Method and Apparatus for Recording on a Record Carrier a Table of Contents Identifying All the Recorded Data Signals

1. Field of the Invention

The invention relates to a method of and apparatus for recording a series of data signals on a record carrier of an inscribable type.

2. Description of the Related Art

Such a method and apparatus are known from NL-A-8700655 (PHN 12.063). The method and the apparatus described therein are suitable for recording EFM modulated signals, such as for example a CD-signal, on record carriers of an inscribable type.

When data signals are recorded it is desirable that, in addition, a table of contents is recorded on the record carrier to store the addresses of the recorded data signals. Indeed, such a table considerably simplifies retrieval of the recorded data signals. A well-known format for such a table of contents is that prescribed by the CD-audio or CD-ROM standard. However, this format is less suitable for use in recording data signals on inscribable record carriers. This is because the format prescribed by the CD-standard of repeatedly recording the "Table of Contents" makes it necessary that for every addition to the "Table of Contents" the recorded information must be adapted in its entirety. For write-once record carriers this presents a substantial problem because it is not possible to re-record the "Table of Contents" on the record carrier after recording of a subsequent data signal. However, also for re-inscribable record carriers continually updating and recording the "Table of Contents" poses a major problem in view of the time needed for this.

On the other hand, the use of a different format which can be updated simply has the disadvantage that the table of contents cannot be processed by read apparatus which is constructed exclusively to read CD-ROM and/or CD-audio discs.

It is an object of the invention to provide a method and apparatus in which the above drawbacks are mitigated.

According to the invention the method is characterized in that after recording of a data signal, address information indicating the position of said data signal on the record carrier is stored in a temporary table of contents, a final table of contents in the form of an address information signal being recorded after the last data signal of the series has been recorded on the record carrier, which final table of contents is derived from the temporary table of contents. The apparatus in accordance with the invention comprises storage means for storing address information in the form of a temporary table of contents after recording of a data signal, and means for recording a final table of contents, derived from the temporary table of contents, in the form of a final address information signal after the last data signal of the series has been recorded.

The use of a temporary table of contents enables recording of the final address information signal to be postponed until the address information of all the data signals of the series is known. In that case recording the "Table of Contents" in a manner as defined by the CD-Audio or CD-ROM standard no longer presents any problem.

An embodiment of the method is characterized in that the temporary table of contents is stored in a memory which forms part of the apparatus for recording the data signals. This embodiment enables signals which fully comply with said CD-standards to be recorded.

Another embodiment of the method is characterized in that the temporary table of contents, in the form of a temporary address information signal, is recorded on the record carrier outside the area intended for recording the data signals and the final address information signal. When standard CD-signals are recorded this embodiment enables the temporary table of contents to be recorded outside the area intended for the storage of signals in conformity with the CD-Audio or CD-ROM standard. Since the CD-Audio and CD-ROM playing equipment does not read the information outside this area, the process of reading a record carrier on which a CD-signal is recorded in conformity with the above method will not be influenced by the presence of the temporary table of contents on the record carrier. Moreover, the temporary table of contents is always available on the record carrier, which means that the data signals can readily be recorded by different recording apparatus. When standard CD-signals are recorded on a disc-shaped record carrier the temporary table of contents can be recorded, for example, before the lead-in track at the inner side of the record carrier or after the lead-out track at the outer side of the record carrier. However, recording the temporary table of contents before the lead-in track may lead to problems of a mechanical nature. This is because recording of the temporary table of contents means that the read head should be movable to an area very close to the centre of rotation of the record carrier. Recording the temporary table of contents after the lead-out track may also give rise to problems. On account of variations in track pitch the variation in the overall playing time of a record carrier is approximately 15%, which makes it difficult to define a location for recording the temporary table of contents after the lead-out track. Moreover, reading information situated very close to the edge is less reliable owing to height variations caused by the position of the disc.

Another embodiment of the method which mitigates said drawbacks is characterized in that the temporary table of contents is recorded on the record carrier as a temporary address information signal, the relationship between the temporary address information signal and the information represented thereby deviating from the relationship between the other recorded signals and the information represented by such other signals. If a record carrier inscribed in conformity with this embodiment of the method is read, the temporary address information signal thus read cannot be processed and will therefore be ignored.

A further embodiment of the method is characterized in that the data signals and the final address information signal comprise first error-detection signals which have a first relationship with the signals in which they are comprised, and the temporary address information signal comprises second error-detection signals which have a second relationship with the signal in which they are comprised, the first and the second relationship being different. This embodiment has the advantage that the manner in which addresses are encoded in the temporary address information signal can be the same as the manner in which the addresses are encoded in the final address information signal, except for the error-detection signals. This has the advantage that conversion of the temporary to the final address information signal can be very simple.

The method in accordance with the invention is very suitable for recording data signals and the final address information signal in the form of a "Table of Contents" as specified by one of the CD-standards (CD-Audio and CD-ROM) on an inscribable record carrier. However, the invention is not limited to such a use and can also be applied to other recording systems in which updating of previously recorded contents information presents problems.

Further embodiments and the advantages thereof will now be described in more detail, by way of example, with reference to FIGS. 1 to 9, in which

FIG. 1 is a plan view of a standard CD-Audio or CD-ROM disc,

FIG. 2 illustrates the format of a subcode Q-frame as recorded in the lead-in track in conformity with the CD-standard.

FIG. 3 shows an example of a table of contents in a format prescribed by the CD-Audio or CD-ROM standard.

FIG. 4, consisting of 4a and 4b, gives an example of a temporary table of contents,

FIG. 5 gives an example of a method in which the addresses of the temporary table of contents can be inserted in the subcode Q-frame,

FIG. 6 shows an embodiment of a recording apparatus in accordance with the invention,

FIG. 7 shows diagrammatically the lay-out of the servo track of an inscribable record carrier,

FIG. 8 is a flow chart of a program for use in the apparatus in accordance with the invention,

FIG. 9 shows diagrammatically the lay-out of a record carrier inscribed in accordance with the invention.

The invention will be clarified by a description of embodiments of methods and apparatus for recording CD-signals on an inscribable record carrier, such that the recorded CD-signals can be read without any problems by apparatus which is constructed to read record carriers of the read-only type such as for example a CD-Audio disc or CD-ROM disc. However, first of all a number of aspects of the CD-Audio and the CD-ROM standard which are essential for a correct understanding of the invention will be described briefly.

FIG. 1 is a plan view of a standard CD-Audio or CD-ROM disc 1. Such a disc is provided with a spiral information track (not shown), in which a CD-signal is recorded. The disc 1 is divided into a plurality of areas, namely:

1) The program area, which is situated between the radii r2 and r3. In this area a plurality of data signals are recorded.

2) The lead-in area, which is situated between the radii r1 and r2. This area comprises a lead-in track, in which the addresses of the data signals are recorded in a "Table of Contents" which is included in the Subcode Q-channel.

3) The lead-out area, which is situated between the radii r3 and r4. This area comprises a lead-out track, which directly adjoins the last data signal and which indicates the end of the program area.

FIG. 2 illustrates the format of the subcode Q-channel frames in the lead-in track. A frame comprises a section S0, S1 intended for synchronizing purposes and a data section comprising 96 bits (DB). The data section is divided into a number of groups. The data section comprises a group of sixteen error-detection bits CRC, which are derived from the other 80 bits of the data section. The error-detection bits CRC are selected in such a way that when the binary number formed by the data bits DB is divided by a predetermined polynomial the remainder is zero. The polynomial for error detection in the subcode Q-channel in accordance with the CD-standard is equal to P(x)=X.sup.16 +X.sup.12 +X.sup.5 +1. For a detailed description of such an error detection reference may be made to J. Watkinson, "The art of digital audio", FOCAL PRESS (ISBN 0-240-51270-7), pp. 201-247.

FIG. 3 shows an example of a "Table of Contents" for the disc 1, in which a series of 6 data signals is recorded. The left-hand column gives the frame numbers of the subcode Q-channel frames. The other two columns specify the contents of the relevant frame. The code 01-06 (hexadecimal) in the second column (POINT) indicates the sequence numbers of the recorded data signals. Column 3 gives the start address for these data signals by means of an absolute time code. The code A0 indicates that the relevant frame specifies the sequence number of the first data signal (in the PMIN-column). The code A1 indicates that the relevant frame specifies the sequence number of the last data signal. The code A2 indicates that the relevant frame specifies the start address of the lead-out track. Every row of the table is recorded three times in the "Table of Contents". Moreover, the "Table of Contents" thus obtained is recorded several times in the lead-in track.

It will be apparent from the above that a "Table of Contents" once it has been composed and recorded cannot be updated with an address of a subsequently added data signal without re-recording the "Table of Contents". If a number of the data signals and a "Table of Contents" should be recorded on a write-once record carrier in such a way that the record carrier thus obtained complies with the abovementioned specifications for the "Table of Contents" as laid down in the CD-ROM or CD-Audio standard, the fact that this "Table of Contents" cannot be extended poses a problem.

Hereinafter a number of embodiments of the method and recording apparatus in accordance with the invention will be described, which solve the above problem.

FIG. 4a shows a temporary table of contents, which specifies the start address and the stop address for the consecutive data signals by means of an absolute time code. The column NO gives the sequence number of the data signal. The column CONTROL indicates whether the data signal concerns audio or other data and whether copying is permitted. For this purpose a similar 4-bit code may be employed as the code laid down in the CD-ROM or CD-Audio standard. Each row of this temporary table of contents may be inserted, for example, in a subcode Q-frame, as is illustrated in FIG. 5. This temporary table of contents can readily be extended with new address information. Data signals can now be recorded on an inscribable record carrier in the following manner. The first of a series of data signals to be recorded is recorded at the beginning of the program area defined by the radii r2 and r3. This beginning can be found, for example, by the method described in published Netherlands Application NL-A-8800152, said application describes a record carrier with a servo track intended for recording data signals and in which positional information is recorded in a track by means of a preformed track modulation. By reading the pre-recorded information it is simple to locate any desired position in the track.

After the first data signal has been recorded the start and the stop address are included in the temporary table of contents. For every subsequent data signal to be recorded the beginning of the still non-inscribed track is determined by means of the temporary table of contents and subsequently the data signal is recorded in the track contiguously with the data signals already recorded and the temporary table of contents is updated with the address information of this data signal. At the instant that it is decided that no further data signals are to be recorded, for example because the record carrier is full, the final "Table of Contents" can be drawn up by means of the temporary table of contents, and the "Table of Contents" thus obtained can be recorded in the lead-in track.

In a first embodiment of the recording method in accordance with the invention the temporary table of contents can be stored, for example, in a semiconductor memory which forms part of the recording apparatus. However, suitably the temporary table of contents is recorded on the record carrier itself, at the instant at which the record carrier leaves the recording apparatus. In that case the consecutive data signals can be recorded by means of different recording apparatus. FIG. 4b shows a suitable format for recording the temporary table of contents. In this table the stop and start address is repeated several times for every data signal. This repeated recording has the advantage that the stop and start addresses can be read very reliably. In practice, it is found that repeating every stop and start address ten times results in a very reliable read-out. In the temporary table of contents shown in FIG. 4 both the start and the stop address are given. However, in principle it would be adequate to store only the start addresses because the "Table of Contents" also specifies only the start addresses.

When the temporary table of contents is recorded on the record carrier and such a record carrier is read by means of apparatus which is intended exclusively for CD-ROM or CD-Audio discs, steps must be taken to ensure that the read process is not disturbed to an undesirable extent by the presence of the recorded temporary table of contents. In an embodiment of the method in accordance with the invention this can be realized simply by recording the temporary table of contents within the area indicated by the radius r1 or outside the area indicated by the radius r4. (This means before the lead-in track or after the lead-out track.) However, recording in the area within the radius r1 may give rise of problems of a mechanical nature because this makes it necessary for the read head to come within a very short distance from the centre of rotation. Recording in the area outside the radius r4 may also present problems because the end of the lead-out track cannot readily be detected on account of variations in track pitch, as a result of which the overall playing time may exhibit a variation of the order of magnitude of 15%.

In a modified version of the method in accordance with the invention the temporary table of contents can be recorded in such a way that the recorded signal does not comply with the requirements imposed by the CD-standard on the relationship between the recorded signals and the information represented thereby. In that case a read error will be detected when the temporary table of contents is read by the CD-ROM or CD-Audio player, so that the signal being read will be ignored. Such a deviating relationship can be obtained very simply for the format illustrated in FIG. 5 by selecting another relationship between the data bits DB and the error-detection bits CRC. This is possible by selecting the error-detection bits in such a way that upon division of the binary number defined by the data bits by another polynomial, for example P*(X)=X.sup.16 +X.sup.15 +X.sup.2 +1, the remainder of this division becomes zero. This has the advantage that the subcode Q-frame thus obtained differs from a format prescribed by the CD-Audio or CD-ROM standard to such a small extent that the contents of the sub-Q-frame can be determined but is regarded as being read erroneously. Preferably, such a temporary address information signal, which exhibits a deviating error code, is recorded in the lead-in track, preferably at the beginning of the lead-in track. However, the signal may also be recorded elsewhere, for example at the beginning of the program area defined by the radii r3 and r2. As described hereinbefore, it is preferred to record the temporary table of contents on the record carrier itself. However, it may be advantage to postpone the recording of additions to the temporary table of contents until the instant at which the user wishes to remove the record carrier from the recording device. In the meantime, the additions to the temporary table of contents may be stored in a memory, for example a solid-state memory, of the recording device.

FIG. 6 shows an embodiment of a recording apparatus in accordance with the invention. The recording apparatus shown in this Figure is an optical read/write apparatus 60 for optically recording and reading EFM-modulated signals on a record carrier 61 of a write-once type. Such a record carrier 61 may comprise an information layer 62 in the form of, for example, a metal layer or a dye layer, in which optically detectable changes can be produced by a radiation beam of sufficiently high intensity. The recording layer 62 comprises a spiral servo track (not shown), which is provided for the purpose for tracking and in which the data signal can be recorded. The positional information, for example in the form of absolute time codes, is recorded in the track by means of a preformed track modulation. Such a record carrier is described in detail in the afore-mentioned Netherlands Application NL-A-8800152. The record carrier is rotated in the customary manner about an axis 64 by means of a motor 63. An optical read/write head 65 is arranged opposite the rotating record carrier 61 to record and/or read the information in the servo track by means of a radiation beam 66. The read/write head 65 is movable in a radial direction by means of a radial positioning device, comprising for example a motor 67 and a spindle 68. The read/write head 65 comprises a system of radiation-sensitive detectors, which convert the beam reflected from the information layer 62 into detection signals, which are applied to an EFM demodulation circuit 69, which converts the EFM modulated signal being read into a subcode Q-signal and a main data signal Vo in a customary manner. The detection signals are also applied to a detection signal processing circuit 70, which derives an address signal ATIP from the signal components in the detection signals which are caused by the performed track modulation.

An example of the circuit 70 is described in detail in Published Netherlands Application NL-A-8800152. The address signal ATIP is applied to a control unit 71, which comprises for example a microprocessor of a customary type. The subcode Q-signal on the output of the circuit 69 is also applied to the microprocessor 71 via an error-detection circuit 72. The error-detection circuit 72 comprises two error detectors 73 and 74, which on the basis of the error-detection bits CRC in the subcode Q-frames determine whether read-out of the subcode Q-frame is effected correctly. The binary number defined by the subcode Q-bits of a subcode Q-frame are then divided by a predetermined polynomial and it is tested whether the remainder of the division is zero. The polynomials used for the two error detectors are different. For example, the error detector 73 employs the polynomial P(x)=X.sup.16 +X.sup.12 +X.sup.5 +1 prescribed by the CD-standard and the error detector 74 employs the polynomial p*(x)=X.sup.16 +X.sup.15 +X.sup.5 +1 which deviates therefrom. The error detectors may comprise, in a customary manner, shift registers and exclusive OR-gates, as is described in detail in, for example, the afore-mentioned book "The art of Digital Audio". The microprocessor 71 can select one of the error detectors 73 or 74 via a signal line 75. The selected error detector applies the data bits of the subcode Q-frame to the microprocessor 71 together with a signal which indicates whether the received signal is correct. The read/write head 65 can be set to the read mode or to a write mode via signal line 76. In the read mode the intensity of the radiation beam 66 is inadequate to produce an optically detectable change in the recording layer 62. In the write mode a radiation beam of an intensity which is high enough to produce the optically detectable change is modulated in conformity with a write signal Vs supplied by an EFM-modulation circuit 77. The EFM-modulation circuit 77 is of a customary type, in which an applied data signal Vi and an applied subcode Q-channel component are converted into a signal which is EFM-modulated in conformity with the CD-standard, which signal is subsequently converted into the write signal Vs. The data bits of the subcode Q-frames, with the exclusion of the error detection bits, are applied to the EFM-modulation circuit 77 via an error-detection-bit generator circuit 78. The circuit 78 derives and inserts the error-detection bits CRC. The circuit 78 comprises two error-detection-bit generators 79 and 80, which in a customary manner derive the error-detection bits by division by a predetermined polynomial. Such a circuit may comprise shift registers and exclusive-OR gates, as described comprehensively in the aforementioned book "The art of Digital Audio". The polynomials used in the error detection generators 79 and 80 are different, the polynomial used in the generator 79 being for example p*(x)=X.sup.16 +X.sup.15 +X.sup.2 +1 and the polynomial used in the generator 80 being P(x)=X.sup.16 +X.sup.12 +X.sup.5 +1 , which is the polynomial as specified by the CD-standard. The microprocessor 71 can select one of the two generators 79 and 80 via a signal line 81. The lay-out of a non-inscribed record carrier will be described in more detail with reference to FIG. 7, before a detailed description of the operation of the read/write device 60 is given.

FIG. 7 shows the spiral servo track diagrammatically as an elongate straight track bearing the reference numeral 82. The record carrier has a centre of rotation ro. The track section LI constitutes the lead-in track. The radii defining the boundaries of the lead-in track are r1 and r2. The values of r1 and r2 are selected in such a way that they are in conformity with the CD-Audio and CD-ROM standard, i.e. the distance from r0 to r1 is 23 mm and the distance from r0 to r2 is 25 mm. The track section following the lead-in track is intended for recording data signals. PMA indicates a section of the lead-in track between r1 and r1'. The section PMA is intended for recording the temporary table of contents. It is to be noted that the length of the temporary table of contents depends on the number of data signals recorded, so that the position of r'1 is not fixed. The maximum number of data signals permissible in conformity with the CD-standard is 99. This means that the maximum difference between r1 and r'1 is approximately 0.2 mm, which is only 10% of the total length of the lead-in track. FIG. 7 also shows the address signal ATIP represented by the preformed track modulation. The signal ATIP indicates the track position expressed in playing time. The value of ATIP is zero at the boundary between the lead-in track section and the track section intended for recording data signals. In the lead-in track the value of ATIP decreases from the maximum time of 99 minutes, 59 seconds, 74 frames and in the section intended for recording the data signals the value of ATIP increases starting from 00:00:00. The operation of the read/write apparatus shown in FIG. 6 will now be explained with reference to FIG. 8.

FIG. 8 shows a flow chart of a control program which is stored in the microprocessor 71 and which is fetched when a data signal is to be recorded. In step S1 of the program the read/write head 75 is brought to the position indicated by the radius r1 under control of the microprocessor 77. By means of the signal ATIP being read, it is possible to determine whether this position is reached. Once this position is reached the section PMA opposite the read head is read in step S2, in which section the temporary table of contents is recorded in the subcode Q-channel. For the purpose of error detection the error detector 79 is selected, which employs the polynomial P*(X).

Moreover, by means of the temporary table of contents thus read the start address is determined where recording the new data signal should start. In step S3 the read head is advanced to this start address. By means of the signal ATIP being read it is again ascertained whether the starting address is reached. Subsequently, step S4 is carried out, in which the read/write head 65 is set to the write mode. Moreover, the error-bit generator 80 employing the polynomial P(x) is selected. During recording the values of the various data-bit groups are determined in conformity with CD-standard, the value of the bit group ATIME (see FIG. 5) being derived from the address signal ATIP being read. Once recording of the data signal to be recorded has been terminated, the read/write head 65 is moved to the track section PMA in step S5, in which section the temporary table of contents is stored, and subsequently the stop and the start address are recorded in the temporary table of contents. This lastmentioned operation is performed during step S6. The start and the stop address are then inserted in a subcode Q-frame in a manner as illustrated in FIG. 5. Moreover, the error-detection-bit generator 79 is selected to insert the error-detection bits, which are then determined in accordance with the polynomial P(x)*, which deviates from the CD-standard.

Subsequently, it is ascertained in step S7 whether the recorded data signal is the last of the series of data signals to be recorded. If this is not the case, the program is terminated. If it is the last signal, step S8 is carried out, in which the final "Table of Contents" in conformity with the CD-standard is derived from the temporary table of contents and is subsequently recorded after the temporary table of contents in the lead-in track 83. Moreover, the lead-out track is recorded in a manner as laid down in the CD-standard. It is to be noted that the program represented by the flow chart in FIG. 8 can be modified in various ways. For example, it is possible to adapt the program in such a way that the adaptations of the temporary table of contents are stored temporarily in the memory of the microprocessor 71 until the instant at which the record carrier 6 is to be removed from the recording apparatus, in which case all additions to the temporary table of contents can be recorded on the record carrier in one recording cycle briefly before removal of the record carrier.

FIG. 9 shows the lay-out of the track 82 for a record carrier obtained by means of the apparatus in accordance with the invention, the Figure also indicating the values of the various bit groups in the subcode Q-frames. In FIG. 9 the lead-out track is referenced LO and the sections in which three different data signals are recorded are referenced DS1, DS2 and DS3 respectively. As will be apparent from FIG. 9, the recording obtained by means of the apparatus in accordance with the invention deviates only slightly from a standard CD-Audio or CD-ROM recording. Only the beginning of the lead-in track differs. However, when this beginning is read by apparatus for reading CD-ROM or CD-Audio discs the subcode Q-frames in which the temporary table of contents has been inserted will be regarded as erroneously read subcode Q-frames on account of the deviating error-detection-bit group CRC. This means that this information will be ignored completely.

In the embodiment of the recording apparatus described above the temporary table of contents is recorded at the beginning of the lead-in track. However, it is alternatively possible to record the temporary table of contents at different locations in the track, for example immediately after the lead-out track or immediately before the lead-in track. In the two lastmentioned cases a deviating error-detection code is not needed. Moreover, it is possible to store the temporary table of contents in a solid-state memory of the recording apparatus. Moreover, it is possible to ensure that during reading of the temporary table of contents this table is ignored by the read apparatus in another manner than by means of a deviating error-detection code, for example by selecting another data format, which differs from the CD-standard, during recording of the temporary table of contents.

Furthermore, it is to be noted that the use of the invention is not limited to the recording of CD-signals. The invention may equally be employed in other recording systems in which the recording format of the table of contents does not allow subsequent extension of the table of contents. For example, it is possible to insert a bit combination in the bit groups ADR and TNO the subcode Q-frame, which combination is not permissible in conformity with the CD-standard. Neither is it necessary to insert the temporary table of contents in the subcode Q-channel. Alternatively, this temporary table of contents may be inserted in other subcode channels, for example in one or more subcode R-W-channels.

Finally, it is to be noted that the use of the invention is not limited to the recording of data signals on write-once record carriers. The invention may also be utilized for recording on re-inscribable record carriers, because in such cases the repeated formatting and recording of the table of contents may be time-consuming in comparison with the time needed for recording and generating the definitive table of contents in accordance with the invention.