of the disc (in the TOC, Table of Contents).
The Lead-in Area extends from a radius of 23 mm from the edge to a radius of 25 mm. This size is required by the need to be
able to store information about a maximum of 99 tracks. The Lead-in Area lets the CD player/drive follow the spiralling pits in
order to synchronise itself with the data found in the program area. The Program Area is the section of the disc which contains
the data. It starts 25 mm out from the centre, extends to a radius of 58mm, and can contain the equivalent of 76 minutes of audio
data. The program area can contain up to 99 tracks (or sessions), each at least 4 seconds long. The Lead-Out Area (or LOA),
containing null data (silence on an audio CD) marks the end of the CD. It starts at a radius of 58 mm and must be at least 0.5 mm
in width (radially). The Lead-Out Area must contain at least 6750 sectors, or 90 seconds of silence at minimum speed (1X). (Diagram below).
Track At Once. This method is used for disabling the laser between two tracks, in order to create a two-second pause between
each track on an audio CD.
Is the process of writing the lead-in and lead-out information to the disc. This process finishes a writing session and creates
a table of contents. "Fixation" is required for a CD-ROM or CD-Audio player to play the disc. When a disc is finalized the
absolute lead-in and lead-out for the entire disc is written, along with information which tells the reader not to look for subsequent
sessions. This final table of contents (TOC) conforms to the ISO 9660 standard, or the recent UDF protocol. This is not tagging,
it is a method of uploading the information of a commercially released CD to the database first.
Tagging music files
ID3 tags are not easily applied to WAV files. In general WAV and Broadcast wav use a different tagging system than mp3, AAC and FLAC.
So if you want to see these tags you won't see them in CD Text from an audio CD (CD-A). Your best bet is to convert them to a lossless
compressed format such as FLAC using Media Monkey or something similar and you can flag them in Media Monkey. This is for files on
your hard drive. If you release a CD commercially or a song, then there are ways to upload the tagging information to the Internet
Gracenote database where "the rest of the world" can see them, even when they insert the CD, as long as they are connected to the
internet. Again, this has nothing to do with CD text. Currently, Windows media player and Itunes do NOT read this information, even
if it is embedded in CD text. Try loading a CD from a music store with your internet connection to the PC turned off. It won't reveal it!
So it's not tagging, it is a matter of uploading the information of a commercially released (or to be released) CD to the database first!
You can cut a CD whose titles will be read on a car player that reads CD text, but not on the computer, they don't read that information.
CD duplication / replication
Replication is a professional process that creates a CD by molding the disk to be an exact copy of the original master. Data cannot be
added or changed in this case. Commercially purchased replicated CDs have already been pressed, meaning that the bumps have been
created using plastic injected into a mold which contains the desired pattern in reverse. A metallic layer is then affixed onto the polycarbonate
substrate, and this layer is itself covered with a protective coating.
Replicated discs will all be exactly identical, from the data down to the
physical layout of the microscopic dents in the plastic. Under a microscope, ignoring material flaws, they will appear exactly the same.
This is because CD Replication is the process of stamping data into an injection molded disc using a glass master. You cannot replicate
an existing disc unless you can obtain the very first original disc used as the master.
Most commercial compact discs are replicated
using a standard industrial process which is initially very expensive to deploy, yet a cost effective system for creating runs of approximately
1000 or more discs. Each stamped disc will be identical and have a longer shelf life as well as being of a higher quality than any disc created
by duplication. The dents in the plastic disc created by the stamped replication process tend to be more precise than the dents put into blank
CDR media by any CD ROM burning drive.
Duplication, on the other hand, refers to burning data to a disk, as is done in home computing. Blank CDs (CD-R) for duplication have
an additional layer (located between the substrate and metallic layer) made of a dye which can be marked (or "burned") by a high-powered
laser (10 times as powerful as the one used for reading them). It is the dye layer which either absorbs or reflects the beam of light emitted
by the laser. manufacturers recommend creating audio discs at reduced writing speeds while some recorders even limit their maximum
speed to 24x when writing audio discs.
In addition to slower recording speeds, some manufacturers also suggest using 74 minute instead
of 80 minute discs. And finally, just because you bought the commercial CD at the store doesn’t necessarily mean that it is a high quality
replicated disc. The company may have used a duplication appliance to create that disc since they planned on selling smaller numbers.
A professional duplication process typically involves a tower of many CD-R drives all chained together, attached to a PC with the master
data. So basically, it does the same thing as you do with your home computer when you burn a copy of a disc, except it burns many
copies onto CDR media at the same time, using many CD-R drives.
Preparation of the Premaster disc for Audio CD manufacture and replication.
This is the step between your final edit (sound mastering) and the making of a glass master, and a much confused term.
Music mastering is the physiological process of attempting to get the best sound out of your recording and producing the
cd as a whole. A premaster is a physical cd disk that has the finished production on in red book format. Another definition -
mastering is a process, that matches premastered audio material with the Demands of unified Pressing-Copying-Standards
to produce the master – or, -premastering is the process of transferring your source into the DDP format (Disc Description
Protocol, the standard specifically designed for optical disc replication) supported by the glass mastering departments of CD
The DDP format has taken over from the previous PCM format. Specific software will rewrite the CD-A files also creating
audio CD Images in conformance with Red Book standard. This in everyday terms means that all of the information required for a
CD player to understand what it has to do are written onto the disk in specific areas. This specialized program is usually only used
by replicating and duplicating businesses. Some of the steps below can be done in the music studio during the final mastering edit.
To prepare a premaster disc
Reading a CD disc.
A laser is shone onto the reflective surface of the disc to read the pattern of pits and lands ("pits", with the gaps between them
referred to as "lands"). Because the depth of the pits is approximately one-quarter to one-sixth of the wavelength of the laser light
used to read the disc, the reflected beam's phase is shifted in relation to the incoming beam, causing destructive interference and
reducing the reflected beam's intensity. This pattern of changing intensity of the reflected beam is converted into binary data. Audio
CDs do not contain a third layer of error correction codes, recording these at high speed may result in more unrecoverable errors or
'clicks' in the audio.
- If needed, trim the songs, redo the fadeouts, adjust the levels, remove noises, resequence songs.
- Leveling the songs so the loudness is even from song to song (Note that the "normalising" that some computer programs do is almost totally
useless and pointless. The ear and skill must be used to judge loudness). Check if volume level falls into the standard range: peaking below 0db.
- Resampling to 44.1 kHz.
- Ensure the songs are properly identified as to their start and stop times.
- PQ codes are inserted to mark the start and stop points of the CD and
- Supply the UPC - Universal Product Code your barcode which can be made at a place called GM1. With some CD recorders,
you may define a thirteen-digit UPC catalog number for the entire disc, which will be written in the disc's Table of Contents. Also known as EAN.
- Supply a 6-digit Amtech order number if required (marketing)
- Supply the ISRC code, believe it or not another identifying code as follows. The ISRC (International Standard Recording Code) is the
international identification system for sound recordings and music videorecordings. Each ISRC is a unique and permanent identifier for a
specific recording which can be permanently encoded into a product as its digital fingerprint. Encoded ISRC provide the means to
automatically identify recordings for royalty payments.
- Supply the CD-Text data. This will be your song names and order of play.
Manufacturers of CD writers (CD-R or CD-RW) are encouraged by the music industry to ensure that every drive
they produce has a unique identifier, which will be encoded by the drive on every disc that it burns: the RID or Recorder Identification
Code. This is a counterpart to the SID—the Source Identification Code, an eight character code beginning with "IFPI" that is usually
stamped on discs produced by CD recording plants.
International Std Recording Code
This code is used only on CDs that are destined for commercial distribution. ISRC codes have 12 characters and use the following format-
- ISO Country: 2 digit code (for example, US for USA).
- Registrant code: 3 digit alpha-numeric, unique reference.
- Year of reference: last 2 digits of the year (for example, 04 for 2004).
- Designation code: a 5 digit, unique number.
CD replication - disc coding
Matrix Information: Matrix information is the letters and numbers printed on a compact disc in the mirror band close to the center hole of the CD.
Matrix information may be printed to be read from the top side (label side) of the CD, while other matrix information may be printed to be read from the
bottom side of the CD. In some instances, matrix information is printed on both the top and bottom sides of the disc, with the bottom side matrix
information being the mastering information, and the top side matrix information being the pressing information. In other instances, both the
mastering and pressing information is printed on the same side of the disc.
The following matrix band information can be found on most compact discs:
Mastering Code -
- Catalog number - The identifying number given to the release by the record company.
- Manufacturer - On some CDs, on the plastic hub around the center hole (not on the shiny part of the disc), there is imprinted information
about the disc manufacturer. (In this discography, this information is indicated in brackets.)
- Manufacturer's Work Order Number - This often is in the form of the scan code that can only be read by a special scanner.
- Pressing Plant - Pressing plant information is often found in the matrix, either as a part of the SID Code or as an abbreviation.
- SID Codes - On many CDs, there are two Source Identification Codes (SID Code) in the matrix band. The SID Code, which was introduced
in April 1994, consists of the letters IFPI (which stands for the International Federation of the Phonographic Industry), followed by 4 or 5
additional characters. There are two different SID Codes found on CDs:
The first SID Code in the matrix band is the "Mastering Code." The Mastering Code begins with "IFPI" followed by a
sequence of digits beginning with the letter L, followed by two numbers that indicate the pressing plant, and then 1 or 2 additional digits
that indicate the Laser Beam Recorder (LBR) that cut the glass master. The Mastering Code is put on the CD at the time the glass
master of the CD is cut by the LBR, and it appears on all subsequent pressings of the CD sourced from that specific glass master.
Mould Code -
The second SID Code on a CD is the "Mould Code." The Mould Code begins with "ifpi" followed by two digits that indicate
the specific pressing plant that pressed the disc, and two additional digits that indicate the unique mould or stamper that pressed the CD.
SID Mould Codes, which indicate where a CD was stamped or pressed
Block Error Rates
Software that will read your disc to determine the extent of Block Error Rates (BLER) and Burst Error Rates (BUR) on your disc -
(KPROBE). All of these hardware and software solutions will tell you if E32 errors exist on the disc. The mastering facility will
require you to verify that there are no "uncorrectable" or E32 errors on the CD-R that you provide.
Some all-purpose software is adequate enough if you are burning CD-Rs for your own library.
However, if your intentions are more professional you may need more powerful software. For instance, a CD replicator (such as Sony's DADC)
needs a "glass master" to faithfully reproduce professional retail-ready CDs. These "glass masters" are created from your desktop CD-R with
the proper software. Toast CD-DA from Adaptec is one such program. There`s also "mastering" software from Sonic Solutions.
The first stage of disc manufacture involves the creation of a glass master and then from that glass master, one or a series of stampers.
Data from the original client master is loaded onto a mastering system hard disk. The mastering software then compares the data to a
variety of industry format standards (red book for audio CD, yellow book for CD-Rom etc) to determine whether the data has been correctly
formatted. If the data is not correctly formatted it is rejected, as any disc created from this information will not play on the intended player
(e.g. standard audio CD player).
Preparation of the 20 cm (8 inch) diameter 6mm thick glass master starts by stripping the old photo-resist
from its surface (since the glass blanks can be recycled). This is followed by cleaning and final washing using de-ionized water. The blank
master is then dried carefully and ready for the next stage. The surface of the clean glass master is then coated with a photo-resist layer
150 microns thick by spin coating. The uniformity of the layer is measured with an infra red laser.
The photo-resist coated glass master is
then baked at about 80 degrees Celcius for 30 minutes. This hardens the photo-resist layer ready for exposing by laser light. The photo-resist
is exposed where laser pits are to be burned in the final disc. The photo-resist surface is then developed to remove the photo-resist exposed
by the laser and therefore create pits in the surface. These pits should extend right through the photo-resist to the glass underneath to achieve
good pit geometries as specified in the Red Book. The glass itself is unaffected by this process.
The active surface (called the "father" -
containing pits) of the developed glass master is then metallized either with silver by evaporation or a nickel or nickel alloy created by sputtering.
The glass master is then played on a Disc Master Player (DMP) to check for any errors. Audio masters are actually listened to at this stage.
A nickel stamper plate results from the metallic layer to form a robust image of the original data set, suitable to place in an injection moulding
line. A reverse image of the stamper can also be taken, with a view to creating several subsequent stampers. Depending on the quality of the
nickel stamper used, a single stamper can be used to replicate up to (approximately) 30k to 50k discs.
The final stage is then making the
reverse image stamper or "mother". The STAMPER edges are then trimmed and the reverse side is polished. The STAMPER is optically
centered and a hole is accurately punched. It is then mechanically formed to fit the record press mold block. The STAMPER is a negative
image and is used to press records.The mother is then form-pressed onto the extruded "children" membranes using high speed hydraulic
presses. This membrane will ultimately contain all the binary information used to play the disc.
Replicated CDs are mass-produced using an injection molding machine. Small granules of raw polycarbonate plastic are fed into the
press while under heat. The liquefied plastic is forced under high pressure into the mold cavity, with the metal stamper forming part of
the cavity. The plastic is allowed to cool and harden.
Once opened, the disc substrate is removed from the mold by a robotic arm, and
moved onto the next stage of production. The cycle time, the time it takes to "stamp" one CD, is usually 2–3 seconds. This method
produces the clear plastic blank part of the disc. After the metallic layer is applied to the clear blank substrate, the disc is then
lacquered and dried.
Optical tests are then performed on the disc in a final pass to search for surface defects and test reflectivity.
A portion of discs are rejected, and the good discs passed onto metal spindles ready for printing.
Commercial Audio CD pressing labs.
When CDs were first manufactured, each stage of disc production took place in a different machine with the discs being manually
transferred between each stage of production. A clean air static free environment was required, which added to the high cost of early
manufacture. As equipment improved, the disc replication process has become more automated, with completed (but unprinted) discs
being produced in a single pass through the molding line and attached finishing station.
Audio disc burning
It has become possible for the home musician or programmer to burn their own CD roms (Read only memory discs), using a CD rom burner,
thus making a duplication.
The main difference between a data CD rom and Audio CD rom is that using interpolation, (a mathematical method of compensation), audio
players can adjust for errors in the retrieval status, while data CD roms write in error correction (as per Mode 1 & Mode 2 standards). PC based
conventional reader/writers do not have audio correction. Interestingly this process is employed to induce copy protection errors into the audio
CD rom that cannot be read by conventional CD rom burners.
Audio disc burning - software
Most audio CD-ROM disks use an AutoPlay feature. This enables convential PC operated CD rom writer / players to play a duplicated audio CD.
That is, when the CD-ROM disk is inserted into a Windows system it automatically loads and executes a program of the manufacturer’s choosing.
The CD-ROM device driver that comes with the system is notified when the user inserts a disk into the CD-ROM drive. When the driver receives
this notification, it tells the system, which immediately looks in the root directory of the CD-ROM disk for a file called AUTORUN.INF, which
stands for "Automatic Run Information." Windows then executes the instructions contained in AUTORUN.INF, typically loading a program
stored on the CD-ROM disk.
However, AutoPlay can also load Internet Explorer or some other program stored on the C: drive. If placed in the
root directory of a CD-ROM disk, this three-line file will cause the program SETUP.EXE on the CD-ROM disk to be automatically loaded and
started whenever the disk is inserted into the CD drive.
You can easily create such a file with Windows Notepad or any other ASCII text editor. However, for a bit more sophistication, you might want
to use one of the several free programs that will create AUTORUN.INF files for you.
`Gear software`, also enables the user to add the necessary data for a disk to become a CD rom – note that these disks will then only
operate as specified by the data that is added to the base information that is to be placed on the disk, an example being a PC gaming
CD. Thus copy security can be written into the disk.
Here`s how it works; A CD-ROM disk comprises an identifier region having a disk
identifier recorded in a security code region. The identifier region and the security code region are provided in one sector of a boot
sector to be read when actuated. The disk identifier includes a preset identification code, and the security code includes at least a
program to be executed after check of the security code, and display data for displaying a license. The disc reader compares what
it sees on the disc with the security code information.
Although this article has been fairly detailed, it will cover the home musician for all of the trials that they will require to pass through the barrier
to professional audio cd disk production. Many smaller labs are in an ideal situation to take the home studio musician under their wing and
release them with 100 plus copies of their origonal music. We havent touched on the subject of the CD disc casing printwork - this can be
added at a later stage to complete the package.
Finally a new method of distributing music in a high audio quality format has given conception to the DVD Audio specification.
Specialist audio suppliers are already supplying audi on DVD with a high sampling and bitrate in an attempt to bridge the audio gap
that exists between analogue and digital music formats.
The base-case DVD-Audio disc is one that contains no graphics, text or motion video
information. This “Pure Audio” disc supports higher fidelity, greater capacity and more
channels than a CD, but it functions in much the same way, with similar track-based
navigation. Pure Audio discs play on both Audio-only and Universal DVD-Audio players,
but they do not play on DVD-Video players.
The core content type of the DVD-Audio format is, obviously, audio. While the DVDVideo
specification gives equal weight to both linear PCM (pulse code modulation) and
compressed audio formats such as Dolby Digital (AC-3), the DVD-Audio specification
puts the priority on delivering the highest possible audio fidelity, and thus focuses
primarily on PCM.
DVD-Audio’s PCM support covers two “families” of sample-rates. One family is based on
the 44.1 kHz rate of the audio CD, and also includes the multiples 88.2 and 176.4
kHz. The other family starts with the 48 kHz rate commonly used in video formats, and
adds 96 and 192 kHz.
DVD-Audio also includes support for several word-lengths, including not only the 16-bit
samples used in CD-Audio, but also 20- and 24-bit samples as well. A longer wordlength
translates into finer resolution and a wider dynamic range.
In order to maintain the highest quality digital audio, 24 bit / 96khz sampling, and to enable multichannel playback
with the same playing time as a conventional CD, Meridian Lossless Packing (MLP) compression system was adopted.
This will enable 74 minutes playing time in these circumstances.