Note: Descriptions are shown in the official language in which they were submitted.
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THE COPY PROTECTION OF DIGITAL AUDIO COMPACT DISCS
The present invention relates to a method of copy protecting a digital
audio compact disc, and to a copy protected digital audio compact disc.
s
Digital audio compact discs (CD-DA) which carry music or other audio can
be played or read by more sophisticated apparatus, such as CD-ROM drives.
This means, for example, that the data on a CD-DA acquired by a user may be
read into a PC by way of its ROM drive and thus copied onto another disc or
'.o other recording medium. The increasing availability of recorders able to
write to
CDs is therefore an enormous threat to the music industry.
The present invention seeks to provide a method of copy protecting a
digital audio compact disc.
According to a first aspect of the present invention there is provided a
method of copy protecting a digital audio compact disc, wherein control data
usable by a data reader is encoded on the compact disc, the copy protection
method comprising the step of rendering selected control data incorrect and/or
zo inaccurate.
With an embodiment of the invention, the incorrect data encoded onto the
CD is either inaccessible to, or not generally read by, an audio player.
Therefore, a legitimate audio CD bought by a user can be played normally on an
zs audio player. However, the incorrect data renders the CD unplayable by a
data
reader. This prevents copying of the data on the compact disc.
Of course, by rendering the audio compact disc unplayable on a data
reader, the user is also prevented from using a CD-ROM drive, for example,
30 legitimately simply to play the music or other audio on the disc.
In this specification the term "audio player" is used to refer to players and
drives arranged to play the audio data on a digital audio compact disc. Such
players will generally be commercially available CD music players which
function
3s solely to play the music or other audio on the CD. It is required that the
incorrect
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data encoded onto the CD does not generally impinge on, or affect the norms!
operation of, such an "audio player".
In this specification, the term "data reader" is used to refer to all players
s and drives which are able to read the data on the disc, for example, by
extracting or otherwise accessing the data on the disc. Such players will
include, therefore, CD-ROM drives. Generally, and as acknowledged above, a
CD-ROM drive, for example, will not only be prevented from making a usable
copy of a legitimate CD-DA, but will generally be prevented from playing a
~o legitimate CD-DA.
In one embodiment of a method of the invention, the data encoded on the
compact disc which has been rendered incorrect is navigation andlor timing
data.
is
For example, data identifying the position on the disc of the Lead-Out is
rendered incorrect in the Lead-In of the disc. Thus, data in the Lead-In which
indicates the Atime at the start of the Lead-Out may be rendered incorrect.
For
example, the data in the Lead-In may show the Atime at the start of the Lead-
2o Out to be zero. Alternatively, the data in the Lead-In may have a value for
the
Atime at the start of the Lead-Out which occurs during a first audio track on
the
compact disc.
Additionally and/or alternatively, the data on the CD defining the nature of
zs the tracks is rendered incorrect.
In a preferred embodiment, the data on the CD identifying the nature of
the tracks incorrectly identifies each audio track as a data track.
3o In a preferred embodiment of a method of the invention, the data encoded
on the disc which is rendered incorrect is data in the Table of Contents (TOC)
of
the compact disc.
Preferably, the control data encoded on the compact disc is altered, to
3s render it incorrect, prior to mastering of the disc.
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The present invention also extends to a copy protected digital audio
compact disc, wherein control data usable by a data reader is encoded on the
compact disc, and wherein selected control data has been rendered incorrect
andlor inaccurate.
s
Preferably, the incorrect data encoded onto the compact disc is either
inaccessible to, or not generally read by, an audio player. This enables the
copy
protected disc to be played normally on an audio player. However, the data
encoded on a copy protected compact disc renders the disc generally
io unplayable by a data reader. This prevents the use of a data reader to
extract
or read the data on the disc, whereby copying of the disc is also prevented.
Of
course, it is no longer possible to use a CD-ROM drive, for example, to play
the
audio on a legitimately acquired copy protected disc,
1s In an embodiment, the incorrect control data on the copy protected disc is
navigation and/or timing data.
For example, incorrect control data is provided in the Lead-In, and
identifies the position on the disc of the Lead-Out. Thus, the incorrect
control
zo data in the Lead-In may indicate incorrectly the Atime at the start of the
Lead-
Out. For example, the incorrect control data in the Lead-In may show the Atime
at the start of the Lead-Out to be zero.
Alternatively, the incorrect control data in the Lead-In may have a value
zs for the Atime at the start of the Lead-Out which occurs during a first
audio track
on the compact disc.
Additionally and/or alternatively, a copy protected digital audio compact
disc of the invention may have incorrect control data encoded onto the disc
3o which defines the nature of the tracks on the disc.
In an embodiment, the incorrect control data incorrectly identifies each
audio track as a data track.
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A copy protected digital audio compact disc of the invention may have
incorrect control data encoded thereon which is control data in the Table of
Contents (TOC) of the disc.
s Embodiments of the present invention will hereinafter be described, by
way of example, with reference to the accompanying drawings, in which:
Figure 1 shows schematically a compact disc showing the spiral data
track,
3o Figure 2 shows the structure of a frame of data encoded on a CD,
Figure 3 illustrates the general data format of the Q-subchannel,
Figure 4 shows the format of the data for the Q-subchannel according to
mode,
Figure 5 shows graphically both Atime and Ttime on a compact disc,
s Figure 6a shows an example of the track definition, with the Table of
Contents, of a CD-DA, and
Figure 6b shows the Table of Contents of the CD-DA of Figure 6a when
the disc has been copy protected.
:?o A digital audio compact disc (CD-DA), which carries music and is to be
played on an audio player such as a conventional CD disc player, is made and
recorded to a standard format known as the Red Book standards. As well as
defining physical properties of the disc, such as its dimensions, and its
optical
properties, such as the laser wavelength, the Red Book also defines the signal
2s format and the data encoding to be used.
As is well known, the use of the Red Book standards ensures that any
CD-DA produced to those standards will play on any audio player produced to
those standards.
Figure 1 shows schematically the spiral track 4 on a CD 6. This spiral
track 4 on a CD-DA is divided into a Lead-In 8, a number of successive music
or
audio tracks as 10, and a Lead-Out 12. The Lead-In track 8 includes a Table of
Contents (TOC) which identifies for the audio player the tracks to follow,
whilst
3s the Lead-Out 12 gives notice that the track 4 is to end.
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An audio player always accesses the Lead-In track 8 on start up. The
music tracks may then be played consecutively as the read head follows the
track 4 from Lead-In to Lead-Out. Alternatively, the player navigates the read
head to the beginning of each audio track as required.
5
All compact disc players and readers are programmed not to move the
read head beyond the start of the Lead-Out track 12. This is to protect the
read
head.
io To the naked eye, a CD-ROM looks exactly the same as a CD-DA and
has the same spiral track divided into sectors. However, data readers, such as
CD-ROM drives, are much more sophisticated and are enabled to read data,
and. process information, from each sector of the compact disc according to
the
nature of that data or information. A data reader can navigate by reading .
is information from each sector whereby the read head can be driven to access
any appropriate part of the spiral track 4 as required.
To ensure that any data reader can read any CD-ROM, the compact discs
and readers are also made to standards known, in this case, as the Yellow Book
2o standards. These Yellow Baok standards incorporate, but extend, the Red
8aok
standards. Hence, a data reader, such as a CD-ROM drive, can be controlled to
play a CD-DA.
The ability of a data reader to access, extract, or otherwise read the data
zs on a CD-DA provides a problem for the music industry. A user can use a CD-
ROM drive to read the data from an audio disc, for example, into a computer
file,
and then that data can be copied. The increasing availability of recorders
able
to record onto compact discs means That individuals and organisations now
have easy access to technology for making perfect copies of audio compact
3o discs. This is of great concern to the music industry.
An audio player, be it a dedicated compact disc music player, or a more
sophisticated CD-ROM drive when controlled to play an audio disc, only looks
for and uses data encoded to Red Book standards. What is more, if there
3s appears to be an inaccuracy in the data, an audio player will generally
continue
to play rather than trying to correct the error. For example, if the read head
has
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navigated to the start of a track and commenced to play that track, the audio
player will continue to play that track to its end, even if it becomes
apparent that
there is some error in the timing information, for example. By contrast, a
data
reader is arranged to identify and correct errors.
s
The present invention therefore suggests that errors should be
deliberately introduced into the encoded data. For example, errors may be
introduced into the Red Book data, but the introduced errors should be of a
type
which are generally transparent to an audio player. Alternatively, the audio
io discs may be encoded with selected and incorrect Yellow Book data which is
not
utilised by an audio player. In each case, the errors are chosen such that a
data
reader is unable to read or play the audio disc. It will be appreciated that a
system of the invention has the disadvantage that a user cannot play a
legitimately acquired audio disc having the copy protection on a data reader
in a
is legitimate manner, that is, simply to play the music recorded on the disc.
However, in view of the potential losses from piracy, the music industry is
willing
to accept that disadvantage.
As the data encoding on a CD-DA and on a CD-ROM is well known and
Zo in accordance with the appropriate standards, it is not necessary to
describe it in
detail herein.
Briefly, the data on a CD is encoded into frames by EFM (eight to
fourteen modulation). Figure 2 shows the format of a frame, and as is apparent
zs therefrom, each frame has sync data, sub-code bits providing control and
display symbols, data bits and parity bits. Each frame includes 24 bytes of
data,
which, for a CD-DA, is audio data.
There are 8 sub-code bits contained in every frame and designated as
3o P,Q,R,S,T,U,V and W. Generally only the P and Q sub-code bits are used in
the
audio format. The standard requires that 98 of the frames of Figure 2 are
grouped into a sector, and the sub-code bits from the 98 frames are collected
to
form sub-code blocks. That is, each sub-code block is constructed a byte at a
time from 98 successive frames. In this way, 8 different subchannels, P to W,
3s are formed. These subchannels contain control data for the disc. The P- and
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Q- subchannels incorporate timing and navigation data for the tracks on the
disc, and generally are the only subchannels utilised on an audio disc.
The data format for a Q-subchannel block assembled from 98 successive
s frames is indicated in Figure 3. As is apparent, the start of the subchannel
block
is indicated by the appearance of sync patterns SO and S1 as the first 2
symbols. The next data bits are control bits to define the contents of a
track.
Thus, the control bits might identify audio content or data content. There
then
follows address information. ADR, which specifies one of four modes for the Q-
to data bits. 72 bits of Q-data succeed the address information, and then
there are
16 CRC, or check, bits which are used for error detection on the control,
address
and Q-data bits.
Figure 4 illustrates the data content of a Q-subchannel block in each of
Is the four modes designated by the address information, ADR. In Mode 0, all
of
the Q-data has a value of zero. In Mode 0, the data of the P-subchannel is
also
set to zero. In Mode 2, the Q-data comprises a catalogue number for the disc,
such as a bar code of the Universal Product Code. In addition, in Mode 2 the
Atime count from adjacent blocks is continued. Mode 3 is used to give ISR code
2o for identifying each music track. In addition, and as is illustrated, in
Mode 3 the
absolute time count, Atime, is continued.
As indicated in Figure 4, in Mode 1 the Q-data in each subchannel block
contains program and time information for individual audio tracks and for the
2s information area of the disc. As is illustrated, there is a different
format for the
Q-data for the Lead-In area to that within the program and Lead-Out areas.
However, in both formats in Mode 1, the Q-data gives information as to the
time
along a track. The running time of a track is referred to as the Ttime, is in
minutes, seconds and frames, and TMin, TSec and TFrame are all components
30 of Ttime. In the program and Lead-Out areas, the Q-data additionally
includes
information about the absolute time, Atime, on the disc in minutes, seconds
and
frames, and Amin, Asec and Aframe are all components of Atime.
Figure 5 shows graphically how Atime and Ttime vary across a disc.
3s Atime is the absolute time across the disc and starts at zero at the
beginning of
the program area. Ttime is the running time within each track and thus starts
at
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zero at the beginning of each track. Thus, and as illustrated in Figure 5,
Atime
increases monotonically across the disc whilst Ttime increases along each
individual track. As is also illustrated in Figure 5, the P-subchannel
includes
flags F which each indicate the start of a respective track. The P-subchannel
s flags also designate the Lead-Out area.
As indicated in Figure 4, in Mode 1 each Q-subchannef block contains the
next consecutive values for Atime and Ttime. When an audio player is to play
an audio track, the head is navigated to the commencement of the track. The
:.o navigation may be by way of the Atime, the Ttime, and/or the P-subchannel
flags, or by some combination thereof. In general, once an audio player has
commenced playing a track, it will continue. Playing of the track is not
generally
stopped if any data errors are located, and thus the audio player effectively
ignores any data errors which arise. Thus, if an audio player can be reliably
is navigated to the commencement of a track, it can be expected to provide a
continuous audio output from that track without problem.
As set out above, in Made 1 the Q-data provides the TOC in the Lead-In
area. Part of a typical TOC is set out in table form in Figure 6a. It will be
seen
Zo therefrom that each track, at 14, is given, at 16, a start address in time
and in
frames from the end of the Lead-In. Each track also has a logical block
address
(LBA) 18 which is calculated from the Atime and provides an address for the
start of the track on the disc. The TOC of an audio disc also identifies the
Atime
from the start of the program area to the start of the Lead-Out as indicated
at 20.
2s However, the applicants have determined that generally audio players do not
read or use the Lead-Out time from the TOC.
Figure 6b shows in table form part of the TOC from Figure 6a after it has
been altered to copy protect the disc. Specifically, it will be seen that, at
20, the
3o Atime from the start of the disc program area to Lead-Out has been set to
zero
indicating that the Lead-Out is at the commencement of the pregap of the first
audio track. A data reader, therefore, accessing the disc 6 will read from the
Lead-In information signifying that the disc does not have a program area and
that the Lead-In is directly followed by the Lead-Out. The data reader will
refuse
3s to move the read head beyond the start of the audio track because it
believes
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that the first track starts within the Lead-Out. A data reader, therefore,
will be
unable to read or play the disc with the TOC of Figure 6b.
It will be appreciated that the values in the tables of Figures 6a and fib
s are given only to illustrate how the information is manipulated to provide
the
copy protection. The actual values of discs in practice may differ from those
shown in the tables.
The TOC of Figure 6b has been altered in a second way which also
~.o prevents proper use by a data reader of the information on the disc. In
this
respect, and as is apparent from Figures 6a and 6b, the tracks on the audio
disc
are all audio tracks as noted at 22. In the TOC of Figure 6b these tracks have
been erroneously identified as data tracks. Thus, even if the data reader is
manipulated to ignore the false Lead-Out information in the TOC, it is told
that
is each of the following tracks contains digital data, rather than analog
audio. Any
reading of those tracks is therefore confused as the player tries to read the
data
but cannot find the appropriate SYNC or sector headers. Errors therefore
result
and the reading is unsatisfactory.
2o In the illustrated embodiment, the Atime has been set to zero to indicate
that the Lead-Out is at the commencement of the pregap of the first audio
track.
It is also possible to set the Atime for the Lead-Out to an alternative,
incorrect,
value. Such an incorrect value will confuse a data reader and will generally
prevent movement of the read head further across the disc than the position
2s indicated by the incorrect Lead-Out time. For example, the Atime value
given in
the TOC for the Lead-Out might indicate a position within the first or a
subsequent audio track.
Where the incorrect Atime value for the start time of the Lead-Out points
3o to a position in the program area of the disc, a data reader may be able to
access audio data on the disc at positions before that indicated by the
incorrect
Atime value. However, the amount of accessible audio data can be kept small.
In the future, audio players may be enabled to read the Lead-Out time, for
example, and in this circumstance, having the incorrect Lead-Out time identify
a
3s position within the first audio track will ensure that the audio player is
able to
play the copy protected disc.
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The embodiments described and illustrated above identify two alterations
that can be made to the data in the Lead-In to an audio disc to copy protect
that
disc. It will be appreciated that any data which is transparent to the audio
player
may be altered to prevent the operation of a data reader. Additionally andlor
alternatively, data may be provided on an audio disc to prevent the generation
of
a digital output from the audio player. It will also be appreciated that
alternative
or additional errors in Red Book or Yellow Book standard data can be
introduced
as required.
to
Further modifications in or variations to the embodiments described
above may be made within the scope of the appended claims of this application.
